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List of Figures
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MySQL Administrator is a program for performing administrative operations, such as configuring your MySQL server, monitoring its status and performance, starting and stopping it, managing users and connections, performing backups, and a number of other administrative tasks.
You can perform most of those tasks using a command line interface such as that provided by mysqladmin or mysql, but MySQL Administrator is advantageous in the following respects:
Its graphical user interface makes it more intuitive to use.
It provides a better overview of the settings that are crucial for the performance, reliability, and security of your MySQL servers.
It displays performance indicators graphically, thus making it easier to determine and tune server settings.
Note that MySQL Administrator will not work with MySQL servers prior to version 4.0.
MySQL Administrator is to a large extent the result of feedback MySQL AB has gotten from many users over a period of several years. However, if you find it's lacking some feature important to you, or if you discover a bug, please use our MySQL Bug System to request features or report problems.
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MySQL Administrator runs on Windows and Linux. You can find MySQL Administrator for the operating system of your choice on the MySQL Downloads page.
MySQL Administrator runs on 32-bit (or better) Windows operating systems, including Windows 95, 98, Me, NT, 2000, and XP.
For Windows 95, 98, and Me, a ZIP file is available that contains the files necessary for the installation of MySQL Administrator. That file is called mysql-administrator-version-win.zip, where version indicates the MySQL Administrator version. You need to download that ZIP file, extract it and change into the directory to where you extracted it. Alternatively, a ZIP file without an installer program is available.
For Windows NT, 2000, and XP, you may also use that ZIP file, but the recommended installation method is to use the MSI file provided for those operating systems.
The installation procedure depends on your operating system:
On Windows 95, 98, and Me, run the SETUP.EXE program that you will find in the directory created by unpacking the ZIP file. Note that most ZIP programs allow you to install directly from the ZIP file, that is without unpacking it in the first place.
On Windows NT, 2000, and XP, right-click on the MSI file and select Install. (The MSI file might not be available for some of the first releases.)
If you are having problems running either of the installers, you can download a ZIP file without an installer as an alternative. That file is called mysqladministrator-version-win-noinstall.zip. Using a ZIP program, unpack it to a directory of your choice. You may want to create shortcuts to MySQLAdministrator.exe for your desktop or quick launch bar.
When using the download files containing an installer, both SETUP.EXE and MSI file will start an installation assistant that guides you through the rest of the installation. During installation, you can choose if you want the installer to place a shortcut in the Start menu, or an icon on the desktop.
Unless you choose otherwise, MySQL Administrator is installed in c:\program directory\MySQL\GUITools\MySQLAdministrator.exe, where program directory is the default directory for programs on your machine. For example, this directory might be c:\program files or c:\programme.
MySQL Administrator runs on Linux machines that have a graphical desktop installed. It is designed to run under the Gnome desktop, but you may also use other desktops, such as KDE. It has been tested on Linux kernel versions 2.4 and 2.6, but it should also run on other versions, and even on a number of Unix-like operating systems.
To install MySQL Administrator, first download the RPM package. The RPM file is called mysql-administrator-version-linux.tar.gz.
To see all files in the RPM package, run this command:
shell> rpm -qpl mysql-administrator-version-linux.tar.gz
version in the RPM filename indicates what version of MySQL Administrator is contained in the package, for example 1.0.0a-alpha.
To install MySQL Administrator, run this command:
shell> gunzip -c mysql-administrator-version-linux.tar.gz | tar xv -C /opt
This installs the application binary in /opt/mysql-administrator/bin. Change into that directory and run mysql-administrator to start the application.
Distribution-specific packages will be available at some point.
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The way you start MySQL Administrator depends on the operating system you are using:
On Windows, start MySQL Administrator by double-clicking its desktop icon, or by selecting its item from the Start menu. Alternatively, you can open a DOS window and start it from the command line:
c:\> c:\program directory\mysql\bin\MySQLAdministrator.exe
program directory is the default directory for programs on your machine, for example c:\program files or c:\programme. If your path contains spaces, you should enclose the command within quote characters. For example:
c:\> "c:\program files\mysql\bin\MySQLAdministrator.exe"
On Linux desktops, start MySQL Administrator by changing directory into /opt/mysql-administrator/bin, and then running mysql-administrator.
Once MySQL Administrator has been started, it displays a connection dialog. You have to specify the MySQL server to which you would like to connect, the credentials needed for authorization on that server, and which machine that server runs on (and which port it listens to). You may also specify a number of other options, if required.
As an alternative to connecting to a running MySQL server, you can run MySQL Administrator in configure-service mode.
Note that MySQL Administrator will not work with MySQL servers prior to version 4.0. If you try to connect to an older server, an error message will appear, telling you that this is not possible.
If the server connection is successfully established, all of the values filled in the fields of the connection dialog will be saved for future connections (see the section that describes how MySQL Administrator stores connection information). The Password field, however, will always be empty: For security reasons, the password is not stored along with the other options, unless you explicitly specify otherwise in the General Options section of the Options dialog.
You can change any of the values in the connection profiles just by overwriting the existing values with new ones. Similarly, if you select another connection profile, you can change any of its values. When you click the Connection drop-down box. That brings up an Options dialog window that has a Connections section for modifying connection profiles. You can find the values you can set in the Connection dialog window in the description of the Connections section of the Options dialog (see Options dialog).
button after changing a profile's values, the changes are stored permanently if a successful connection to the MySQL server is established. However, the preferred method for changing a profile is to click the button next to theNormally, you will use MySQL Administrator to connect to a running MySQL server. This is done by starting the program and specifying in the Connection dialog which server to connect to.
Alternatively, you can run MySQL Administrator in configure-service mode. This is useful in the following cases:
When you want to start a MySQL server from within MySQL Administrator. Obviously, you cannot connect to a server that is not running, so you will have to use the configure-service mode to start that server. Note that, at the moment, you can only start servers on the same machine where MySQL Administrator is running (that is on the local host).
When you have multiple servers running on your machine. On Windows, MySQL Administrator only allows to configure the Windows service that is listed first in the Windows services management when running in normal mode. This means that if you have more than one Windows service, you can only configure the first one of those, no matter which server you have connected to. If you want to configure a service other than the first service, you will have to run MySQL Administrator in configure-service mode.
To start MySQL Administrator in configure-service mode, hold down the CTRL key in the Connection dialog. The button will toggle to when that key is pressed.
Clicking on the
button will skip the normal mode, thus starting MySQL Administrator in configure-service mode.Under Installed Services in the sidebar, you can select the service that you wish to configure, or the server that you want to stop or start. In configure-service mode, as opposed to normal mode, there is only a subset of the sections in the sidebar avaiable:
The Service Control section allows you to start and stop a MySQL server, and to configure the Windows service managing that server.
The Startup Variables section allows you to set variables for server startup.
Both of those sections are described in detail below.
The Options dialog of MySQL Administrator allows you to configure connection profiles, general program settings, and more. You can open the Options dialog window using one of the following methods:
In the Connection dialog window, click the button.
In the main window that appears after connecting to a MySQL server (or in configure-service mode), select from the menu.
In the sidebar of that dialog, you can select the section you wish to configure. The sections each contain three buttons on the lower right side of the window:
applies and saves changes.
discards any changes you have made.
closes the Options dialog window.
If you make changes, but do not apply them before changing to another section or before closing the window, MySQL Administrator prompts you, asking whether or not you want to save your changes.
[PD] It's kind of weird that the "General Options" section in this dialog doesn't occur first...? [SH] I agree, but I am not the programmer :-) The Administrator section allows you to specify what MySQL Administrator will display in the User Administration section:
Show Global Privileges: If checked, the Global Privileges tab will be visible in the User Administration section. In that tab, you can grant users global privileges (as opposed to privileges on a database, table, or column level only). This may affect security. See The MySQL Access Privilege System for details. If unchecked, the Global Privileges tab will not be visible in the User Administration section.
Show Table/Column Privileges: In most situations, it is sufficient to grant either global or database privileges for users. You can hide the Table/Column Privileges tab in the User Administration section by enabling this checkbox.
The General Options section allows you to specify a number of settings that are valid not only for MySQL Administrator, but also for other graphical MySQL applications. At the time of writing, MySQL Administrator is the first and only program of the MySQL GUI suite (GUI = graphical user interface), but other programs will follow soon.
Show Tip of Day: If checked, a pop-up window with the tip of the day appears at program startup.
Store Window Positions: When an application is started the next time, its recent window positions will be reused.
Store Passwords: If checked, passwords are stored in the MySQL Administrator's connection profile. In this case, you can select the password storage method:
Plaintext means they are stored without encryption; this can be insecure. Obscured means they are encrypted using a weak algorithm (and you could find the encryption key used in the source code). This encryption method, however, is operating system independent. The default is Plaintext.
Language: Select the interface language. The default is English.
Application Font: You may change the font and font size by clicking the
button.[PD] This should be "Character Set", not "Charset", which is jargony. Charset: This drop-down box allows you to select a character set. The default value is DEFAULT_CHARSET, which stands for the default character set used by your operating system.
The Connections section allows you to created, edit, and delete connection profiles. The center box displays a list of currently available profiles, together with a history of connections that were made without being stored in a profile. You can collapse or expand both Connections and History by double-clicking them. [PD] Problem: What does it mean to click "Connections". There are two things labeled "Connections" in this window. Problem one of them should be renamed so it's not ambiguous what this term means.
Connections are automatically added to History whenever you establish a connection to a MySQL server without using one of the profiles stored under Connections. They do not appear in the drop-down box of the Connection dialog, but you can use any of them by manually typing its name in the Connection box of the Connection dialog.
To edit an existing connection profile, click on its name and change the values that appear in the Connection Parameters and Advanced Parameters tabs, then click on the
button to save your changes.[PD] There appears to be no way to specify the pathname of a Unix socket file or a named pipe name? Are shared memory connections supported? When you select a connection profile from either the Connections or History list, the Connection Parameters tab displays the following fields:
Connection: The connection profile label. This is the name by which you refer to the profile and that appears in the Connection drop-down box of the Connection dialog. It may contain any characters, including spaces. Choose distinctive names so that you can easily tell which profiles they refer to. The names can help you distinguish connections to different MySQL servers, or connections as different MySQL users to a given server. Here are some examples:
Localhost as root
Localhost, Mike (not so privileged)
Remote machine XYZ where I'm superuser
Username: The username used to connect to the MySQL server.
Password: The password used to connect to the MySQL server. Note that passwords are not stored in the connection profile, unless you specify otherwise in the General Options section.
Hostname: The name of the host machine where the MySQL server runs.
Port: The TCP/IP port that the MySQL server listens to on the host machine.
Type: Specifies the protocol used to connect to the database server. The default protocol is MySQL (which uses the native MySQL protocol). The other protocols listed are not being used by MySQL Administrator. If you choose a protocol other than MySQL, MySQL Administrator ignores it.
Schema: MySQL Administrator ignores entries made in this field. It is for use by other programs of the MySQL graphical tools suite.
Notes: You can use this field to enter comments or additional information describing the connection profile.
Note that the Advanced Parameters tab may not be available in some of the first releases of MySQL Administrator. If that is the case in the version you are using, you can still set those parameters in the Connection dialog. Use the button of that dialog to display the Advanced Connection Options.
When you select a connection profile from either the Connections or History list, the Advanced Parameters tab displays the following checkboxes:
Use compression protocol: If checked, the communication between MySQL Administrator and the MySQL server will be compressed, which may increase speed. This corresponds to starting a MySQL command-line tool with the --compress option.
Return number of found rows, not number of affected rows: By default, MySQL returns the number of rows changed by the last UPDATE, deleted by the last DELETE or inserted by the last INSERT statement. When this option is checked, the server returns the number of rows matched by the WHERE statement for UPDATE statements.
Ignore spaces after function names, make them reserved words: Normally, any refereence to a function name in an SQL statement must be followed immediately by anopening parenthesis. If this option is checked, spaces may appear between the function name and the parenthesis, like this:
COUNT (*)
Enabling this option has the effect that function names become reserved word. This option corresponds to starting a MySQL command-line tool with the --ignore-spaces option.
Allow interactive_timeout seconds of inactivity before disconnect: Normally, the connection is closed by the MySQL server after a certain period of inactivity on the client side. This period can be set with the interactive_timeout variable. [SH] Mike: This leave me wondering how you would set interactive_timeout in MySQL Administrator. If checked, the server will not close the connection unless the period of inactivity exceeds the value set by interactive_timeout. This corresponds to starting a MySQL command-line tool with the --connect-timeout=seconds option.
Enable LOAD DATA LOCAL handling: By default, the LOCAL option of the LOAD DATA statement is disabled for security reasons. Enabling this option will allow to load data from the local machine (that is where MySQL Administrator is running). This option corresponds to starting a MySQL command-line tool with the --local-infile=1 option. (Note that this option is ineffective unless the MySQL server allows LOCAL handling.)
If an error occurs when you select a connection profile and attempt to establish a connection to the MySQL server named in the profile, MySQL Administrator displays a window containing error information (see figure). [PD] The figure says "MySQL Error Nr". "Nr" would be better as "Number".
Normally, this means either that the credentials specified in the profile are wrong (wrong username, wrong password), or that you do not have privileges to connect to the MySQL server from the machine where MySQL Administrator runs. You can find more information about the error in the Causes of Access denied Errors section.
However, another cause of connection failure is that there might be a network problem that prevents you from reaching the machine where the MySQL server is running. For this reason, the error dialog provides a
button. Clicking this button will send an ICMP PING request to the MySQL server host machine. If the host machine is available over the network, you will see something like this:Reply from 127.0.0.1: Time=0ms TTL=128 Reply from 127.0.0.1: Time=1ms TTL=128
This would indicate that the machine is reachable, and that the cause of connection failure is not a network problem. In contrast to this, a network error might show up like this:
Could not resolve hostname remotemachine
This would indicate that the machine where the MySQL server is running is unreachable over the network.
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After you have successfully connected to your MySQL server, the main window of MySQL Administrator appears (see figure). The main window contains a sidebar, a working area, and menus with submenus.
[SH] Mike: Need new graphics from Mike (with annotations!)The sidebar consists of the following sections:
Server Information: Information about the MySQL server you are connected to, about MySQL Administrator and the machine that it runs on, and about your connection.
Service Control: Start and stop the MySQL server. On Windows, you can also configure the MySQL service.
Startup Variables: Configure the startup variables for the MySQL server.
Server Connections: View or kill current connections to the MySQL server (also called threads).
User Administration: Administer existing users, add new users, and delete existing users.
Health: Graphical displays of a number of usage or hitrate values that affect server performance, and a hierarchical view of system and status variables.
Server Logs: View log file entries.
Backup: Plan and administer backup projects, select the databases to be backed up, and start the backup process.
Restore: Restore databases from existing backups.
Replication Status: View information about replication master and slave servers.
Catalogs: View information about databases, tables, columns, indexes, and rows; optimize tables.
The following sections describe each of these in detail.
You can change the width of the sidebar in the main window by dragging the separator between sidebar and working area. To hide the sidebar completely, click on the marked area in the separator (located in the vertical center of it). To make the sidebar visible again, double-click the marked area (which then forms the left margin of the main window).
While the sidebar allows you to select the sections, the working area displays information, or fields, that pertain to the selected section. For some sections, the working area is split into two or more tabs.
Opens the Connection dialog, allowing you to open another connection to a MySQL server. You may open an arbitrary number of connections. MySQL Administrator opens a new main window for each successfully established connection. Connections may be to the same or different servers. Multiple connections may be opened using the same profile or different profiles.
Opens the Options dialog, with the Connections section preselected.
Opens the Options dialog, with the Connections section preselected. Furthermore, a new connection profile labeled New Connection is created, which is also preselected. The fields are filled with the values of the most recent connection. You can edit the values and save the settings in the new profile. You may also want to rename the profile from New Connection to something more appropriate. If you click the button without saving your changes with the button, you will be prompted as to whether you want to save or discard your changes.
The working area.
, , and commands allow you to cut, copy, or paste selected text in theOpens the Options dialog window.
The sidebar. Selecting an item from this menu is the same as clicking the section with the same name from the sidebar.
menu selects sections from theThe
menu starts other programs.This menu item is available only if MySQL Administrator finds the executable of the MySQL command-line client. At the moment, it will look up locations like c:\mysql\bin, d:\mysql\bin, and c:\program directory\mysql\bin to find mysql.exe. If it is found, you can start the command-line client with this command. MySQL Administrator will use the credentials provided in the Connection dialog to start a server connection using the command-line client.
Opens a window displaying the MySQL Administrator section of the MySQL reference manual. [SH] Mike: Should be "Help" only to make clear it will not load the MySQL online manual from www.mysql.com/doc/
Provides basic information about connection, server, and client.
Connected to MySQL Server Instance [SH] Mike: The label name is gruesome (why not just "Connection"?).
Information about the parameters used to connect to the MySQL server.
User: Username used for the current connection to the MySQL server.
Host: The hostname of the machine where the MySQL server runs. This is either identical to the name listed in Network Name, or it is localhost. The former indicates that you are connecting to a server that either runs on a remote machine, or that you have specified a hostname different from localhost when connecting. The latter indicates that the MySQL server runs on the same machine where MySQL Administrator runs.
Port: The port used for the connection to the MySQL server.
Server Information
Information about the MySQL server and the host where it is running.
MySQL Version: The version of the MySQL server.
Network Name: The hostname of the machine where the MySQL server runs.
[PD] "IP" is ambiguous because there are IP numbers and IP addresses. IP: The IP number of the host where the MySQL server runs.
Client Information
Information about MySQL Administrator and the client host on which it is running.
Version: The version of MySQL Administrator, and the version number of the MySQL client/server protocol.
Network name: The name of the host where MySQL Administrator runs.
IP: The IP number of the host where MySQL Administrator runs.
Operating System: Information about the operating system on which MySQL Administrator runs.
Hardware: Information about the hardware on which MySQL Administrator runs.
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This section allows you to start and stop the MySQL server you have connected to. At the moment, this is only possible if the server is running on the same machine where MySQL Administrator runs. In future releases, MySQL servers will have an Instance Manager that allows you to also start and stop MySQL servers on remote machines. Also, you can start and stop the server only if a service has been configured. If the server runs as a stand-alone application, the Service Control section is not available.
Note that it is actually possible to stop a MySQL server running on a remote machine even now. You should not do that, however, because there is no way of restarting it using MySQL Administrator at the moment.
The Configure Service tab is available only for MySQL servers that run under Windows.
The Start/Stop Service tab displays the status of the MySQL service. This service starts and stops the MySQL server. Under Service Status, a text message indicates whether or not the service has been started. If the service is running, the button label is
button. Click it to stop the server. If the service is stopped, the button label is . Click it to start the service.Under Log Messages, you will find messages that the MySQL server produces when it starts or stops. Messages produced by the server during startup look something like this:
Trying to start the server ... 040119 18:33:41 InnoDB: Started MySql: ready for connections. Version: '4.0.16-max-nt-log' socket: '' port: 3306 Server was started.
When the server stops, it produces messages such as these:
Trying to stop the server ... 040119 18:31:45 MySql: Normal shutdown 040119 18:31:46 MySql: Forcing close of thread 11 user: 'superuser' 040119 18:31:46 MySql: Forcing close of thread 8 user: 'superuser' ... Server was stopped.
The details and format of the messages might vary depending on the version of the MySQL server you are using and its configuration.
This tab allows configuration of the Windows service that starts and stops the MySQL server, as well as setting some options for the server itself. This tab is specific to MySQL servers running under operating systems of the Windows NT family, including Windows NT, Windows 2000, and Windows XP; it is not available for servers running under a different operating system. Obviously, you need to have a Windows service installed before you can configure it. The Starting MySQL as a Windows Service section describes how to set up a Windows service.
Note that if you have more than one MySQL server running as a Windows service, you should run MySQL Administrator in configure-service mode to administer these services. In normal mode, you can only administer the Windows service listed first in the Windows service manager, no matter which server you are connected to.
Note that the settings in the Server Features group take effect only after restarting the MySQL server.
The following settings are available:
Service Settings
Launch MySQL server automatically: If checked, the Windows service starts the MySQL server automatically on operating system startup.
Display Name: The display name of the Windows service (not the service name!) as it will appear in the Windows services manager when displaying the properties of that service.
Service Description: The description of the Windows service as it will appear in the Windows services manager.
Option File
Config Filename:[SH] Mike: "Config" is ugly. Suggestion: Filename [PD] Right. Don't use truncated words like Config in labels. Should either be written out, or, if that's too long, try to pick a different term. You can enter the pathname of the server option file. MySQL will enter that information in the Windows registry, and the Windows service starting the MySQL server will use that file, rather than the default file (c:\windows installation directory\my.ini). Note that this is available for MySQL servers as of version 4.0.3 only. Details about the server option files can be found in the Preparing the Windows MySQL Environment section. [PD] If this file is passed to the server as the --defaults-option (which I suspect is the case), the server will read only the [mysqld] option group in the file.
Section Name: [SH] FILL IN Setting a value other than mysqld is most useful when running multiple servers; see Running Multiple Servers on Windows. [SH] This is likely to change; need to document the changed behaviour.
Server Features
Note that all server features will only take effect after the MySQL server has been restarted.
Support for InnoDB: If checked, the MySQL server is started with support for InnoDB tables. If unchecked, it doesn't start the InnoDB storage engine; this saves memory, but InnoDB tables cannot be used. If this checkbox is unchecked and greyed out, it means that your MySQL server isn't compiled with support for InnoDB tables. (This is, for example, true for some versions that run under a commercial license.) You can find more information on InnoDB tables in the MySQL Table Types section.
Be careful when disabling this option! If any databases on the MySQL server contain InnoDB tables, disabling this option makes those tables inaccessible.
Support for BDB: If checked, the MySQL server is started with support for BDB tables. If unchecked, it doesn't start the BDB storage engine; this saves memory, but BDB tables cannot be used. If this checkbox is unchecked and greyed out, it means that your MySQL server isn't compiled with support for BDB tables. (This is, for example, true for non-max versions.) You can find more information on BDB tables in the MySQL Table Types section.
Be careful when disabling this option! If any databases on the MySQL server contain BDB tables, disabling this option makes those tables inaccessible.
Named Pipes: On operating systems of the Windows NT family, including Windows NT, Windows 2000, and Windows XP, you may use named pipes to connect to a MySQL server running on the local machine, rather than connecting via TCP/IP. If this option is checked, named pipe connections are allowed. Note that named pipes are slower than TCP/IP in many Windows configurations. See the Selecting a Windows Server section for details.
Debug Information (slow): If checked, the MySQL server is started with an option that allows for easier debugging of problems. Using this option slows down the server significantly, so it is recommended only for debugging purposes. If the MySQL server has not been compiled with debugging support, this option is greyed out. See the mysqld Command-line Options section for details.
Path to Binary: Contains the pathname of the MySQL server binary file as it is listed in the Windows service manager (for example c:\mysql\bin\mysqld-max-nt). Note that the the Windows service manager does not display the .exe extension.
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This section allows you to set variables that the MySQL server reads on startup. These variables are stored in the option file of the server. On Windows, the option file is called my.ini, and it is located in the Windows installation directory (for example, C:\WinNT\my.ini). Note that it can alternatively be stored in C:\, in which case it is named my.cnf. Also note that there can be more than one option file. On operating systems other than Windows, the option file is called my.cnf, regardless where it resides. On Windows, MySQL Administrator allows you to store the option file in any location you specify. You can find more information on the MySQL option files in the Option Files section.
Note that the server reads variables stored in the option files only at server startup. After changing an option file, you must restart the server for the changes to take effect. You can do this using the Service Control section. and buttons in the
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This section allows you to view and manage the current connections to the server (also called threads). If you have the PROCESS privilege, you can see all threads. If you have the SUPER privilege, you can also terminate threads other than your own. (Note that the SUPER privilege is available for MySQL servers as of version 4.0.3 only.) Otherwise, you can see your own threads only. You can find more information about threads in the SHOW PROCESSLIST section. For more information on the PROCESS and the SUPER privilege (and other available privileges as well), see Privileges Provided by MySQL.
Note that you will see an additional thread for the user under which you are connected when you have clicked the Health section within your current MySQL Administrator session. The values displayed in that section are retrieved from the MySQL server via a separate connection.
This tab allows you to view all connections to the server (threads). Initially, those are sorted by their PID (MySQL process identification number), but you can change that order by clicking on the appropriate headings (User, Host, etc.). [SH] This is not implemented yet. You can select a thread by clicking on it. You can select more than one thread using mouse or keyboard.
To reload the process list from the server, press the
button.If you have selected one or more threads, you can terminate them by clicking the
button, or by right-clicking on that thread. Remember that you need the PROCESS privilege to see threads other than your own, and the SUPER privilege to kill threads other than your own. Furthermore, note that MySQL Administrator imposes a restriction that prevents you from terminating your own threads. On Windows, using the button on your own threads does not have an effect; on Linux, that button is disabled when selecting your own threads.This tab displays all connections to the server (threads), but in a different way than the Threads tab does: You will rather see users, not individual threads in the first place. The number of connections a user has currently established to the MySQL server is listed under Num.. Right-clicking on a username and selecting will also display the Full Name and the Description, as specified in the User Information tab of the User Administration section. Initially, users are sorted by their MySQL Username, but you can change that order by clicking on the appropriate headings (Num., Full Name, or Description). [SH] Not implemented yet. Clicking on a username will display the individual threads of that user in the lower box of that tab, ordered by PID. Likewise, you can change that order by clicking on the appropriate headings. [SH] Not implemented yet.
Clicking on a user will enable the
button, which allows you to terminate all threads of that user with a single click. That command is also available by right-clicking on the username. Clicking on an individual thread in the lower box will enable the button, which is used to terminate a connection. That command is available by right-clicking on a thread, too.To reload the user list from the server, press the
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This section allows you to administer existing users, add new users, and delete existing users. For more information on the MySQL user account management and privilege system, see the MySQL User Account Management section.
Existing users are listed in the lower left area of the sidebar. If there are many user accounts on your MySQL server, the field with the magnifying-glass icon may be handy for filtering the users you are looking for. Typing in t or T, for example, will set the filter to users whose names begin with a t. The filter works in a case-insensitive fashion.
If you are an experienced MySQL user, you will notice that users are not listed the typical MySQL way (user@host), but rather with their usernames only. If double-clicking on a username does not show subcategories for that user, this means that the user's privileges are not restricted to a specific host, or hosts. If there are subcategories, the user's privileges are restricted to a specific host, or set of hosts. You may assign various (and different) sets of privileges, depending on the host from which the user connects to the MySQL server. That concept is described in detail in the Access Control, Stage 1: Connection Verification section.
Note that MySQL Administrator has a different concept of what a user is than MySQL has. In MySQL, a user is always identified by a username/host combination. This means that, for example, 'brian'@'%' may be a user completely different from 'brian'@'localhost'. The former might be Brian Miller, while the latter might be Brian Schultz. That distinction does not hold true for MySQL Administrator: User brian is always a particular user, no matter from which host he connects to the MySQL server. That said, 'brian'@'%' may still have privileges different from 'brian'@'localhost'.
For example, you might have a user called superuser. If double-clicking on that username shows two subcategories, localhost and athena, this means that the user has a specific set of privileges if he/she connects from localhost, and a (probably different) set of privileges if he/she connects from athena.
Right-clicking on a username, or on one of the subcategories a user might have, provides access to the following commands:
Add a new User: Selecting this command adds a new user with the default name New User to the user list. You will have to fill in at least a username in the MySQL User field of the User Information tab, which, after applying this change, will also rename that user in the user accounts list.
Add a Host from which the User can connect: [SH] Mike: Remove "a" -> Add Host. Allows you to specify a host from which the user can connect. This command is unavailable if you right-click on a subcategory.
Remove Host from which the User can connect: Allows you to remove a host from which the user can connect. This command is unavailable unless you right-click on a subcategory.
Clone User: Makes a copy of the selected user, including all subcategories. The new user is called New User until you specify another name in the MySQL User field of the User Information tab. With that command, you can therefore create a user with identical privileges. [SH] Not yet implemented.
Delete User: Allows you to delete the selected user. You will be prompted to confirm that you really want to delete that user.
Refresh User List: Rereads the user list from the MySQL server. This is helpful when other users (on other connections) are editing user accounts. Note that selecting that command will collapse all subcategories.
The fields in this tab are unavailable unless you either click on a username in the User Accounts area of the sidebar, or create a new user in that sidebar or using the button on this tab. In the former case, the fields are filled with the information stored for that user, in the latter case, all fields are empty.
Note that all fields will be stored only when you click the
button. If you don't want to save your changes, click the button.The values you enter in the fields of this tab are stored on the MySQL server. The fields in the Login Information group of this tab are stored in the user table of the mysql database, while the fields in the Additional Information group are stored in the user_info table of the mysql database. The latter table is created the first time you add a new user, or change an existing user. Its contents may look like this:
mysql> SELECT * FROM mysql.user_info \G *************************** 1. row ************ User: superuser Full_name: Stefan Hinz Description: MySQL Documentation Team Email: stefan@mysql.com Contact_information: Phone: +49 30 123456789 Fax: +49 30 987654321 ICQ: 123456789 Icon:
Login Information
MySQL User: Username that is specified when connecting to the MySQL server. Note that this username has nothing to do with usernames you might use elsewhere on your operating system. It is recommendable not to use special characters or spaces for that username.
Password: Password that is specified when connecting to the MySQL server. Note that this password has nothing to do with passwords you might use elsewhere on your operating system. It is recommendable not to use special characters or spaces for that password. It is, however, recommendable to use non-trivial passwords. A very trivial password might be abcde, while a non-trivial password might be lEtusMak3iThartdoGesz. Note that it is not mandatory to specify a password, although it is highly recommendable to do so.
Confirm Password: Fill in the password once again to make sure you do not accidentally introduce a typo.
Additional Information
All information specified here is optional.
Full Name: As opposed to the username in MySQL User, the full name may contain any characters, including spaces.
Description: Additional description of user.
Email: Email address of user.
Contact Information: More contact information, like postal address, or messenger information. [SH] Mike: messager -> messenger
Icon: Rather than using the default icon, you may select a different icon by pressing the [SH] Mike: In which directory?, or use an icon of your own. In the latter case, be aware that the icon has to be exactly 48 by 48 pixels in size, and its file format has to be PNG (portable network graphics).
button. You can either use one of the buttons that are shipped with MySQL Administrator
This tab is available only if the Show Global Privileges checkbox in the Administrator section of the Options dialog has been checked.
Under Assigned Privileges, you find the global privileges assigned to the selected user. For more information about those privileges, see the Privileges Provided by MySQL section. Global means that those privileges apply to the MySQL server in general (like the Shutdown privilege), or to all databases on the server (like the SELECT privilege).
Privileges not assigned to the user are listed under Available Privileges. You can remove privileges by selecting them in the left box, and then clicking the button. Removed privileges will appear in the Available Privileges box. You can assign privileges by selecting them in the Available Privileges box, and then clicking the button.
This tab allows you to grant privileges on a schema level. In MySQL, a schema is the same as a database. To grant privileges for a specific database, click on the database name in the left box. (You cannot select more than one database at a time.)
Privileges not assigned to the user are listed under Available Privileges. You can remove privileges by selecting them in the left box, and then clicking the button. Removed privileges will appear in the Available Privileges box. You can assign privileges by selecting them in the Available Privileges box, and then clicking the button.
This tab is available only if the Show Table/Column Privileges checkbox in the Administrator section of the Options dialog has been checked. It allows you to grant privileges on a table level or on a column level.
To access the tables, double-click on the schema (database) name containing that table. You will not see and cannot grant privileges on a schema level in this tab; if you want to do that, use the Global Privileges tab instead. Also, you cannot select more than one table at a time.
If you want to grant privileges on a column level, double-click on the table name; this will give you access to its columns. You cannot select more than one column at a time.
Privileges not assigned to the user are listed under Available Privileges. You can remove privileges by selecting them in the left box, and then clicking the button. Removed privileges will appear in the Available Privileges box. You can assign privileges by selecting them in the Available Privileges box, and then clicking the button.
This section provides graphical information about the MySQL server's current performance, load, and other indicators such as disk usage and server variables. Note that clicking on that section will open an additional connection to the MySQL server, which you can see when viewing threads and users in the Server Connections section.
This tab provides information about connections to the MySQL server.
Connection Usage: Displays a percentage of the maximum number of simultaneous clients allowed. If that value gets close to 100%, this probably means that you should raise that maximum number, which you can do in the Startup Variables section. The display also shows the current value of that maximum. For more information on server connections, see the SHOW VARIABLES and Too many connections Error sections.
Traffic: [SH] FILL IN
Number of SQL Queries: [SH] Mike: No idea what "100%" might be based on. It can't be max_user_connections, nor any other variable I'm aware of. [SH] FILL IN
This tab provides information about memory caches that affect the performance of the MySQL server. For each cache, there is a display that shows the current hitrate or usage of the cache, and a display that shows the hitrate or usage for the last minutes. The size of the latter display depends on the size of the working area of the main window.
Query Cache Hitrate: When in use, the query cache of the MySQL server stores the text of a SELECT query together with the corresponding result that was sent to the client. If an identical query is later received, the server will retrieve the results from the query cache rather than parsing and executing the same query again. The hitrate indicates the ratio of queries that were cached and queries that were not cached. The higher the hitrate, the better the performance of the server regarding SELECT queries. See the MySQL Query Cache section for details.
Key Efficiency: Information about the key buffer.
This tab provides information about the status variables of the MySQL server. In the left box of the working area, you find categories and subcategories. Double-click on a category name to expand or collapse its subcategories.
For each category, and each subcategory, the status variables are listed in the right box of the working area, together with their values, and with a short explanation. The status variables are described in detail in the SHOW STATUS section.
Use the
button to make MySQL Administrator retrieve the variables and their values once again.Right-clicking in the right box allows you to copy variables to the clipboard.
This tab provides information about the system variables of the MySQL server. In the left box of the working area, you can find categories and subcategories. Double-click on a category name to expand or collapse its subcategories.
For each category, and each subcategory, the system variables are listed in the right box of the working area, together with their values, and with a short explanation. The system variables are described in detail in the SHOW VARIABLES section.
System variables that can be set at runtime are marked as editable, that is they are prefixed with an icon different from the variables that cannot be set at runtime. Double-clicking on editable variables will open a dialog where you can specify another value for the variable. The changes you make will take effect as soon as you click the SET Syntax section.
button in that dialog. Click if you want to keep the current value. In MySQL Administrator, system variables are set on a global level only. Note that you need appropriate privileges to change variables globally. You can find more information on global variables in theUse the
button to make MySQL Administrator retrieve the variables and their values once again.Right-clicking in the right box allows you to copy variables to the clipboard.
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For all tabs in this section, the working area is split into two boxes. Above the boxes, there is a bar which allows you to navigate through the log files when those have many entries. Clicking in that bar will display only part of that big logfile. Clicking on the left end of the bar will show the very first log file entries, while clicking on the right end will show the very last lines of the log file.
Note that you can view log files that are stored on the machine where MySQL Administrator is running only. At the moment, you cannot view log files of a MySQL server that is running on another machine, unless those happen to be stored on the machine where MySQL Administrator is running (which is rather unlikely). [SH] Mike: True?
Also note that some tabs may be disabled. This may be due to the before mentioned reason, but it may also mean that the log file in question has not been enabled on the MySQL server you are connected to. You can enable the various log files in the Startup Variables section.
While the right box displays the complete contents of the log file selected, in exactly the same format that the log file uses, the left box provides information about the most important events, in a format that is easier to read. In the right box, you might, for example, see something like this:
040105 12:30:07 InnoDB: Started
That same information would be displayed in the left box like this:
05 Jan 12:30 InnoDB Startup
Clicking on an event in the left box will jump to the corresponding log file entry in the right box.
Each tab has three buttons:
opens a dialog where you can specify a search term to look for in the log file. If it's found, it will be marked as selected in the right box. This command is available by right-clicking in the right box, too.
current log file contents that you may store for documenting or analysis purposes. This command is available by right-clicking in the right box, too.
opens a dialog that allows you to specify the path and file name where the log file should be stored. By default, MySQL Administrator suggests ErrorLog.txt, SlowLog.txt, or GeneralLog.txt as a filename. Note that executing that command does not affect the actual log file in any way; it just creates a copy of thewill reload the log files.
Displays the MySQL server's error log. The error log file contains information indicating when the MySQL server was started and stopped and also any critical errors found when running. For more information about that log file, see The Error Log.
Displays the MySQL server's slow query log. If enabled (which you can do in the Startup Variables section), the MySQL server writes a log file containing all SQL commands that took more than a specific number of seconds to execute. (That number can be configured by the long_query_time variable; its default value is 10 seconds.) The time to get the initial table locks are not counted as execution time. For more information about that log file, see The Slow Query Log.
Displays the MySQL server's general query log. This log can be very useful when you suspect an error in a client and want to know exactly what the MySQL server thought the client sent to it. For more information about that log file, see The General Query Log.
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This section allows you to create backup projects, and to perform backups. If you are an experienced MySQL user, you will notice that this section works like a graphical wrapper around the mysqldump command-line client (while it actually uses a different code base), with the additional convenience of saving your backup projects within MySQL Administrator.
Existing backup projects are listed in the lower left area of the sidebar. If there are many backup projects, the field with the magnifying-glass icon may be handy for filtering the projects you are looking for. Typing in t or T, for example, will set the filter to projects whose names begin with a t. The filter works in a case-insensitive fashion.
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This section is split into two tabs: General and Restore Content. It allows you to restore data backed up in a backup file.
In this tab, you specify which backup file should be used for the restore procedure.
File to restore: Specify path and filename of the backup file. You can browse for that file by clicking the
button.Target Schema: At the moment, the only available option is Original Schema. Tables will be restored in the schema (database) where they were backed up from.
Backup Type: At the moment, the only available option is SQL Files. Those are backup files containing SQL statements that restore schemata (databases), tables, and the contained data.
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This section gives you an overview over your MySQL replication environment. Of course, you will only see something in this section if replication has been set up. Another prerequisite is that you are connected to the master server. [SH] Mike: True? [SH] FILL IN
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This section allows you to view catalogs, schemata, tables and their properties, and to perform a number of operations on tables. Existing catalogs and schemata are listed in the lower left area of the sidebar. If there are many schemata on your MySQL server, the field with the magnifying-glass icon may be handy for filtering the schemata you are looking for. Typing in t or T, for example, will set the filter to schemata whose names begin with a t. The filter works in a case-insensitive fashion.
Select the schema (database) that you wish to view. Right-clicking on any schema allows you to refresh the catalogs/schemata list. Double-clicking a schema will expand its tables, indexes, and users. Clicking on those subcategories selects the appropriate tab (Schema Tables, Indexes, or Users).
This tab is split into two boxes. The upper box shows information about the tables contained in the selected schema (database). Besides the table name you see the table type, the row format, the number of rows, and the data length of the contained tables. For more information see the MySQL Table Types section. For MyISAM tables, you also find the date and time when the table was last modified, under Update Time. You can update the list of table by pressing the button.
The tables are ordered by table name initially, but you may change that sorting by clicking on the appropriate headings (Type, Row Format, etc.). [SH] Not yet implemented
You may select more than one table in the upper box using the mouse or the keyboard. For the selected tables, you can perform two operations:
OPTIMIZE TABLE Syntax section.
: This corresponds to the OPTIMIZE TABLE SQL command and should be used if you have deleted a large part of a table or if you have made many changes to a table with variable-length rows (tables that have VARCHAR, BLOB, or TEXT columns). Deleted records are maintained in a linked list and subsequent INSERT operations reuse old record positions. You can use that command to reclaim the unused space and to defragment the datafile. Note that table optimization works for MyISAM and BDB tables only. For more information, see theREPAIR TABLE Syntax section.
: This corresponds to the REPAIR TABLE SQL command and should be used in case of table problems. Note that this command works for MyISAM tables only. For more information, see the
Clicking on a table name in the upper box will display its properties in the lower box.
This tab lists the name, the datatype, and optionally the comment for each column of the selected table. The latter is available as of MySQL version 4.1 only. The symbols preceding the column names indicate whether or not the column is part of an index.
This tab lists the indexes of the selected table. Besides the index names and the columns that form that index, you can also see the index type (PRIMARY, UNIQUE, etc.) and other information about the table's indexes. You could also get that information by issuing a SHOW INDEX SQL command in a command-line client (see Retrieving Information about Database, Tables, Columns, and Indexes section). For more information about indexes, see the Column Indexes section.
In this tab, you find detailed information about the selected table. That information could also be retrieved by issuing a SHOW TABLE STATUS LIKE 'tbl' SQL command. For more information, see the SHOW TABLE STATUS section.
In this tab, you find detailed information about the rows of the selected table. That information could also be retrieved by issuing a SHOW TABLE STATUS LIKE 'tbl' SQL command. For more information, see the SHOW TABLE STATUS section.
While the Indexes tab in the lower box of the Schema Tables tab displays the indexes for the selected table only, this tab provides an overview over all indexes of all tables contained in the selected schema (database). Initially, you will see tables (possibly listed more than once, whenever they contain more than one index), the indexes in those tables, and some additional information about those indexes. That information could also be retrieved by issuing a SHOW TABLE STATUS SQL command. For more information, see the SHOW TABLE STATUS section.
Double-clicking on a table name will expand the subcategories of that index, so that you can see which table columns form that index.
Connection profiles are stored in the MySQL Administrator's installation directory, in a file called mysqlx_user_connections.xml. The contents of that file look like this:
<?xml version="1.0"?> <user_connections> <last_connection>1</last_connection> <password_storage_type>2</password_storage_type> <user_connection> <connection_name></connection_name> <username>root</username> <hostname>localhost</hostname> <port>3306</port> <schema></schema> <advanced_options/> <storage_path></storage_path> <notes></notes> <connection_type>0</connection_type> <storage_type>2</storage_type> <password></password> </user_connection> ...
You may edit that file manually, but take care not to invalidate the XML. When applying changes by editing and saving that file, those changes will show up the next time you open the Connections section of the Options dialog. You do not need to restart MySQL Administrator for the changes to take effect.
As a database administrator, you may also edit that file according to your preferences, and then copy it to any machine where MySQL Administrator runs on. This makes it easy to have identical connection profiles on all machines, without having to set up those profiles individually on each of the machines.
Besides the documentation you are just reading (which is written in DocBook XML), MySQL Administrator uses a number of XML files for internal purposes.
mysqlx_options.xml: Stores options selected in the Options dialog.
mysqlx_status_variables.xml: Stores the status variables known to MySQL Administrator, so that they can be assigned descriptions in various languages (see below for the XML file containing those descriptions). Those descriptions will show up in the Status Variables tab of the Health section. You can select the language of the descriptions in the General Options section of the Options dialog. That file also determines in which categories or subcategories a variable will appear, and the order in which categories and subcategories appear. It does not, however, determine in which order variables appear within a category or subcategory, as those are sorted lexically by MySQL Administrator.
mysqlx_system_variables.xml: Stores the system variables known to MySQL Administrator, so that they can be assigned descriptions in various languages (see below for the XML file containing those descriptions). Those descriptions will show up in the System Variables tab of the Health section. You can select the language of the descriptions in the General Options section of the Options dialog. That file also determines in which categories or subcategories a variable will appear, and the order in which categories and subcategories appear. It does not, however, determine in which order variables appear within a category or subcategory, as those are sorted lexically by MySQL Administrator.
mysqlx_translations_administrator.xml: Stores descriptions specific to MySQL Administrator, like descriptions for status and server variables, or category names, or labels used in dialogs. Here is an excerpt from that file, which contains English and German texts:
<textgroup id="MySQLVariables"> <text id="status_var_group_General"> <trans xml:lang="en">General</trans> <trans xml:lang="de">Allgemein</trans> </text> <text id="status_var_Uptime"> <trans xml:lang="en">How many seconds the server has been up.</trans> </text> ... <textgroup id="Form_InstanceForm"> <text id="FileMI"> <trans xml:lang="en">&File</trans> <trans xml:lang="de">&Datei</trans> </text> <text id="NewConnectionMI"> <trans xml:lang="en">&New Connection ...</trans> <trans xml:lang="de">&Neue Verbindung ...</trans> </text> <text id="SaveConnectionMI"> <trans xml:lang="en">&Save Connection ...</trans> <trans xml:lang="de">Verbindung &speichern ...</trans> </text> <text id="CloseMI"> <trans xml:lang="en">Clos&e</trans> <trans xml:lang="de">Be&enden</trans> </text> </textgroup> ...
From that excerpt, you can learn a number of things:
A description (called text) does not necessarily have to be translated (see status_var_Uptime). If it isn't, English will be used instead.
Adding another translation is as simple as adding another <trans xml:lang="language"> tag.
Therefore, translating the software is a painless task; however, please have a look at the Notes for Translators below!
mysqlx_translations_general.xml: Stores terms and descriptions that appear not only in MySQL Administrator, but also in other graphical MySQL programs. Its format, however, is identical with the format of the mysqlx_translations_administrator.xml file. Here is an excerpt from that file:
<textgroup id="ResourceStrings"> <text id="OKBtn"> <trans xml:lang="en">OK</trans> </text> <text id="CancelBtn"> <trans xml:lang="en">Cancel</trans> <trans xml:lang="de">Abbruch</trans> </text> ...
mysqlx_user_connections.xml: This file is described in How MySQL Administrator Stores Connections.
You may find that MySQL Administrator is not available in your prefered language, or that its documentation is not available in that language. If you would like to translate the software, or its documentation, or participate in that translation, please contact the MySQL documentation team before starting your translation!
The MySQL documentation team's address is <docs@mysql.com>. In your mail, please state what you would like to translate (MySQL Administrator, or its documentation, or both, or even the whole MySQL reference manual, if you dare), and give some information regarding your background:
What is your name?
In which country and city are you located?
How long have you used MySQL?
Have you done other translations?
Will you work alone, or with a group of translators?
What's your timetable regarding the translation?
What is your motivation for translating?
We will get back to you as soon as possible.
The format used for both software and documentation is DocBook XML. From that base format, all other available formats (HTML, CHM, PDF, etc.) are being generated. It would be a pity if you started translating, say, the HTML version of this documentation, because we will not be able to use it in that format. Also, you might find that someone else has already done that translation. So, once again, please contact the MySQL documentation team first!
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MySQL Administrator incorporates PCRE and PNG support.
Regular expression support is provided by the PCRE library package, which is open source software, written by Philip Hazel, and copyright by the University of Cambridge, England. The source for the PCRE library can be found at: ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/.
PNG support for the Windows version is provided by the TPNGImage component which is open source software, written and copyright by Gustavo Daud. The source for the TPNGImage can be found at: http://pngdelphi.sourceforge.net.
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The MySQL (R) software delivers a very fast, multi-threaded, multi-user, and robust SQL (Structured Query Language) database server. MySQL Server is intended for mission-critical, heavy-load production systems as well as for embedding into mass-deployed software. MySQL is a trademark of MySQL AB.
The MySQL software is Dual Licensed. Users can choose to use the MySQL software as an Open Source/Free Software product under the terms of the GNU General Public License (http://www.fsf.org/licenses/) or can purchase a standard commercial license from MySQL AB. See Licensing and Support.
The MySQL web site (http://www.mysql.com/) provides the latest information about the MySQL software.
The following list describes some sections of particular interest in this manual:
For information about the company behind the MySQL Database Server, see What is MySQL AB.
For a discussion about the capabilities of the MySQL Database Server, see Features.
For installation instructions, see Installing.
For tips on porting the MySQL Database Software to new architectures or operating systems, see Porting.
For information about upgrading from a Version 4.0 release, see Upgrading-from-4.0.
For information about upgrading from a Version 3.23 release, see Upgrading-from-3.23.
For information about upgrading from a Version 3.22 release, see Upgrading-from-3.22.
For a tutorial introduction to the MySQL Database Server, see Tutorial.
For examples of SQL and benchmarking information, see the benchmarking directory (sql-bench in the distribution).
For a history of new features and bug fixes, see News.
For a list of currently known bugs and misfeatures, see Bugs.
For future plans, see TODO.
For a list of all the contributors to this project, see Credits.
Important:
Reports of errors (often called bugs), as well as questions and comments, should be sent to the general MySQL mailing list. See Mailing-list. See Bug reports.
The mysqlbug script should be used to generate bug reports on Unix. (Windows distributions contain a file mysqlbug.txt in the base directory that can be used as a template for a bug report.)
For source distributions, the mysqlbug script can be found in the scripts directory. For binary distributions, mysqlbug can be found in the bin directory (/usr/bin for the MySQL-server RPM package).
If you have found a sensitive security bug in MySQL Server, please let us know immediately by sending an email message to <security@mysql.com>.
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This is the MySQL reference manual; it documents MySQL up to Version 5.0.0-alpha. Functional changes are always indicated with reference to the version, so this manual is also suitable if you are using an older version of the MySQL software (such as 3.23 or 4.0-production). There are also references for version 5.0 (development).
Being a reference manual, it does not provide general instruction on SQL or relational database concepts. It also will not teach you how to use your operating system or command line interpreter.
As the MySQL Database Software is under constant development, the manual is also updated frequently. The most recent version of this manual is available at http://www.mysql.com/documentation/ in many different formats, including HTML, PDF, and Windows HLP versions.
The primary document is the Texinfo file. The HTML version is produced automatically using a modified version of texi2html. The plain text and Info versions are produced with makeinfo. The PostScript version is produced using texi2dvi and dvips. The PDF version is produced with pdftex.
The index can assist you in finding information in the manual. For online use, you can try the searchable version of the manual available at http://www.mysql.com/doc/.
If you have any suggestions concerning additions or corrections to this manual, please send them to the documentation team at <docs@mysql.com>.
This manual was initially written by David Axmark and Michael (Monty) Widenius. It is now maintained by the MySQL Documentation Team, consisting of Arjen Lentz, Paul DuBois and Stefan Hinz. For the many other contributors, see Credits.
The copyright (2004) to this manual is owned by the Swedish company MySQL AB. See Copyright.
This manual uses certain typographical conventions:
constant | Constant-width font is used for command names and options; SQL statements; database, table, and column names; C and Perl code; and environment variables. Example: ``To see how mysqladmin works, invoke it with the --help option.'' |
filename | Constant-width font with surrounding quotes is used for filenames and pathnames. Example: ``The distribution is installed under the /usr/local/ directory.'' |
c | Constant-width font with surrounding quotes is also used to indicate character sequences. Example: ``To specify a wildcard, use the % character.'' |
italic | Italic font is used for emphasis, like this. |
boldface | Boldface font is used in table headings and to convey especially strong emphasis. |
When commands are shown that are meant to be executed by a particular program, the program is indicated by a prompt shown before the command. For example, shell> indicates a command that you execute from your login shell, and mysql> indicates a statement that you execute from the mysql client program:
shell> type a shell command here mysql> type a mysql statement here
The ``shell'' is your command interpreter. On Unix, this is typically a program such as sh or csh. On Windows, the equivalent is command.com or cmd.exe, typically run in a Windows console.
Note that to enter a command or statement from an example, you do not type the prompt shown in the example.
Commands to set shell variables are shown using Bourne shell syntax. If you are using csh or tcsh, you will need to issue commands somewhat differently. For example, the sequence to set an environment variable and run a command looks like this in Bourne shell syntax:
shell> VARNAME=value some_command
For csh or tcsh, you would execute the sequence like this:
shell> setenv VARNAME value shell> some_command
Database, table, and column names must often be substituted into commands. To indicate that such substitution is necessary, this manual uses db_name, tbl_name, and col_name. For example, you might see a statement like this:
mysql> SELECT col_name FROM db_name.tbl_name;
This means that if you were to enter a similar statement, you would supply your own database, table, and column names, perhaps like this:
mysql> SELECT author_name FROM biblio_db.author_list;
SQL keywords are not case sensitive and may be written in uppercase or lowercase. This manual uses uppercase.
In syntax descriptions, square brackets ([ and ]) are used to indicate optional words or clauses. For example, in the following statement, IF EXISTS is optional:
DROP TABLE [IF EXISTS] tbl_name
When a syntax element consists of a number of alternatives, the alternatives are separated by vertical bars (|). When one member from a set of choices may be chosen, the alternatives are listed within square brackets ([ and ]):
TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)
When one member from a set of choices must be chosen, the alternatives are listed within braces ({ and }):
{DESCRIBE | DESC} tbl_name {col_name | wild}
An ellipsis (...) indicates the omission of a section of a statement, typically to provide a shorter version of more complex syntax. For example, INSERT ... SELECT is shorthand for the form of INSERT statement that is followed by a SELECT statement.
An ellipsis can also indicate that the preceding syntax element of a statement may be repeated. In the following example, multiple reset_option values may be given, with each of those after the first preceded by commas:
RESET reset_option [,reset_option] ...
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MySQL, the most popular Open Source SQL database management system, is developed, distributed, and supported by MySQL AB. MySQL AB is a commercial company, founded by the MySQL developers, that builds its business by providing services around the MySQL database management system. See What is MySQL AB.
The MySQL web site (http://www.mysql.com/) provides the latest information about MySQL software and MySQL AB.
MySQL is a database management system. | A database is a structured collection of data. It may be anything from a simple shopping list to a picture gallery or the vast amounts of information in a corporate network. To add, access, and process data stored in a computer database, you need a database management system such as MySQL Server. Since computers are very good at handling large amounts of data, database management systems play a central role in computing, as stand-alone utilities or as parts of other applications. |
MySQL is a relational database management system. | A relational database stores data in separate tables rather than putting all the data in one big storeroom. This adds speed and flexibility. The SQL part of ``MySQL'' stands for ``Structured Query Language''. SQL is the most common standardized language used to access databases and is defined by the ANSI/ISO SQL Standard.(The SQL standard has been evolving since 1986 and several versions exist. In this manual, ``SQL-92'' refers to the standard released in 1992, ``SQL-99'' refers to the standard released in 1999, and ``SQL:2003'' refers to the next version of the standard. We use the term ``the SQL standard'' to mean the current version of the SQL Standard at any time.) |
MySQL software is Open Source. | Open Source means that it is possible for anyone to use and modify the software. Anybody can download the MySQL software from the Internet and use it without paying anything. If you wish, you may study the source code and change it to suit your needs. The MySQL software uses the GPL (GNU General Public License), http://www.fsf.org/licenses/, to define what you may and may not do with the software in different situations. If you feel uncomfortable with the GPL or need to embed MySQL code into a commercial application, you can buy a commercially licensed version from us. See MySQL licenses. |
Why use the MySQL Database Server? | The MySQL Database Server is very fast, reliable, and easy to use. If that is what you are looking for, you should give it a try. MySQL Server also has a practical set of features developed in close cooperation with our users. You can find a performance comparison of MySQL Server with other database managers on our benchmark page. See MySQL Benchmarks. MySQL Server was originally developed to handle large databases much faster than existing solutions and has been successfully used in highly demanding production environments for several years. Though under constant development, MySQL Server today offers a rich and useful set of functions. Its connectivity, speed, and security make MySQL Server highly suited for accessing databases on the Internet. |
The technical features of MySQL Server | The MySQL Database Software is a client/server system that consists of a multi-threaded SQL server that supports different backends, several different client programs and libraries, administrative tools, and a wide range of application programming interfaces (APIs). We also provide MySQL Server as a multi-threaded library which you can link into your application to get a smaller, faster, easier-to-manage product. |
There is a large amount of contributed MySQL software available. | It is very likely that you will find that your favorite application or language already supports the MySQL Database Server. |
The official way to pronounce MySQL is ``My Ess Que Ell'' (not ``my sequel''), but we don't mind if you pronounce it as ``my sequel'' or in some other localized way.
We started out with the intention of using mSQL to connect to our tables using our own fast low-level (ISAM) routines. However, after some testing, we came to the conclusion that mSQL was not fast enough or flexible enough for our needs. This resulted in a new SQL interface to our database but with almost the same API interface as mSQL. This API was designed to allow third-party code that was written for use with mSQL to be ported easily for use with MySQL.
The derivation of the name MySQL is not clear. Our base directory and a large number of our libraries and tools have had the prefix ``my'' for well over 10 years. However, co-founder Monty Widenius's daughter is also named My. Which of the two gave its name to MySQL is still a mystery, even for us.
The name of the MySQL Dolphin (our logo) is Sakila. Sakila was chosen by the founders of MySQL AB from a huge list of names suggested by users in our ``Name the Dolphin'' contest. The winning name was submitted by Ambrose Twebaze, an open source software developer from Swaziland, Africa. According to Ambrose, the name Sakila has its roots in SiSwati, the local language of Swaziland. Sakila is also the name of a town in Arusha, Tanzania, near Ambrose's country of origin, Uganda.
The following list describes some of the important characteristics of the MySQL Database Software. See MySQL 4.0 Nutshell.
Internals and Portability
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Column Types
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Commands and Functions
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Security
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Scalability and Limits
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Connectivity
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Localization
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Clients and Tools
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This section addresses the questions ``How stable is MySQL Server?'' and ``Can I depend on MySQL Server in this project?'' We will try to clarify these issues and answer some important questions that concern many potential users. The information in this section is based on data gathered from the mailing list, which is very active in identifying problems as well as reporting types of use.
The original code stems back to the early 1980s. It provides a stable code base, and the ISAM table format used by the original storage engine remains backward-compatible. At TcX, the predecessor of MySQL AB, MySQL code has worked in projects since mid-1996, without any problems. When the MySQL Database Software initially was released to a wider public, our new users quickly found some pieces of ``untested code''. Each new release since then has had fewer portability problems (even though each new release has also had many new features).
Each release of the MySQL Server has been usable. Problems have occurred only when users try code from the ``gray zones.'' Naturally, new users don't know what the gray zones are; this section therefore attempts to document those areas that are currently known. The descriptions mostly deal with Version 3.23 and 4.0 of MySQL Server. All known and reported bugs are fixed in the latest version, with the exception of those listed in the bugs section, which are design-related. See Bugs.
The MySQL Server design is multi-layered with independent modules. Some of the newer modules are listed here with an indication of how well-tested each of them is:
Replication --- Gamma | Large groups of servers using replication are in production use, with good results. Work on enhanced replication features is continuing in MySQL 5.x. |
InnoDB tables --- Stable (in 3.23 from 3.23.49) | The InnoDB transactional storage engine has been declared stable in the MySQL 3.23 tree, starting from version 3.23.49. InnoDB is being used in large, heavy-load production systems. |
BDB tables --- Gamma | The Berkeley DB code is very stable, but we are still improving the BDB transactional storage engine interface in MySQL Server, so it will take some time before this is as well tested as the other table types. |
Full-text searches --- Beta | Full-text searching works but is not yet widely used. Important enhancements have been implemented in MySQL 4.0. |
Connector/ODBC 3.51 (uses ODBC SDK 3.51) --- Stable | In wide production use. Some issues brought up appear to be application-related and independent of the ODBC driver or underlying database server. |
Automatic recovery of MyISAM tables --- Gamma | This status applies only to the new code in the MyISAM storage engine that checks if the table was closed properly on open and executes an automatic check/repair of the table if it wasn't. |
Bulk-insert --- Alpha | New feature in MyISAM tables in MySQL 4.0 for faster insert of many rows. |
Locking --- Gamma | This is very system-dependent. On some systems there are big problems using standard operating system locking (fcntl()). In these cases, you should run mysqld with the --skip-external-locking flag. Problems are known to occur on some Linux systems, and on SunOS when using NFS-mounted filesystems. |
Paying customers receive high-quality support directly from MySQL AB. MySQL AB also provides the MySQL mailing list as a community resource where anyone may ask questions.
Bugs are usually fixed right away with a patch. For serious bugs, there is almost always a new release.
MySQL Version 3.22 had a 4 GB (4 gigabyte) limit on table size. With the MyISAM storage engine in MySQL Version 3.23, the maximum table size was increased to 8 million terabytes (2 ^ 63 bytes). With this larger allowed table size, the maximum effective table size for MySQL databases now normally is determined by operating system constraints on file sizes, not by MySQL internal limits.
The InnoDB storage engine maintains InnoDB tables within a tablespace that can be created from several files. This allows a table to exceed the maximum individual file size. The tablespace can include raw disk partitions, which allows extremely large tables. The maximum tablespace size is 64 TB.
The following table lists some examples of operating system file-size limits:
Operating System | File-Size Limit |
Linux-Intel 32-bit | 2 GB, much more when using LFS |
Linux-Alpha | 8 TB (?) |
Solaris 2.5.1 | 2 GB (4GB possible with patch) |
Solaris 2.6 | 4 GB (can be changed with flag) |
Solaris 2.7 Intel | 4 GB |
Solaris 2.7 UltraSPARC | 512 GB |
On Linux 2.2, you can get MyISAM tables larger than 2 GB in size by using the LFS patch for the ext2 filesystem. On Linux 2.4, patches also exist for ReiserFS to get support for big files. Most current Linux distributions are based on kernel 2.4 and already include all the required Large File Support (LFS) patches. However, the maximum available file size still depends on several factors, one of them being the file system used to store MySQL tables.
For a very detailed overview about LFS in Linux, have a look at Andreas Jaeger's ``Large File Support in Linux'' page at http://www.suse.de/~aj/linux_lfs.html.
By default, MySQL creates MyISAM tables with an internal structure that allows a maximum size of about 4 GB. You can check the maximum table size for a table with the SHOW TABLE STATUS command or with the myisamchk -dv table_name. See SHOW.
If you need a MyISQM table that will be larger than 4 GB in size (and your operating system supports large files), the CREATE TABLE statement allows AVG_ROW_LENGTH and MAX_ROWS options. See CREATE TABLE. You can also change these options with ALTER TABLE after the table has been created, to increase the table's maximum allowable size. See ALTER TABLE.
Other ways to work around file-size limits for MyISAM tables are as follows:
If your large table is read-only, you can use myisampack to compress it. myisampack usually compresses a table by at least 50%, so you can have, in effect, much bigger tables. myisampack also can merge multiple tables into a single table. See myisampack.
Another way to get around the operating system file limit for MyISAM datafiles is by using the RAID options. See CREATE TABLE.
MySQL includes a MERGE library that allows you to handle a collection of MyISAM tables that have identical structure as a single MERGE table. See MERGE tables.
The MySQL Server itself has no problems with Year 2000 (Y2K) compliance:
MySQL Server uses Unix time functions that handle dates into the year 2037 for TIMESTAMP values. For DATE and DATETIME values, dates through the year 9999 are accepted.
All MySQL date functions are implemented in one source file, sql/time.cc, and are coded very carefully to be year 2000-safe.
In MySQL Version 3.22 and later, the YEAR column type can store years 0 and 1901 to 2155 in one byte and display them using two or four digits. All 2-digit years are considered to be in the range 1970 to 2069, which means that if you store 01 in a YEAR column, MySQL Server treats it as 2001.
The following simple demonstration illustrates that MySQL Server doesn't have any problems with dates until after the year 2030:
mysql> DROP TABLE IF EXISTS y2k; Query OK, 0 rows affected (0.01 sec) mysql> CREATE TABLE y2k (date DATE, -> date_time DATETIME, -> time_stamp TIMESTAMP); Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO y2k VALUES -> ('1998-12-31','1998-12-31 23:59:59',19981231235959), -> ('1999-01-01','1999-01-01 00:00:00',19990101000000), -> ('1999-09-09','1999-09-09 23:59:59',19990909235959), -> ('2000-01-01','2000-01-01 00:00:00',20000101000000), -> ('2000-02-28','2000-02-28 00:00:00',20000228000000), -> ('2000-02-29','2000-02-29 00:00:00',20000229000000), -> ('2000-03-01','2000-03-01 00:00:00',20000301000000), -> ('2000-12-31','2000-12-31 23:59:59',20001231235959), -> ('2001-01-01','2001-01-01 00:00:00',20010101000000), -> ('2004-12-31','2004-12-31 23:59:59',20041231235959), -> ('2005-01-01','2005-01-01 00:00:00',20050101000000), -> ('2030-01-01','2030-01-01 00:00:00',20300101000000), -> ('2050-01-01','2050-01-01 00:00:00',20500101000000); Query OK, 13 rows affected (0.01 sec) Records: 13 Duplicates: 0 Warnings: 0 mysql> SELECT * FROM y2k; +------------+---------------------+----------------+ | date | date_time | time_stamp | +------------+---------------------+----------------+ | 1998-12-31 | 1998-12-31 23:59:59 | 19981231235959 | | 1999-01-01 | 1999-01-01 00:00:00 | 19990101000000 | | 1999-09-09 | 1999-09-09 23:59:59 | 19990909235959 | | 2000-01-01 | 2000-01-01 00:00:00 | 20000101000000 | | 2000-02-28 | 2000-02-28 00:00:00 | 20000228000000 | | 2000-02-29 | 2000-02-29 00:00:00 | 20000229000000 | | 2000-03-01 | 2000-03-01 00:00:00 | 20000301000000 | | 2000-12-31 | 2000-12-31 23:59:59 | 20001231235959 | | 2001-01-01 | 2001-01-01 00:00:00 | 20010101000000 | | 2004-12-31 | 2004-12-31 23:59:59 | 20041231235959 | | 2005-01-01 | 2005-01-01 00:00:00 | 20050101000000 | | 2030-01-01 | 2030-01-01 00:00:00 | 20300101000000 | | 2050-01-01 | 2050-01-01 00:00:00 | 00000000000000 | +------------+---------------------+----------------+ 13 rows in set (0.00 sec)
The final TIMESTAMP column value is zero because the final year (2050) exceeds the TIMESTAMP maximum. The TIMESTAMP datatype, which is used to store the current time, supports values that range from 19700101000000 to 20300101000000 on 32-bit machines (signed value). On 64-bit machines, TIMESTAMP handles values up to 2106 (unsigned value).
The example also shows that the DATE and DATETIME datatypes have no problems with the dates used. They handle dates through the year 9999.
Although MySQL Server itself is Y2K-safe, you may run into problems if you use it with applications that are not Y2K-safe. For example, many old applications store or manipulate years using 2-digit values (which are ambiguous) rather than 4-digit values. This problem may be compounded by applications that use values such as 00 or 99 as ``missing'' value indicators. Unfortunately, these problems may be difficult to fix because different applications may be written by different programmers, each of whom may use a different set of conventions and date-handling functions.
Thus, even though MySQL Server has no Y2K problems, it is the application's responsibility to provide unambiguous input. See Y2K issues for MySQL Server's rules for dealing with ambiguous date input data that contains 2-digit year values.
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MySQL AB is the company of the MySQL founders and main developers. MySQL AB was originally established in Sweden by David Axmark, Allan Larsson, and Michael ``Monty'' Widenius.
The developers of the MySQL server are all employed by the company. We are a virtual organization with people in a dozen countries around the world. We communicate extensively over the Internet every day with one another and with our users, supporters, and partners.
We are dedicated to developing the MySQL database software and promoting it to new users. MySQL AB owns the copyright to the MySQL source code, the MySQL logo and trademark, and this manual. See What-is.
The MySQL core values show our dedication to MySQL and Open Source.
We want the MySQL Database Software to be:
The best and the most widely used database in the world
Available to, and affordable by all
Easy to use
Continuously improving while remaining fast and safe
Fun to use and improve
Free from bugs
MySQL AB and the people at MySQL AB:
Promote Open Source philosophy and support the Open Source community
Aim to be good citizens
Prefer partners that share our values and mind-set
Answer email and provide support
Are a virtual company, networking with others
Work against software patents
The MySQL web site (http://www.mysql.com/) provides the latest information about MySQL and MySQL AB.
By the way, the ``AB'' part of the company name is the acronym for the Swedish ``aktiebolag'', or ``stock company.'' It translates to ``MySQL, Inc.'' In fact, MySQL Inc. and MySQL GmbH are examples of MySQL AB subsidiaries. They are located in the US and Germany, respectively.
One of the most common questions we encounter is: ``How can you make a living from something you give away for free?'' This is how:
MySQL AB makes money on support, services, commercial licenses, and royalties.
We use these revenues to fund product development and to expand the MySQL business.
The company has been profitable since its inception. In October 2001, we accepted venture financing from leading Scandinavian investors and a handful of business angels. This investment is used to solidify our business model and build a basis for sustainable growth.
MySQL AB is run and owned by the founders and main developers of the MySQL database. The developers are committed to providing support to customers and other users in order to stay in touch with their needs and problems. All our support is provided by qualified developers. Really tricky questions are answered by Michael Monty Widenius, principal author of the MySQL Server. See Support.
For more information and ordering support at various levels, see http://www.mysql.com/support/ or contact our sales staff at <sales@mysql.com>.
MySQL AB delivers MySQL and related training worldwide. We offer both open courses and in-house courses tailored to the specific needs of your company. MySQL Training is also available through our partners, the Authorized MySQL Training Centers.
Our training material uses the same example databases used in our documentation and our sample applications, and is always updated to reflect the latest MySQL version. Our trainers are backed by the development team to guarantee the quality of the training and the continuous development of the course material. This also ensures that no questions raised during the courses remain unanswered.
Attending our training courses will enable you to achieve your MySQL application goals. You will also:
Save time.
Improve the performance of your applications.
Reduce or eliminate the need for additional hardware, decreasing cost.
Enhance security.
Increase customers' and co-workers' satisfaction.
Prepare yourself for MySQL Certification.
If you are interested in our training as a potential participant or as a training partner, please visit the training section at http://www.mysql.com/training/ or contact us at: <training@mysql.com>.
For details about the MySQL Certification Program, please see http://www.mysql.com/certification/.
MySQL AB and its Authorized Partners offer consulting services to users of MySQL Server and to those who embed MySQL Server in their own software, all over the world.
Our consultants can help you design and tune your databases, construct efficient queries, tune your platform for optimal performance, resolve migration issues, set up replication, build robust transactional applications, and more. We also help customers embed MySQL Server in their products and applications for large-scale deployment.
Our consultants work in close collaboration with our development team, which ensures the technical quality of our professional services. Consulting assignments range from 2-day power-start sessions to projects that span weeks and months. Our expertise not only covers MySQL Server---it also extends into programming and scripting languages such as PHP, Perl, and more.
If you are interested in our consulting services or want to become a consulting partner, please visit the consulting section of our web site at http://www.mysql.com/consulting/ or contact our consulting staff at <consulting@mysql.com>.
The MySQL database is released under the GNU General Public License (GPL). This means that the MySQL software can be used free of charge under the GPL. If you do not want to be bound by the GPL terms (such as the requirement that your application must also be GPL), you may purchase a commercial license for the same product from MySQL AB; see http://www.mysql.com/products/pricing.html. Since MySQL AB owns the copyright to the MySQL source code, we are able to employ Dual Licensing, which means that the same product is available under GPL and under a commercial license. This does not in any way affect the Open Source commitment of MySQL AB. For details about when a commercial license is required, please see MySQL licenses.
We also sell commercial licenses of third-party Open Source GPL software that adds value to MySQL Server. A good example is the InnoDB transactional storage engine that offers ACID support, row-level locking, crash recovery, multi-versioning, foreign key support, and more. See InnoDB.
MySQL AB has a worldwide partner program that covers training courses, consulting and support, publications, plus reselling and distributing MySQL and related products. MySQL AB Partners get visibility on the http://www.mysql.com/ web site and the right to use special versions of the MySQL trademarks to identify their products and promote their business.
If you are interested in becoming a MySQL AB Partner, please email <partner@mysql.com>.
The word MySQL and the MySQL dolphin logo are trademarks of MySQL AB. See MySQL AB Logos and Trademarks. These trademarks represent a significant value that the MySQL founders have built over the years.
The MySQL web site (http://www.mysql.com/) is popular among developers and users. In December 2003, we served 16 million page views. Our visitors represent a group that makes purchase decisions and recommendations for both software and hardware. Twelve percent of our visitors authorize purchase decisions, and only nine percent are not involved in purchase decisions at all. More than 65% have made one or more online business purchases within the last half-year, and 70% plan to make one in the next few months.
The MySQL web site (http://www.mysql.com/) provides the latest information about MySQL and MySQL AB.
For press services and inquiries not covered in our News releases (http://www.mysql.com/news/), please send email to <press@mysql.com>.
If you have a valid support contract with MySQL AB, you will get timely, precise answers to your technical questions about the MySQL software. For more information, see Support. On our web site, see http://www.mysql.com/support/, or send an email message to <sales@mysql.com>.
For information about MySQL training, please visit the training section at http://www.mysql.com/training/. If you have restricted access to the Internet, please contact the MySQL AB training staff via email at <training@mysql.com>. See Business Services Training.
For information on the MySQL Certification Program, please see http://www.mysql.com/certification/. See Business Services Training.
If you're interested in consulting, please visit the consulting section of our web site at http://www.mysql.com/consulting/. If you have restricted access to the Internet, please contact the MySQL AB consulting staff via email at <consulting@mysql.com>. See Business Services Consulting.
Commercial licenses may be purchased online at https://order.mysql.com/. There you will also find information on how to fax your purchase order to MySQL AB. More information about licensing can be found at http://www.mysql.com/products/pricing.html. If you have questions regarding licensing or you want a quote for a high-volume license deal, please fill in the contact form on our web site (http://www.mysql.com/) or send email to <licensing@mysql.com> (for licensing questions) or to <sales@mysql.com> (for sales inquiries). See MySQL licenses.
If you represent a business that is interested in partnering with MySQL AB, please send email to <partner@mysql.com>. See Business Services Partnering.
For more information on the MySQL trademark policy, refer to http://www.mysql.com/company/trademark.html or send email to <trademark@mysql.com>. See MySQL AB Logos and Trademarks.
If you are interested in any of the MySQL AB jobs listed in our jobs section (http://www.mysql.com/company/jobs/), please send email to <jobs@mysql.com>. Please do not send your CV as an attachment, but rather as plain text at the end of your email message.
For general discussion among our many users, please direct your attention to the appropriate mailing list. See Questions.
Reports of errors (often called bugs), as well as questions and comments, should be sent to the general MySQL mailing list. See Mailing-list. If you have found a sensitive security bug in MySQL Server, please let us know immediately by sending an email message to <security@mysql.com>. See Bug reports.
If you have benchmark results that we can publish, please contact us via email at <benchmarks@mysql.com>.
If you have suggestions concerning additions or corrections to this manual, please send them to the manual team via email at <docs@mysql.com>.
For questions or comments about the workings or content of the MySQL web site (http://www.mysql.com/), please send email to <webmaster@mysql.com>.
MySQL AB has a privacy policy, which can be read at http://www.mysql.com/company/privacy.html. For any queries regarding this policy, please send email to <privacy@mysql.com>.
For all other inquires, please send an email to <info@mysql.com>.
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This section describes MySQL support and licensing arrangements.
Technical support from MySQL AB means individualized answers to your unique problems direct from the software engineers who code the MySQL database engine.
We try to take a broad and inclusive view of technical support. Almost any problem involving MySQL software is important to us if it's important to you. Typically customers seek help on how to get different commands and utilities to work, remove performance bottlenecks, restore crashed systems, understand the impact of operating system or networking issues on MySQL, set up best practices for backup and recovery, utilize APIs, and so on. Our support covers only the MySQL server and our own utilities, not third-party products that access the MySQL server, though we try to help with these where we can.
Detailed information about our various support options is given at http://www.mysql.com/support/, where support contracts can also be ordered online. If you have restricted access to the Internet, please contact our sales staff via email at <sales@mysql.com>.
Technical support is like life insurance. You can live happily without it for years. However, when your hour arrives, it becomes critically important, but it's too late to buy it. If you use MySQL Server for important applications and encounter sudden difficulties, it may be too time consuming to figure out all the answers yourself. You may need immediate access to the most experienced MySQL troubleshooters available, those employed by MySQL AB.
MySQL AB owns the copyright to the MySQL source code, the MySQL logos and trademarks and this manual. See What is MySQL AB. Several different licenses are relevant to the MySQL distribution:
All the MySQL-specific source in the server, the mysqlclient library and the client, as well as the GNU readline library is covered by the GNU General Public License. See GPL license. The text of this license can be found as the file COPYING in the distribution.
The GNU getopt library is covered by the GNU Lesser General Public License. See http://www.fsf.org/licenses/.
Some parts of the source (the regexp library) are covered by a Berkeley-style copyright.
Older versions of MySQL (3.22 and earlier) are subject to a stricter license (http://www.mysql.com/products/mypl.html). See the documentation of the specific version for information.
The MySQL reference manual is currently not distributed under a GPL-style license. Use of the manual is subject to the following terms:
Conversion to other formats is allowed, but the actual content may not be altered or edited in any way.
You may create a printed copy for your own personal use.
For all other uses, such as selling printed copies or using (parts of) the manual in another publication, prior written agreement from MySQL AB is required.
Please send an email message to <docs@mysql.com> for more information or if you are interested in doing a translation.
For information about how the MySQL licenses work in practice, please refer to MySQL licenses. Also see MySQL AB Logos and Trademarks.
The MySQL software is released under the GNU General Public License (GPL), which is probably the best known Open Source license. The formal terms of the GPL license can be found at http://www.fsf.org/licenses/. See also http://www.fsf.org/licenses/gpl-faq.html and http://www.gnu.org/philosophy/enforcing-gpl.html.
Since the MySQL software is released under the GPL, it may often be used for free, but for certain uses you may want or need to buy commercial licenses from MySQL AB at https://order.mysql.com/. See http://www.mysql.com/products/licensing.html for more information.
Older versions of MySQL (3.22 and earlier) are subject to a stricter license (http://www.mysql.com/products/mypl.html). See the documentation of the specific version for information.
Please note that the use of the MySQL software under commercial license, GPL, or the old MySQL license does not automatically give you the right to use MySQL AB trademarks. See MySQL AB Logos and Trademarks.
The GPL license is contagious in the sense that when a program is linked to a GPL program all the source code for all the parts of the resulting product must also be released under the GPL. If you do not follow this GPL requirement, you break the license terms and forfeit your right to use the GPL program altogether. You also risk damages.
You need a commercial license:
When you link a program with any GPL code from the MySQL software and don't want the resulting product to be licensed under GPL, perhaps because you want to build a commercial product or keep the added non-GPL code closed source for other reasons. When purchasing commercial licenses, you are not using the MySQL software under GPL even though it's the same code.
When you distribute a non-GPL application that only works with the MySQL software and ship it with the MySQL software. This type of solution is considered to be linking even if it's done over a network.
When you distribute copies of the MySQL software without providing the source code as required under the GPL license.
When you want to support the further development of the MySQL database even if you don't formally need a commercial license. Purchasing support directly from MySQL AB is another good way of contributing to the development of the MySQL software, with immediate advantages for you. See Support.
If you require a license, you will need one for each installation of the MySQL software. This covers any number of CPUs on a machine, and there is no artificial limit on the number of clients that connect to the server in any way.
For commercial licenses, please visit our website at http://www.mysql.com/products/licensing.html. For support contracts, see http://www.mysql.com/support/. If you have special needs or you have restricted access to the Internet, please contact our sales staff via email at <sales@mysql.com>.
You can use the MySQL software for free under the GPL if you adhere to the conditions of the GPL. For additional details, including answers to common questions about the GPL, see the generic FAQ from the Free Software Foundation at http://www.fsf.org/licenses/gpl-faq.html. Common uses of the GPL include:
When you distribute both your own application and the MySQL source code under the GPL with your product.
When you distribute the MySQL source code bundled with other programs that are not linked to or dependent on the MySQL system for their functionality even if you sell the distribution commercially. This is called mere aggregation in the GPL license.
When you are not distributing any part of the MySQL system, you can use it for free.
When you are an Internet Service Provider (ISP), offering web hosting with MySQL servers for your customers. We encourage people to use ISPs that have MySQL support, as this will give them the confidence that their ISP will, in fact, have the resources to solve any problems they may experience with the MySQL installation. Even if an ISP does not have a commercial license for MySQL Server, their customers should at least be given read access to the source of the MySQL installation so that the customers can verify that it is correctly patched.
When you use the MySQL database software in conjunction with a web server, you do not need a commercial license (so long as it is not a product you distribute). This is true even if you run a commercial web server that uses MySQL Server, because you are not distributing any part of the MySQL system. However, in this case we would like you to purchase MySQL support because the MySQL software is helping your enterprise.
If your use of MySQL database software does not require a commercial license, we encourage you to purchase support from MySQL AB anyway. This way you contribute toward MySQL development and also gain immediate advantages for yourself. See Support.
If you use the MySQL database software in a commercial context such that you profit by its use, we ask that you further the development of the MySQL software by purchasing some level of support. We feel that if the MySQL database helps your business, it is reasonable to ask that you help MySQL AB. (Otherwise, if you ask us support questions, you are not only using for free something into which we've put a lot a work, you're asking us to provide free support, too.)
Many users of the MySQL database want to display the MySQL AB dolphin logo on their web sites, books, or boxed products. We welcome and encourage this, although it should be noted that the word MySQL and the MySQL dolphin logo are trademarks of MySQL AB and may only be used as stated in our trademark policy at http://www.mysql.com/company/trademark.html.
The MySQL dolphin logo was designed by the Finnish advertising agency Priority in 2001. The dolphin was chosen as a suitable symbol for the MySQL database management system, which is like a smart, fast, and lean animal, effortlessly navigating oceans of data. We also happen to like dolphins.
The original MySQL logo may only be used by representatives of MySQL AB and by those having a written agreement allowing them to do so.
We have designed a set of special Conditional Use logos that may be downloaded from our web site at http://www.mysql.com/press/logos.html and used on third-party web sites without written permission from MySQL AB. The use of these logos is not entirely unrestricted but, as the name implies, subject to our trademark policy that is also available on our web site. You should read through the trademark policy if you plan to use them. The requirements are basically as follows:
Use the logo you need as displayed on the http://www.mysql.com/ site. You may scale it to fit your needs, but may not change colors or design, or alter the graphics in any way.
Make it evident that you, and not MySQL AB, are the creator and owner of the site that displays the MySQL trademark.
Don't use the trademark in a way that is detrimental to MySQL AB or to the value of MySQL AB trademarks. We reserve the right to revoke the right to use the MySQL AB trademark.
If you use the trademark on a web site, make it clickable, leading directly to http://www.mysql.com/.
If you use the MySQL database under GPL in an application, your application must be Open Source and must be able to connect to a MySQL server.
Contact us via email at <trademark@mysql.com> to inquire about special arrangements to fit your needs.
You need written permission from MySQL AB before using MySQL logos in the following cases:
When displaying any MySQL AB logo anywhere except on your web site.
When displaying any MySQL AB logo except the Conditional Use logos mentioned previously on web sites or elsewhere.
Due to legal and commercial reasons we monitor the use of MySQL trademarks on products, books, and other items. We usually require a fee for displaying MySQL AB logos on commercial products, since we think it is reasonable that some of the revenue is returned to fund further development of the MySQL database.
MySQL partnership logos may be used only by companies and persons having a written partnership agreement with MySQL AB. Partnerships include certification as a MySQL trainer or consultant. For more information, please see Partnering.
MySQL AB welcomes references to the MySQL database, but it should be noted that the word MySQL is a trademark of MySQL AB. Because of this, you must append the trademark symbol (TM) to the first or most prominent use of the word MySQL in a text and, where appropriate, state that MySQL is a trademark of MySQL AB. For more information, please refer to our trademark policy at http://www.mysql.com/company/trademark.html.
Table of Contents
This section provides a snapshot of the MySQL development roadmap, including major features implemented or planned for MySQL 4.0, 4.1, 5.0, and 5.1. The following sections provide information for each release series.
The production release series is MySQL 4.0, which was declared stable for production use as of Version 4.0.12, released in March 2003. This means that future 4.0 development will be limited only to making bug fixes. For the older MySQL 3.23 series, only critical bug fixes will be made.
Active MySQL development currently is taking place in the MySQL 4.1 and 5.0 release series. This means that new features are being added to MySQL 4.1 and MySQL 5.0. Both 4.1 and 5.0 are available now in alpha status.
Before upgrading from one release series to the next, please see the notes at Upgrade.
Plans for some of the most requested features are summarized in the following table.
Feature | MySQL version |
Unions | 4.0 |
Subqueries | 4.1 |
R-trees | 4.1 (for MyISAM tables) |
Stored procedures | 5.0 |
Views | 5.0 or 5.1 |
Cursors | 5.0 |
Foreign keys | 5.1 (already implemented in 3.23 for InnoDB) |
Triggers | 5.1 |
Full outer join | 5.1 |
Constraints | 5.1 |
Long awaited by our users, MySQL Server 4.0 is now available in production status.
MySQL 4.0 is available for download from http://www.mysql.com/ and from our mirrors. MySQL 4.0 has been tested by a large number of users and is in production use at many large sites.
The major new features of MySQL Server 4.0 are geared toward our existing business and community users, enhancing the MySQL database software as the solution for mission-critical, heavy-load database systems. Other new features target the users of embedded databases.
Speed enhancements
| |
Embedded MySQL Server introduced
| |
InnoDB storage engine as standard
| |
New functionality
| |
Standards compliance, portability, and migration
| |
Internationalization
| |
Usability enhancements |
In the process of implementing features for new users, we have not forgotten
requests from our loyal community of existing users.
|
The news section of this manual includes a more in-depth list of features. See News-4.0.x.
The libmysqld embedded server library makes MySQL Server suitable for a vastly expanded realm of applications. By using this library, developers can embed MySQL Server into various applications and electronics devices, where the end user has no knowledge of there actually being an underlying database. Embedded MySQL Server is ideal for use behind the scenes in Internet appliances, public kiosks, turnkey hardware/software combination units, high performance Internet servers, self-contained databases distributed on CD-ROM, and so on.
Many users of libmysqld will benefit from the MySQL Dual Licensing. For those not wishing to be bound by the GPL, the software is also made available under a commercial license. The embedded MySQL library uses the same interface as the normal client library, so it is convenient and easy to use. See libmysqld.
MySQL Server 4.0 laid the foundation for new features implemented in MySQL 4.1, such as subqueries and Unicode support, and for the work on stored procedures being done in version 5.0. These features come at the top of the wish list of many of our customers.
With these additions, critics of the MySQL Database Server have to be more imaginative than ever in pointing out deficiencies in the MySQL database management system. Already well-known for its stability, speed, and ease of use, MySQL Server will be able to fulfill the requirement checklists of very demanding buyers.
The features listed in this section are implemented in MySQL 4.1. A few other features are still planned for MySQL 4.1. See TODO MySQL 4.1.
Most new features being coded are or will be available in MySQL 5.0. See TODO MySQL 5.0.
Support for subqueries and derived tables
| |
Speed enhancements
| |
New functionality
| |
Standards compliance, portability, and migration
| |
Internationalization
| |
Usability enhancements
|
The news section of this manual includes a more in-depth list of features. See News-4.1.x.
New features are being added to MySQL 4.1. The alpha version is already available for download. See Nutshell Ready for Immediate Use.
The set of features that are being added to version 4.1 is mostly fixed. Additional development is already ongoing for version 5.0. MySQL 4.1 will go through the steps of Alpha (during which time new features might still be added/changed), Beta (when we have feature freeze and only bug corrections will be done), and Gamma (indicating that a production release is just weeks ahead). At the end of this process, MySQL 4.1 will become the new production release.
MySQL 4.1 is currently in the alpha stage, and binaries are available for download at http://www.mysql.com/downloads/mysql-4.1.html. All binary releases pass our extensive test suite without any errors on the platforms on which we test. See News-4.1.x.
For those wishing to use the most recent development source for MySQL 4.1, we make our 4.1 BitKeeper repository publicly available. See Installing source tree.
New development for MySQL is focused on the 5.0 release, featuring Stored Procedures and other new features. See TODO MySQL 5.0.
For those wishing to take a look at the bleeding edge of MySQL development, we make our BitKeeper repository for MySQL version 5.0 publicly available. See Installing source tree. As of December 2003, binary builds of version 5.0 are also available.
Table of Contents
This section summarizes the features that we plan to implement in MySQL Server. The items are ordered by release series. Within a list, items are shown in approximately the order they will be done.
Note: If you are an enterprise level user with an urgent need for a particular feature, please contact <sales@mysql.com> to discuss sponsoring options. Targeted financing by sponsor companies allows us to allocate additional resources for specific purposes. One example of a feature sponsored in the past is replication.
The features below are not yet implemented in MySQL 4.1, but are planned for implementation before MySQL 4.1 moves into its beta phase. For a list what is already done in MySQL 4.1, see Nutshell 4.1 features.
Stable OpenSSL support (MySQL 4.0 supports rudimentary, not 100% tested, support for OpenSSL).
More testing of prepared statements.
More testing of multiple character sets for one table.
The following features are planned for inclusion into MySQL 5.0. Some of the features such as stored procedures are complete and are included in MySQL 5.0 alpha, which is available now. Others such as cursors are only partially available. Expect these and other features to mature and be fully supported in upcoming releases.
Note that because we have many developers that are working on different projects, there will also be many additional features. There is also a small chance that some of these features will be added to MySQL 4.1. For a list what is already done in MySQL 4.1, see Nutshell 4.1 features.
For those wishing to take a look at the bleeding edge of MySQL development, we make our BitKeeper repository for MySQL version 5.0 publicly available. See Installing source tree. As of December 2003, binary builds of version 5.0 are also available.
Stored Procedures
| |
New functionality
| |
Standards compliance, portability and migration
| |
Speed enhancements
| |
Usability enhancements
|
The news section of this manual includes a more in-depth list of features. See News-5.0.x.
New functionality
| |
Speed enhancements
| |
Usability enhancements
|
New functionality
| |
Standards compliance, portability and migration
| |
Speed enhancements
| |
Internationalization
| |
Usability enhancements
| |
New operating systems
|
Implement function: get_changed_tables(timeout,table1,table2,...).
Change reading through tables to use memmap when possible. Now only compressed tables use memmap.
Make the automatic timestamp code nicer. Add timestamps to the update log with SET TIMESTAMP=#;.
Use read/write mutex in some places to get more speed.
Simple views (implemented in stepwise fashion up to full functionality). See ANSI diff Views.
Automatically close some tables if a table, temporary table, or temporary file gets error 23 (too many open files).
Better constant propagation. When an occurrence of col_name=n is found in an expression, for some constant n, replace other occurrences of col_name within the expression with n. Currently, this is done only for some simple cases.
Change all const expressions with calculated expressions if possible.
Optimize key = expression comparisons. At the moment only key = field or key = constant comparisons are optimized.
Join some of the copy functions for nicer code.
Change sql_yacc.yy to an inline parser to reduce its size and get better error messages.
Change the parser to use only one rule per different number of arguments in function.
Use of full calculation names in the order part (for ACCESS97).
MINUS, INTERSECT, and FULL OUTER JOIN. (Currently UNION [in 4.0] and LEFT|RIGHT OUTER JOIN are supported.)
Allow SQL_OPTION MAX_SELECT_TIME=#, for placing a time limit on a query.
Allow updates to be logged to a database.
Enhance LIMIT to allow retrieval of data from the end of a result set.
Alarm around client connect/read/write functions.
Please note the changes to mysqld_safe: according to FSSTND (which Debian tries to follow) PID files should go into /var/run/<progname>.pid and log files into /var/log. It would be nice if you could put the "DATADIR" in the first declaration of "pidfile" and "log", so the placement of these files can be changed with a single statement.
Allow a client to request logging.
Allow the LOAD DATA INFILE statement to read files that have been compressed with gzip.
Fix sorting and grouping of BLOB columns (partly solved now).
Change to use semaphores when counting threads. One should first implement a semaphore library for MIT-pthreads.
Add full support for JOIN with parentheses.
As an alternative to the one-thread-per-connection model, manage a pool of threads to handle queries.
Allow GET_LOCK() to obtain more than one lock. When doing this, one must also handle the possible deadlocks this change will introduce.
Table of Contents
This section introduces you to the MySQL mailing lists and provides some guidelines as to how the lists should be used. When you subscribe to a mailing list, you will receive all postings to the list as email messages. You can also to send your own questions and answers to the list.
To subscribe to or unsubscribe from any of the mailing lists described in this section, visit http://lists.mysql.com/. Please do not send messages about subscribing or unsubscribing to any of the mailing lists, because such messages are distributed automatically to thousands of other users.
Your local site may have many subscribers to a MySQL mailing list. If so, the site may have a local mailing list, so that messages sent from lists.mysql.com to your site are propagated to the local list. In such cases, please contact your system administrator to be added to or dropped from the local MySQL list.
If you wish to have traffic for a mailing list go to a separate mailbox in your mail program, set up a filter based on the message headers. You can use either the List-ID: or Delivered-To: headers to identify list messages.
The MySQL mailing lists are as follows:
announce | This list is for announcements of new versions of MySQL and related programs. This is a low-volume list to which all MySQL users should subscribe. |
mysql | This is the main list for general MySQL discussion. Please note that some topics are better discussed on the more-specialized lists. If you post to the wrong list, you may not get an answer. |
mysql-digest | This is the mysql list in digest form. Subscribing to this list means you will get all list messages, sent as one large mail message once a day. |
bugs | This list will be of interest to you if you want to stay informed about issues reported since the last release of MySQL or if you want to be actively involved in the process of bug hunting and fixing. See Bug reports. |
bugs-digest | This is the bugs list in digest form. |
internals | This list is for people who work on the MySQL code. This is also the forum for discussions on MySQL development and post patches. |
internals-digest | This is the internals list in digest form. |
mysqldoc | This list is for people who work on the MySQL documentation: people from MySQL AB, translators, and other community members. |
mysqldoc-digest | This is the mysqldoc list in digest form. |
benchmarks | This list is for anyone interested in performance issues. Discussions concentrate on database performance (not limited to MySQL) but also include broader categories such as performance of the kernel, file system, disk system, and so on. |
benchmarks-digest | This is the benchmarks list in digest form. |
packagers | This list is for discussions on packaging and distributing MySQL. This is the forum used by distribution maintainers to exchange ideas on packaging MySQL and on ensuring that MySQL looks and feels as similar as possible on all supported platforms and operating systems. |
packagers-digest | This is the packagers list in digest form. |
java | This list is for discussions about the MySQL server and Java.It is mostly used to discuss JDBC drivers, including MySQL Connector/J. |
java-digest | This is the java list in digest form. |
win32 | This list is for all topics concerning the MySQL software on Microsoft operating systems, such as Windows 9x/Me/NT/2000/XP. |
win32-digest | This is the win32 list in digest form. |
myodbc | This list is for all topics concerning connecting to the MySQL server with ODBC. |
myodbc-digest | This is the myodbc list in digest form. |
mysqlcc | This list is for all topics concerning the MySQL Control Center graphical client. |
mysqlcc-digest | This is the mysqlcc list in digest form. |
plusplus | This list is for all topics concerning programming with the C++ API to MySQL. |
plusplus-digest | This is the plusplus list in digest form. |
msql-mysql-modules | This list is for all topics concerning the Perl support for MySQL with msql-mysql-modules, which is now named DBD::mysql. |
msql-mysql-modules-digest | This is the msql-mysql-modules list in digest form. |
If you're unable to get an answer to your questions from a MySQL mailing list, one option is to purchase support from MySQL AB. This will put you in direct contact with MySQL developers. See Support.
The following table shows some MySQL mailing lists in languages other than English. These lists are not operated by MySQL AB.
<mysql-france-subscribe@yahoogroups.com> | A French mailing list. |
<list@tinc.net> | A Korean mailing list. Email subscribe mysql your@email.address to this list. |
<mysql-de-request@lists.4t2.com> | A German mailing list. Email subscribe mysql-de your@email.address to this list. You can find information about this mailing list at http://www.4t2.com/mysql/. |
<mysql-br-request@listas.linkway.com.br> | A Portuguese mailing list. Email subscribe mysql-br your@email.address to this list. |
<mysql-alta@elistas.net> | A Spanish mailing list. Email subscribe mysql your@email.address to this list. |
Before posting a bug report or question, please do the following:
Start by searching the MySQL online manual at http://www.mysql.com/doc/. We try to keep the manual up to date by updating it frequently with solutions to newly found problems. The change history appendix (http://www.mysql.com/doc/en/News.html) can be particularly useful since it is quite possible that a newer version already contains a solution to your problem.
Search in the bugs database at http://bugs.mysql.com/ to see whether the bug has already been reported and fixed.
Search the MySQL mailing list archives at http://lists.mysql.com/.
You can also use http://www.mysql.com/search/ to search all the web pages (including the manual) that are located at the MySQL AB web site.
If you can't find an answer in the manual or the archives, check with your local MySQL expert. If you still can't find an answer to your question, please follow the guidelines on sending mail to a MySQL mailing list, outlined in the next section, before contacting us.
The normal place to report bugs is http://bugs.mysql.com/, which is the address for our bugs database. This database is public, and can be browsed and searched by anyone. If you log into the system, you will also be able to enter new reports.
Writing a good bug report takes patience, but doing it right the first time saves time both for us and for yourself. A good bug report, containing a full test case for the bug, makes it very likely that we will fix the bug in the next release. This section will help you write your report correctly so that you don't waste your time doing things that may not help us much or at all.
We encourage everyone to use the mysqlbug script to generate a bug report (or a report about any problem). mysqlbug can be found in the scripts directory (source distribution) and in the bin directory under your MySQL installation directory (binary distribution). If you are unable to use mysqlbug (for instance, if you are running on Windows), it is still vital that you include all the necessary information noted in this section (most importantly a description of the operating system and the MySQL version).
The mysqlbug script helps you generate a report by determining much of the following information automatically, but if something important is missing, please include it with your message. Please read this section carefully and make sure that all the information described here is included in your report.
Preferably, you should test the problem using the latest production or development version of MySQL Server before posting. Anyone should be able to repeat the bug by just using 'mysql test < script' on the included test case or by running the shell or Perl script that is included in the bug report.
All bugs posted in the bugs database at http://bugs.mysql.com/ will be corrected or documented in the next MySQL release. If only minor code changes are needed to correct a problem, we will also post a patch that fixes the problem.
If you have found a sensitive security bug in MySQL, please send an email to <security@mysql.com>.
If you have a repeatable bug report, please report it to the bugs database at http://bugs.mysql.com/. Note that even in this case it's good to run the mysqlbug script first to find information about your system. Any bug that we are able to repeat has a high chance of being fixed in the next MySQL release.
To report other problems, you can use one of the MySQL mailing lists.
Remember that it is possible for us to respond to a message containing too much information, but not to one containing too little. People often omit facts because they think they know the cause of a problem and assume that some details don't matter. A good principle is: If you are in doubt about stating something, state it. It is faster and less troublesome to write a couple more lines in your report than to wait longer for the answer if we must ask you to provide information that was missing from the initial report.
The most common errors made in bug reports are (a) not including the version number of the MySQL distribution used and (b) not fully describing the platform on which the MySQL server is installed (including the platform type and version number). This is highly relevant information, and in 99 cases out of 100 the bug report is useless without it. Very often we get questions like, ``Why doesn't this work for me?'' Then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has already been fixed in newer MySQL versions. Sometimes the error is platform-dependent; in such cases, it is next to impossible for us to fix anything without knowing the operating system and the version number of the platform.
If you compiled MySQL from source, remember also to provide information about your compiler, if it is related to the problem. Often people find bugs in compilers and think the problem is MySQL-related. Most compilers are under development all the time and become better version by version. To determine whether your problem depends on your compiler, we need to know what compiler you use. Note that every compiling problem should be regarded as a bug and reported accordingly.
It is most helpful when a good description of the problem is included in the bug report. That is, give a good example of everything you did that led to the problem and describe, in exact detail, the problem itself. The best reports are those that include a full example showing how to reproduce the bug or problem. See Reproduceable test case.
If a program produces an error message, it is very important to include the message in your report. If we try to search for something from the archives using programs, it is better that the error message reported exactly matches the one that the program produces. (Even the case should be observed.) You should never try to remember what the error message was; instead, copy and paste the entire message into your report.
If you have a problem with Connector/ODBC (MyODBC), please try to generate a MyODBC trace file and send it with your report. See MyODBC bug report.
Please remember that many of the people who will read your report will do so using an 80-column display. When generating reports or examples using the mysql command-line tool, you should therefore use the --vertical option (or the \G statement terminator) for output that would exceed the available width for such a display (for example, with the EXPLAIN SELECT statement; see the example later in this section).
Please include the following information in your report:
The version number of the MySQL distribution you are using (for example, MySQL Version 4.0.12). You can find out which version you are running by executing mysqladmin version. mysqladmin can be found in the bin directory under your MySQL installation directory.
The manufacturer and model of the machine on which you experience the problem.
The operating system name and version. If you work with Windows, you can usually get the name and version number by double-clicking your ``My Computer'' icon and pulling down the ``Help/About Windows'' menu. For most Unix-like operating systems, you can get this information by executing the command uname -a.
Sometimes the amount of memory (real and virtual) is relevant. If in doubt, include these values.
If you are using a source distribution of the MySQL software, the name and version number of the compiler used is needed. If you have a binary distribution, the distribution name is needed.
If the problem occurs during compilation, include the exact error messages and also a few lines of context around the offending code in the file where the error occurrs.
If mysqld died, you should also report the query that crashed mysqld. You can usually find this out by running mysqld with logging enabled. See Using log files.
If a database table is related to the problem, include the output from mysqldump --no-data db_name tbl_name1 tbl_name2 .... This is very easy to do and is a powerful way to get information about any table in a database. The information will help us create a situation matching the one you have.
For speed-related bugs or problems with SELECT statements, you should always include the output of EXPLAIN SELECT ..., and at least the number of rows that the SELECT statement produces. You should also include the output from SHOW CREATE TABLE tbl_name for each involved table. The more information you give about your situation, the more likely it is that someone can help you.
The following is an example of a very good bug report. It should be posted with the mysqlbug script. The example uses the mysql command-line tool. Note the use of the \G statement terminator for statements whose output width would otherwise exceed that of an 80-column display device.
mysql> SHOW VARIABLES; mysql> SHOW COLUMNS FROM ...\G <output from SHOW COLUMNS> mysql> EXPLAIN SELECT ...\G <output from EXPLAIN> mysql> FLUSH STATUS; mysql> SELECT ...; <A short version of the output from SELECT, including the time taken to run the query> mysql> SHOW STATUS; <output from SHOW STATUS>
If a bug or problem occurs while running mysqld, try to provide an input script that will reproduce the anomaly. This script should include any necessary source files. The more closely the script can reproduce your situation, the better. If you can make a reproducible test case, you should post it on http://bugs.mysql.com/ for high-priority treatment.
If you can't provide a script, you should at least include the output from mysqladmin variables extended-status processlist in your mail to provide some information on how your system is performing.
If you can't produce a test case with only a few rows, or if the test table is too big to be mailed to the mailing list (more than 10 rows), you should dump your tables using mysqldump and create a README file that describes your problem.
Create a compressed archive of your files using tar and gzip or zip, and use ftp to transfer the archive to ftp://support.mysql.com/pub/mysql/secret/. Then enter the problem into our bugs database at http://bugs.mysql.com/.
If you think that the MySQL server produces a strange result from a query, include not only the result, but also your opinion of what the result should be, and an account describing the basis for your opinion.
When giving an example of the problem, it's better to use the variable names, table names, etc., that exist in your actual situation than to come up with new names. The problem could be related to the name of a variable or table. These cases are rare, perhaps, but it is better to be safe than sorry. After all, it should be easier for you to provide an example that uses your actual situation, and it is by all means better for us. In case you have data you don't want to show to others, you can use ftp to transfer it to ftp://support.mysql.com/pub/mysql/secret/. If the data is really top secret and you don't want to show it even to us, then go ahead and provide an example using other names, but please regard this as the last choice.
Include all the options given to the relevant programs, if possible. For example, indicate the options that you use when you start the mysqld server as well as the options that you use to run any MySQL client programs. The options to programs like mysqld and mysql, and to the configure script, are often keys to answers and are very relevant. It is never a bad idea to include them. If you use any modules, such as Perl or PHP, please include the version numbers of those as well.
If your question is related to the privilege system, please include the output of mysqlaccess, the output of mysqladmin reload, and all the error messages you get when trying to connect. When you test your privileges, you should first run mysqlaccess. After this, execute mysqladmin reload version and try to connect with the program that gives you trouble. mysqlaccess can be found in the bin directory under your MySQL installation directory.
If you have a patch for a bug, do include it. But don't assume the patch is all we need, or that we will use it, if you don't provide some necessary information such as test cases showing the bug that your patch fixes. We might find problems with your patch or we might not understand it at all; if so, we can't use it.
If we can't verify exactly what the purpose of the patch is, we won't use it. Test cases will help us here. Show that the patch will handle all the situations that may occur. If we find a borderline case (even a rare one) where the patch won't work, it may be useless.
Guesses about what the bug is, why it occurs, or what it depends on are usually wrong. Even the MySQL team can't guess such things without first using a debugger to determine the real cause of a bug.
Indicate in your bug report that you have checked the reference manual and mail archive so that others know you have tried to solve the problem yourself.
If you get a parse error, please check your syntax closely. If you can't find something wrong with it, it's extremely likely that your current version of MySQL Server doesn't support the syntax you are using. If you are using the current version and the manual at http://www.mysql.com/doc/ doesn't cover the syntax you are using, MySQL Server doesn't support your query. In this case, your only options are to implement the syntax yourself or email <licensing@mysql.com> and ask for an offer to implement it.
If the manual covers the syntax you are using, but you have an older version of MySQL Server, you should check the MySQL change history to see when the syntax was implemented. In this case, you have the option of upgrading to a newer version of MySQL Server. See News.
If your problem is that your data appears corrupt or you get errors when you access a particular table, you should first check and then try to repair your tables with CHECK TABLE and REPAIR TABLE or with myisamchk. See MySQL Database Administration.
If you are running Windows, please check that lower_case_table_names is 1 or 2 with SHOW VARIABLES LIKE 'lower_case_table_names'.
If you often get corrupted tables, you should try to find out when and why this happens. In this case, the error log in the MySQL data directory may contain some information about what happened. (This is the file with the .err suffix in the name.) See Error log. Please include any relevant information from this file in your bug report. Normally mysqld should never crash a table if nothing killed it in the middle of an update. If you can find the cause of mysqld dying, it's much easier for us to provide you with a fix for the problem. See What is crashing.
If possible, download and install the most recent version of MySQL Server and check whether it solves your problem. All versions of the MySQL software are thoroughly tested and should work without problems. We believe in making everything as backward-compatible as possible, and you should be able to switch MySQL versions without difficulty. See Which version.
If you are a support customer, please cross-post the bug report to <mysql-support@mysql.com> for higher-priority treatment, as well as to the appropriate mailing list to see whether someone else has experienced (and perhaps solved) the problem.
For information on reporting bugs in MyODBC, see ODBC Problems.
For solutions to some common problems, see Problems.
When answers are sent to you individually and not to the mailing list, it is considered good etiquette to summarize the answers and send the summary to the mailing list so that others may have the benefit of responses you received that helped you solve your problem.
If you consider your answer to have broad interest, you may want to post it to the mailing list instead of replying directly to the individual who asked. Try to make your answer general enough that people other than the original poster may benefit from it. When you post to the list, please make sure that your answer is not a duplication of a previous answer.
Try to summarize the essential part of the question in your reply; don't feel obliged to quote the entire original message.
Please don't post mail messages from your browser with HTML mode turned on. Many users don't read mail with a browser.
In addition to the various MySQL mailing lists, you can find experienced community people on IRC (Internet Relay Chat). These are the best networks/channels currently known to us:
freenode (see http://www.freenode.net/ for servers)
#mysql Primarily MySQL questions but other database and SQL questions welcome.
#mysqlphp Questions about MySQL+PHP, a popular combination.
#mysqlperl Questions about MySQL+Perl, another popular combination.
EFnet (see http://www.efnet.org/ for servers)
#mysql MySQL questions.
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Table of Contents
This section describes how MySQL relates to the ANSI/ISO SQL standards. MySQL Server has many extensions to the SQL standard, and here you will find out what they are and how to use them. You will also find information about functionality missing from MySQL Server, and how to work around some differences.
Our goal is to not restrict MySQL Server usability for any usage without a very good reason for doing so. Even if we don't have the resources to perform development for every possible use, we are always willing to help and offer suggestions to people who are trying to use MySQL Server in new territories.
One of our main goals with the product is to continue to work toward compliance with the SQL-99 standard, but without sacrificing speed or reliability. We are not afraid to add extensions to SQL or support for non-SQL features if this greatly increases the usability of MySQL Server for a large segment of our user base. (The new HANDLER interface in MySQL Server 4.0 is an example of this strategy. See HANDLER.)
We will continue to support transactional and non-transactional databases to satisfy both mission-critical 24/7 usage and heavy web/logging usage.
MySQL Server was designed from the start to work with medium size databases (10-100 million rows, or about 100 MB per table) on small computer systems. We will continue to extend MySQL Server to work even better with terabyte-size databases, as well as to make it possible to compile a reduced MySQL version that is more suitable for hand-held devices and embedded usage. The compact design of the MySQL server makes development in both of these directions possible without any conflicts in the source tree.
We are currently not targeting realtime support, though you can already do a lot of things with our replication capabilities.
Database cluster support is planned to begin sometime in 2004 through implementation of a new storage engine.
We are looking at providing XML support in the database server.
Entry-level SQL-92. ODBC levels 0-3.51.
We are aiming toward supporting the full SQL-99 standard, but without making concessions to speed and quality of the code.
The MySQL server can operate in different SQL modes, and can apply these modes differentially for different clients. This allows applications to tailor server operation to their own requirements.
Modes define what SQL syntax MySQL should support and what kind of validation checks it should perform on the data. This makes it easier to use MySQL in a lot of different environments and to use MySQL together with other database servers.
You can set the default SQL mode by starting mysqld with the --sql-mode="modes" option. Beginning with MySQL 4.1, you can also change the mode after startup time by setting the sql_mode variable with a SET [SESSION|GLOBAL] sql_mode="modes" statement.
For more information on setting the server mode, see Server SQL mode.
You can tell mysqld to use the ANSI mode with the --ansi startup option. See Server options.
Running the server in ANSI mode is the same as starting it with these options:
--sql-mode=REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ONLY_FULL_GROUP_BY --transaction-isolation=SERIALIZABLE
In MySQL 4.1, you can achieve the same effect with these two statements:
SET GLOBAL TRANSACTION ISOLATION LEVEL SERIALIZABLE; SET GLOBAL sql_mode = "REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ONLY_FULL_GROUP_BY";
See SQL mode.
In MySQL 4.1.1, the sql_mode options shown can be also be set with:
SET GLOBAL sql_mode="ansi";
In this case, the value of the sql_mode variable will be set to all options that are relevant for ANSI mode. You can check the result by doing:
mysql> SET GLOBAL sql_mode="ansi"; mysql> SELECT @@GLOBAL.sql_mode; -> "REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ONLY_FULL_GROUP_BY,ANSI"
MySQL Server includes some extensions that you probably will not find in other SQL databases. Be warned that if you use them, your code will not be portable to other SQL servers. In some cases, you can write code that includes MySQL extensions, but is still portable, by using comments of the form /*! ... */. In this case, MySQL Server will parse and execute the code within the comment as it would any other MySQL statement, but other SQL servers will ignore the extensions. For example:
SELECT /*! STRAIGHT_JOIN */ col_name FROM table1,table2 WHERE ...
If you add a version number after the '!' character, the syntax within the comment will be executed only if the MySQL version is equal to or newer than the specified version number:
CREATE /*!32302 TEMPORARY */ TABLE t (a INT);
This means that if you have Version 3.23.02 or newer, MySQL Server will use the TEMPORARY keyword.
The following descriptions list MySQL extensions, organized by category.
Organization of data on disk |
MySQL Server maps each database to a directory under the MySQL
data directory, and tables within a database to filenames in the database
directory.
This has a few implications:
|
General language syntax |
|
SQL statement syntax |
|
Column types |
|
Functions and operators |
|
For a prioritized list indicating when new extensions will be added to MySQL Server, you should consult the online MySQL TODO list at http://www.mysql.com/doc/en/TODO.html. That is the latest version of the TODO list in this manual. See TODO.
We try to make MySQL Server follow the ANSI SQL standard (SQL-92/SQL-99) and the ODBC SQL standard, but MySQL Server performs operations differently in some cases:
For VARCHAR columns, trailing spaces are removed when the value is stored. See Bugs.
In some cases, CHAR columns are silently converted to VARCHAR columns when you define a table or alter its structure. See Silent column changes.
Privileges for a table are not automatically revoked when you delete a table. You must explicitly issue a REVOKE statement to revoke privileges for a table. See GRANT.
MySQL Version 4.1 supports subqueries and derived tables. A subquery is a SELECT statement nested within another statement. A derived table (an unnamed view) is a subquery in the FROM clause of another statement. See Subqueries.
For MySQL versions older than 4.1, most subqueries can be rewritten using joins or other methods. See Rewriting subqueries for examples that show how to do this.
MySQL Server doesn't support the Sybase SQL extension: SELECT ... INTO TABLE .... Instead, MySQL Server supports the SQL-99 syntax INSERT INTO ... SELECT ..., which is basically the same thing. See INSERT SELECT.
INSERT INTO tblTemp2 (fldID) SELECT tblTemp1.fldOrder_ID FROM tblTemp1 WHERE tblTemp1.fldOrder_ID > 100;
Alternatively, you can use SELECT INTO OUTFILE ... or CREATE TABLE ... SELECT.
From version 5.0, MySQL supports SELECT ... INTO with user variables. The same syntax may also be used inside stored procedures using cursors and local variables. See SELECT INTO Statement.
MySQL Server (version 3.23-max and all versions 4.0 and above) supports transactions with the InnoDB and BDB transactional storage engines. InnoDB provides full ACID compliance. See Table types.
The other non-transactional storage engines in MySQL Server (such as MyISAM) follow a different paradigm for data integrity called ``Atomic Operations.'' In transactional terms, MyISAM tables effectively always operate in AUTOCOMMIT=1 mode. Atomic operations often offer comparable integrity with higher performance.
With MySQL Server supporting both paradigms, you can decide whether your applications are best served by the speed of atomic operations or the use of transactional features. This choice can be made on a per-table basis.
As noted, the trade off for transactional vs. non-transactional table types lies mostly in performance. Transactional tables have significantly higher memory and diskspace requirements, and more CPU overhead. On the other hand, transactional table types such as InnoDB also offer many significant features. MySQL Server's modular design allows the concurrent use of different storage engines to suit different requirements and deliver optimum performance in all situations.
But how does one use the features of MySQL Server to maintain rigorous integrity even with the non-transactional MyISAM tables, and how do these features compare with the transactional table types?
If your applications are written in a way that is dependent on being able to call ROLLBACK rather than COMMIT in critical situations, transactions are more convenient. Transactions also ensure that unfinished updates or corrupting activities are not committed to the database; the server is given the opportunity to do an automatic rollback and your database is saved.
If you use non-transactional tables, MySQL Server in almost all cases allows you to resolve potential problems by including simple checks before updates and by running simple scripts that check the databases for inconsistencies and automatically repair or warn if such an inconsistency occurs. Note that just by using the MySQL log or even adding one extra log, one can normally fix tables perfectly with no data integrity loss.
More often than not, critical transactional updates can be rewritten to be atomic. Generally speaking, all integrity problems that transactions solve can be done with LOCK TABLES or atomic updates, ensuring that you never will get an automatic abort from the server, which is a common problem with transactional database systems.
Even a transactional system can lose data if the server goes down. The difference between different systems lies in just how small the time-lap is where they could lose data. No system is 100% secure, only ``secure enough.'' Even Oracle, reputed to be the safest of transactional database systems, is reported to sometimes lose data in such situations.
To be safe with MySQL Server, whether using transactional tables or not, you only need to have backups and have binary logging turned on. With this you can recover from any situation that you could with any other transactional database system. It is always good to have backups, independent of which database system you use.
The transactional paradigm has its benefits and its drawbacks. Many users and application developers depend on the ease with which they can code around problems where an abort appears to be, or is necessary. However, even if you are new to the atomic operations paradigm, or more familiar with transactions, do consider the speed benefit that non-transactional tables can offer on the order of three to five times the speed of the fastest and most optimally tuned transactional tables.
In situations where integrity is of highest importance, MySQL Server offers transaction-level reliability and integrity even for non-transactional tables. If you lock tables with LOCK TABLES, all updates will stall until any integrity checks are made. If you obtain a READ LOCAL lock (as opposed to a write lock) for a table that allows concurrent inserts at the end of the table, reads are allowed, as are inserts by other clients. The new inserted records will not be seen by the client that has the read lock until it releases the lock. With INSERT DELAYED you can queue inserts into a local queue, until the locks are released, without having the client wait for the insert to complete. See INSERT DELAYED.
``Atomic,'' in the sense that we mean it, is nothing magical. It only means that you can be sure that while each specific update is running, no other user can interfere with it, and there will never be an automatic rollback (which can happen with transactional tables if you are not very careful). MySQL Server also guarantees that there will not be any dirty reads.
Following are some techniques for working with non-transactional tables:
Loops that need transactions normally can be coded with the help of LOCK TABLES, and you don't need cursors to update records on the fly.
To avoid using ROLLBACK, you can use the following strategy:
Use LOCK TABLES ... to lock all the tables you want to access.
Test the conditions that must be true before performing the update.
Update if everything is okay.
Use UNLOCK TABLES to release your locks.
This is usually a much faster method than using transactions with possible rollbacks, although not always. The only situation this solution doesn't handle is when someone kills the threads in the middle of an update. In this case, all locks will be released but some of the updates may not have been executed.
You can also use functions to update records in a single operation. You can get a very efficient application by using the following techniques:
Modify fields relative to their current value.
Update only those fields that actually have changed.
For example, when we are doing updates to some customer information, we update only the customer data that has changed and test only that none of the changed data, or data that depends on the changed data, has changed compared to the original row. The test for changed data is done with the WHERE clause in the UPDATE statement. If the record wasn't updated, we give the client a message: ''Some of the data you have changed has been changed by another user.'' Then we show the old row versus the new row in a window, so the user can decide which version of the customer record he should use.
This gives us something that is similar to column locking but is actually even better because we only update some of the columns, using values that are relative to their current values. This means that typical UPDATE statements look something like these:
UPDATE tablename SET pay_back=pay_back+125; UPDATE customer SET customer_date='current_date', address='new address', phone='new phone', money_he_owes_us=money_he_owes_us-125 WHERE customer_id=id AND address='old address' AND phone='old phone';
As you can see, this is very efficient and works even if another client has changed the values in the pay_back or money_he_owes_us columns.
In many cases, users have wanted LOCK TABLES and/or ROLLBACK for the purpose of managing unique identifiers. This can be handled much more efficiently without locking or rolling back by using an AUTO_INCREMENT column and either the SQL function LAST_INSERT_ID() or the C API function mysql_insert_id(). See Information functions. See mysql_insert_id().
You can generally code around the need for row-level locking. Some situations really do need it, and InnoDB tables support row-level locking. With MyISAM tables, you can use a flag column in the table and do something like the following:
UPDATE tbl_name SET row_flag=1 WHERE id=ID;
MySQL returns 1 for the number of affected rows if the row was found and row_flag wasn't already 1 in the original row.
You can think of it as though MySQL Server changed the preceding query to:
UPDATE tbl_name SET row_flag=1 WHERE id=ID AND row_flag <> 1;
Stored procedures are implemented in MySQL version 5.0. See Stored Procedures.
Triggers are scheduled for implementation in MySQL version 5.1. A trigger is effectively a type of stored procedure, one that is invoked when a particular event occurs. For example, you could set up a stored procedure that is triggered each time a record is deleted from a transactional table and that stored procedure automatically deletes the corresponding customer from a customer table when all their transactions are deleted.
In MySQL Server 3.23.44 and up, the InnoDB storage engine supports checking of foreign key constraints, including CASCADE, ON DELETE, and ON UPDATE. See InnoDB foreign key constraints.
For storage engines other than InnoDB, MySQL Server parses the FOREIGN KEY syntax in CREATE TABLE statements, but does not use or store it. In the future, the implementation will be extended to store this information in the table specification file so that it may be retrieved by mysqldump and ODBC. At a later stage, foreign key constraints will be implemented for MyISAM tables as well.
Foreign key enforcement offers several benefits to database developers:
Assuming proper design of the relationships, foreign key constraints make it more difficult for a programmer to introduce an inconsistency into the database.
Centralized checking of constraints by the database server makes it unnecessary to perform these checks on the application side. This eliminates the possibility that different applications may not all check the constraints in the same way.
Using cascading updates and deletes can simplify the application code.
Properly designed foreign key rules aid in documenting relationships between tables.
Do keep in mind that these benefits come at the cost of additional overhead for the database server to perform the necessary checks. Additional checking by the server affects performance, which for some applications may be sufficiently undesirable as to be avoided if possible. (Some major commercial applications have coded the foreign-key logic at the application level for this reason.)
MySQL gives database developers the choice of which approach to use. If you don't need foreign keys and want to avoid the overhead associated with enforcing referential integrity, you can choose another table type instead, such as MyISAM. (For example, the MyISAM storage engine offers very fast performance for applications that perform only INSERT and SELECT operations, because the inserts can be performed concurrently with retrievals. See Table locking.)
If you choose not to take advantage of referential integrity checks, keep the following considerations in mind:
In the absence of server-side foreign key relationship checking, the application itself must handle relationship issues. For example, it must take care to insert rows into tables in the proper order, and to avoid creating orphaned child records. It must also be able to recover from errors that occur in the middle of multiple-record insert operations.
If ON DELETE is the only referential integrity capability an application needs, note that as of MySQL Server 4.0, you can use multiple-table DELETE statements to delete rows from many tables with a single statement. See DELETE.
A workaround for the lack of ON DELETE is to add the appropriate DELETE statement to your application when you delete records from a table that has a foreign key. In practice, this is often as quick as using foreign keys, and is more portable.
Be aware that the use of foreign keys can in some instances lead to problems:
Foreign key support addresses many referential integrity issues, but it is still necessary to design key relationships carefully to avoid circular rules or incorrect combinations of cascading deletes.
It is not uncommon for a DBA to create a topology of relationships that makes it difficult to restore individual tables from a backup. (MySQL alleviates this difficulty by allowing you to temporarily disable foreign key checks when reloading a table that depends on other tables. See InnoDB foreign key constraints. As of MySQL 4.1.1, mysqldump generates dump files that take advantage of this capability automatically when reloaded.)
Note that foreign keys in SQL are used to check and enforce referential integrity, not to join tables. If you want to get results from multiple tables from a SELECT statement, you do this by performing a join between them:
SELECT * FROM table1,table2 WHERE table1.id = table2.id;
See JOIN. See example-Foreign keys.
The FOREIGN KEY syntax without ON DELETE ... is often used by ODBC applications to produce automatic WHERE clauses.
Views are currently being implemented, and will appear in the 5.0 or 5.1 version of MySQL Server. Unnamed views (derived tables, a subquery in the FROM clause of a SELECT) are already implemented in version 4.1.
Historically, MySQL Server has been most used in applications and on web systems where the application writer has full control over database usage. Usage has shifted over time, and so we find that an increasing number of users now regard views as an important feature.
Views are useful for allowing users to access a set of relations (tables) as if it were a single table, and limiting their access to just that. Views can also be used to restrict access to rows (a subset of a particular table). One does not require views to restrict access to columns, as MySQL Server has a sophisticated privilege system. See Privilege system.
Many DBMS don't allow updates to a view. Instead, you have to perform the updates on the individual tables. In designing an implementation of views, our goal, as much as is possible within the confines of SQL, is full compliance with ``Codd's Rule #6'' for relational database systems: All views that are theoretically updatable, should in practice also be updatable.
Some other SQL databases use -- to start comments. MySQL Server uses # as the start comment character. You can also use the C comment style /* this is a comment */ with MySQL Server. See Comments.
MySQL Server Version 3.23.3 and above support the -- comment style, provided the comment is followed by a space (or by a control character such as a newline). The requirement for a space is to prevent problems with automatically generated SQL queries that have used something like the following code, where we automatically insert the value of the payment for !payment!:
UPDATE tbl_name SET credit=credit-!payment!
Think about what happens if the value of payment is a negative value such as -1:
UPDATE tbl_name SET credit=credit--1
credit--1 is a legal expression in SQL, but if -- is interpreted as the start of a comment, part of the expression is discarded. The result is a statement that has a completely different meaning than intended:
UPDATE tbl_name SET credit=credit
The statement produces no change in value at all! This illustrates that allowing comments to start with -- can have serious consequences.
Using our implementation of this method of commenting in MySQL Server Version 3.23.3 and up, credit--1 is actually safe.
Another safe feature is that the mysql command-line client removes all lines that start with --.
The following information is relevant only if you are running a MySQL version earlier than 3.23.3:
If you have an SQL program in a text file that contains -- comments, you should use the replace utility as follows to convert the comments to use # characters:
shell> replace " --" " #" < text-file-with-funny-comments.sql \ | mysql database
instead of the usual:
shell> mysql database < text-file-with-funny-comments.sql
You can also edit the command file ``in place'' to change the -- comments to # comments:
shell> replace " --" " #" -- text-file-with-funny-comments.sql
Change them back with this command:
shell> replace " #" " --" -- text-file-with-funny-comments.sql
MySQL allows you to work with both transactional tables that allow rollback and non-transactional tables that do not, so constraint handling is a bit different in MySQL than in other databases.
We have to handle the case when you have updated a lot of rows in a non-transactional table that cannot roll back when an error occurs.
The basic philosophy is to try to give an error for anything that we can detect at compile time but try to recover from any errors we get at runtime. We do this in most cases, but not yet for all. See TODO future.
The options MySQL has when an error occurs are to stop the statement in the middle or to recover as well as possible from the problem and continue.
The following sections describe what happens for the different types of constraints.
Normally you will get an error when you try to INSERT or UPDATE a row that causes a primary key, unique key or foreign key violation. If you are using a transactional storage engine such as InnoDB, MySQL will automatically roll back the transaction. If you are using a non-transactional storage engine, MySQL will stop at the incorrect row and leave any remaining rows unprocessed.
To make life easier, MySQL supports an IGNORE keyword for most commands that can cause a key violation (such as INSERT IGNORE and UPDATE IGNORE). In this case, MySQL will ignore any key violation and continue with processing the next row. You can get information about what MySQL did with the mysql_info() API function. See mysql_info(). In MySQL 4.1 and up, you also can use the SHOW WARNINGS statement. See SHOW WARNINGS.
Note that for the moment only InnoDB tables support foreign keys. See InnoDB foreign key constraints. Foreign key support in MyISAM tables is scheduled for implementation in MySQL 5.1.
To be able to support easy handling of non-transactional tables all columns in MySQL have default values.
If you insert an ``incorrect'' value in a column, such as a NULL in a NOT NULL column or a too-large numerical value in a numerical column, MySQL sets the column to the ``best possible value'' instead of producing an error. For numerical values, this is either 0, the smallest possible value or the largest possible value. For strings, this is either the empty string or the longest possible string that can be in the column.
This means that if you try to store NULL into a column that doesn't take NULL values, MySQL Server instead stores 0 or '' (the empty string). This last behavior can, for single row inserts, be changed with the -DDONT_USE_DEFAULT_FIELDS compile option.) See configure options. This causes INSERT statements to generate an error unless you explicitly specify values for all columns that require a non-NULL value.
The reason for the preceding rules is that we can't check these conditions until the query has begun executing. We can't just roll back if we encounter a problem after updating a few rows, because the table type may not support rollback. The option of terminating the statement is not that good; in this case, the update would be ``half done,'' which is probably the worst possible scenario. In this case it's better to ``do the best you can'' and then continue as if nothing happened.
This means that you should generally not use MySQL to check column content. Instead, the application should ensure that is passes only legal values to MySQL.
In MySQL 5.0, we plan to improve this by providing warnings when automatic column conversions occur, plus an option to let you roll back statements that attempt to perform a disallowed column value assignment, as long as the statement uses only transactional tables.
In MySQL 4.x, ENUM is not a real constraint, but is a more efficient way to define columns that can only contain a given set of values. This is because of the same reasons NOT NULL is not honored. See constraint NOT NULL.
If you insert an incorrect value into an ENUM column, it will be set to the reserved enumeration value 0, which will be displayed as an empty string in string context. See ENUM.
If you insert an incorrect value into a SET column, the incorrect value is ignored. For example, if the column can contain the values 'a', 'b', and 'c', an attempt to assign 'a,x,b,y' results in a value of 'a,b'. See SET.
The following known errors or bugs are not fixed in MySQL 3.23 because fixing them would involve changing a lot of code that could introduce other even worse bugs. The bugs are also classified as ``not fatal'' or ``bearable.''
You can get a deadlock if you use LOCK TABLE to lock multiple tables and then in the same connection use DROP TABLE to drop one of them while another thread is trying to lock it. (To break the deadlock, you can use KILL to terminate any of the threads involved.) This issue is resolved in MySQL 4.0.12.
SELECT MAX(key_column) FROM t1,t2,t3... where one of the tables are empty doesn't return NULL but instead returns the maximum value for the column. This issue is resolved in MySQL 4.0.11.
DELETE FROM heap_table without a WHERE clause doesn't work on a locked HEAP table.
The following known errors or bugs are not fixed in MySQL 4.0 because fixing them would involve changing a lot of code that could introduce other even worse bugs. The bugs are also classified as ``not fatal'' or ``bearable.''
In a UNION, the first SELECT determines the type, max_length and NULL properties for the resulting columns. This issue is resolved in MySQL 4.1.1; the property values are based on the rows from all UNION parts.
The following problems are known and fixing them is a high priority:
Dropping a FOREIGN KEY constraint doesn't work in replication as the constraint may have another name.
You cannot mix UNION ALL and UNION DISTINCT in the same query. If you use ALL for one UNION, it is used for all of them.
If one user has a long running transaction and another user drops a table that is updated in the transaction, there is small chance that the binary log may contain the DROP TABLE command before the table is used in the transaction itself. We plan to fix this in 5.0 by having the DROP TABLE wait until the table is not used in any transaction.
When inserting a big integer value (between 2^63 and 2^64-1) into a decimal/string column, it is inserted as a negative value because the number is evaluated in a signed integer context. It is planned to be fixed in 4.1.
FLUSH TABLES WITH READ LOCK does not block CREATE TABLE or COMMIT, which make cause a problem with the binary log position when doing a full backup of tables and the binary log.
ANALYZE TABLE on a BDB table may in some cases make the table unusable until one has restarted mysqld. If this happens, you will see errors of the following form in the MySQL error file:
001207 22:07:56 bdb: log_flush: LSN past current end-of-log
MySQL accepts parentheses in the FROM part of a SELECT statement, but silently ignores them. The reason for not giving an error is that many clients that automatically generate queries add parentheses in the FROM part even where they are not needed.
Concatenating many RIGHT JOINS or combining LEFT and RIGHT join in the same query may not give a correct answer as MySQL only generates NULL rows for the table preceding a LEFT or before a RIGHT join. This will be fixed in 5.0 at the same time we add support for parentheses in the FROM part.
Don't execute ALTER TABLE on a BDB table on which you are running multiple-statement transactions until all those transactions complete. (The transaction will probably be ignored.)
ANALYZE TABLE, OPTIMIZE TABLE, and REPAIR TABLE may cause problems on tables for which you are using INSERT DELAYED.
Doing a LOCK TABLE ... and FLUSH TABLES ... doesn't guarantee that there isn't a half-finished transaction in progress on the table.
BDB tables are a bit slow to open. If you have many BDB tables in a database, it will take a long time to use the mysql client on the database if you are not using the -A option or if you are using rehash. This is especially notable when you have a large table cache.
Replication uses query-level logging: The master writes the executed queries to the binary log. This is a very fast, compact, and efficient logging method that works perfectly in most cases. Though we have never heard of it actually occurring, it is theoretically possible for the data on the master and slave to become different if a query is designed in such a way that the data modification is non-deterministic, that is, left to the will of the query optimizer. (That generally is not a good practice anyway, even outside of replication!) For example:
CREATE ... SELECT or INSERT ... SELECT statements that insert zero or NULL values into an AUTO_INCREMENT column.
DELETE if you are deleting rows from a table which has foreign keys with ON DELETE CASCADE properties.
REPLACE ... SELECT, INSERT IGNORE ... SELECT if you have duplicate key values in the inserted data.
IF and only if all these queries have NO ORDER BY clause guaranteeing a deterministic order.
Indeed, for example for INSERT ... SELECT with no ORDER BY, the SELECT may return rows in a different order (which will result in a row having different ranks, hence getting a different number in the auto_increment column), depending on the choices made by the optimizers on the master and slave. A query will be optimized differently on the master and slave only if:
The files used by the two queries are not exactly the same; for example OPTIMIZE TABLE was run on the master tables and not on the slave tables (to fix this, since MySQL 4.1.1, OPTIMIZE, ANALYZE and REPAIR are written to the binary log).
The table is stored in a different storage engine on the master than on the slave. (It is possible to use different storage engines on the master and slave. For example, you can use InnoDB on the master, but MyISAM on the slave if the slave has less available disk space.)
MySQL buffer sizes (key_buffer_size, etc.) are different on the master and slave.
The master and slave run different MySQL versions, and the optimizer code is different between these versions.
This problem may also affect database restoration using mysqlbinlog|mysql.
The easiest way to avoid this problem in all cases is add an ORDER BY clause to such non-deterministic queries to ensure that the rows are always stored or modified in the same order. In future MySQL versions, we will automatically add an ORDER BY clause when needed.
The following problems are known and will be fixed in due time:
Log files are based on hostnames (if you don't specify a file name with the startup option). For now you have to use options like --log-bin=old_host_name-bin if you change your host name to something else. Another option is to just rename the old files to reflect your hostname change. See Server options.
mysqlbinlog will not delete temporary files left after a LOAD DATA INFILE command. See mysqlbinlog.
RENAME doesn't work with TEMPORARY tables or tables used in a MERGE table.
When using the RPAD() function in a query that has to be resolved by using a temporary table, all resulting strings will have rightmost spaces removed. This is an example of such a query:
SELECT RPAD(t1.column1, 50, ' ') AS f2, RPAD(t2.column2, 50, ' ') AS f1 FROM table1 as t1 LEFT JOIN table2 AS t2 ON t1.record=t2.joinID ORDER BY t2.record;
The final result of this bug is that you will not be able to get spaces on the right side of the resulting values. The problem also occurs for any other string function that adds spaces to the right.
The reason for this is due to the fact that HEAP tables, which are used first for temporary tables, are not capable of handling VARCHAR columns.
This behavior exists in all versions of MySQL. It will be fixed in one of the 4.1 series releases.
Due to the way table definition files are stored, you cannot use character 255 (CHAR(255)) in table names, column names, or enumerations. This is scheduled to be fixed in version 5.1 when we have new table definition format files.
When using SET CHARACTER SET, you can't use translated characters in database, table, and column names.
You can't use _ or % with ESCAPE in LIKE ... ESCAPE.
If you have a DECIMAL column with a number stored in different formats (+01.00, 1.00, 01.00), GROUP BY may regard each value as a different value.
DELETE FROM merge_table used without a WHERE clause will clear only the mapping for the table, not delete everything in the mapped tables.
You cannot build the server in another directory when using MIT-pthreads. Because this requires changes to MIT-pthreads, we are not likely to fix this. See MIT-pthreads.
BLOB values can't ``reliably'' be used in GROUP BY or ORDER BY or DISTINCT. Only the first max_sort_length bytes are used when comparing BLOB values in these cases. The default value of max_sort_length value is 1024. It can be changed at server startup time. A workaround for most cases is to use a substring. For example: SELECT DISTINCT LEFT(blob,2048) FROM tbl_name.
Numeric calculations are done with BIGINT or DOUBLE (both are normally 64 bits long). It depends on the function which precision one gets. The general rule is that bit functions are done with BIGINT precision, IF, and ELT() with BIGINT or DOUBLE precision and the rest with DOUBLE precision. You should try to avoid using unsigned long long values if they resolve to be bigger than 63 bits (9223372036854775807) for anything other than bit fields. MySQL Server 4.0 has better BIGINT handling than 3.23.
All string columns, except BLOB and TEXT columns, automatically have all trailing spaces removed when retrieved. For CHAR types this is okay. The bug is that in MySQL Server, VARCHAR columns are treated the same way.
You can only have up to 255 ENUM and SET columns in one table.
In MIN(), MAX(), and other aggregate functions, MySQL currently compares ENUM and SET columns by their string value rather than by the string's relative position in the set.
mysqld_safe redirects all messages from mysqld to the mysqld log. One problem with this is that if you execute mysqladmin refresh to close and reopen the log, stdout and stderr are still redirected to the old log. If you use --log extensively, you should edit mysqld_safe to log to 'hostname'.err instead of 'hostname'.log so you can easily reclaim the space for the old log by deleting the old one and executing mysqladmin refresh.
In the UPDATE statement, columns are updated from left to right. If you refer to an updated column, you will get the updated value instead of the original value. For example:
mysql> UPDATE tbl_name SET KEY=KEY+1,KEY=KEY+1;
This will increment KEY by 2, not 1.
You can refer to multiple temporary tables in the same query, but you cannot refer to any given temporary table more than once. For example, the following doesn't work:
mysql> SELECT * FROM temporary_table, temporary_table AS t2;
The optimizer may handle DISTINCT differently if you are using 'hidden' columns in a join or not. In a join, hidden columns are counted as part of the result (even if they are not shown) while in normal queries hidden columns don't participate in the DISTINCT comparison. We will probably change this in the future to never compare the hidden columns when executing DISTINCT.
An example of this is:
SELECT DISTINCT mp3id FROM band_downloads WHERE userid = 9 ORDER BY id DESC;
and
SELECT DISTINCT band_downloads.mp3id FROM band_downloads,band_mp3 WHERE band_downloads.userid = 9 AND band_mp3.id = band_downloads.mp3id ORDER BY band_downloads.id DESC;
In the second case you may in MySQL Server 3.23.x get two identical rows in the result set (because the values in the hidden id column may differ).
Note that this happens only for queries where you don't have the ORDER BY columns in the result, something that you are not allowed to do in SQL-92.
Because MySQL Server allows you to work with table types that don't support transactions, and thus can't roll back data, some things behave a little differently in MySQL Server than in other SQL servers. This is just to ensure that MySQL Server never needs to do a rollback for an SQL statement. This may be a little awkward at times as column values must be checked in the application, but this will actually give you a nice speed increase as it allows MySQL Server to do some optimizations that otherwise would be very hard to do.
If you set a column to an incorrect value, MySQL Server will, instead of doing a rollback, store the best possible value in the column:
If you try to store a value outside the range in a numerical column, MySQL Server instead stores the smallest or largest possible value in the column.
If you try to store a string that doesn't start with a number into a numerical column, MySQL Server stores 0.
If you try to store NULL into a column that doesn't allow NULL values, MySQL Server stores 0 or '' (the empty string) in it instead. (This behavior can, however, be changed with the -DDONT_USE_DEFAULT_FIELDS compile option.)
MySQL allows you to store some wrong date values into DATE and DATETIME columns (like '2000-02-31' or '2000-02-00'). The idea is that it's not the job of the SQL server to validate dates. If MySQL can store a date value and retrieve exactly the same value, MySQL stores it as given. If the date is totally wrong (outside the server's ability to store it), the special date value '0000-00-00' is stored in the column instead.
If you set an ENUM column to an unsupported value, it is set to the error value empty string, with numeric value 0.
If you set a SET column to an unsupported value, the value is ignored.
If you execute a PROCEDURE on a query that returns an empty set, in some cases the PROCEDURE will not transform the columns.
Creation of a table of type MERGE doesn't check if the underlying tables are of compatible types.
MySQL Server can't yet handle NaN, -Inf, and Inf values in DOUBLE columns. Using these will cause problems when trying to export and import data. We should as an intermediate solution change NaN to NULL (if possible) and -Inf and Inf to the minimum respective maximum possible double value.
If you use ALTER TABLE to first add a UNIQUE index to a table used in a MERGE table and then use ALTER TABLE to add a normal index on the MERGE table, the key order will be different for the tables if there was an old key that was not unique in the table. This is because ALTER TABLE puts UNIQUE indexes before normal indexes to be able to detect duplicate keys as early as possible.
The following are known bugs in earlier versions of MySQL:
You can get a hung thread if you do a DROP TABLE on a table that is one among many tables that is locked with LOCK TABLES.
In the following case you can get a core dump:
Delayed insert handler has pending inserts to a table.
LOCK table with WRITE.
FLUSH TABLES.
Before MySQL Server Version 3.23.2 an UPDATE that updated a key with a WHERE on the same key may have failed because the key was used to search for records and the same row may have been found multiple times:
UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100;
A workaround is to use:
mysql> UPDATE tbl_name SET KEY=KEY+1 WHERE KEY+0 > 100;
This will work because MySQL Server will not use an index on expressions in the WHERE clause.
Before MySQL Server Version 3.23, all numeric types were treated as fixed-point fields. That means you had to specify how many decimals a floating-point field should have. All results were returned with the correct number of decimals.
For platform-specific bugs, see the sections about compiling and porting. See Installing source. See Porting.
Table of Contents
This chapter describes how to obtain and install MySQL:
Determine whether your platform is supported. Please note that not all supported systems are equally good for running MySQL on them. On some it is much more robust and efficient than others. See Which OS for details.
Choose a distribution to install. Several versions of MySQL are available, and most are available in serveral distribution formats. You can choose from pre-packaged distributions containing binary (precompiled) programs or source code. When in doubt, use a binary distribution. We also provide public access to our current source tree, for those who want to see our most recent developments and help us test new code. To determine which version and type of distribution you should use, see Which version.
Download the distribution that you want to install. For a list of sites from which you can obtain MySQL, see Getting MySQL. You can verify the integrity of the distribution using the instructions in Verifying Package Integrity.
Install the distribution. For binary distributions, use the instructions in in Installing binary. For source distributions, use the instructions in Installing source. Additional installation procedures include the following:
For post-installation procedures, see Post-installation. These procedures apply whether you install MySQL using a binary or source distribution.
If you plan to upgrade an existing version of MySQL to a newer version rather than installing MySQL for the first time, see Upgrade for information about upgrade procedures and about issues that you should consider before upgrading.
If you want to run the MySQL benchmark scripts, Perl support for MySQL must be available. See Perl support.
The last part of the chapter provides information on system-specific problems you may run into.
Table of Contents
Before installing MySQL, you should do the following:
Determine whether or not MySQL runs on your platform.
Choose a distribution to install.
Download the distribution and verify its integrity.
This section contains the information necessary to carry out these steps. After doing so, you can use the instructions in later sections of the chapter to install the distribution that you choose.
After you have downloaded the package, you should make sure that the MD5 checksum matches the one provided on the MySQL download pages. Each package has an individual checksum that you can verify with the following command, where package_name is the name of the package you downloaded:
shell> md5sum package_name
Note, that not all operating systems support the md5sum command---on some it is simply called md5, others do not ship it at all. On Linux, it is part of the GNU Text Utilities package, which is available for a wide range of platforms. You can download the source code from http://www.gnu.org/software/textutils/ as well. If you have OpenSSL installed, you can also use the command openssl md5 package_name instead. A DOS/Windows implementation of the md5 command is available from http://www.fourmilab.ch/md5/.
Example:
shell> md5sum mysql-standard-4.0.17-pc-linux-i686.tar.gz 60f5fe969d61c8f82e4f7f62657e1f06 mysql-standard-4.0.17-pc-linux-i686.tar.gz
You should verify that the resulting checksum (the string of hexadecimal digits) matches the one displayed on the download page immediately below the respective package.
Another method of verifying the integrity and authenticity of a package is to use cryptographic signatures. This is more reliable than using MD5 checksums, but requires more work.
Beginning with MySQL 4.0.10 (February 2003), MySQL AB started signing downloadable packages with GnuPG (GNU Privacy Guard). GnuPG is an Open Source alternative to the very well-known Pretty Good Privacy (PGP) by Phil Zimmermann. See http://www.gnupg.org/ for more information about GnuPG and how to obtain and install it on your system. Most Linux distributions already ship with GnuPG installed by default. For more information about OpenPGP, see http://www.openpgp.org/.
To verify the signature for a specific package, you first need to obtain a copy of MySQL AB's public GPG build key <build@mysql.com>. You can either cut and paste it directly from here, or obtain it from http://www.keyserver.net/.
Key ID: pub 1024D/5072E1F5 2003-02-03 MySQL Package signing key (www.mysql.com) <build@mysql.com> Fingerprint: A4A9 4068 76FC BD3C 4567 70C8 8C71 8D3B 5072 E1F5 Public Key (ASCII-armored): -----BEGIN PGP PUBLIC KEY BLOCK----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org mQGiBD4+owwRBAC14GIfUfCyEDSIePvEW3SAFUdJBtoQHH/nJKZyQT7h9bPlUWC3 RODjQReyCITRrdwyrKUGku2FmeVGwn2u2WmDMNABLnpprWPkBdCk96+OmSLN9brZ fw2vOUgCmYv2hW0hyDHuvYlQA/BThQoADgj8AW6/0Lo7V1W9/8VuHP0gQwCgvzV3 BqOxRznNCRCRxAuAuVztHRcEAJooQK1+iSiunZMYD1WufeXfshc57S/+yeJkegNW hxwR9pRWVArNYJdDRT+rf2RUe3vpquKNQU/hnEIUHJRQqYHo8gTxvxXNQc7fJYLV K2HtkrPbP72vwsEKMYhhr0eKCbtLGfls9krjJ6sBgACyP/Vb7hiPwxh6rDZ7ITnE kYpXBACmWpP8NJTkamEnPCia2ZoOHODANwpUkP43I7jsDmgtobZX9qnrAXw+uNDI QJEXM6FSbi0LLtZciNlYsafwAPEOMDKpMqAK6IyisNtPvaLd8lH0bPAnWqcyefep rv0sxxqUEMcM3o7wwgfN83POkDasDbs3pjwPhxvhz6//62zQJ7Q7TXlTUUwgUGFj a2FnZSBzaWduaW5nIGtleSAod3d3Lm15c3FsLmNvbSkgPGJ1aWxkQG15c3FsLmNv bT6IXQQTEQIAHQUCPj6jDAUJCWYBgAULBwoDBAMVAwIDFgIBAheAAAoJEIxxjTtQ cuH1cY4AnilUwTXn8MatQOiG0a/bPxrvK/gCAJ4oinSNZRYTnblChwFaazt7PF3q zIhMBBMRAgAMBQI+PqPRBYMJZgC7AAoJEElQ4SqycpHyJOEAn1mxHijft00bKXvu cSo/pECUmppiAJ41M9MRVj5VcdH/KN/KjRtW6tHFPYhMBBMRAgAMBQI+QoIDBYMJ YiKJAAoJELb1zU3GuiQ/lpEAoIhpp6BozKI8p6eaabzF5MlJH58pAKCu/ROofK8J Eg2aLos+5zEYrB/LsrkCDQQ+PqMdEAgA7+GJfxbMdY4wslPnjH9rF4N2qfWsEN/l xaZoJYc3a6M02WCnHl6ahT2/tBK2w1QI4YFteR47gCvtgb6O1JHffOo2HfLmRDRi Rjd1DTCHqeyX7CHhcghj/dNRlW2Z0l5QFEcmV9U0Vhp3aFfWC4Ujfs3LU+hkAWzE 7zaD5cH9J7yv/6xuZVw411x0h4UqsTcWMu0iM1BzELqX1DY7LwoPEb/O9Rkbf4fm Le11EzIaCa4PqARXQZc4dhSinMt6K3X4BrRsKTfozBu74F47D8Ilbf5vSYHbuE5p /1oIDznkg/p8kW+3FxuWrycciqFTcNz215yyX39LXFnlLzKUb/F5GwADBQf+Lwqq a8CGrRfsOAJxim63CHfty5mUc5rUSnTslGYEIOCR1BeQauyPZbPDsDD9MZ1ZaSaf anFvwFG6Llx9xkU7tzq+vKLoWkm4u5xf3vn55VjnSd1aQ9eQnUcXiL4cnBGoTbOW I39EcyzgslzBdC++MPjcQTcA7p6JUVsP6oAB3FQWg54tuUo0Ec8bsM8b3Ev42Lmu QT5NdKHGwHsXTPtl0klk4bQk4OajHsiy1BMahpT27jWjJlMiJc+IWJ0mghkKHt92 6s/ymfdf5HkdQ1cyvsz5tryVI3Fx78XeSYfQvuuwqp2H139pXGEkg0n6KdUOetdZ Whe70YGNPw1yjWJT1IhMBBgRAgAMBQI+PqMdBQkJZgGAAAoJEIxxjTtQcuH17p4A n3r1QpVC9yhnW2cSAjq+kr72GX0eAJ4295kl6NxYEuFApmr1+0uUq/SlsQ== =YJkx -----END PGP PUBLIC KEY BLOCK-----
You can import this key into your public GPG keyring by using gpg --import. See the GPG documentation for more info on how to work with public keys.
After you have downloaded and imported the public build key, download your desired MySQL package and the corresponding signature, which also is available from the download page. The signature file has the same name as the distribution file with an .asc extension. For example:
Distribution file | mysql-standard-4.0.17-pc-linux-i686.tar.gz |
Signature file | mysql-standard-4.0.17-pc-linux-i686.tar.gz.asc |
Make sure that both files are stored in the same directory and then run the following command to verify the signature for the distribution file:
shell> gpg --verify package_name.asc
Example:
shell> gpg --verify mysql-standard-4.0.17-pc-linux-i686.tar.gz.asc gpg: Warning: using insecure memory! gpg: Signature made Mon 03 Feb 2003 08:50:39 PM MET using DSA key ID 5072E1F5 gpg: Good signature from "MySQL Package signing key (www.mysql.com) <build@mysql.com>"
The "Good signature" message indicates that everything is all right.
For RPM packages, there is no separate signature. RPM packages actually have a built-in GPG signature and MD5 checksum. You can verify a package by running the following command:
shell> rpm --checksig package_name.rpm
Example:
shell> rpm --checksig MySQL-server-4.0.10-0.i386.rpm MySQL-server-4.0.10-0.i386.rpm: md5 gpg OK
Note: If you are using RPM 4.1 and it complains about (GPG) NOT OK (MISSING KEYS: GPG#5072e1f5) (even though you have imported it into your GPG public keyring), you need to import the key into the RPM keyring first. RPM 4.1 no longer uses your GPG keyring (and GPG itself), but rather maintains its own keyring (because it's a system-wide application and the GPG public keyring is a user-specific file). To import the MySQL public key into the RPM keyring, use rpm --import. For example, if you have the public key stored in a file named mysql_pubkey.asc, import it using this command:
shell> rpm --import mysql_pubkey.asc
If you notice that the MD5 checksum or GPG signatures do not match, first try to download the respective package one more time, perhaps from another mirror site. If you repeatedly cannot successfully verify the integrity of the package, please notify us about such incidents including the full package name and the download site you have been using at <webmaster@mysql.com> or <build@mysql.com>. Do not report downloading problems using the bug-reporting system.
This section lists the operating systems on which you can expect to be able to run MySQL.
We use GNU Autoconf, so it is possible to port MySQL to all modern systems that have a C++ compiler and a working implementation of POSIX threads. (Thread suport is needed for the server. To compile only the client code, the only requirement is a C++ compiler.) We use and develop the software ourselves primarily on Linux (SuSE and Red Hat), FreeBSD, and Sun Solaris (Versions 8 and 9).
MySQL has been reported to compile successfully on the following combinations of operating system and thread package. Note that for many operating systems, native thread support works only in the latest versions.
AIX 4.x, 5.x with native threads. See IBM-AIX.
Amiga.
BSDI 2.x with the MIT-pthreads package. See BSDI.
BSDI 3.0, 3.1 and 4.x with native threads. See BSDI.
DEC Unix 4.x with native threads. See Alpha-DEC-UNIX.
FreeBSD 2.x with the MIT-pthreads package. See FreeBSD.
FreeBSD 3.x and 4.x with native threads. See FreeBSD.
FreeBSD 4.x with Linuxthreads. See FreeBSD.
HP-UX 10.20 with the DCE threads or the MIT-pthreads package. See HP-UX 10.20.
HP-UX 11.x with the native threads. See HP-UX 11.x.
Linux 2.0+ with LinuxThreads 0.7.1+ or glibc 2.0.7+. See Linux.
Mac OS X. See Mac OS X.
NetBSD 1.3/1.4 Intel and NetBSD 1.3 Alpha (Requires GNU make). See NetBSD.
Novell NetWare 6.0. See NetWare installation.
OpenBSD > 2.5 with native threads. OpenBSD < 2.5 with the MIT-pthreads package. See OpenBSD.
OS/2 Warp 3, FixPack 29 and OS/2 Warp 4, FixPack 4. See OS/2.
SCO OpenServer with a recent port of the FSU Pthreads package. See SCO.
SCO UnixWare 7.1.x. See SCO UnixWare.
SGI Irix 6.x with native threads. See SGI-Irix.
Solaris 2.5 and above with native threads on SPARC and x86. See Solaris.
SunOS 4.x with the MIT-pthreads package. See Solaris.
Tru64 Unix
Windows 9x, Me, NT, 2000, and XP. See Windows installation.
Not all platforms are equally well-suited for running MySQL. How well a certain platform is suited for a high-load mission-critical MySQL server is determined by the following factors:
General stability of the thread library. A platform may have an excellent reputation otherwise, but MySQL will be only as stable as the thread library if that library is unstable in the code that is called by MySQL, even if everything else is perfect.
The ability of the kernel and/or thread library to take advantage of symmetric multi-processor (SMP) systems. In other words, when a process creates a thread, it should be possible for that thread to run on a different CPU than the original process.
The ability of the kernel and/or the thread library to run many threads which acquire and release a mutex over a short critical region frequently without excessive context switches. In other words, if the implementation of pthread_mutex_lock() is too anxious to yield CPU time, this will hurt MySQL tremendously. If this issue is not taken care of, adding extra CPUs will actually make MySQL slower.
General filesystem stability and performance.
If your tables are big, the ability of the filesystem to deal with large files at all and to deal with them efficiently.
Our level of expertise here at MySQL AB with the platform. If we know a platform well, we enable platform-specific optimizations and fixes at compile time. We can also provide advice on configuring your system optimally for MySQL.
The amount of testing we have done internally for similar configurations.
The number of users that have successfully run MySQL on that platform in similar configurations. If this number is high, the chances of encountering platform-specific surprises are much smaller.
Based on the preceding criteria, the best platforms for running MySQL at this point are x86 with SuSE Linux 8.2, 2.4 kernel, and ReiserFS (or any similar Linux distribution) and SPARC with Solaris (2.7-9). FreeBSD comes third, but we really hope it will join the top club once the thread library is improved. We also hope that at some point we will be able to include into the top category all other platforms on which MySQL currently compiles and runs okay, but not quite with the same level of stability and performance. This will require some effort on our part in cooperation with the developers of the operating system and library components that MySQL depends on. If you are interested in improving one of those components, are in a position to influence its development, and need more detailed instructions on what MySQL needs to run better, send an email message to the MySQL internals mailing list. See Mailing-list.
Please note that the purpose of the preceding comparison is not to say that one operating system is better or worse than another in general. We are talking only about choosing an OS for the specific purpose of running MySQL. With this in mind, the result of this comparison would be different if we considered more factors. And in some cases, the reason one OS is better than the other could simply be that we have put forth more effort into testing on and optimizing for that particular platform. We are just stating our observations to help you decide which platform to use MySQL in your setup.
When preparing to install MySQL, you should decide which version to use. MySQL development occurs in several release series, and you can pick the one that best fits your needs. After deciding which version to install, you can choose a distribution format. Releases are available in binary or source format.
The first decision to make is whether you want to use a production (stable) release or a development release. In the MySQL development process, multiple release series co-exist, each at a different stage of maturity:
MySQL 5.0 is the newest development release series and is under very active development for new features. Until recently it was available only in preview form from the BitKeeper source repository. An early alpha release has now been issued to allow more widespread testing.
MySQL 4.1 is a development release series to which major new features have been added. It is still at alpha status. Sources and binaries are available for use and testing on development systems.
MySQL 4.0 is the current stable/production-quality release series. New releases are issued for bugfixes. No new features are added that could diminish the code stability.
MySQL 3.23 is the old stable/production-quality release series. This series is retired, so new releases are issued only to fix critical bugs.
We don't believe in a complete freeze, as this also leaves out bug fixes and things that ``must be done.'' ``Somewhat frozen'' means that we may add small things that ``almost surely will not affect anything that's already working.'' Naturally, relevant bugfixes from an earlier series propagate to later series.
Normally, if you are beginning to use MySQL for the first time or trying to port it to some system for which there is no binary distribution, we recommend going with the production release series. Currently this is MySQL 4.0. Note that all MySQL releases, even those from development series, are checked with the MySQL benchmarks and an extensive test suite before being issued.
If you are running an old system and want to upgrade, but don't want to take chances with a non-seamless upgrade, you should upgrade to the latest version in the same release series you are using (where only the last part of the version number is newer than yours). We have tried to fix only fatal bugs and make small, relatively safe changes to that version.
If you want to use new features not present in the production release series, you can use a version from a development series. Note that development releases are not as stable as production releases.
If you want to use the very latest sources containing all current patches and bugfixes, you can use one of our BitKeeper repositories. These are not ``releases'' as such, but are available as previews of the code on which future releases will be based.
The MySQL naming scheme uses release names that consist of three numbers and a suffix, for example, mysql-4.1.0-alpha. The numbers within the release name are is interpreted like this:
The first number (4) is the major version and also describes the file format. All Version 4 releases have the same file format.
The second number (1) is the release level. Taken together, the major version and release level constitute the release series number.
The third number (0) is the version number within the release series. This is incremented for each new release. Usually you want the latest version for the series you have chosen.
For each minor update, the last number in the version string is incremented. When there are major new features or minor incompatibilities with previous versions, the second number in the version string is incremented. When the file format changes, the first number is increased.
Release names also include a suffix to indicates the stability level of the release. Releases within a series progress through a set of suffixes to indicate how the stability level improves. The possible suffixes are:
alpha indicates that the release contains some large section of new code that hasn't been 100% tested. Known bugs (usually there are none) should be documented in the News section. See News. There are also new commands and extensions in most alpha releases. Active development that may involve major code changes can occur in an alpha release, but everything will be tested before issuing a release. For this reason, there should be no known bugs in any MySQL release.
beta means that all new code has been tested. No major new features that could cause corruption in old code are added. There should be no known bugs. A version changes from alpha to beta when there haven't been any reported fatal bugs within an alpha version for at least a month and we have no plans to add any features that could make any old command unreliable.
gamma is a beta that has been around a while and seems to work fine. Only minor fixes are added. This is what many other companies call a release.
If there is no suffix, it means that the version has been run for a while at many different sites with no reports of bugs other than platform-specific bugs. Only critical bug fixes are applied to the release. This is what we call a production (stable) release.
MySQL uses a naming scheme that is slightly different from most other products. In general, it's relatively safe to use any version that has been out for a couple of weeks without being replaced with a new version within the release series.
All releases of MySQL are run through our standard tests and benchmarks to ensure that they are relatively safe to use. Because the standard tests are extended over time to check for all previously found bugs, the test suite keeps getting better.
Note that all releases have been tested at least with:
An internal test suite | The mysql-test directory contains an extensive set of test cases. We run these tests for virtually every server binary. See MySQL test suite for more information about this test suite. |
The MySQL benchmark suite | This suite runs a range of common queries. It is also a test to see whether the latest batch of optimizations actually made the code faster. See MySQL Benchmarks. |
The crash-me test | This test tries to determine what features the database supports and what its capabilities and limitations are. See MySQL Benchmarks. |
Another test is that we use the newest MySQL version in our internal production environment, on at least one machine. We have more than 100 gigabytes of data to work with.
After choosing which version of MySQL to install, you should decide whether to use a binary distribution or a source distribution. In most cases you should probably use a binary distribution, if one exists for your platform. Binary distributions are available in native format for many platforms, such as RPM files for Linux or DMG package installers for Mac OS X. Distributions also are available as Zip archives or compressed tar files.
Reasons to choose a binary distribution include the following:
Binary distributions generally are easier to install than source distributions.
To satisfy different user requirements, we provide two different binary versions: one compiled with the non-transactional storage engines (a small, fast binary), and one configured with the most important extended options like transaction-safe tables. Both versions are compiled from the same source distribution. All native MySQL clients can connect to both MySQL versions.
The extended MySQL binary distribution is marked with the -max suffix and is configured with the same options as mysqld-max. See mysqld-max.
If you want to use the MySQL-Max RPM, you must first install the standard MySQL-server RPM.
Circumstances under which you probably will be better off with a source installation include the following:
You want to install MySQL at some explicit location. The standard binary distributions are ``ready to run'' at any place, but you may want to have even more flexibility to place MySQL components where you want.
You want to configure mysqld with some extra features that are not in the standard binary distributions. Here is a list of the most common extra options that you may want to use:
--with-innodb (default for MySQL 4.0 and onwards)
--with-berkeley-db (not available on all platforms)
--with-raid
--with-libwrap
--with-named-z-libs (This is done for some of the binaries)
--with-debug[=full]
You want to configure mysqld without some features that are included in the standard binary distributions. For example, distributions normally are compiled with support for all character sets. If you want a smaller MySQL server, you can recompile it with support for only the character sets you need.
You have a special compiler (like pgcc) or want to use compiler options that are better optimized for your processor. Binary distributions are compiled with options that should work on a variety of processors from the same processor family.
You want to use the latest sources from one of the BitKeeper repositories to have access to all current bugfixes. For example, if you have found a bug and reported it to the MySQL development team, the bugfix will be committed to the source repository and you can access it there. The bugfix will not appear in a release until a release actually is issued.
You want to read (or modify) the C and C++ code that makes up MySQL. For this purpose, you should get a source distribution, because the source code is always the ultimate manual. Source distributions also contain more tests and examples than binary distributions.
MySQL is evolving quite rapidly here at MySQL AB and we want to share new developments with other MySQL users. We try to make a release when we have very useful features that others seem to have a need for.
We also try to help out users who request features that are easy to implement. We take note of what our licensed users want to have, and we especially take note of what our extended email supported customers want and try to help them out.
No one has to download a new release. The News section will tell you if the new release has something you really want. See News.
We use the following policy when updating MySQL:
Releases are issued within each release series. For each release, the last number in the version is one more than the previous release within the same series.
Production (stable) releases are meant to appear about 1-2 times a year, but if small bugs are found, a release with only bug fixes will be issued.
Working releases/bug fixes to old releases are meant to appear about every 4-8 weeks.
Binary distributions for some platforms are made by us for major releases. Other people may make binary distributions for other systems, but probably less frequently.
We usually make fixes available as soon as we have identified and corrected small or non-critical but annoying bugs. The fixes are available immediately from our public BitKeeper repositories, and will be included in the next release.
If by any chance a fatal bug is found in a release, we will make a new release as soon as possible. We would like other companies to do this, too.
We put a lot of time and effort into making our releases bug free. To our knowledge, we have not released a single MySQL version with any known ``fatal'' repeatable bugs. (A fatal bug is something that crashes MySQL under normal usage, produces incorrect answers for normal queries, or has a security problem.)
We have documented all open problems, bugs, and issues that are dependent on design decisions. See Bugs.
Our aim is to fix everything that is fixable without risk of making a stable MySQL version less stable. In certain cases, this means we can fix an issue in the development versions, but not in the stable (production) version. Naturally, we document such issues so that users are aware.
Here is a description of how our build process works:
We monitor bugs from our customer support list, the bugs database at http://bugs.mysql.com/, and the MySQL external mailing lists.
All reported bugs for live versions are entered into the bugs database.
When we fix a bug, we always try to make a test case for it and include it into our test system to ensure that the bug will never recur without being detected. (About 90% of all fixed bugs have a test case.)
We also create test cases for all new features we add to MySQL.
Before we start to build a new MySQL release, we ensure that all reported repeatable bugs for the MySQL version (3.23.x, 4.0.x, etc) are fixed. If something is impossible to fix (due to some internal design decision in MySQL) we document this in the manual. See Bugs.
We do a build on all platforms for which we support binaries (15+ platforms) and run our test suite and benchmark suite on all of them.
We will not publish a binary for a platform for which the test or benchmark suite fails. If it's a general error in the source, we fix this and do the build plus tests on all systems again, from scratch.
The build and test process takes 2-3 days). If we receive a report regarding a fatal bug during this process (for example, one that causes a core dump), we fix the problem and restart the build process.
After publishing the binaries on http://www.mysql.com/, we send out an announcement message to the mysql and announce mailing lists. See Mailing-list. The announcement message contains a list of all changes to the release and any known problems with the release. (The ``known problems'' section in the release notes has only been needed in a handful of releases.)
To quickly give our users access to the latest MySQL features, we do a new MySQL release every 4-8 weeks. Source code snapshots are built daily and are available at http://downloads.mysql.com/snapshots.php.
If we, after the release is done, get any bug reports that there was (after all) anything critically wrong with the build on a specific platform, we will fix this at once and build a new 'a' release for that platform. Thanks to our large user base, problems are found quickly.
Our track record for making good releases is quite good. In the last 150 releases, we had to do a new build for less than 10 releases (in 3 of these cases, the bug was a faulty glibc library on one of our build machines that took us a long time to track down).
As a service, we at MySQL AB provide a set of binary distributions of MySQL that are compiled at our site or at sites where customers kindly have given us access to their machines.
In addition to the binaries provided in platform-specific package formats (see Quick Standard Installation), we do offer binary distributions for a number of platforms in the form of of compressed tar files (.tar.gz).
These distributions are generated using the script Build-tools/Do-compile which compiles the source code and creates the binary tar.gz archive using scripts/make_binary_distribution These binaries are configured and built with the following compilers and options.
Binaries built on MySQL AB development systems:
Linux 2.4.xx x86 with gcc 2.95.3: | CFLAGS="-O2 -mcpu=pentiumpro" CXX=gcc CXXFLAGS="-O2 -mcpu=pentiumpro -felide-constructors" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --enable-assembler --disable-shared --with-client-ldflags=-all-static --with-mysqld-ldflags=-all-static |
Linux 2.4.xx Intel Itanium 2 with ecc (Intel C++ Itanium Compiler 7.0): | CC=ecc CFLAGS="-O2 -tpp2 -ip -nolib_inline" CXX=ecc CXXFLAGS="-O2 -tpp2 -ip -nolib_inline" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile |
Linux 2.4.xx Intel Itanium with ecc (Intel C++ Itanium Compiler 7.0): | CC=ecc CFLAGS=-tpp1 CXX=ecc CXXFLAGS=-tpp1 ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile |
Linux 2.4.xx alpha with ccc (Compaq C V6.2-505 / Compaq C++ V6.3-006): | CC=ccc CFLAGS="-fast -arch generic" CXX=cxx CXXFLAGS="-fast -arch generic -noexceptions -nortti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --with-mysqld-ldflags=-non_shared --with-client-ldflags=-non_shared --disable-shared |
Linux 2.4.xx s390 with gcc 2.95.3: | CFLAGS="-O2" CXX=gcc CXXFLAGS="-O2 -felide-constructors" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared --with-client-ldflags=-all-static --with-mysqld-ldflags=-all-static |
Linux 2.4.xx x86_64 (AMD64) with gcc 3.2.1: | CXX=gcc ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared |
Sun Solaris 8 x86 with gcc 3.2.3: | CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --localstatedir=/usr/local/mysql/data --libexecdir=/usr/local/mysql/bin --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared --with-innodb |
Sun Solaris 8 SPARC with gcc 3.2: | CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --enable-assembler --with-named-z-libs=no --with-named-curses-libs=-lcurses --disable-shared |
Sun Solaris 8 SPARC 64-bit with gcc 3.2: | CC=gcc CFLAGS="-O3 -m64 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -m64 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --enable-assembler --with-named-z-libs=no --with-named-curses-libs=-lcurses --disable-shared |
Sun Solaris 9 SPARC with gcc 2.95.3: | CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --enable-assembler --with-named-curses-libs=-lcurses --disable-shared |
Sun Solaris 9 SPARC with cc-5.0 (Sun Forte 5.0): | CC=cc-5.0 CXX=CC ASFLAGS="-xarch=v9" CFLAGS="-Xa -xstrconst -mt -D_FORTEC_ -xarch=v9" CXXFLAGS="-noex -mt -D_FORTEC_ -xarch=v9" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --enable-assembler --with-named-z-libs=no --enable-thread-safe-client --disable-shared |
IBM AIX 4.3.2 ppc with gcc 3.2.3: | CFLAGS="-O2 -mcpu=powerpc -Wa,-many " CXX=gcc CXXFLAGS="-O2 -mcpu=powerpc -Wa,-many -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --with-named-z-libs=no --disable-shared |
IBM AIX 4.3.3 ppc with xlC_r (IBM Visual Age C/C++ 6.0): | CC=xlc_r CFLAGS="-ma -O2 -qstrict -qoptimize=2 -qmaxmem=8192" CXX=xlC_r CXXFLAGS ="-ma -O2 -qstrict -qoptimize=2 -qmaxmem=8192" ./configure --prefix=/usr/local/mysql --localstatedir=/usr/local/mysql/data --libexecdir=/usr/local/mysql/bin --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --with-named-z-libs=no --disable-shared --with-innodb |
IBM AIX 5.1.0 ppc with gcc 3.3: | CFLAGS="-O2 -mcpu=powerpc -Wa,-many" CXX=gcc CXXFLAGS="-O2 -mcpu=powerpc -Wa,-many -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --with-server-suffix="-pro" --enable-thread-safe-client --enable-local-infile --with-named-z-libs=no --disable-shared |
HP-UX 10.20 pa-risc1.1 with gcc 3.1: | CFLAGS="-DHPUX -I/opt/dce/include -O3 -fPIC" CXX=gcc CXXFLAGS="-DHPUX -I/opt/dce /include -felide-constructors -fno-exceptions -fno-rtti -O3 -fPIC" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --with-pthread --with-named-thread-libs=-ldce --with-lib-ccflags=-fPIC --disable-shared |
HP-UX 11.11 pa-risc2.0 64bit with aCC (HP ANSI C++ B3910B A.03.33): | CC=cc CXX=aCC CFLAGS=+DD64 CXXFLAGS=+DD64 ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared |
HP-UX 11.11 pa-risc2.0 32bit with aCC (HP ANSI C++ B3910B A.03.33): | CC=cc CXX=aCC CFLAGS="+DAportable" CXXFLAGS="+DAportable" ./configure --prefix=/usr/local/mysql --localstatedir=/usr/local/mysql/data --libexecdir=/usr/local/mysql/bin --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared --with-innodb |
Apple Mac OS X 10.2 powerpc with gcc 3.1: | CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared |
FreeBSD 4.7 i386 with gcc 2.95.4: | CFLAGS=-DHAVE_BROKEN_REALPATH ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --enable-assembler --with-named-z-libs=not-used --disable-shared |
QNX Neutrino 6.2.1 i386 with gcc 2.95.3qnx-nto 20010315: | CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared |
The following binaries are built on third-party systems kindly provided to MySQL AB by other users. Please note that these are only provided as a courtesy. Since MySQL AB does not have full control over these systems, we can provide only limited support for the binaries built on these systems.
SCO Unix 3.2v5.0.6 i386 with gcc 2.95.3: | CFLAGS="-O3 -mpentium" LDFLAGS=-static CXX=gcc CXXFLAGS="-O3 -mpentium -felide-constructors" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --with-named-z-libs=no --enable-thread-safe-client --disable-shared |
SCO OpenUnix 8.0.0 i386 with CC 3.2: | CC=cc CFLAGS="-O" CXX=CC ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --with-named-z-libs=no --enable-thread-safe-client --disable-shared |
Compaq Tru64 OSF/1 V5.1 732 alpha with cc/cxx (Compaq C V6.3-029i / DIGITAL C++ V6.1-027): | CC="cc -pthread" CFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all" CXX="cxx -pthread" CXXFLAGS="-O4 -ansi_alias -fast -inline speed -speculate all -noexceptions -nortti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --with-prefix=/usr/local/mysql --with-named-thread-libs="-lpthread -lmach -lexc -lc" --disable-shared --with-mysqld-ldflags=-all-static |
SGI Irix 6.5 IP32 with gcc 3.0.1: | CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared |
FreeBSD/sparc64 5.0 with gcc 3.2.1: | CFLAGS=-DHAVE_BROKEN_REALPATH ./configure --prefix=/usr/local/mysql --localstatedir=/usr/local/mysql/data --libexecdir=/usr/local/mysql/bin --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --disable-shared --with-innodb |
The following compile options have been used for binary packages MySQL AB used to provide in the past. These binaries are no longer being updated, but the compile options are listed here for reference purposes.
Linux 2.2.xx SPARC with egcs 1.1.2: | CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex --enable-thread-safe-client --enable-local-infile --enable-assembler --disable-shared |
Linux 2.2.x with x686 with gcc 2.95.2: | CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3 -mpentiumpro -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static --disable-shared --with-extra-charsets=complex |
SunOS 4.1.4 2 sun4c with gcc 2.7.2.1: | CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors" ./configure --prefix=/usr/local/mysql --disable-shared --with-extra-charsets=complex --enable-assembler |
SunOS 5.5.1 (and above) sun4u with egcs 1.0.3a or 2.90.27 or gcc 2.95.2 and newer: | CC=gcc CFLAGS="-O3" CXX=gcc CXXFLAGS="-O3 -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-low-memory --with-extra-charsets=complex --enable-assembler |
SunOS 5.6 i86pc with gcc 2.8.1: | CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-low-memory --with-extra-charsets=complex |
BSDI BSD/OS 3.1 i386 with gcc 2.7.2.1: | CC=gcc CXX=gcc CXXFLAGS=-O ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex |
BSDI BSD/OS 2.1 i386 with gcc 2.7.2: | CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex |
AIX 2 4 with gcc 2.7.2.2: | CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex |
Anyone who has more optimal options for any of the preceding configurations listed can always mail them to the MySQL internals mailing list. See Mailing-list.
RPM distributions prior to MySQL Version 3.22 are user-contributed. Beginning with Version 3.22, the RPM distributions are generated by us at MySQL AB.
If you want to compile a debug version of MySQL, you should add --with-debug or --with-debug=full to the preceding configure lines and remove any -fomit-frame-pointer options.
For the Windows distribution, please see Windows installation.
Check the MySQL homepage (http://www.mysql.com/) for information about the current version and for downloading instructions.
Our main mirror is located at http://mirrors.sunsite.dk/mysql/.
For a complete up-to-date list of MySQL web/download mirrors, see http://www.mysql.com/downloads/mirrors.html. There you will also find information about becoming a MySQL mirror site and how to report a bad or out-of-date mirror.
After you have downloaded the MySQL package that suits your needs and before you attempt to install it, you should make sure it is intact and has not been tampered with.
MySQL AB offers three means of integrity checking:
MD5 checksums
Cryptographic signatures using GnuPG, the GNU Privacy Guard
For RPM packages, the built-in RPM integrity verification mechanism
The following sections describe how to use these methods.
This section describes the default layout of the directories created by installing binary and source distributions.
On Windows, the default installation directory is C:\mysql, which has the following subdirectories:
Directory | Contents of directory |
bin | Client programs and the mysqld server |
data | Log files, databases |
Docs | Documentation |
examples | Example programs and scripts |
include | Include (header) files |
lib | Libraries |
scripts | Utility scripts |
share | Error message files |
Installations created from Linux RPM distributions result in files under the following system directories:
Directory | Contents of directory |
/usr/bin | Client programs |
/usr/sbin | mysqld server |
/var/lib/mysql | Log files, databases |
/usr/share/doc/packages | Documentation |
include | Include (header) files |
lib | Libraries |
scripts | mysql_install_db |
/usr/share/mysql | Error message and character set files |
sql-bench | Benchmarks |
On Unix, a tar file binary distribution is installed by unpacking it at the installation location you choose (typically /usr/local/mysql) and creates the following directories in that location:
Directory | Contents of directory |
bin | Client programs and the mysqld server |
data | Log files, databases |
docs | Documentation, ChangeLog |
include | Include (header) files |
lib | Libraries |
scripts | mysql_install_db |
share/mysql | Error message files |
sql-bench | Benchmarks |
A source distribution is installed after you configure and compile it. By default, the installation step installs files under /usr/local, in the following subdirectories:
Directory | Contents of directory |
bin | Client programs and scripts |
include/mysql | Include (header) files |
info | Documentation in Info format |
lib/mysql | Libraries |
libexec | The mysqld server |
share/mysql | Error message files |
sql-bench | Benchmarks and crash-me test |
var | Databases and log files |
Within an installation directory, the layout of a source installation differs from that of a binary installation in the following ways:
The mysqld server is installed in the libexec directory rather than in the bin directory.
The data directory is var rather than data.
mysql_install_db is installed in the bin directory rather than in the scripts directory.
The header file and library directories are include/mysql and lib/mysql rather than include and lib.
You can create your own binary installation from a compiled source distribution by executing the scripts/make_binary_distribution script from the top directory of the source distribution.
Table of Contents
This section covers the installation of MySQL on platforms where we offer packages using the native packaging format of the respective platform. (This is also known as performing a ``binary install.'') However, binary distributions of MySQL are available for many other platforms as well. See Installing binary for generic installation instructions for these packages that apply to all platforms.
See General Installation Issues for more information on what other binary distributions are available and how to obtain them.
The installation process for MySQL on Windows has the following steps:
Install the distribution.
Set up an option file if necessary.
Select the server you want to use.
Start the server.
Assign passwords to the initial MySQL accounts.
MySQL for Windows is available in two distribution formats:
The binary distribution contains a setup program that installs everything you need so that you can start the server immediately.
The source distribution contains all the code and support files for building the executables using the VC++ 6.0 compiler.
Generally speaking, you should use the binary distribution. It's simpler, and you need no additional tools to get MySQL up and running.
This section describes how to install MySQL on Windows using a binary distribution. To install using a source distribution, see Windows source build.
To run MySQL on Windows, you need the following:
A 32-bit Windows operating system such as 9x, Me, NT, 2000, or XP. The NT family (Windows NT, 2000, and XP) permits you to run the MySQL server as a service. See NT start.
TCP/IP protocol support.
A copy of the MySQL binary distribution for Windows, which can be downloaded from http://www.mysql.com/downloads/.
Note: The distribution files are supplied with a zipped format and we recommend the use of an adequate FTP client with resume feature to avoid corruption of files during the download process.
A ZIP program to unpack the distribution file.
Enough space on the hard drive to unpack, install, and create the databases in accordance with your requirements.
If you plan to connect to the MySQL server via ODBC, you also need the MyODBC driver. See ODBC.
If you need tables with a size larger than 4 GB, install MySQL on an NTFS or newer filesystem. Don't forget to use MAX_ROWS and AVG_ROW_LENGTH when you create tables. See CREATE TABLE.
To install MySQL on Windows using a binary distribution, follow this procedure:
If you are working on a Windows NT, 2000, or XP machine, make sure you have logged in as a user with administrator privileges.
If you are doing an upgrade of an earlier MySQL installation, it is necessary to stop the current server. On Windows NT, 2000, or XP machines, if you are running the server as a Windows service, stop it as follows from the command prompt:
C:\> NET STOP MySQL
If you plan to use a different server after the upgrade (for example, if you want to run mysqld-max rather than mysqld), remove the existing service:
C:\mysql\bin> mysqld --remove
You can reinstall the service to use the proper server after upgrading.
If you are not running the MySQL server as a service, stop it like this:
C:\mysql\bin> mysqladmin -u root shutdown
Exit the WinMySQLAdmin program if it is running.
Unzip the distribution file to a temporary directory.
Run the setup.exe program to begin the installation process. If you want to install MySQL into a location other than the default directory (C:\mysql), use the Browse button to specify your preferred directory. If you do not install MySQL into the default location, you will need to specify the location whenever you start the server. The easiest way to do this is to use an option file, as described in Windows prepare environment.
Finish the install process.
Important note: Early alpha Windows distributions for MySQL 4.1 do not contain any installer program. A 4.1 distribution is a ZIP file that you just unzip in the location where you want to install MySQL. For example, to install mysql-4.1.1-alpha-win.zip as C:\mysql, unzip the distribution file on the C: drive, then rename the resulting mysql-4.1.1-alpha directory to mysql.
If you are upgrading to MySQL 4.1 from an earlier version, you will want to preserve your existing data directory that contains the grant tables in the mysql database and your own databases. Before installing 4.1, stop the server if it is running, and save your data directory to another location. Then either rename the existing C:\mysql directory or remove it. Install 4.1 as described in the preceding paragraph, and then replace its data directory with your old data directory. Start the new server and update the grant tables. This will avoid loss of your current databases. See Upgrading-grant-tables.
If you need to specify startup options when you run the server, you can indicate them on the command line or place them in an option file. For options that will be used every time the server starts, you will find it most convenient to use an option file to specify your MySQL configuration. This is true particularly under the following circumstances:
The installation or data directory locations are different from the default locations (C:\mysql and C:\mysql\data).
You need to tune the server settings. For example, to use the InnoDB transactional tables in MySQL version 3.23, you must manually create two new directories to hold the InnoDB data and log files---such as, C:\ibdata and C:\iblogs. You will also need to add some extra lines to the option file, as described in InnoDB start. (As of MySQL 4.0, InnoDB creates its datafiles and log files in the data directory by default. This means you need not configure InnoDB explicitly. You may still do so if you wish, and an option file will be useful in this case, too.)
On Windows, the MySQL installer places the data directory directly under the directory where you install MySQL. If you would like to use a data directory in a different location, you should copy the entire contents of the data directory to the new location. For example, by default, the installer places MySQL in C:\mysql and the data directory in C:\mysql\data. If you want to use a data directory of E:\mydata, you must do two things:
Move the data directory from C:\mysql\data to E:\mydata.
Use a --datadir option to specify the new data directory location each time you start the server.
When the MySQL server starts on Windows, it looks for options in two files: The my.ini file in the Windows directory, and the C:\my.cnf file. The Windows directory typically is named something like C:\WINDOWS or C:\WinNT. You can determine its exact location from the value of the WINDIR environment variable using the following command:
C:\> echo %WINDIR%
MySQL looks for options first in the my.ini file, then in the my.cnf file. However, to avoid confusion, it's best if you use only one file. If your PC uses a boot loader where the C: drive isn't the boot drive, your only option is to use the my.ini file. Whichever one you use, it must be a plain text file.
An option file can be created and modified with any text editor, such as the Notepad program. For example, if MySQL is installed at D:\mysql and the data directory is located as D:\mydata\data, you can create the option file and set up a [mysqld] section to specify values for the basedir and datadir parameters:
[mysqld] # set basedir to your installation path basedir=D:/mysql # set datadir to the location of your data directory datadir=D:/mydata/data
Note that Windows pathnames are specified in option files using forward slashes rather than backslashes. If you do use backslashes, you must double them.
Another way to manage an option file is to use the the WinMySQLAdmin tool. You can find WinMySQLAdmin in the bin directory of your MySQL installation, as well as a help file containing instructions for using it. WinMySQLAdmin has the capability of editing your option file, but note these points:
WinMySQLAdmin uses only the my.ini file.
If WinMySQLAdmin finds a C:\my.cnf file, it will in fact rename it to C:\my_cnf.bak to disable it.
Now you are ready to test starting the server.
Starting with MySQL 3.23.38, the Windows distribution includes both the normal and the MySQL-Max server binaries. Here is a list of the different MySQL servers from which you can choose:
Binary | Description |
mysqld | Compiled with full debugging and automatic memory allocation checking, symbolic links, and InnoDB and BDB tables. |
mysqld-opt | Optimized binary. From version 4.0 on, InnoDB is enabled. Before 4.0, this server includes no transactional table support. |
mysqld-nt | Optimized binary for NT/2000/XP with support for named pipes. |
mysqld-max | Optimized binary with support for symbolic links, and InnoDB and BDB tables. |
mysqld-max-nt | Like mysqld-max, but compiled with support for named pipes. |
All of the preceding binaries are optimized for modern Intel processors but should work on any Intel i386-class or higher processor.
MySQL supports TCP/IP on all Windows platforms. The mysqld-nt and mysql-max-nt servers support named pipes on NT, 2000, and XP. However, the default is to use TCP/IP regardless of the platform. (Named pipes are slower than TCP/IP in many Windows configurations.)
Named pipe use is subject to these conditions:
Starting from MySQL 3.23.50, named pipes are enabled only if you start the server with the --enable-named-pipe option. It is now necessary to use this option explicitly because some users have experienced problems shutting down the MySQL server when named pipes are used.
Named pipe connections are allowed only by the mysqld-nt or mysqld-max-nt servers, and only if the server is run on a version of Windows that supports named pipes (NT, 2000, XP).
These servers can be run on Windows 98 or Me, but only if TCP/IP is installed; named pipe connections cannot be used.
On Windows 95, these servers cannot be used.
On Windows 95, 98, or Me, MySQL clients always connect to the server using TCP/IP. (This will allow any machine on your network to connect to your MySQL server.) Because of this, you must make sure that TCP/IP support is installed on your machine before starting MySQL. You can find TCP/IP on your Windows CD-ROM.
Note that if you are using an old Windows 95 release (for example, OSR2), it's likely that you have an old Winsock package; MySQL requires Winsock 2! You can get the newest Winsock from http://www.microsoft.com/. Windows 98 has the new Winsock 2 library, so it is unnecessary to update the library.
On NT-based systems such as Windows NT, 2000, or XP, clients have two options. They can use TCP/IP, or they can use a named pipe if the server supports named pipe connections.
For information about which server binary to run, see Windows prepare environment.
This section gives a general overview of starting the MySQL server. The following sections provide more specific information for particular versions of Windows.
The examples in these sections assume that MySQL is installed under the default location of C:\mysql. Adjust the pathnames shown in the examples if you have MySQL installed in a different location.
Testing is best done from a command prompt in a console window (a ``DOS window''). This way you can have the server display status messages in the window where they are easy to see. If something is wrong with your configuration, these messages will make it easier for you to identify and fix any problems.
Make sure you are in the directory where the server is located, then enter this command:
C:\mysql\bin> mysqld --console
For servers that include InnoDB support, you should see the following messages as the server starts:
InnoDB: The first specified datafile c:\ibdata\ibdata1 did not exist: InnoDB: a new database to be created! InnoDB: Setting file c:\ibdata\ibdata1 size to 209715200 InnoDB: Database physically writes the file full: wait... InnoDB: Log file c:\iblogs\ib_logfile0 did not exist: new to be created InnoDB: Setting log file c:\iblogs\ib_logfile0 size to 31457280 InnoDB: Log file c:\iblogs\ib_logfile1 did not exist: new to be created InnoDB: Setting log file c:\iblogs\ib_logfile1 size to 31457280 InnoDB: Log file c:\iblogs\ib_logfile2 did not exist: new to be created InnoDB: Setting log file c:\iblogs\ib_logfile2 size to 31457280 InnoDB: Doublewrite buffer not found: creating new InnoDB: Doublewrite buffer created InnoDB: creating foreign key constraint system tables InnoDB: foreign key constraint system tables created 011024 10:58:25 InnoDB: Started
When the server finishes its startup sequence, you should see something like this, which indicates that the server is ready to service client connections:
mysqld: ready for connections Version: '4.0.14-log' socket: '' port: 3306
The server will continue to write to the console any further diagnostic output it produces. You can open a new console window in which to run client programs.
If you omit the --console option, the server writes diagnostic output to the error log in the data directory. The error log is the file with the .err extension.
The accounts that are listed in the MySQL grant tables initially have no passwords. After starting the server, you should set up passwords for them using the instructions in Post-installation.
The MySQL server can be started manually from the command line. This can be done on any version of Windows.
To start the mysqld server from the command line, you should start a console window (a ``DOS'' window) and enter this command:
shell> C:\mysql\bin\mysqld
On non-NT versions of Windows, this will start mysqld in the background. That is, after the server starts, you should see another command prompt. If you start the server this way on Windows NT, 2000, or XP, the server will run in the foreground and no command prompt will appear until the server exits. Because of this, you should open another console window to run client programs while the server is running.
You can stop the MySQL server by executing this command:
shell> C:\mysql\bin\mysqladmin -u root shutdown
This invokes the MySQL administrative utility mysqladmin to connect to the server and tell it to shut down. The command connects as root, which is the default administrative account in the MySQL grant system. Please note that users in the MySQL grant system are wholly independent from any login users under Windows.
If mysqld doesn't start, check the error log to see whether the server wrote any messages there to indicate the cause of the problem. The error log is located in the C:\mysql\data directory. It is the file with a suffix of .err. You can also try to start the server as mysqld --console; in this case, you may get some useful information on the screen that may help solve the problem.
The last option is to start mysqld with --standalone --debug. In this case mysqld will write a log file C:\mysqld.trace that should contain the reason why mysqld doesn't start. See Making trace files.
Use mysqld --help to display all the options that mysqld understands!
On the NT family (Windows NT, 2000, or XP), the recommended way to run MySQL is to install it as a Windows service. Then Windows starts and stops the MySQL server automatically when Windows starts and stops. A server installed as a service can also be controlled from the command line using NET commands, or with the graphical Services utility.
The Services utility (the Windows Service Control Manager) can be found in the Windows Control Panel (under Administrative Tools on Windows 2000). It is advisable to close the Services utility while performing server installation or removal operations from this command line. This prevents some odd errors.
To get MySQL to work with TCP/IP on Windows NT 4, you must install service pack 3 (or newer)!
Before installing MySQL as a Windows service, you should first stop the current server if it is running by using the following command:
shell> C:\mysql\bin\mysqladmin -u root shutdown
This invokes the MySQL administrative utility mysqladmin to connect to the server and tell it to shut down. The command connects as root, which is the default administrative account in the MySQL grant system. Please note that users in the MySQL grant system are wholly independent from any login users under Windows.
Now install the server as a service:
shell> mysqld --install
If you have problems installing mysqld as a service using just the server name, try installing it using its full pathname:
shell> C:\mysql\bin\mysqld --install
As of MySQL 4.0.2, you can specify a specific service name after the --install option. As of MySQL 4.0.3, you can in addition specify a --defaults-file option after the service name to indicate where the server should obtain options when it starts. The rules that determine the service name and option files the server uses are as follows:
If you specify no service name, the server uses the default service name of MySQL and the server reads options from the [mysqld] group in the standard option files.
If you specify a service name after the --install option, the server ignores the [mysqld] option group and instead reads options from the group that has the same name as the service. The server reads options from the standard option files.
If you specify a --defaults-file option after the service name, the server ignores the standard option files and reads options only from the [mysqld] group of the named file.
Note: Prior to MySQL 4.0.17, a server installed as a Windows service has problems starting if its pathname or the service name contains spaces. For this reason, avoid installing MySQL in a directory such as C:\Program Files or using a service name containing spaces.
In the usual case that you install the server with --install but no service name, the server is installed with a service name of MySQL.
As a more complex example, consider the following command (which should be entered on a single line):
shell> C:\mysql\bin\mysqld --install mysql --defaults-file=C:\my-opts.cnf
Here, a service name is given after the --install option. If no --defaults-file option had been given, this command would have the effect of causing the server to read the [mysql] group from the standard option files. (This would be a bad idea, because that option group is for use by the mysql client program.) However, because the --defaults-file option is present, the server reads options only from the named file, and only from the [mysqld] option group.
You can also specify options as ``Start parameters'' in the Windows Services utility before you start the MySQL service.
Once a MySQL server is installed as a service, Windows will start the service automatically whenever Windows starts. The service also can be started immediately from the Services utility, or by using the command NET START MySQL. The NET command is not case sensitive.
Please note that when run as a service, mysqld has no access to a console window, so no messages can be seen there. If mysqld doesn't start, check the error log to see whether the server wrote any messages there to indicate the cause of the problem. The error log is located in the C:\mysql\data directory. It is the file with a suffix of .err.
When mysqld is running as a service, it can be stopped by using the Services utility, the command NET STOP MySQL, or the command mysqladmin shutdown. If the service is running when Windows shuts down, Windows will stop the server automatically.
From MySQL version 3.23.44, you have the choice of installing the server as a Manual service if you don't wish the service to be started automatically during the boot process. To do this, use the --install-manual option rather than the --install option:
shell> C:\mysql\bin\mysqld --install-manual
To remove a server that is installed as a service, first stop it if it is running. Then use the --remove option to remove it:
shell> mysqld --remove
For MySQL versions older than 3.23.49, one problem with automatic MySQL service shutdown is that Windows waited only for a few seconds for the shutdown to complete, then killed the database server process if the time limit was exceeded. This had the potential to cause problems. (For example, the InnoDB storage engine had to perform crash recovery at the next startup.) Starting from MySQL version 3.23.49, Windows waits longer for the MySQL server shutdown to complete. If you notice this still is not enough for your installation, it is safest not to run the MySQL server as a service. Instead, start it from the command-line prompt, and stop it with mysqladmin shutdown.
This change to tell Windows to wait longer when stopping the MySQL server works for Windows 2000 and XP. It does not work for Windows NT, where Windows waits only 20 seconds for a service to shut down, and after that kills the service process. You can increase this default by opening the Registry Editor \winnt\system32\regedt32.exe and editing the value of WaitToKillServiceTimeout at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control in the Registry tree. Specify the new larger value in milliseconds. For example, the value 120000 tells Windows NT to wait up to 120 seconds.
If you don't want to start mysqld as a service, you can start it from the command line the same way as for versions of Windows that are not based on NT. For instructions, see Win95 start.
You can test whether the MySQL server is working by executing any of the following commands:
C:\> C:\mysql\bin\mysqlshow C:\> C:\mysql\bin\mysqlshow -u root mysql C:\> C:\mysql\bin\mysqladmin version status proc C:\> C:\mysql\bin\mysql test
If mysqld is slow to respond to TCP/IP connections from client programs on Windows 9x/Me, there is probably a problem with your DNS. In this case, start mysqld with the --skip-name-resolve option and use only localhost and IP numbers in the Host column of the MySQL grant tables.
You can force a MySQL client to use a named pipe connection rather than TCP/IP by specifying the --pipe option or by specifying . (period) as the host name. Use the --socket option to specify the name of the pipe. In MySQL 4.1, you should use the --protocol=PIPE option.
There are two versions of the MySQL command-line tool:
Binary | Description |
mysql | Compiled on native Windows, offering limited text editing capabilities. |
mysqlc | Compiled with the Cygnus GNU compiler and libraries, which offers readline editing. |
If you want to use mysqlc, you must have a copy of the cygwinb19.dll library installed somewhere that mysqlc can find it. Current distributions of MySQL include this library in the same directory as mysqlc (the bin directory under the base directory of your MySQL installation). If your distribution does not have the cygwinb19.dll library in the bin directory, look for it in the lib directory and copy it to your Windows system directory (\Windows\system or similar place).
MySQL for Windows has by now proven itself to be very stable. The Windows version of MySQL has the same features as the corresponding Unix version, with the following exceptions:
Windows 95 and threads | Windows 95 leaks about 200 bytes of main memory for each thread creation. Each connection in MySQL creates a new thread, so you shouldn't run mysqld for an extended time on Windows 95 if your server handles many connections! Other versions of Windows don't suffer from this bug. |
Concurrent reads | MySQL depends on the pread() and pwrite() calls to be able to mix INSERT and SELECT. Currently we use mutexes to emulate pread()/pwrite(). We will, in the long run, replace the file level interface with a virtual interface so that we can use the readfile()/writefile() interface on NT/2000/XP to get more speed. The current implementation limits the number of open files MySQL can use to 1024, which means that you will not be able to run as many concurrent threads on NT/2000/XP as on Unix. |
Blocking read |
MySQL uses a blocking read for each connection, which
has the following implications:
|
DROP DATABASE | You can't drop a database that is in use by some thread. |
Killing MySQL from the task manager | You can't kill MySQL from the task manager or with the shutdown utility in Windows 95. You must take it down with mysqladmin shutdown. |
Case-insensitive names | Filenames are not case sensitive on Windows, so MySQL database and table names are also not case sensitive on Windows. The only restriction is that database and table names must be specified using the same case throughout a given statement. See Name case sensitivity. |
The \ pathname separator character |
Pathname components in Windows 95 are separated by the \ character,
which is also the escape character in MySQL. If you are using LOAD DATA INFILE or SELECT ... INTO OUTFILE,
use Unix style filenames with / characters:
mysql> LOAD DATA INFILE "C:/tmp/skr.txt" INTO TABLE skr; mysql> SELECT * INTO OUTFILE 'C:/tmp/skr.txt' FROM skr;Alternatively, you must double the \ character: mysql> LOAD DATA INFILE "C:\\tmp\\skr.txt" INTO TABLE skr; mysql> SELECT * INTO OUTFILE 'C:\\tmp\\skr.txt' FROM skr; |
Problems with pipes. |
Pipes doesn't work reliably in the Windows command-line prompt. If the
pipe includes the character ^Z / CHAR(24), Windows will think it
has encountered end-of-file and abort the program.
This is mainly a problem when you try to apply a binary log as follows:
mysqlbinlog binary-log-name | mysql --user=rootIf you get a problem applying the log and suspect it's because of an ^Z / CHAR(24) character you can use the following workaround: mysqlbinlog binary-log-file --result-file=/tmp/bin.sql mysql --user=root --execute "source /tmp/bin.sql"The latter command also can be used to reliably read in any SQL file that may contain binary data. |
Can't open named pipe error |
If you use a MySQL Version 3.22 server on NT with the newest MySQL client
programs, you will get the following error:
error 2017: can't open named pipe to host: . pipe...This is because the release version of MySQL uses named pipes on NT by default. You can avoid this error by using the --host=localhost option to the new MySQL clients or create an option file C:\my.cnf that contains the following information: [client] host = localhostStarting from 3.23.50, named pipes are enabled only if mysqld-nt or mysqld-max-nt is started with --enable-named-pipe. |
Access denied for user error |
If you attempt to run a MySQL client program to connect to a server
running on the same machine, but get the error Access denied for user: 'some-user@unknown' to database 'mysql', this means
that MySQL can't resolve your hostname properly.
To fix this, you should create a file \windows\hosts with the
following information:
127.0.0.1 localhost |
ALTER TABLE | While you are executing an ALTER TABLE statement, the table is locked from being used by other threads. This has to do with the fact that on Windows, you can't delete a file that is in use by another threads. In the future, we may find some way to work around this problem. |
DROP TABLE | DROP TABLE on a table that is in use by a MERGE table will not work on Windows because the MERGE handler does the table mapping hidden from the upper layer of MySQL. Because Windows doesn't allow you to drop files that are open, you first must flush all MERGE tables (with FLUSH TABLES) or drop the MERGE table before dropping the table. We will fix this at the same time we introduce views. |
DATA DIRECTORY and INDEX DIRECTORY | The DATA DIRECTORY and INDEX DIRECTORY options for CREATE TABLE are ignored on Windows, because Windows doesn't support symbolic links. These options also are ignored on systems that have a non-functional realpath() call. |
Here are some open issues for anyone who might want to help us improve MySQL on Windows:
Add some nice start and shutdown icons to the MySQL installation.
It would be really nice to be able to kill mysqld from the task manager. For the moment, you must use mysqladmin shutdown.
Port readline to Windows for use in the mysql command-line tool.
GUI versions of the standard MySQL clients (mysql, mysqlshow, mysqladmin, and mysqldump) would be nice.
It would be nice if the socket read and write functions in net.c were interruptible. This would make it possible to kill open threads with mysqladmin kill on Windows.
Add macros to use the faster thread-safe increment/decrement methods provided by Windows.
The recommended way to install MySQL on Linux is by using the RPM packages. The MySQL RPMs are currently built on a SuSE Linux 7.3 system but should work on most versions of Linux that support rpm and use glibc.
If you have problems with an RPM file (for example, if you receive the error ``Sorry, the host 'xxxx' could not be looked up''), see Binary notes-Linux.
In most cases, you only need to install the MySQL-server and MySQL-client packages to get a functional MySQL installation. The other packages are not required for a standard installation. If you want to run a MySQL-Max server that has additional capabilities, you should install the MySQL-Max RPM. However, you should do so only after installing the MySQL-server RPM. See mysqld-max.
If you get a dependency failure when trying to install the MySQL 4.0 packages (for example, ``error: removing these packages would break dependencies: libmysqlclient.so.10 is needed by ...''), you should also install the package MySQL-shared-compat, which includes both the shared libraries for backward compatibility (libmysqlclient.so.12 for MySQL 4.0 and libmysqlclient.so.10 for MySQL 3.23).
Many Linux distributions still ship with MySQL 3.23 and they usually link applications dynamically to save disk space. If these shared libraries are in a separate package (for example, MySQL-shared), it is sufficient to simply leave this package installed and just upgrade the MySQL server and client packages (which are statically linked and do not depend on the shared libraries). For distributions that include the shared libraries in the same package as the MySQL server (for example, Red Hat Linux), you could either install our 3.23 MySQL-shared RPM, or use the MySQL-shared-compat package instead.
The following RPM packages are available:
MySQL-server-VERSION.i386.rpm
The MySQL server. You will need this unless you only want to connect to a MySQL server running on another machine. Please note: Server RPM files were called MySQL-VERSION.i386.rpm before MySQL 4.0.10. That is, they did not have -server in the name.
MySQL-Max-VERSION.i386.rpm
The MySQL-Max server. This server has additional capabilities that the one provided in the MySQL-server RPM does not. You must install the MySQL-server RPM first, because the MySQL-Max RPM depends on it.
MySQL-client-VERSION.i386.rpm
The standard MySQL client programs. You probably always want to install this package.
MySQL-bench-VERSION.i386.rpm
Tests and benchmarks. Requires Perl and the DBD::mysql module.
MySQL-devel-VERSION.i386.rpm
The libraries and include files that are needed if you want to compile other MySQL clients, such as the Perl modules.
MySQL-shared-VERSION.i386.rpm
This package contains the shared libraries (libmysqlclient.so*) that certain languages and applications need to dynamically load and use MySQL.
MySQL-shared-compat-VERSION.i386.rpm
This package includes the shared libraries for both MySQL 3.23 and MySQL 4.0. Install this package instead of MySQL-shared, if you have applications installed that are dynamically linked against MySQL 3.23 but you want to upgrade to MySQL 4.0 without breaking the library dependencies. This package is available since MySQL 4.0.13.
MySQL-embedded-VERSION.i386.rpm
The embedded MySQL server library (from MySQL 4.0).
MySQL-VERSION.src.rpm
This contains the source code for all of the previous packages. It can also be used to rebuild the RPMs on other architectures (for example, Alpha or SPARC).
To see all files in an RPM package (for example, a MySQL-server RPM), run:
shell> rpm -qpl MySQL-server-VERSION.i386.rpm
To perform a standard minimal installation, run:
shell> rpm -i MySQL-server-VERSION.i386.rpm shell> rpm -i MySQL-client-VERSION.i386.rpm
To install just the client package, run:
shell> rpm -i MySQL-client-VERSION.i386.rpm
RPM provides a feature to verify the integrity and authenticity of packages before installing them. If you would like to learn more about this feature please see Verifying Package Integrity.
The server RPM places data under the /var/lib/mysql directory. The RPM also creates the appropriate entries in /etc/init.d/ to start the server automatically at boot time. (This means that if you have performed a previous installation and have made changes to its startup script, you may want to make a copy of the script so you don't lose it when you install a newer RPM.) See Automatic start for more information on how MySQL can be started automatically on system startup.
If you want to install the MySQL RPM on older Linux distributions that do not support initialization scripts in /etc/init.d (directly or via a symlink), you should create a symbolic link that points to the location where your initialization scripts actually are installed. For example, if that location is /etc/rc.d/init.d, use these commands before installing the RPM to create /etc/init.d as a symbolic link that points there:
shell> cd /etc; ln -s rc.d/init.d .
However, all current major Linux distributions should already support the new directory layout that uses /etc/init.d, because it is required for LSB (Linux Standard Base) compliance.
If the RPM files that you install include MySQL-server, the mysqld server should be up and running after installation. You should now be able to start using MySQL. See Post-installation.
If something goes wrong, you can find more information in the binary installation chapter. See Installing binary.
Beginning with MySQL 4.0.11, you can install MySQL on Mac OS X 10.2 (``Jaguar'') using a Mac OS X binary package in PKG format instead of the binary tarball distribution. Please note that older versions of Mac OS X (for example, 10.1.x) are not supported by this package.
The package is located inside a disk image (.dmg) file, that you first need to mount by double-clicking its icon in the Finder. It should then mount the image and display its contents.
NOTE: Before proceeding with the installation, be sure to shut down all running MySQL server instances by either using the MySQL Manager Application (on Mac OS X Server) or via mysqladmin shutdown on the command line.
To actually install the MySQL PKG file, double click on the package icon. This launches the Mac OS X Package Installer, which will guide you through the installation of MySQL.
Due to a bug in the Mac OS X package installer, you may sometimes see the error message You cannot install this software on this disk. (null) in the destination disk selection dialogue. If this error occurs, simply click the Go Back button once to return to the previous screen. Then click Continue to advance to the destination disk selection again, and you should be able to choose the destination disk correctly. We have reported this bug to Apple and they are investigating this problem.
The Mac OS X PKG of MySQL will install itself into /usr/local/mysql-<version> and will also install a symbolic link /usr/local/mysql, pointing to the new location. If a directory named /usr/local/mysql already exists, it will be renamed to /usr/local/mysql.bak first. Additionally, it will install the grant tables in the mysql database by executing mysql_install_db after the installation.
The installation layout is similar to the one of the binary distribution; all MySQL binaries are located in the directory /usr/local/mysql/bin. The MySQL socket file is created as /tmp/mysql.sock by default. See Installation layouts.
MySQL installation requires a Mac OS X user account named mysql (a user account with this name should exist by default on Mac OS X 10.2 and up).
If you are running Mac OS X Server, you already have a version of MySQL installed. The versions of MySQL that ship with Mac OS X Server versions are shown in the following table:
Mac OS X Server Version | MySQL Version |
10.2-10.2.2 | 3.23.51 |
10.2.3-10.2.6 | 3.23.53 |
10.3 | 4.0.14 |
10.3.2 | 4.0.16 |
This manual section covers the installation of the official MySQL Mac OS X PKG only. Make sure to read Apple's help about installing MySQL (Run the ``Help View'' application, select ``Mac OS X Server'' help, and do a search for ``MySQL'' and read the item entitled ``Installing MySQL'').
Especially note that for pre-installed versions of MySQL on Mac OS X Server, you should start mysqld with safe_mysqld instead of mysqld_safe if the MySQL is older than version 4.0.
If you previously used Marc Liyanage's MySQL packages for Mac OS X from http://www.entropy.ch, you can simply follow the update instructions for packages using the binary installation layout as given on his pages.
If you are upgrading from Marc's 3.23.xx versions or from the Mac OS X Server version of MySQL to the official MySQL PKG, you also need to convert the existing MySQL privilege tables to the current format, because some new security privileges have been added. See Upgrading-grant-tables.
If you would like to automatically start up MySQL during system bootup, you also need to install the MySQL Startup Item. Starting with MySQL 4.0.15, it is part of the Mac OS X installation disk images as a separate installation package. Simply double-click the MySQLStartupItem.pkg icon and follow the instructions to install it.
Note that the Startup Item need be installed only once! There is no need to install it each time you upgrade the MySQL package later.
The Startup Item will be installed into /Library/StartupItems/MySQL. It adds a variable MYSQLCOM=-YES- to the system configuration file /etc/hostconfig. If you would like to disable the automatic startup of MySQL, simply change this variable to MYSQLCOM=-NO-.
On Mac OS X Server, the default MySQL installation uses the variable MYSQL in /etc/hostconfig. The MySQL AB Startup Item installer disables this variable by setting it to MYSQL=-NO-. This avoids boot time conflicts with the MYSQLCOM variable used by the MySQL AB Startup Item. However, it does not shut down an already running MySQL server.
After the installation, you can start up MySQL by running the following commands in a terminal window. Please note that you must have administrator privileges to perform this task.
If you have installed the Startup Item:
shell> sudo /Library/StartupItems/MySQL/MySQL start (Enter your password, if necessary) (Press Control-D or enter "exit" to exit the shell)
If you don't use the Startup Item, enter the following command sequence:
shell> cd /usr/local/mysql shell> sudo ./bin/mysqld_safe (Enter your password, if necessary) (Press Control-Z) shell> bg (Press Control-D or enter "exit" to exit the shell)
You should now be able to connect to the MySQL server, for example, by running /usr/local/mysql/bin/mysql.
If you are installing MySQL for the first time, please remember to set a password for the MySQL root user!
This is done with the following two commands:
/usr/local/mysql/bin/mysqladmin -u root password <password> /usr/local/mysql/bin/mysqladmin -u root -h `hostname` password <password>
Please make sure that the hostname command in the second line is enclosed by backtick characters (`), so the shell can replace it with the output of the command (which is the hostname of your system)!
You might want to also add aliases to your shell's resource file to access mysql and mysqladmin from the command line. The syntax for tcsh is:
alias mysql /usr/local/mysql/bin/mysql alias mysqladmin /usr/local/mysql/bin/mysqladmin
For bash, use:
alias mysql=/usr/local/mysql/bin/mysql alias mysqladmin=/usr/local/mysql/bin/mysqladmin
Even better, add /usr/local/mysql/bin to your PATH environment variable. For example, add the following line to your $HOME/.tcshrc file if your shell is tcsh:
setenv PATH ${PATH}:/usr/local/mysql/bin
If no .tcshrc file exists in your home directory, create it with a text editor.
If you are upgrading an existing installation, please note that installing a new MySQL PKG does not remove the directory of an older installation. Unfortunately, the Mac OS X Installer does not yet offer the functionality required to properly upgrade previously installed packages.
To use your existing databases with the new installation, you'll need to copy the contents of the old data directory to the new data directory. Make sure neither the old server nor the new one is running when you do this. After you have copied over the MySQL database files from the previous installation and have successfully started the new server, you should consider removing the old installation files to save disk space. Additionally, you should also remove older versions of the Package Receipt directories located in /Library/Receipts/mysql-<version>.pkg.
Porting MySQL to NetWare was an effort spearheaded by Novell. Novell customers will be pleased to note that NetWare 6.5 will ship with bundled MySQL binaries, complete with an automatic commercial use license for all servers running that version of NetWare.
As of version 4.0.11, the MySQL server is available for Novell NetWare in binary package form. MySQL for NetWare is compiled using a combination of Metrowerks CodeWarrior for NetWare and special cross-compilation versions of the GNU autotools.
In order to host MySQL, the NetWare server must meet these requirements:
NetWare version 6.5, or NetWare 6.0 with Support Pack 3 installed (You can obtain this at http://support.novell.com/filefinder/13659/index.html). The system must meet Novell's minimum requirements to run the respective version of NetWare.
MySQL data, as well as the binaries themselves, must be installed on an NSS volume; traditional volumes are not supported.
The binary package for NetWare can be obtained at http://www.mysql.com/downloads/.
To install MySQL for NetWare, use the following procedure:
If you are upgrading from a prior installation, stop the MySQL server. This is done from the server console, using the following command:
SERVER: mysqladmin -u root shutdown
Log on to the target server from a client machine with access to the location where you will install MySQL.
Extract the binary package zip file onto the server. Be sure to allow the paths in the zip file to be used. It is safe to simply extract the file to SYS:\.
If you are upgrading from a prior installation, you may need to copy the data directory (for example, SYS:MYSQL\DATA) now, as well as my.cnf if you have customized it. You can then delete the old copy of MySQL.
You may wish to rename the directory to something more consistent and easy to use. We recommend using SYS:MYSQL; examples in the manual will use this to refer to the installation directory in general.
At the server console, add a search path for the directory containing the MySQL NLMs. For example:
SERVER: SEARCH ADD SYS:MYSQL\BIN
Install the initial database, if needed, by executing mysql_install_db at the server console.
Start the MySQL server using mysqld_safe at the server console.
To finish the installation, you should also add the following commands to autoexec.ncf. For example, if your MySQL installation is in SYS:MYSQL and you want MySQL to start automatically, you could add these lines:
#Starts the MySQL 4.0.x database server SEARCH ADD SYS:MYSQL\BIN MYSQLD_SAFE
If you are running MySQL on NetWare 6.0, we strongly suggest that you use the --skip-external-locking option on the command line:
#Starts the MySQL 4.0.x database server SEARCH ADD SYS:MYSQL\BIN MYSQLD_SAFE --skip-external-locking
It will also be neccesary to use CHECK TABLE and REPAIR TABLE instead of myisamchk, because myisamchk makes use of external locking. External locking is known to have problems on NetWare 6.0; the problem has been eliminated in NetWare 6.5.
If there was an existing installation of MySQL on the server, be sure to check for existing MySQL startup commands in autoexec.ncf, and edit or delete them as necessary.
Binary distributions of MySQL for HP-UX are distributed as HP depot files or as tar files. To use the depot file you must be running at least HP-UX 10.x to have access to HP's software depot tools. To install the HP-UX tar.gz distribution, you must have a copy of GNU tar.
The HP version of MySQL was compiled on an HP 9000/8xx server under HP-UX 10.20, and uses MIT-pthreads. It is known to work well under this configuration. MySQL Version 3.22.26 and newer can also be built with HP's native thread package.
Other configurations that may work:
HP 9000/7xx running HP-UX 10.20+
HP 9000/8xx running HP-UX 10.30
The following configurations almost definitely won't work:
HP 9000/7xx or 8xx running HP-UX 10.x where x < 2
HP 9000/7xx or 8xx running HP-UX 9.x
To install the distribution, use one of the commands here, where /path/to/depot is the full pathname of the depot file:
To install everything, including the server, client and development tools:
shell> /usr/sbin/swinstall -s /path/to/depot mysql.full
To install only the server:
shell> /usr/sbin/swinstall -s /path/to/depot mysql.server
To install only the client package:
shell> /usr/sbin/swinstall -s /path/to/depot mysql.client
To install only the development tools:
shell> /usr/sbin/swinstall -s /path/to/depot mysql.developer
The depot places binaries and libraries in /opt/mysql and data in /var/opt/mysql. The depot also creates the appropriate entries in /etc/init.d and /etc/rc2.d to start the server automatically at boot time. Obviously, this entails being root to install.
This section covers the installation of MySQL binary distributions that are provided for various platforms in the form of tar files (files with a .tar.gz extension). See MySQL binaries for a detailed list.
In addition to these generic packages, we also offer binaries in platform-specific package formats for selected platforms. See Quick Standard Installation for more information on how to install these.
You need the following tools to install a MySQL tar file binary distribution:
GNU gunzip to uncompress the distribution.
A reasonable tar to unpack the distribution. GNU tar is known to work. Some operating systems come with a pre-installed version of tar that is known to have problems. For example, Sun tar and Mac OS X tar are known to have problems with long filenames. In such cases, you should install GNU tar first. On Mac OS X, you can use the pre-installed gnutar program.
If you run into problems, please always use mysqlbug when posting questions to a MySQL mailing list. Even if the problem isn't a bug, mysqlbug gathers system information that will help others solve your problem. By not using mysqlbug, you lessen the likelihood of getting a solution to your problem. You will find mysqlbug in the bin directory after you unpack the distribution. See Bug reports.
The basic commands you must execute to install and use a MySQL binary distribution are:
shell> groupadd mysql shell> useradd -g mysql mysql shell> cd /usr/local shell> gunzip < /path/to/mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s full-path-to-mysql-VERSION-OS mysql shell> cd mysql shell> scripts/mysql_install_db shell> chown -R root . shell> chown -R mysql data shell> chgrp -R mysql . shell> bin/mysqld_safe --user=mysql &
For versions of MySQL older than 4.0, substitute bin/safe_mysqld for bin/mysqld_safe in the final command.
A more detailed description follows.
To install a binary distribution, follow these steps, then proceed to Post-installation, for post-installation setup and testing:
Add a user and group for mysqld to run as:
shell> groupadd mysql shell> useradd -g mysql mysql
These commands add the mysql group and the mysql user. The syntax for useradd and groupadd may differ slightly on different versions of Unix. They may also be called adduser and addgroup. You may wish to call the user and group something else instead of mysql.
Pick the directory under which you want to unpack the distribution, and move into it. In the following example, we unpack the distribution under /usr/local (The following instructions, therefore, assume you have permission to create files and directories in /usr/local. If that directory is protected, you will need to perform the installation as root.)
Obtain a distribution file from one of the sites listed in Getting MySQL.
MySQL tar file binary distributions have names like mysql-VERSION-OS.tar.gz, where VERSION is a number (for example, 4.0.17), and OS indicates the type of operating system for which the distribution is intended (for example, pc-linux-gnu-i586). For a given release, binary distributions for all platforms are built from the same MySQL source distribution.
Change into the intended installation directory:
shell> cd /usr/local
Unpack the distribution, which will create the installation directory. Then create a symbolic link to that directory:
shell> gunzip < /path/to/mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s full-path-to-mysql-VERSION-OS mysql
The tar command creates a directory named mysql-VERSION-OS. The ln command makes a symbolic link to that directory. This lets you refer more easily to the installation directory as /usr/local/mysql.
With GNU tar, no separate invocation of gunzip is necessary. You can replace the first line with the following alternative command to uncompress and extract the distribution:
shell> tar zxvf /path/to/mysql-VERSION-OS.tar.gz
Change into the installation directory:
shell> cd mysql
You will find several files and subdirectories in the mysql directory. The most important for installation purposes are the bin and scripts subdirectories.
bin | This directory contains client programs and the server. You should add the full pathname of this directory to your PATH environment variable so that your shell finds the MySQL programs properly. See Environment variables. |
scripts | This directory contains the mysql_install_db script used to initialize the mysql database containing the grant tables that store the server access permissions. |
If you haven't installed MySQL before, you must create the MySQL grant tables:
shell> scripts/mysql_install_db
Note that for MySQL versions older than Version 3.22.10, mysql_install_db left the server running after creating the grant tables. This is no longer true; you will need to restart the server after performing the remaining steps in this procedure.
Change ownership of program binaries to root and ownership of the data directory to the user that you will run mysqld as. Assuming that you are located in the installation directory (/usr/local/mysql), the commands look like this:
shell> chown -R root . shell> chown -R mysql data shell> chgrp -R mysql .
The first command changes the owner attribute of the files to the root user. The second changes the owner attribute of the data directory to the mysql user. The third changes the group attribute to the mysql group.
If you would like MySQL to start automatically when you boot your machine, you can copy support-files/mysql.server to the location where your system has its startup files. More information can be found in the support-files/mysql.server script itself and in Automatic start.
You can set up new accounts using the bin/mysql_setpermission script if you install the DBI and DBD::mysql Perl modules. For instructions, see Perl support.
If you would like to use mysqlaccess and have the MySQL distribution in some non-standard place, you must change the location where mysqlaccess expects to find the mysql client. Edit the bin/mysqlaccess script at approximately line 18. Search for a line that looks like this:
$MYSQL = '/usr/local/bin/mysql'; # path to mysql executable
Change the path to reflect the location where mysql actually is stored on your system. If you do not do this, you will get a Broken pipe error when you run mysqlaccess.
After everything has been unpacked and installed, you should test your distribution.
You can start the MySQL server with the following command:
shell> bin/mysqld_safe --user=mysql &
For versions of MySQL older than 4.0, substitute bin/safe_mysqld for bin/mysqld_safe in the command.
Now proceed to mysqld_safe, and Post-installation.
Table of Contents
Before you proceed with the source installation, check first to see whether our binary is available for your platform and whether it will work for you. We put a lot of effort into making sure that our binaries are built with the best possible options.
You need the following tools to build and install MySQL from source:
GNU gunzip to uncompress the distribution.
A reasonable tar to unpack the distribution. GNU tar is known to work. Some tar implementations that come pre-installed with the operating system (for example, Sun tar) is known to have problems with long file names). In that case, you should install GNU tar first.
A working ANSI C++ compiler. gcc 2.95.2 or later, egcs 1.0.2 or later or egcs 2.91.66, SGI C++, and SunPro C++ are some of the compilers that are known to work. libg++ is not needed when using gcc. gcc 2.7.x has a bug that makes it impossible to compile some perfectly legal C++ files, such as sql/sql_base.cc. If you only have gcc 2.7.x, you must upgrade your gcc to be able to compile MySQL. gcc 2.8.1 is also known to have problems on some platforms, so it should be avoided if a new compiler exists for the platform.
gcc 2.95.2 or later is recommended when compiling MySQL Version 3.23.x.
A good make program. GNU make is always recommended and is sometimes required. If you have problems, we recommend trying GNU make 3.75 or newer.
If you are using a recent version of gcc, recent enough to understand the -fno-exceptions option, it is very important that you use it. Otherwise, you may compile a binary that crashes randomly. We also recommend that you use -felide-constructors and -fno-rtti along with -fno-exceptions. When in doubt, do the following:
CFLAGS="-O3" CXX=gcc CXXFLAGS="-O3 -felide-constructors \ -fno-exceptions -fno-rtti" ./configure \ --prefix=/usr/local/mysql --enable-assembler \ --with-mysqld-ldflags=-all-static
On most systems this will give you a fast and stable binary.
If you run into problems, please always use mysqlbug when posting questions to a MySQL mailing list. Even if the problem isn't a bug, mysqlbug gathers system information that will help others solve your problem. By not using mysqlbug, you lessen the likelihood of getting a solution to your problem. You will find mysqlbug in the scripts directory after you unpack the distribution. See Bug reports.
The basic commands you must execute to install a MySQL source distribution are:
shell> groupadd mysql shell> useradd -g mysql mysql shell> gunzip < mysql-VERSION.tar.gz | tar -xvf - shell> cd mysql-VERSION shell> ./configure --prefix=/usr/local/mysql shell> make shell> make install shell> cp support-files/my-medium.cnf /etc/my.cnf shell> cd /usr/local/mysql shell> bin/mysql_install_db shell> chown -R root . shell> chown -R mysql var shell> chgrp -R mysql . shell> bin/mysqld_safe --user=mysql &
For versions of MySQL older than 4.0, substitute bin/safe_mysqld for bin/mysqld_safe in the final command.
If you start from a source RPM, do the following:
shell> rpm --rebuild --clean MySQL-VERSION.src.rpm
This will make a binary RPM that you can install.
A more detailed description follows.
To install a source distribution, follow these steps, then proceed to Post-installation, for post-installation initialization and testing:
Add a user and group for mysqld to run as:
shell> groupadd mysql shell> useradd -g mysql mysql
These commands add the mysql group and the mysql user. The syntax for useradd and groupadd may differ slightly on different versions of Unix. They may also be called adduser and addgroup. You may wish to call the user and group something else instead of mysql.
Pick the directory under which you want to unpack the distribution, and move into it.
Obtain a distribution file from one of the sites listed in Getting MySQL. MySQL source distributions are provided as compressed tar archives and have names like mysql-VERSION.tar.gz, where VERSION is a number like 5.0.0-alpha.
Unpack the distribution into the current directory:
shell> gunzip < /path/to/mysql-VERSION.tar.gz | tar xvf -
This command creates a directory named mysql-VERSION.
With GNU tar, no separate invocation of gunzip is necessary. You can use the following alternative command to uncompress and extract the distribution:
shell> tar zxvf /path/to/mysql-VERSION-OS.tar.gz
Change into the top-level directory of the unpacked distribution:
shell> cd mysql-VERSION
Note that currently you must configure and build MySQL from this top-level directory. You cannot build it in a different directory.
Configure the release and compile everything:
shell> ./configure --prefix=/usr/local/mysql shell> make
When you run configure, you might want to specify some options. Run ./configure --help for a list of options. configure options, discusses some of the more useful options.
If configure fails and you are going to send mail to a MySQL mailing list to ask for assistance, please include any lines from config.log that you think can help solve the problem. Also include the last couple of lines of output from configure. Post the bug report using the mysqlbug script. See Bug reports.
If the compile fails, see Compilation problems, for help with a number of common problems.
Install the distribution:
shell> make install
If you want to set up an option file, use one of those present in the support-files directory as template. For example:
shell> cp support-files/my-medium.cnf /etc/my.cnf
You might need to run these commands as root.
If you want to configure support for InnoDB tables, you should edit the /etc/my.cnf file, remove the # character before the option lines that start with innodb_..., and modify the option values to be what you want. See Option files, and InnoDB start.
Change location into the installation directory:
shell> cd /usr/local/mysql
If you haven't installed MySQL before, you must create the MySQL grant tables:
shell> bin/mysql_install_db
Note that for MySQL versions older than Version 3.22.10, mysql_install_db left the server running after creating the grant tables. This is no longer true; you will need to restart the server after performing the remaining steps in this procedure.
Change ownership of binaries to root and ownership of the data directory to the user that you will run mysqld as. Assuming that you are located in the installation directory (/usr/local/mysql), the commands look like this:
shell> chown -R root . shell> chown -R mysql var shell> chgrp -R mysql .
The first command changes the owner attribute of the files to the root user. The second changes the owner attribute of the data directory to the mysql user. The third changes the group attribute to the mysql group.
If you would like MySQL to start automatically when you boot your machine, you can copy support-files/mysql.server to the location where your system has its startup files. More information can be found in the support-files/mysql.server script itself and in Automatic start.
You can set up new accounts using the bin/mysql_setpermission script if you install the DBI and DBD::mysql Perl modules. For instructions, see Perl support.
After everything has been installed, you should initialize and test your distribution using this command:
shell> /usr/local/mysql/bin/mysqld_safe --user=mysql &
For versions of MySQL older than 4.0, substitute bin/safe_mysqld for bin/mysqld_safe in the command.
If that command fails immediately and prints mysqld ended, you can find some information in the file mysql-data-directory/'hostname'.err. The likely reason is that you already have another mysqld server running. See Multiple servers.
Now proceed to Post-installation.
The configure script gives you a great deal of control over how you configure a MySQL source distribution. Typically you do this using options on the configure command-line. You can also affect configure using certain environment variables. See Environment variables. For a list of options supported by configure, run this command:
shell> ./configure --help
Some of the more commonly used configure options are described here:
To compile just the MySQL client libraries and client programs and not the server, use the --without-server option:
shell> ./configure --without-server
If you don't have a C++ compiler, mysql will not compile (it is the one client program that requires C++). In this case, you can remove the code in configure that tests for the C++ compiler and then run ./configure with the --without-server option. The compile step will still try to build mysql, but you can ignore any warnings about mysql.cc. (If make stops, try make -k to tell it to continue with the rest of the build even if errors occur.)
If you want to get an embedded MySQL library (libmysqld.a) you should use the --with-embedded-server option.
If you don't want your log files and database directories located under /usr/local/var, use a configure command, something like one of these:
shell> ./configure --prefix=/usr/local/mysql shell> ./configure --prefix=/usr/local \ --localstatedir=/usr/local/mysql/data
The first command changes the installation prefix so that everything is installed under /usr/local/mysql rather than the default of /usr/local. The second command preserves the default installation prefix, but overrides the default location for database directories (normally /usr/local/var) and changes it to /usr/local/mysql/data. After you have compiled MySQL, you can change these options with option files. See Option files.
If you are using Unix and you want the MySQL socket located somewhere other than the default location (normally in the directory /tmp or /var/run) use a configure command like this:
shell> ./configure \ --with-unix-socket-path=/usr/local/mysql/tmp/mysql.sock
Note that the given file must be an absolute pathname. You can also later change the location of mysql.sock by using a MySQL option file. See Problems with mysql.sock.
If you want to compile statically linked programs (for example, to make a binary distribution, to get more speed, or to work around problems with some Red Hat Linux distributions), run configure like this:
shell> ./configure --with-client-ldflags=-all-static \ --with-mysqld-ldflags=-all-static
If you are using gcc and don't have libg++ or libstdc++ installed, you can tell configure to use gcc as your C++ compiler:
shell> CC=gcc CXX=gcc ./configure
When you use gcc as your C++ compiler, it will not attempt to link in libg++ or libstdc++. This may be a good idea to do even if you have the above libraries installed, as some versions of these libraries have caused strange problems for MySQL users in the past.
The following list indicates some compilers and environment variable settings that are commonly used with each one.
, gcc 2.7.2: | CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors" |
egcs 1.0.3a: | CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors \ -fno-exceptions -fno-rtti" |
gcc 2.95.2: | CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3 -mpentiumpro \ -felide-constructors -fno-exceptions -fno-rtti" |
pgcc 2.90.29 or newer: | CFLAGS="-O3 -mpentiumpro -mstack-align-double" CXX=gcc \ CXXFLAGS="-O3 -mpentiumpro -mstack-align-double \ -felide-constructors -fno-exceptions -fno-rtti" |
In most cases you can get a reasonably optimal MySQL binary by using the options from the preceding list and adding the following options to the configure line:
--prefix=/usr/local/mysql --enable-assembler \ --with-mysqld-ldflags=-all-static
The full configure line would, in other words, be something like the following for all recent gcc versions:
CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3 -mpentiumpro \ -felide-constructors -fno-exceptions -fno-rtti" ./configure \ --prefix=/usr/local/mysql --enable-assembler \ --with-mysqld-ldflags=-all-static
The binaries we provide on the MySQL web site at http://www.mysql.com/ are all compiled with full optimization and should be perfect for most users. See MySQL binaries. There are some configuration setings you can tweak to make an even faster binary, but this is only for advanced users. See Compile and link options.
If the build fails and produces errors about your compiler or linker not being able to create the shared library libmysqlclient.so.# (# is a version number), you can work around this problem by giving the --disable-shared option to configure. In this case, configure will not build a shared libmysqlclient.so.# library.
You can configure MySQL not to use DEFAULT column values for non-NULL columns (that is, columns that are not allowed to be NULL). See constraint NOT NULL.
shell> CXXFLAGS=-DDONT_USE_DEFAULT_FIELDS ./configure
The effect of this flag is to cause any INSERT statement to fail unless it provides explicit values for all columns that require a non-NULL value.
By default, MySQL uses the ISO-8859-1 (Latin1) character set. To change the default set, use the --with-charset option:
shell> ./configure --with-charset=CHARSET
CHARSET may be one of big5, cp1251, cp1257, czech, danish, dec8, dos, euc_kr, gb2312, gbk, german1, hebrew, hp8, hungarian, koi8_ru, koi8_ukr, latin1, latin2, sjis, swe7, tis620, ujis, usa7, or win1251ukr. See Character sets.
If you want to convert characters between the server and the client, you should take a look at the SET CHARACTER SET command. See SET.
Warning: If you change character sets after having created any tables, you will have to run myisamchk -r -q --set-character-set=charset on every table. Your indexes may be sorted incorrectly otherwise. (This can happen if you install MySQL, create some tables, then reconfigure MySQL to use a different character set and reinstall it.)
With the configure option --with-extra-charsets=LIST, you can define which additional character sets should be compiled into the server. LIST is either a list of character sets separated with spaces, complex to include all characters that can't be dynamically loaded, or all to include all character sets into the binaries.
To configure MySQL with debugging code, use the --with-debug option:
shell> ./configure --with-debug
This causes a safe memory allocator to be included that can find some errors and that provides output about what is happening. See Debugging server.
If your client programs are using threads, you also must compile a thread-safe version of the MySQL client library with the --enable-thread-safe-client configure options. This will create a libmysqlclient_r library with which you should link your threaded applications. See Threaded clients.
Options that pertain to particular systems can be found in the system-specific section of this manual. See Operating System Specific Notes.
Caution: You should read this section only if you are interested in helping us test our new code. If you just want to get MySQL up and running on your system, you should use a standard release distribution (either a binary or source distribution will do).
To obtain our most recent development source tree, use these instructions:
Download BitKeeper from http://www.bitmover.com/cgi-bin/download.cgi. You will need Bitkeeper 3.0 or newer to access our repository.
Follow the instructions to install it.
After BitKeeper is installed, first go to the directory you want to work from, and then use one of the following commands to clone the MySQL version branch of your choice:
To clone the old 3.23 branch, use this command:
shell> bk clone bk://mysql.bkbits.net/mysql-3.23 mysql-3.23
To clone the 4.0 stable (production) branch, use this command:
shell> bk clone bk://mysql.bkbits.net/mysql-4.0 mysql-4.0
To clone the 4.1 alpha branch, use this command:
shell> bk clone bk://mysql.bkbits.net/mysql-4.1 mysql-4.1
To clone the 5.0 development branch, use this command:
shell> bk clone bk://mysql.bkbits.net/mysql-5.0 mysql-5.0
In the preceding examples the source tree will be set up in the mysql-3.23/, mysql-4.0/, mysql-4.1/, or mysql-5.0/ subdirectory of your current directory.
If you are behind a firewall and can only initiate HTTP connections, you can also use BitKeeper via HTTP.
If you are required to use a proxy server, set the environment variable http_proxy to point to your proxy:
shell> export http_proxy="http://your.proxy.server:8080/"
Now, simply replace the bk:// with http:// when doing a clone. Example:
shell> bk clone http://mysql.bkbits.net/mysql-4.1 mysql-4.1
The initial download of the source tree may take a while, depending on the speed of your connection---please be patient.
You will need GNU make, autoconf 2.53 (or newer), automake 1.5, libtool 1.4, and m4 to run the next set of commands. Even though many operating systems already come with their own implementation of make, chances are high that the compilation will fail with strange error messages. Therefore, it is highly recommended that you use GNU make (sometimes named gmake) instead.
Fortunately, a large number of operating systems already ship with the GNU toolchain preinstalled or supply installable packages of these. In any case, they can also be downloaded from the following locations:
If you are trying to configure MySQL 4.1 or later, you will also need GNU bison 1.75 or later. Older versions of bison may report this error:
sql_yacc.yy:#####: fatal error: maximum table size (32767) exceeded
Note: The maximum table size is not actually exceeded, the error is caused by bugs in older versions of bison.
Versions of MySQL before version 4.1 may also compile with other yacc implementations (for example, BSD yacc 91.7.30). For later versions, GNU bison is required.
The following example shows the typical commands required to configure a source tree. The first cd command changes location into the top-level directory of the tree; replace mysql-4.0 with the appropriate directory name.
shell> cd mysql-4.0 shell> bk -r edit shell> aclocal; autoheader; autoconf; automake shell> (cd innobase; aclocal; autoheader; autoconf; automake) shell> (cd bdb/dist; sh s_all) shell> ./configure # Add your favorite options here make
The command lines that change directory into the innobase and bdb/dist directories are used to configure the InnoDB and Berkeley DB (BDB) storage engines. You can omit these command lines if you to not require InnoDB or BDB support.
If you get some strange error during this stage, check that you really have libtool installed.
A collection of our standard configuration scripts is located in the BUILD/ subdirectory. You may find it more convenient to use the BUILD/compile-pentium-debug script than the preceding set of shell commands.. To compile on a different architecture, modify the script by removing flags that are Pentium-specific.
When the build is done, run make install. Be careful with this on a production machine; the command may overwrite your live release installation. If you have another installation of MySQL, we recommend that you run ./configure with different values for the --prefix, --with-tcp-port, and --unix-socket-path options than those used for your production server.
Play hard with your new installation and try to make the new features crash. Start by running make test. See MySQL test suite.
If you have gotten to the make stage and the distribution does not compile, please report it in our bugs database at http://bugs.mysql.com/. If you have installed the latest versions of the required GNU tools, and they crash trying to process our configuration files, please report that also. However, if you execute aclocal and get a command not found error or a similar problem, do not report it. Instead, make sure all the necessary tools are installed and that your PATH variable is set correctly so that your shell can find them.
After the initial bk clone operation to obtain the source tree, you should run bk pull periodically to get updates.
You can examine the change history for the tree with all the diffs by using bk revtool. If you see some funny diffs or code that you have a question about, do not hesitate to send email to the MySQL internals mailing list. See Mailing-list. Also, if you think you have a better idea on how to do something, send an email message to the same address with a patch. bk diffs will produce a patch for you after you have made changes to the source. If you do not have the time to code your idea, just send a description.
BitKeeper has a nice help utility that you can access via bk helptool.
Please note that any commits (bk ci or bk citool) will trigger the posting of a message with the changeset to our internals mailing list, as well as the usual openlogging.org submission with just the changeset comments. Generally, you wouldn't need to use commit (since the public tree will not allow bk push), but rather use the bk diffs method described previously.
You can also browse changesets, comments, and source code online. For example, to browse this information for MySQL 4.1, go to http://mysql.bkbits.net:8080/mysql-4.1.
The manual is in a separate tree which can be cloned with:
shell> bk clone bk://mysql.bkbits.net/mysqldoc mysqldoc
There are also public BitKeeper trees for MySQL Control Center and Connector/ODBC. They can be cloned respectively as follows.
To clone MySQL Control center, use this command:
shell> bk clone http://mysql.bkbits.net/mysqlcc mysqlcc
To clone Connector/ODBC, use this command:
shell> bk clone http://mysql.bkbits.net/myodbc3 myodbc3
All MySQL programs compile cleanly for us with no warnings on Solaris or Linux using gcc. On other systems, warnings may occur due to differences in system include files. See MIT-pthreads for warnings that may occur when using MIT-pthreads. For other problems, check the following list.
The solution to many problems involves reconfiguring. If you do need to reconfigure, take note of the following:
If configure is run after it already has been run, it may use information that was gathered during its previous invocation. This information is stored in config.cache. When configure starts up, it looks for that file and reads its contents if it exists, on the assumption that the information is still correct. That assumption is invalid when you reconfigure.
Each time you run configure, you must run make again to recompile. However, you may want to remove old object files from previous builds first because they were compiled using different configuration options.
To prevent old configuration information or object files from being used, run these commands before re-running configure:
shell> rm config.cache shell> make clean
Alternatively, you can run make distclean.
The following list describes some of the problems when compiling MySQL that have been found to occur most often:
If you get errors when compiling sql_yacc.cc, such as the ones shown here, you have probably run out of memory or swap space:
Internal compiler error: program cc1plus got fatal signal 11
or:
Out of virtual memory
or:
Virtual memory exhausted
The problem is that gcc requires huge amounts of memory to compile sql_yacc.cc with inline functions. Try running configure with the --with-low-memory option:
shell> ./configure --with-low-memory
This option causes -fno-inline to be added to the compile line if you are using gcc and -O0 if you are using something else. You should try the --with-low-memory option even if you have so much memory and swap space that you think you can't possibly have run out. This problem has been observed to occur even on systems with generous hardware configurations, and the --with-low-memory option usually fixes it.
By default, configure picks c++ as the compiler name and GNU c++ links with -lg++. If you are using gcc, that behavior can cause problems during configuration such as this:
configure: error: installation or configuration problem: C++ compiler cannot create executables.
You might also observe problems during compilation related to g++, libg++, or libstdc++.
One cause of these problems is that you may not have g++, or you may have g++ but not libg++, or libstdc++. Take a look at the config.log file. It should contain the exact reason why your C++ compiler didn't work. To work around these problems, you can use gcc as your C++ compiler. Try setting the environment variable CXX to "gcc -O3". For example:
shell> CXX="gcc -O3" ./configure
This works because gcc compiles C++ sources as well as g++ does, but does not link in libg++ or libstdc++ by default.
Another way to fix these problems is to install g++, libg++, and libstdc++. We would however like to recommend you to not use libg++ or libstdc++ with MySQL as this will only increase the binary size of mysqld without giving you any benefits. Some versions of these libraries have also caused strange problems for MySQL users in the past.
Using gcc as the C++ compiler is also required, if you want to compile MySQL with RAID functionality (see CREATE TABLE for more info on RAID table type) and you are using GNU gcc version 3 and above. If you get errors like the ones below during the linking stage when you configure MySQL to compile with the option --with-raid, try to use gcc as your C++ compiler by defining the above mentioned environment variable CXX:
gcc -O3 -DDBUG_OFF -rdynamic -o isamchk isamchk.o sort.o libnisam.a ../mysys/libmysys.a ../dbug/libdbug.a ../strings/libmystrings.a -lpthread -lz -lcrypt -lnsl -lm -lpthread ../mysys/libmysys.a(raid.o)(.text+0x79): In function `my_raid_create':: undefined reference to `operator new(unsigned)' ../mysys/libmysys.a(raid.o)(.text+0xdd): In function `my_raid_create':: undefined reference to `operator delete(void*)' ../mysys/libmysys.a(raid.o)(.text+0x129): In function `my_raid_open':: undefined reference to `operator new(unsigned)' ../mysys/libmysys.a(raid.o)(.text+0x189): In function `my_raid_open':: undefined reference to `operator delete(void*)' ../mysys/libmysys.a(raid.o)(.text+0x64b): In function `my_raid_close':: undefined reference to `operator delete(void*)' collect2: ld returned 1 exit status
If your compile fails with errors, such as any of the following, you must upgrade your version of make to GNU make:
making all in mit-pthreads make: Fatal error in reader: Makefile, line 18: Badly formed macro assignment
or:
make: file `Makefile' line 18: Must be a separator (:
or:
pthread.h: No such file or directory
Solaris and FreeBSD are known to have troublesome make programs.
GNU make Version 3.75 is known to work.
If you want to define flags to be used by your C or C++ compilers, do so by adding the flags to the CFLAGS and CXXFLAGS environment variables. You can also specify the compiler names this way using CC and CXX. For example:
shell> CC=gcc shell> CFLAGS=-O3 shell> CXX=gcc shell> CXXFLAGS=-O3 shell> export CC CFLAGS CXX CXXFLAGS
See MySQL binaries, for a list of flag definitions that have been found to be useful on various systems.
If you get an error message like this, you need to upgrade your gcc compiler:
client/libmysql.c:273: parse error before `__attribute__'
gcc 2.8.1 is known to work, but we recommend using gcc 2.95.2 or egcs 1.0.3a instead.
If you get errors such as those shown here when compiling mysqld, configure didn't correctly detect the type of the last argument to accept(), getsockname(), or getpeername():
cxx: Error: mysqld.cc, line 645: In this statement, the referenced type of the pointer value ''length'' is ''unsigned long'', which is not compatible with ''int''. new_sock = accept(sock, (struct sockaddr *)&cAddr, &length);
To fix this, edit the config.h file (which is generated by configure). Look for these lines:
/* Define as the base type of the last arg to accept */ #define SOCKET_SIZE_TYPE XXX
Change XXX to size_t or int, depending on your operating system. (Note that you will have to do this each time you run configure because configure regenerates config.h.)
The sql_yacc.cc file is generated from sql_yacc.yy. Normally the build process doesn't need to create sql_yacc.cc, because MySQL comes with an already generated copy. However, if you do need to re-create it, you might encounter this error:
"sql_yacc.yy", line xxx fatal: default action causes potential...
This is a sign that your version of yacc is deficient. You probably need to install bison (the GNU version of yacc) and use that instead.
On Debian Linux 3.0, you need to install gawk instead of the default mawk, if you want to compile MySQL 4.1 or higher with Berkeley DB support.
If you need to debug mysqld or a MySQL client, run configure with the --with-debug option, then recompile and link your clients with the new client library. See Debugging client.
If you get a compilation error on Linux (e.g. SuSE Linux 8.1 or Red Hat Linux 7.3) similar to the following one:
libmysql.c:1329: warning: passing arg 5 of `gethostbyname_r' from incompatible pointer type libmysql.c:1329: too few arguments to function `gethostbyname_r' libmysql.c:1329: warning: assignment makes pointer from integer without a cast make[2]: *** [libmysql.lo] Error 1
By default, the configure script attempts to determine the correct number of arguments by using g++ the GNU C++ compiler. This test yields wrong results, if g++ is not installed. There are two ways to work around this problem:
Make sure that the GNU C++ g++ is installed. On some Linux distributions, the required package is called gpp, on others it is named gcc-c++.
Use gcc as your C++ compiler by setting the CXX environment variable to gcc:
export CXX="gcc"
Please note that you need to run configure again afterwards.
This section describes some of the issues involved in using MIT-pthreads.
Note that on Linux you should not use MIT-pthreads but use the installed LinuxThreads implementation instead. See Linux.
If your system does not provide native thread support, you will need to build MySQL using the MIT-pthreads package. This includes older FreeBSD systems, SunOS 4.x, Solaris 2.4 and earlier, and some others. See Which OS.
Note that, beginning with MySQL 4.0.2, MIT-pthreads are no longer part of the source distribution. If you require this package, you need to download it separately from http://www.mysql.com/Downloads/Contrib/pthreads-1_60_beta6-mysql.tar.gz
After downloading, extract this source archive into the top level of the MySQL source directory. It will create a new subdirectory mit-pthreads.
On most systems, you can force MIT-pthreads to be used by running configure with the --with-mit-threads option:
shell> ./configure --with-mit-threads
Building in a non-source directory is not supported when using MIT-pthreads because we want to minimise our changes to this code.
The checks that determine whether to use MIT-pthreads occur only during the part of the configuration process that deals with the server code. If you have configured the distribution using --without-server to build only the client code, clients will not know whether MIT-pthreads is being used and will use Unix socket connections by default. Because Unix socket files do not work under MIT-pthreads on some platforms, this means you will need to use -h or --host when you run client programs.
When MySQL is compiled using MIT-pthreads, system locking is disabled by default for performance reasons. You can tell the server to use system locking with the --external-locking option. This is only needed if you want to be able to run two MySQL servers against the same datafiles (not recommended).
Sometimes the pthread bind() command fails to bind to a socket without any error message (at least on Solaris). The result is that all connections to the server fail. For example:
shell> mysqladmin version mysqladmin: connect to server at '' failed; error: 'Can't connect to mysql server on localhost (146)'
The solution to this is to kill the mysqld server and restart it. This has only happened to us when we have forced down the server and done a restart immediately.
With MIT-pthreads, the sleep() system call isn't interruptible with SIGINT (break). This is only noticeable when you run mysqladmin --sleep. You must wait for the sleep() call to terminate before the interrupt is served and the process stops.
When linking, you may receive warning messages like these (at least on Solaris); they can be ignored:
ld: warning: symbol `_iob' has differing sizes: (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4; file /usr/lib/libc.so value=0x140); /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken ld: warning: symbol `__iob' has differing sizes: (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4; file /usr/lib/libc.so value=0x140); /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken
Some other warnings also can be ignored:
implicit declaration of function `int strtoll(...)' implicit declaration of function `int strtoul(...)'
We haven't gotten readline to work with MIT-pthreads. (This isn't needed, but may be interesting for someone.)
These instructions describe how to build MySQL binaries from source for versions 4.1 and above on Windows. Instructions are provided for building binaries from a standard source distribution or from the BitKeeper tree that contains the latest development source.
Note: The instructions in this document are strictly for users who want to test MySQL on Windows from the latest source distribution or from the BitKeeper tree. For production use, MySQL AB does not advise using a MySQL server built by yourself from source. Normally, it is best to use precompiled binary distributions of MySQL that are built specifically for optimal performance on Windows by MySQL AB. Instructions for installing a binary distributions are available at Windows installation.
To build MySQL on Windows from source, you need the following compiler and resources available on your Windows system:
VC++ 6.0 compiler (updated with 4 or 5 SP and pre-processor package). The pre-processor package is necessary for the macro assembler. More details at: http://msdn.microsoft.com/vstudio/downloads/updates/sp/vs6/sp5/faq.aspx.
Approximately 45 MB disk space.
64 MB RAM.
You'll also need a MySQL source distribution for Windows. There are two ways you can get a source distribution for MySQL version 4.1 and above:
Obtain a source distribution packaged by MySQL AB for the particular version of MySQL in which you are interested. Prepackaged source distributions are available for released versions of MySQL and can be obtained from http://www.mysql.com/downloads/.
You can package a source distribution yourself from the latest BitKeeper developer source tree. If you plan to do this, you must create the package on a Unix system and then transfer it to your Windows system. (The reason for this is that some of the configuration and build steps require tools that work only on Unix.) The BitKeeper approach thus requires:
A system running Unix, or a Unix-like system such as Linux.
BitKeeper 3.0 installed on that system. You can obtain BitKeeper from http://www.bitkeeper.com/.
If you are using a Windows source distribution, you can go directly to Windows VC++ Build. To build from the BitKeeper tree, proceed to Windows BitKeeper Build.
If you find something not working as expected, or you have suggestions about ways to improve the current build process on Windows, please send a message to the win32 mailing list. See Mailing-list.
Note: MySQL 4.1 and above VC++ workspace files are compatible with Microsoft Visual Studio 6.0 and above(7.0/.NET) editions and tested by MySQL AB staff before each release.
Follow this procedure to build MySQL:
Create a work directory (for example, workdir).
Unpack the source distribution in the aforementioned directory using WinZip or other Windows tools that can read .zip files.
Start the VC++ 6.0 compiler.
In the File menu, select Open Workspace.
Open the mysql.dsw workspace you find in the work directory.
From the Build menu, select the Set Active Configuration menu.
Click over the screen selecting mysqld - Win32 Debug and click OK.
Press F7 to begin the build of the debug server, libraries, and some client applications.
Compile the release versions that you want, in the same way.
Debug versions of the programs and libraries are placed in the client_debug and lib_debug directories. Release versions of the programs and libraries are placed in the client_release and lib_release directories. Note that if you want to build both debug and release versions, you can select the ``build all'' option from the Build menu.
Test the server. The server built using the preceding instructions will expect that the MySQL base directory and data directory are C:\mysql and C:\mysql\data by default. If you want to test your server using the source tree root directory and its data directory as the base directory and data directory, you will need to tell the server their pathnames. You can either do this on the command line with the --basedir and --datadir options, or place appropriate options in an option file (C:\my.cnf or the my.ini file in your Windows directory). If you have an existing data directory elsewhere that you want to use, you can specify its pathname instead.
Start your server from the client_release or client_debug directory, depending on which server you want to use. The general server startup instructions are at Windows installation. You'll need to to adapt the instructions appropriately if you want to use a different base directory or data directory.
When the server is running in standalone fashion or as a service based on your configuration, try to connect to it from the mysql interactive command line utility that exists in your client_release or client_debug directory.
When you are satisifed that the programs you have built are working correctly, stop the server. Then install MySQL as follows:
Create the directories where you want to install MySQL. For example, to install into C:\mysql, use these commands:
C: mkdir \mysql mkdir \mysql\bin mkdir \mysql\data mkdir \mysql\share mkdir \mysql\scripts
If you want to compile other clients and link them to MySQL, you should also create several additional directories:
mkdir \mysql\include mkdir \mysql\lib mkdir \mysql\lib\debug mkdir \mysql\lib\opt
If you want to benchmark MySQL, create this directory:
mkdir \mysql\sql-bench
Benchmarking requires Perl support.
From the workdir directory, copy into the C:\mysql directory the following directories:
copy client_release\*.exe C:\mysql\bin copy client_debug\mysqld.exe C:\mysql\bin\mysqld-debug.exe xcopy scripts\*.* C:\mysql\scripts /E xcopy share\*.* C:\mysql\share /E
If you want to compile other clients and link them to MySQL, you should also copy several libraries and header files:
copy lib_debug\mysqlclient.lib C:\mysql\lib\debug copy lib_debug\libmysql.* C:\mysql\lib\debug copy lib_debug\zlib.* C:\mysql\lib\debug copy lib_release\mysqlclient.lib C:\mysql\lib\opt copy lib_release\libmysql.* C:\mysql\lib\opt copy lib_release\zlib.* C:\mysql\lib\opt copy include\*.h C:\mysql\include copy libmysql\libmysql.def C:\mysql\include
If you want to benchmark MySQL, you should also do this:
xcopy sql-bench\*.* C:\mysql\bench /E
Set up and start the server in the same way as for the binary Windows distribution. See Windows installation.
To create a Windows source package from the current BitKeeper source tree, use the following instructions. Please note that this procedure must be performed on a system running a Unix or Unix-like operating system. (The procedure is known to work well on Linux, for example.)
Clone the BitKeeper source tree for MySQL (version 4.1 or above, as desired). For more information how to clone the source tree, see the instructions at Installing source tree.
Configure and build the distribution so that you have a server binary to work with. One way to do this is to run the following command in the top-level directory of your source tree:
shell> ./BUILD/compile-pentium-max
After making sure that the build process completed successfully, run the following utility script from top-level directory of your source tree:
shell> ./scripts/make_win_src_distribution
This script creates a Windows source package, to be used on your Windows system. You can supply different options to the script based on your needs. It accepts the following options:
--debug Print information about script operations, do not create package --tmp Specify the temporary location --suffix Suffix name for the package --dirname Directory name to copy files (intermediate) --silent Do not print verbose list of files processed --tar Create tar.gz package instead of .zip package --help Show this help message
By default, make_win_src_distribution creates a zipped archive with the name mysql-VERSION-win-src.zip, where VERSION represents the version of your MySQL source tree.
Copy or upload to your Windows machine the Windows source package that you have just created. To compile it, use the instructions in Windows VC++ Build.
In your source files, you should include my_global.h before mysql.h:
#include <my_global.h> #include <mysql.h>
my_global.h includes any other files needed for Windows compatibility (such as windows.h) if you compile your program on Windows.
You can either link your code with the dynamic libmysql.lib library, which is just a wrapper to load in libmysql.dll on demand, or link with the static mysqlclient.lib library.
Note that because the MySQL client libraries are compiled as threaded libraries, you should also compile your code to be multi-threaded!
Table of Contents
There are some issues you should address after installing MySQL. For example, on Unix, you should create the MySQL grant tables. On all platforms, an important security concern is that the initial accounts in the grant tables have no passwords. You should assign passwords to prevent unauthorized access to the MySQL server.
The following sections describe post-installation procedures for Windows systems and for Unix systems.
On Windows, the grant tables do not have to be created. MySQL Windows distributions include the grant tables already set up in the mysql database under the data directory. However, you should assign passwords to the accounts.
The default privileges on Windows give all local users full privileges to all databases without specifying a password. To make MySQL more secure, you should set a password for all users and remove the row in the mysql.user table that has Host="localhost" and User="".
You should also add a password for the root user. The following example starts by removing the anonymous user that has all privileges, then sets a root user password:
C:\> C:\mysql\bin\mysql mysql mysql> DELETE FROM user WHERE Host='localhost' AND User=''; mysql> FLUSH PRIVILEGES; mysql> QUIT C:\> C:\mysql\bin\mysqladmin -u root password your_password
After you've set the password, if you want to shut down the mysqld server, you can do so using this command:
C:\> mysqladmin --user=root --password=your_password shutdown
If you are using a server from a very old version of MySQL, the mysqladmin command to set the password will fail with an error: parse error near 'SET password'. The solution to this problem is to upgrade to a newer version of MySQL.
With the current MySQL versions you can easily add new users and change privileges with GRANT and REVOKE commands. See GRANT.
After you install MySQL on Unix, you need to initialize the grant tables, start the server, and make sure that the server works okay. You may also wish to arrange for the server to be started and stopped automatically when your system starts and stops.
Normally you install the grant tables and start the server like this for installation from a source distribution:
shell> cd mysql_installation_directory shell> bin/mysql_install_db shell> bin/mysqld_safe --user=mysql &
For a binary distribution (not RPM or PKG packages), do this:
shell> cd mysql_installation_directory shell> scripts/mysql_install_db shell> bin/mysqld_safe --user=mysql &
The mysql_install_db script creates the mysql database that holds all database privileges, and the test database that you can use to test MySQL. The script also creates privilege table entries for root accounts and anonymous-user accounts. The entries are created without passwords. The mysqld_safe script starts the mysqld server. (For versions of MySQL older than 4.0, use safe_mysqld rather than mysqld_safe.)
mysql_install_db will not overwrite any old privilege tables, so it should be safe to run in any circumstances. If you don't want to have the test database you can remove it with mysqladmin -u root drop test after starting the server.
Testing is most easily done from the top-level directory of the MySQL distribution. For a binary distribution, this is your installation directory (typically something like /usr/local/mysql). For a source distribution, this is the main directory of your MySQL source tree.
In the commands shown in this section and in the following subsections, BINDIR is the path to the location in which programs like mysqladmin and mysqld_safe are installed. For a binary distribution, this is the bin directory within the distribution. For a source distribution, BINDIR is probably /usr/local/bin, unless you specified an installation directory other than /usr/local when you ran configure. EXECDIR is the location in which the mysqld server is installed. For a binary distribution, this is the same as BINDIR. For a source distribution, EXECDIR is probably /usr/local/libexec.
Testing is described in detail:
If necessary, start the mysqld server and set up the initial MySQL grant tables containing the privileges that determine how users are allowed to connect to the server. This is normally done with the mysql_install_db script:
shell> scripts/mysql_install_db
Typically, mysql_install_db needs to be run only the first time you install MySQL. Therefore, if you are upgrading an existing installation, you can skip this step. (However, mysql_install_db is quite safe to use and will not update any tables that already exist, so if you are unsure of what to do, you can always run mysql_install_db.)
mysql_install_db creates six tables (user, db, host, tables_priv, columns_priv, and func) in the mysql database. A description of the initial privileges is given in Default privileges. Briefly, these privileges allow the MySQL root user to do anything, and allow anybody to create or use databases with a name of test or starting with test_.
If you don't set up the grant tables, the following error will appear in the log file when you start the server:
mysqld: Can't find file: 'host.frm'
This may also happen with a binary MySQL distribution if you don't start MySQL by executing exactly ./bin/mysqld_safe. See mysqld_safe.
You might need to run mysql_install_db as root. However, if you prefer, you can run the MySQL server as an unprivileged (non-root) user, provided that the user can read and write files in the database directory. Instructions for running MySQL as an unprivileged user are given in Changing MySQL user.
If you have problems with mysql_install_db, see mysql_install_db.
There are some alternatives to running the mysql_install_db script as it is provided in the MySQL distribution:
You may want to edit mysql_install_db before running it, to change the initial privileges that are installed into the grant tables. This is useful if you want to install MySQL on a lot of machines with the same privileges. In this case you probably should need only to add a few extra INSERT statements to the mysql.user and mysql.db tables.
If you want to change the contents of the grant tables after installing them, you can run mysql_install_db, then use mysql -u root mysql to connect to the grant tables as the MySQL root user and issue SQL statements to modify the grant tables directly.
It is possible to re-create the grant tables completely after they have already been created. You might want to do this if you've already installed the tables but then want to re-create them after editing mysql_install_db.
For more information about these alternatives, see Default privileges.
Start the MySQL server like this:
shell> cd mysql_installation_directory shell> bin/mysqld_safe &
For versions of MySQL older than 4.0, substitute bin/safe_mysqld for bin/mysqld_safe in the final command.
If you have problems starting the server, see Starting server.
Use mysqladmin to verify that the server is running. The following commands provide a simple test to check that the server is up and responding to connections:
shell> BINDIR/mysqladmin version shell> BINDIR/mysqladmin variables
The output from mysqladmin version varies slightly depending on your platform and version of MySQL, but should be similar to that shown here:
shell> BINDIR/mysqladmin version mysqladmin Ver 8.40 Distrib 4.0.18, for linux on i586 Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB This software comes with ABSOLUTELY NO WARRANTY. This is free software, and you are welcome to modify and redistribute it under the GPL license Server version 4.0.18-log Protocol version 10 Connection Localhost via Unix socket TCP port 3306 UNIX socket /tmp/mysql.sock Uptime: 16 sec Threads: 1 Questions: 9 Slow queries: 0 Opens: 7 Flush tables: 2 Open tables: 0 Queries per second avg: 0.000 Memory in use: 132K Max memory used: 16773K
To see what else you can do with mysqladmin, invoke it with the --help option.
Verify that you can shut down the server:
shell> BINDIR/mysqladmin -u root shutdown
Verify that you can restart the server. Do this using mysqld_safe or by invoking mysqld directly. For example:
shell> BINDIR/mysqld_safe --log &
If mysqld_safe fails, try running it from the MySQL installation directory (if you are not already there). If that doesn't work, see Starting server.
Run some simple tests to verify that the server is working. The output should be similar to what is shown here:
shell> BINDIR/mysqlshow +-----------+ | Databases | +-----------+ | mysql | +-----------+ shell> BINDIR/mysqlshow mysql Database: mysql +--------------+ | Tables | +--------------+ | columns_priv | | db | | func | | host | | tables_priv | | user | +--------------+ shell> BINDIR/mysql -e "SELECT host,db,user FROM db" mysql +------+--------+------+ | host | db | user | +------+--------+------+ | % | test | | | % | test_% | | +------+--------+------+
There is also a benchmark suite in the sql-bench directory (under the MySQL installation directory) that you can use to compare how MySQL performs on different platforms. The benchmark suite is written in Perl. It uses the Perl DBI module to provide a database-independent interface to the various databases. The following additional Perl modules are required to run the benchmark suite:
DBI DBD::mysql Data::Dumper Data::ShowTable
These modules can be obtained from CPAN http://www.cpan.org/. See Perl installation.
The sql-bench/Results directory contains the results from many runs against different databases and platforms. To run all tests, execute these commands:
shell> cd sql-bench shell> run-all-tests
If you don't have the sql-bench directory, you probably installed MySQL using RPM files other than the source RPM. (The source RPM includes the sql-bench benchmark directory.) In this case, you must first install the benchmark suite before you can use it. Beginning with MySQL Version 3.22, there are separate benchmark RPM files named mysql-bench-VERSION-i386.rpm that contain benchmark code and data.
If you have a source distribution, there are also tests in its tests subdirectory that you can run. For example, to run auto_increment.tst, do this:
shell> BINDIR/mysql -vvf test < ./tests/auto_increment.tst
The expected result of the test can be found in the ./tests/auto_increment.res file.
The purpose of the mysql_install_db script is to generate new MySQL privilege tables. It will not overwrite existing MySQL privilege tables, and it will not affect any other data.
If you want to re-create your privilege tables, you should take down the mysqld server, if it's running, and then do something like:
mv mysql-data-directory/mysql mysql-data-directory/mysql-old mysql_install_db
This section lists problems you might encounter when you run mysql_install_db:
mysql_install_db doesn't install the grant tables |
You may find that mysql_install_db fails to install the grant
tables and terminates after displaying the following messages:
Starting mysqld daemon with databases from XXXXXX mysqld endedIn this case, you should examine the log file very carefully. The log should be located in the directory XXXXXX named by the error message, and should indicate why mysqld didn't start. If you don't understand what happened, include the log when you post a bug report. See Bug reports. |
There is already a mysqld process running | In this case, you probably don't have to run mysql_install_db at all. You have to run mysql_install_db only once, when you install MySQL the first time. |
Installing a second mysqld server doesn't work when one server is running | This can happen when you already have an existing MySQL installation, but want to put a new installation in a different location (for example, for testing, or perhaps you simply want to run two installations at the same time). Generally the problem that occurs when you try to run the second server is that it tries to use the same socket and port as the old one. In this case you will get the error message: Can't start server: Bind on TCP/IP port: Address already in use or Can't start server: Bind on unix socket.... See Multiple servers. |
You don't have write access to /tmp |
If you don't have write access to create a socket file at the default place
(in /tmp) or permission to create temporary files in /tmp,
you will get an error when running mysql_install_db or when
starting or using mysqld.
You can specify a different socket and temporary directory as follows:
shell> TMPDIR=/some_tmp_dir/ shell> MYSQL_UNIX_PORT=/some_tmp_dir/mysqld.sock shell> export TMPDIR MYSQL_UNIX_PORTSee Problems with mysql.sock. some_tmp_dir should be the path to some directory for which you have write permission. See Environment variables. After this, you should be able to run mysql_install_db and start the server with these commands: shell> scripts/mysql_install_db shell> BINDIR/mysqld_safe & |
mysqld crashes immediately |
If you are running Red Hat Version 5.0 with a version of glibc older than
2.0.7-5, you should make sure you have installed all glibc patches.
There is a lot of information about this in the MySQL mail
archives. Links to the mail archives are available online at
http://lists.mysql.com/.
Also, see Linux.
You can also start mysqld manually using the --skip-grant-tables
option and add the privilege information yourself using mysql:
shell> BINDIR/mysqld_safe --skip-grant-tables & shell> BINDIR/mysql -u root mysqlFrom mysql, manually execute the SQL commands in mysql_install_db. Make sure you run mysqladmin flush-privileges or mysqladmin reload afterward to tell the server to reload the grant tables. |
Generally, you start the mysqld server in one of these ways:
By invoking mysqld directly. This works on any platform.
By running the MySQL server as a Windows service. This can be done on Windows NT, 2000, and XP. For instructions, see NT start.
By invoking mysql.server. This script is used primarily at system startup and shutdown on systems that use System V-style run directories. It is described more fully later in this section.
By invoking mysqld_safe, which tries to determine the proper options for mysqld and then runs it with those options. This script is used on systems based on BSD Unix. It also is invoked by mysql.server. See mysqld_safe.
The mysql.server and mysqld_safe scripts can be used to start the server automatically at system startup time. mysql.server can also be used to stop the server.
The mysql.server script can be used to start or stop the server by invoking it with start or stop arguments:
shell> mysql.server start shell> mysql.server stop
mysql.server can be found in the share/mysql directory under the MySQL installation directory or in the support-files directory of the MySQL source tree.
Note that if you use the Linux RPM package (MySQL-server-VERSION.rpm), the mysql.server script has already been installed as /etc/init.d/mysql. You don't have to install it manually. See Linux-RPM for more information on the Linux RPM packages.
On Mac OS X, you can install a separate MySQL Startup Item package to enable the automatic startup of MySQL on system bootup. See Mac OS X installation for details.
Before mysql.server starts the server, it changes the directory to the MySQL installation directory, then invokes mysqld_safe. You might need to edit mysql.server if you have a binary distribution that you've installed in a non-standard location. Modify it to cd into the proper directory before it runs mysqld_safe. If you want the server to run as some specific user, add an appropriate user line to the /etc/my.cnf file, as shown later in this section.
mysql.server stop brings down the server by sending a signal to it. You can also stop the server manually by executing mysqladmin shutdown.
You need to add these start and stop commands to the appropriate places in your /etc/rc* files when you want to start up MySQL automatically on your server.
On most current Linux distributions, it is sufficient to copy the file mysql.server into the /etc/init.d directory (or /etc/rc.d/init.d on older Red Hat systems). Afterwards, run the following command to enable the startup of MySQL on system bootup:
shell> chkconfig --add mysql.server
On FreeBSD startup scripts generally should go in /usr/local/etc/rc.d/. The rc(8) manual page also states that scripts in this directory are only executed, if their basename matches the shell globbing pattern *.sh. Any other files or directories present within the directory are silently ignored. In other words, on FreeBSD you should install the file mysql.server as /usr/local/etc/rc.d/mysql.server.sh to enable automatic startup.
As an alternative to the above, some operating systems also use /etc/rc.local or /etc/init.d/boot.local to start additional services on bootup. To start up MySQL using this method, you could append something like the following to it:
/bin/sh -c 'cd /usr/local/mysql; ./bin/mysqld_safe --user=mysql &'
You can also add options for mysql.server in a global /etc/my.cnf file. A typical /etc/my.cnf file might look like this:
[mysqld] datadir=/usr/local/mysql/var socket=/var/tmp/mysql.sock port=3306 user=mysql [mysql.server] basedir=/usr/local/mysql
The mysql.server script understands the following options: datadir, basedir, and pid-file.
The following table shows which option groups each startup script reads from option files:
Script | Option groups |
mysqld | [mysqld], [server] and [mysqld-major-version] |
mysql.server | [mysql.server], [mysqld], and [server] |
mysqld_safe | [mysqld], [server], and [mysqld_safe] |
For backward compatibility, mysql.server also reads the [mysql_server] group and mysqld_safe also reads the [safe_mysqld] group. However, you should update your option files to use the [mysql.server] and [mysqld_safe] groups instead.
See Option files.
If you are going to use storage engines that support transactional tables (InnoDB, BDB), you should first create a my.cnf file and set startup options for the engines you plan to use. See Table types.
When the mysqld server starts, it changes location to the data directory. This is where it expects to write log files and the pid (process ID) file, and where it expects to find databases.
The data directory location is hardwired in when the distribution is compiled. However, if mysqld expects to find the data directory somewhere other than where it really is on your system, it will not work properly. If you have problems with incorrect paths, you can find out what options mysqld allows and what the default path settings are by invoking mysqld with the --help option. You can override the defaults by specifying the correct pathnames as command-line arguments to mysqld. (These options can be used with mysqld_safe as well.)
Normally you should need to tell mysqld only the base directory under which MySQL is installed. You can do this with the --basedir option. You can also use --help to check the effect of changing path options (note that --help must be the final option of the mysqld command). For example:
shell> EXECDIR/mysqld --basedir=/usr/local --help
Once you determine the path settings you want, start the server without the --help option.
Whichever method you use to start the server, if it fails to start up correctly, check the log file to see if you can find out why. Log files are located in the data directory (typically /usr/local/mysql/data for a binary distribution, /usr/local/var for a source distribution, and \mysql\data\mysql.err on Windows). Look in the data directory for files with names of the form host_name.err and host_name.log where host_name is the name of your server host. Then check the last few lines of these files:
shell> tail host_name.err shell> tail host_name.log
Look for something like the following in the log file:
000729 14:50:10 bdb: Recovery function for LSN 1 27595 failed 000729 14:50:10 bdb: warning: ./test/t1.db: No such file or directory 000729 14:50:10 Can't init databases
This means that you didn't start mysqld with --bdb-no-recover and Berkeley DB found something wrong with its log files when it tried to recover your databases. To be able to continue, you should move away the old Berkeley DB log file from the database directory to some other place, where you can later examine it. The log files are named log.0000000001, where the number will increase over time.
If you are running mysqld with BDB table support and mysqld core dumps at start this could be because of some problems with the BDB recovery log. In this case you can try starting mysqld with --bdb-no-recover. If this helps, then you should remove all log.* files from the data directory and try starting mysqld again.
If you get the following error, it means that some other program (or another mysqld server) is already using the TCP/IP port or socket mysqld is trying to use:
Can't start server: Bind on TCP/IP port: Address already in use
or:
Can't start server: Bind on unix socket...
Use ps to make sure that you don't have another mysqld server running. If you can't find another server running, you can try to execute the command telnet your-host-name tcp-ip-port-number and press Enter a couple of times. If you don't get an error message like telnet: Unable to connect to remote host: Connection refused, something is using the TCP/IP port mysqld is trying to use. See Problems Running mysql_install_db and Multiple servers.
If mysqld is currently running, you can find out what path settings it is using by executing this command:
shell> mysqladmin variables
or:
shell> mysqladmin -h 'your-host-name' variables
If you get Errcode 13, which means Permission denied, when starting mysqld this means that you didn't have the right to read/create files in the MySQL database or log directory. In this case you should either start mysqld as the root user or change the permissions for the involved files and directories so that you have the right to use them.
If mysqld_safe starts the server but you can't connect to it, you should make sure you have an entry in /etc/hosts that looks like this:
127.0.0.1 localhost
This problem occurs only on systems that don't have a working thread library and for which MySQL must be configured to use MIT-pthreads.
If you can't get mysqld to start you can try to make a trace file to find the problem. See Making trace files.
If you are using InnoDB tables, refer to the InnoDB-specific startup options. See InnoDB start.
If you are using BDB (Berkeley DB) tables, you should familiarise yourself with the different BDB-specific startup options. See BDB start.
Table of Contents
As a general rule, we recommend that when upgrading from one release series to another, you should go to the next series rather than skipping a series. For example, if you currently are running MySQL 3.23 and wish to upgrade to a newer series, upgrade to MySQL 4.0 rather than to 4.1 or 5.0.
Before you do an upgrade, you should back up your old databases.
You can always move the MySQL format files and datafiles between different versions on the same architecture as long as you have the same base version of MySQL. The current base version is 4. If you change the character set when running MySQL, you must run myisamchk -r -q --set-character-set=charset on all tables. Otherwise, your indexes may not be ordered correctly, because changing the character set may also change the sort order.
If you are cautious about using new versions, you can always rename your old mysqld to something like mysqld-old-version-number. If your new mysqld then does something unexpected, you can simply shut it down and restart with your old mysqld.
If, after an upgrade, you experience problems with recompiled client programs, such as Commands out of sync or unexpected core dumps, you probably have used an old header or library file when compiling your programs. In this case you should check the date for your mysql.h file and libmysqlclient.a library to verify that they are from the new MySQL distribution. If not, please recompile your programs.
If problems occur, such as that the new mysqld server doesn't want to start or that you can't connect without a password, check that you don't have some old my.cnf file from your old installation. You can check this with: program-name --print-defaults. If this outputs anything other than the program name, you have an active my.cnf file that affects server operation.
It is a good idea to rebuild and reinstall the Perl DBD::mysql module whenever you install a new release of MySQL. The same applies to other MySQL interfaces as well, such as the Python MySQLdb module.
In general, you should do the following when upgrading to MySQL 5.0 from an earlier version:
Read the 5.0 news items to see what significant new features you can use in 5.0. See News-5.0.x.
If you are running MySQL Server on Windows, please also see Windows upgrading.
If you are using replication, please also see Replication Upgrade for information on upgrading your replication setup.
MySQL 5.0 adds support for stored procedures. This support requires the proc table in the mysql database. To create this file you should run the mysql_fix_privilege_tables script. This is described in Upgrading-grant-tables.
Several visible behaviors have changed between MySQL 4.0 and MySQL 4.1 to fix some critical bugs and make MySQL more compatible with the ANSI SQL standard. These changes may affect your applications.
Some of the 4.1 behaviors can be tested in 4.0 before performing a full upgrade to 4.1. We have added to later MySQL 4.0 releases (from 4.0.12 on) a --new startup option for mysqld.
This option gives you the 4.1 behavior for the most critical changes. You can also enable these behaviors for a given client connection with the SET @@new=1 command, or turn them off if they are on with SET @@new=0.
If you believe that some of the 4.1 changes will affect you, we recommend that before upgrading to 4.1, you download the latest MySQL 4.0 version and run it with the --new option by adding the following to your config file:
[mysqld-4.0] new
That way you can test the new behaviors in 4.0 to make sure that your applications work with them. This will help you have a smooth painless transition when you perform a full upgrade to 4.1 later. Doing it the above way will ensure that you don't accidently later run the 4.1 version with the --new option.
The following list describes changes that may affect applications and that you should watch out for when upgrading to version 4.1:
TIMESTAMP is now returned as a string in 'YYYY-MM-DD HH:MM:SS' format. (The --new option can be used from 4.0.12 on to make a 4.0 server behave as 4.1 in this respect.) If you want to have the value returned as a number (like Version 4.0 does) you should add +0 to TIMESTAMP columns when you retrieve them:
mysql> SELECT ts_col + 0 FROM tbl_name;
Display widths for TIMESTAMP columns are no longer supported. For example, if you declare a column as TIMESTAMP(10), the (10) is ignored.
These changes were necessary for SQL standards compliance. In a future version, a further change will be made (backward compatible with this change), allowing the timestamp length to indicate the desired number of digits for fractions of a second.
Binary values such as 0xFFDF now are assumed to be strings instead of numbers. This fixes some problems with character sets where it's convenient to input a string as a binary value. With this change, you should use CAST() if you want to compare binary values numerically as integers:
mysql> SELECT CAST(0xFEFF AS UNSIGNED INTEGER) < CAST(0xFF AS UNSIGNED INTEGER); -> 0
If you don't use CAST(), a lexical string comparison will be done:
mysql> SELECT 0xFEFF < 0xFF; -> 1
Using binary items in a numeric context or comparing them using the = operator should work as before. (The --new option can be used from 4.0.13 on to make a 4.0 server behave as 4.1 in this respect.)
For functions that produce a DATE, DATETIME, or TIME value, the result returned to the client now is fixed up to have a temporal type. For example, in MySQL 4.1, you get this result:
mysql> SELECT CAST("2001-1-1" as DATETIME); -> '2001-01-01 00:00:00'
In MySQL 4.0, the result is different:
mysql> SELECT CAST("2001-1-1" as DATETIME); -> '2001-01-01'
DEFAULT values no longer can be specified for AUTO_INCREMENT columns. (In 4.0, a DEFAULT value is silently ignored; in 4.1, an error occurs).
LIMIT no longer accept negative arguments. Use 18446744073709551615 instead of -1.
SERIALIZE is no longer a valid mode value for the sql_mode variable. You should use SET TRANSACTION ISOLATION LEVEL SERIALIZABLE instead. SERIALIZE is no longer valid for the --sql-mode option for mysqld, either. Use --transaction-isolation=SERIALIZABLE instead.
All tables and string columns now have a character set. See Charset. Character set information is displayed by SHOW CREATE TABLE and mysqldump. (MySQL versions 4.0.6 and above can read the new dump files; older versions cannot.)
The table definition format used in .frm files has changed slightly in 4.1. MySQL 4.0 versions from 4.0.11 on can read the new .frm format directly, but older versions cannot. If you need to move tables from 4.1 to a version earlier than 4.0.11, you should use mysqldump. See mysqldump.
If you are running multiple servers on the same Windows machine, you should use a different --shared_memory_base_name option on all machines.
The interface to aggregated UDF functions has changed a bit. You must now declare a xxx_clear() function for each aggregate function XXX().
In general, upgrading to 4.1 from an earlier MySQL version involves the following steps:
Check the changes listed earlier in this section to see whether there are any that may affect your applications.
Read the 4.1 news items to see what significant new features you can use in 4.1. See News-4.1.x.
If you are running MySQL Server on Windows, please also see Windows upgrading.
Important note: Early alpha Windows distributions for MySQL 4.1 do not contain any installer program. See Windows binary installation for instructions on how to install such a distribution.
If you are using replication, please also see Replication Upgrade for information on upgrading your replication setup.
After upgrading, update the grant tables to generate the new longer Password column that is needed for secure handling of passwords. The procedure uses mysql_fix_privilege_tables and is described in Upgrading-grant-tables.
The password hashing mechanism has changed in 4.1 to provide better security, but this may cause compatibility problems if you still have clients that use the client library from 4.0 or earlier. (It is very likely that you will have 4.0 clients in situations where clients connect from remote hosts that have not yet upgraded to 4.1). The following list indicates some possible upgrade strategies. They represent various tradeoffs between the goal of compatibility with old clients and the goal of security.
Don't upgrade to 4.1. No behavior will change, but you cannot use any of the new features provided by the 4.1 client/server protocol, either. (MySQL 4.1 has an extended client/server protocol that offers such features as prepared statements and multiple result sets.) See C API Prepared statements.
Upgrade to 4.1 and run the mysql_fix_privilege_tables script to widen the Password column in the user table so that it can hold long password hashes. But run the server with the --old-passwords option to provide backward compatibility that allows pre-4.1 clients to continue to connect to their short-hash accounts. Eventually, when all your clients are upgraded to 4.1, you can stop using the --old-passwords server option. You can also change the passwords for your MySQL accounts to use the new more secure format.
Upgrade to 4.1 and run the mysql_fix_privilege_tables script to widen the Password column in the user table. If you know that all clients also have been upgraded to 4.1, don't run the server with the --old-passwords option. Instead, change the passwords on all existing accounts so that they have the new format. A pure-4.1 installation is the most secure.
Further background on password hashing with respect to client authentication and password-changing operations may be found in Password hashing.
In general, you should do the following when upgrading to MySQL 4.0 from an earlier version:
After upgrading, update the grant tables to add new privileges and features. The procedure uses the mysql_fix_privilege_tables script and is described in Upgrading-grant-tables.
Edit any MySQL startup scripts or configure files to not use any of the deprecated options described later in this section.
Convert your old ISAM files to MyISAM files with the mysql_convert_table_format database script. (This is a Perl script; it requires that DBI be installed.) To convert the tables in a given database, use this command:
shell> mysql_convert_table_format database db_name
Note that this should only be used if all tables in the given database are ISAM or MyISAM tables. To avoid converting tables of other types to MyISAM, you can explicitly list the names of your ISAM tables after the database name on the command line. You can also issue a ALTER TABLE table_name TYPE=MyISAM statement for each ISAM table to convert it to MyISAM.
To find out the table type for a given table, use this statement:
mysql> SHOW TABLE STATUS LIKE 'tbl_name';
Ensure that you don't have any MySQL clients that use shared libraries (like the Perl DBD::mysql module). If you do, you should recompile them, because the data structures used in libmysqlclient.so have changed. The same applies to other MySQL interfaces as well, such as the Python MySQLdb module.
If you are running MySQL Server on Windows, please also see Windows upgrading.
If you are using replication, please also see Replication Upgrade for information on upgrading your replication setup.
MySQL 4.0 will work even if you don't do the above, but you will not be able to use the new security privileges that MySQL 4.0 and you may run into problems when upgrading later to MySQL 4.1 or newer. The ISAM file format still works in MySQL 4.0 but it's deprecated and will be disabled (not compiled in by default) in MySQL 4.1. MyISAM tables should be used instead.
Old clients should work with a Version 4.0 server without any problems.
Even if you do the above, you can still downgrade to MySQL 3.23.52 or newer if you run into problems with the MySQL 4.0 series. In this case, you must use mysqldump to dump any tables that use full-text indexes and reload the dump file into the 3.23 server. This is necessary because 4.0 uses a new format for full-text indexing.
The following is a more complete list that tells what you must watch out for when upgrading to version 4.0:
MySQL 4.0 has a lot of new privileges in the mysql.user table. See GRANT.
To get these new privileges to work, you must update the grant tables. The procedure is described in Upgrading-grant-tables. Until you do this, all users have the SHOW DATABASES, CREATE TEMPORARY TABLES, and LOCK TABLES privileges. SUPER and EXECUTE privileges take their value from PROCESS. REPLICATION SLAVE and REPLICATION CLIENT take their values from FILE.
If you have any scripts that create new users, you may want to change them to use the new privileges. If you are not using GRANT commands in the scripts, this is a good time to change your scripts to use GRANT instead of modifying the grant tables directly..
From version 4.0.2 on, the option --safe-show-database is deprecated (and no longer does anything). See Privileges options.
If you get Access denied errors for new users in version 4.0.2 and up, you should check if you need some of the new grants that you didn't need before. In particular, you will need REPLICATION SLAVE (instead of FILE) for new slaves.
safe_mysqld is renamed to mysqld_safe. For backward compatibility, binary distributions will for some time include safe_mysqld as a symlink to mysqld_safe.
InnoDB support is now included by default in binary distributions. If you build MySQL from source, InnoDB is configured in by default. If you do not use InnoDB and want to save memory when running a server that has InnoDB support enabled, use the --skip-innodb server startup option. To compile MySQL without InnoDB support, run configure with the --without-innodb option.
The startup parameters myisam_max_extra_sort_file_size and myisam_max_extra_sort_file_size are now given in bytes (they were given in megabytes before 4.0.3).
External system locking of MyISAM/ISAM files is now turned off by default. Your can turn this on by doing --external-locking. (However, this is never needed for most users.)
The following startup variables/options have been renamed:
Old Name | New Name |
myisam_bulk_insert_tree_size | bulk_insert_buffer_size |
query_cache_startup_type | query_cache_type |
record_buffer | read_buffer_size |
record_rnd_buffer | read_rnd_buffer_size |
sort_buffer | sort_buffer_size |
warnings | log-warnings |
--err-log | --log-error (for mysqld_safe) |
The startup options record_buffer, sort_buffer and warnings will still work in MySQL 4.0 but are deprecated.
The following SQL variables have changed name.
Old Name | New Name |
SQL_BIG_TABLES | BIG_TABLES |
SQL_LOW_PRIORITY_UPDATES | LOW_PRIORITY_UPDATES |
SQL_MAX_JOIN_SIZE | MAX_JOIN_SIZE |
SQL_QUERY_CACHE_TYPE | QUERY_CACHE_TYPE |
The old names still work in MySQL 4.0 but are deprecated.
You have to use SET GLOBAL SQL_SLAVE_SKIP_COUNTER=# instead of SET SQL_SLAVE_SKIP_COUNTER=#.
The mysqld startup options --skip-locking and --enable-locking were renamed to --skip-external-locking and --external-locking.
SHOW MASTER STATUS now returns an empty set if binary logging is not enabled.
SHOW SLAVE STATUS now returns an empty set if slave is not initialized.
mysqld now has the option --temp-pool enabled by default as this gives better performance with some operating systems (most notably Linux).
DOUBLE and FLOAT columns now honor the UNSIGNED flag on storage (before, UNSIGNED was ignored for these columns).
ORDER BY col_name DESC sorts NULL values last, as of MySQL 4.0.11. In 3.23 and in earlier 4.0 versions, this was not always consistent.
SHOW INDEX has two more columns (Null and Index_type) than it had in 3.23.
CHECK, LOCALTIME and LOCALTIMESTAMP are now reserved words.
The result of all bitwise operators (|, &, <<, >>, and ~)) is now unsigned. This may cause problems if you are using them in a context where you want a signed result. See Cast Functions.
Note: when you use subtraction between integer values where one is of type UNSIGNED, the result will be unsigned. In other words, before upgrading to MySQL 4.0, you should check your application for cases where you are subtracting a value from an unsigned entity and want a negative answer or subtracting an unsigned value from an integer column. You can disable this behavior by using the --sql-mode=NO_UNSIGNED_SUBTRACTION option when starting mysqld. See Cast Functions.
To use MATCH ... AGAINST (... IN BOOLEAN MODE) with your tables, you need to rebuild them with REPAIR TABLE table_name USE_FRM.
LOCATE() and INSTR() are case-sensitive if one of the arguments is a binary string. Otherwise they are case-insensitive.
STRCMP() now uses the current character set when performing comparisons. This makes the default comparison behavior case insensitive unless one or both of the operands are binary strings.
HEX(string) now returns the characters in string converted to hexadecimal. If you want to convert a number to hexadecimal, you should ensure that you call HEX() with a numeric argument.
In 3.23, INSERT INTO ... SELECT always had IGNORE enabled. In 4.0.1, MySQL will stop (and possibly roll back) by default in case of an error unless you specify IGNORE.
The old C API functions mysql_drop_db(), mysql_create_db(), and mysql_connect() are no longer supported unless you compile MySQL with CFLAGS=-DUSE_OLD_FUNCTIONS. However, it is preferable to change client programs to use the new 4.0 API instead.
In the MYSQL_FIELD structure, length and max_length have changed from unsigned int to unsigned long. This should not cause any problems, except that they may generate warning messages when used as arguments in the printf() class of functions.
You should use TRUNCATE TABLE when you want to delete all rows from a table and you don't need to obtain a count of the number of rows that were deleted. (DELETE FROM table_name returns a row count in 4.0, and TRUNCATE TABLE is faster.)
You will get an error if you have an active LOCK TABLES or transaction when trying to execute TRUNCATE TABLE or DROP DATABASE.
You should use integers to store values in BIGINT columns (instead of using strings, as you did in MySQL 3.23). Using strings will still work, but using integers is more efficient.
The format of SHOW OPEN TABLES has changed.
Multi-threaded clients should use mysql_thread_init() and mysql_thread_end(). See Threaded clients.
If you want to recompile the Perl DBD::mysql module, use a recent version. Version 2.9003 is recommended. Versions older than 1.2218 should not be used because they use the deprecated mysql_drop_db() call.
RAND(seed) returns a different random number series in 4.0 than in 3.23; this was done to further differentiate RAND(seed) and RAND(seed+1).
The default type returned by IFNULL(A,B) is now set to be the more 'general' of the types of A and B. (The general-to-specific order is string, REAL or INTEGER).
MySQL Version 3.23 supports tables of the new MyISAM type and the old ISAM type. You don't have to convert your old tables to use these with Version 3.23. By default, all new tables will be created with type MyISAM (unless you start mysqld with the --default-table-type=isam option). You can convert an ISAM table to MyISAM format with ALTER TABLE table_name TYPE=MyISAM or the Perl script mysql_convert_table_format.
Version 3.22 and 3.21 clients will work without any problems with a Version 3.23 server.
The following list tells what you have to watch out for when upgrading to Version 3.23:
All tables that use the tis620 character set must be fixed with myisamchk -r or REPAIR TABLE.
If you do a DROP DATABASE on a symbolically linked database, both the link and the original database are deleted. (This didn't happen in 3.22 because configure didn't detect the availability of the readlink() system call.)
OPTIMIZE TABLE now works only for MyISAM tables. For other table types, you can use ALTER TABLE to optimize the table. During OPTIMIZE TABLE, the table is now locked to prevent it from being used by other threads.
The MySQL client mysql is now by default started with the option --no-named-commands (-g). This option can be disabled with --enable-named-commands (-G). This may cause incompatibility problems in some cases---for example, in SQL scripts that use named commands without a semicolon. Long format commands still work from the first line.
Date functions that work on parts of dates (like MONTH()) will now return 0 for 0000-00-00 dates. (In MySQL 3.22, these functions returned NULL.)
If you are using the german character sort order for ISAM tables, you must repair them with isamchk -r, because we have made some changes in the sort order.
The default return type of IF() now depends on both arguments and not only the first argument.
AUTO_INCREMENT columns should not be used to store negative numbers. The reason for this is that negative numbers caused problems when wrapping from -1 to 0. You should not store 0 in AUTO_INCREMENT columns, either; CHECK TABLE will complain about 0 values because they may change if you dump and restore the table. AUTO_INCREMENT for MyISAM tables is now handled at a lower level and is much faster than before. In addition, for MyISAM tables, old numbers are no longer reused, even if you delete rows from the table.
CASE, DELAYED, ELSE, END, FULLTEXT, INNER, RIGHT, THEN, and WHEN are now reserved words.
FLOAT(X) is now a true floating-point type and not a value with a fixed number of decimals.
When declaring columns using a DECIMAL(length,dec) type, the length argument no longer includes a place for the sign or the decimal point.
A TIME string must now be of one of the following formats: [[[DAYS] [H]H:]MM:]SS[.fraction] or [[[[[H]H]H]H]MM]SS[.fraction].
LIKE now compares strings using the same character comparison rules as for the = operator. If you require the old behavior, you can compile MySQL with the CXXFLAGS=-DLIKE_CMP_TOUPPER flag.
REGEXP is now case-insensitive if neither of the strings are binary strings.
When you check or repair MyISAM (.MYI) tables, you should use the CHECK TABLE statement or the myisamchk command. For ISAM (.ISM) tables, use the isamchk command.
If you want your mysqldump files to be compatible between MySQL Version 3.22 and Version 3.23, you should not use the --opt or --all option to mysqldump.
Check all your calls to DATE_FORMAT() to make sure there is a % before each format character. (MySQL Version 3.22 and later already allowed this syntax.)
mysql_fetch_fields_direct() is now a function (it used to be a macro) and it returns a pointer to a MYSQL_FIELD instead of a MYSQL_FIELD.
mysql_num_fields() can no longer be used on a MYSQL* object (it's now a function that takes a MYSQL_RES* value as an argument). With a MYSQL* object, you should now use mysql_field_count() instead.
In MySQL Version 3.22, the output of SELECT DISTINCT ... was almost always sorted. In Version 3.23, you must use GROUP BY or ORDER BY to obtain sorted output.
SUM() now returns NULL instead of 0 if there are no matching rows. This is required by SQL-99.
An AND or OR with NULL values will now return NULL instead of 0. This mostly affects queries that use NOT on an AND/OR expression as NOT NULL = NULL.
LPAD() and RPAD() now shorten the result string if it's longer than the length argument.
Nothing that affects compatibility has changed between versions 3.21 and 3.22. The only pitfall is that new tables that are created with DATE type columns will use the new way to store the date. You can't access these new columns from an old version of mysqld.
After installing MySQL Version 3.22, you should start the new server and then run the mysql_fix_privilege_tables script. This will add the new privileges that you need to use the GRANT command. If you forget this, you will get Access denied when you try to use ALTER TABLE, CREATE INDEX, or DROP INDEX. The procedure for updating the grant tables is described in Upgrading-grant-tables.
The C API interface to mysql_real_connect() has changed. If you have an old client program that calls this function, you must place a 0 for the new db argument (or recode the client to send the db element for faster connections). You must also call mysql_init() before calling mysql_real_connect(). This change was done to allow the new mysql_options() function to save options in the MYSQL handler structure.
The mysqld variable key_buffer has been renamed to key_buffer_size, but you can still use the old name in your startup files.
If you are running a version older than Version 3.20.28 and want to switch to Version 3.21, you need to do the following:
You can start the mysqld Version 3.21 server with the --old-protocol option to use it with clients from a Version 3.20 distribution. In this case, the new client function mysql_errno() will not return any server error, only CR_UNKNOWN_ERROR (but it works for client errors), and the server uses the old pre-3.21 password() checking rather than the new method.
If you are not using the --old-protocol option to mysqld, you will need to make the following changes:
All client code must be recompiled. If you are using ODBC, you must get the new MyODBC 2.x driver.
The script scripts/add_long_password must be run to convert the Password field in the mysql.user table to CHAR(16).
All passwords must be reassigned in the mysql.user table (to get 62-bit rather than 31-bit passwords).
The table format hasn't changed, so you don't have to convert any tables.
MySQL Version 3.20.28 and above can handle the new user table format without affecting clients. If you have a MySQL version earlier than Version 3.20.28, passwords will no longer work with it if you convert the user table. So to be safe, you should first upgrade to at least Version 3.20.28 and then upgrade to Version 3.21.
The new client code works with a 3.20.x mysqld server, so if you experience problems with 3.21.x, you can use the old 3.20.x server without having to recompile the clients again.
If you are not using the --old-protocol option to mysqld, old clients will be unable to connect and will issue the following error message:
ERROR: Protocol mismatch. Server Version = 10 Client Version = 9
The Perl DBI interface also supports the old mysqlperl interface. The only change you have to make if you use mysqlperl is to change the arguments to the connect() function. The new arguments are: host, database, user, and password (note that the user and password arguments have changed places).
The following changes may affect queries in old applications:
HAVING must now be specified before any ORDER BY clause.
The parameters to LOCATE() have been swapped.
There are some new reserved words. The most notable are DATE, TIME, and TIMESTAMP.
When upgrading MySQL under Windows, please follow these steps:
Download the latest Windows distribution of MySQL.
Choose a time of day with low usage, where a maintenance break is acceptable.
Alert the users that still are active about the maintenance break.
Stop the running MySQL Server (for example, with NET STOP MySQL or with the Services utility if you are running MySQL as a service, or with mysqladmin shutdown otherwise).
Exit the WinMySQLAdmin program if it is running.
Run the installation script of the Windows distribution, by clicking the "Install" button in WinZip and following the installation steps of the script.
Important note: Early alpha Windows distributions for MySQL 4.1 do not contain any installer program. See Windows binary installation for instructions on how to install such a distribution.
You may either overwrite your old MySQL installation (usually located at C:\mysql), or install it into a different directory, such as C:\mysql4. Overwriting the old installation is recommended.
Restart the server (for example, with NET START MySQL if you run MySQL as a service, or by invoking mysqld directly otherwise).
Update the grant tables. The procedure is described in Upgrading-grant-tables.
Possible error situations:
A system error has occurred. System error 1067 has occurred. The process terminated unexpectedly.
This error means that your my.cnf file (by default C:\my.cnf) contains an option that cannot be recognized by MySQL. You can verify that this is the case by trying to restart MySQL with the my.cnf file renamed, for example, to my_cnf.old to prevent the server from using it. Once you have verified it, you need to identify which option is the culprit. Create a new my.cnf file and move parts of the old file to it (restarting the server after you move each part) until you determine which option causes server startup to fail.
Some releases introduce changes to the structure of the grant tables (the tables in the mysql database) to add new privileges or features. To make sure that your grant tables are current when you update to a new version of MySQL, you should update your grant tables as well.
On Unix or Unix-like systems, update the grant tables by running the mysql_fix_privilege_tables script:
shell> mysql_fix_privilege_tables
You must run this script while the server is running. It attempts to connect to the server running on the local host as root. If your root account requires a password, indicate the password on the command line. For MySQL 4.1 and up, specify the password like this:
shell> mysql_fix_privilege_tables --password=root_password
Prior to MySQL 4.1, specify the password like this:
shell> mysql_fix_privilege_tables root_password
The mysql_fix_privilege_tables script performs any actions necessary to convert your grant tables to the current format. You may see some Duplicate column name warnings as it runs; they can be ignored.
After running the script, stop the server and restart it.
On Windows systems, there isn't an easy way to update the grant tables until MySQL 4.0.15. From version 4.0.15 on, MySQL distributions include a mysql_fix_privilege_tables.sql SQL script that you can run using the mysql client. If your MySQL installation is located at C:\mysql, the commands look like this:
C:\mysql\bin> mysql -u root -p mysql mysql> SOURCE C:\mysql\scripts\mysql_fix_privilege_tables.sql
If your installation is located in some other directory, adjust the pathnames appropriately.
The mysql command will prompt you for the root password; enter it when prompted.
As with the Unix procedure, you may see some Duplicate column name warnings as mysql processes the statements in the mysql_fix_privilege_tables.sql script; they can be ignored.
After running the script, stop the server and restart it.
If you are using MySQL Version 3.23 or later, you can copy the .frm, .MYI, and .MYD files for MyISAM tables between different architectures that support the same floating-point format. (MySQL takes care of any byte-swapping issues.) See MyISAM Tables.
The MySQL ISAM data and index files (.ISD and *.ISM, respectively) are architecture-dependent and in some cases operating system-dependent. If you want to move your applications to another machine that has a different architecture or operating system than your current machine, you should not try to move a database by simply copying the files to the other machine. Use mysqldump instead.
By default, mysqldump will create a file containing SQL statements. You can then transfer the file to the other machine and feed it as input to the mysql client.
Try mysqldump --help to see what options are available. If you are moving the data to a newer version of MySQL, you should use mysqldump --opt to take advantage of any optimizations that result in a dump file that is smaller and can be processed faster.
The easiest (although not the fastest) way to move a database between two machines is to run the following commands on the machine on which the database is located:
shell> mysqladmin -h 'other hostname' create db_name shell> mysqldump --opt db_name \ | mysql -h 'other hostname' db_name
If you want to copy a database from a remote machine over a slow network, you can use:
shell> mysqladmin create db_name shell> mysqldump -h 'other hostname' --opt --compress db_name \ | mysql db_name
You can also store the result in a file, then transfer the file to the target machine and load the file into the database there. For example, you can dump a database to a file on the source machine like this:
shell> mysqldump --quick db_name | gzip > db_name.contents.gz
(The file created in this example is compressed.) Transfer the file containing the database contents to the target machine and run these commands there:
shell> mysqladmin create db_name shell> gunzip < db_name.contents.gz | mysql db_name
You can also use mysqldump and mysqlimport to transfer the database. For big tables, this is much faster than simply using mysqldump. In the following commands, DUMPDIR represents the full pathname of the directory you use to store the output from mysqldump.
First, create the directory for the output files and dump the database:
shell> mkdir DUMPDIR shell> mysqldump --tab=DUMPDIR db_name
Then transfer the files in the DUMPDIR directory to some corresponding directory on the target machine and load the files into MySQL there:
shell> mysqladmin create db_name # create database shell> cat DUMPDIR/*.sql | mysql db_name # create tables in database shell> mysqlimport db_name DUMPDIR/*.txt # load data into tables
Also, don't forget to copy the mysql database because that's where the grant tables (user, db, host) are stored. You may have to run commands as the MySQL root user on the new machine until you have the mysql database in place.
After you import the mysql database on the new machine, execute mysqladmin flush-privileges so that the server reloads the grant table information.
Table of Contents
This section discusses issues that have been found to occur on Linux. The first few subsections describe general operating sytem-related issues, problems that can occur when using binary or source distributions, and post-installation issues. The remaining subsections discuss problems that occur with Linux on specific platforms.
Note that most of these problems occur on older versions of Linux. If you are running a recent version, you likely will see none of them.
MySQL needs at least Linux Version 2.0.
Warning: We have seen some strange problems with Linux 2.2.14 and MySQL on SMP systems. We also have reports from some MySQL users that they have encountered serious stability problems using MySQL with kernel 2.2.14. If you are using this kernel, you should upgrade to 2.2.19 (or newer) or to a 2.4 kernel. If you have a multiple-CPU box, then you should seriously consider using 2.4 as this will give you a significant speed boost. Your system also will be more stable.
When using LinuxThreads you will see a minimum of three mysqld processes running. These are in fact threads. There will be one thread for the LinuxThreads manager, one thread to handle connections, and one thread to handle alarms and signals.
The Linux-Intel binary and RPM releases of MySQL are configured for the highest possible speed. We are always trying to use the fastest stable compiler available.
The binary release is linked with -static, which means you do not normally need to worry about which version of the system libraries you have. You need not install LinuxThreads, either. A program linked with -static is slightly larger than a dynamically linked program, but also slightly faster (3-5%). However, one problem with a statically linked program is that you can't use user-defined functions (UDFs). If you are going to write or use UDFs (this is something for C or C++ programmers only), you must compile MySQL yourself using dynamic linking.
A known issue with binary distributions is that on older Linux systems that use libc (such as Red Hat 4.x or Slackware), you will get some non-fatal problems with hostname resolution. If your system uses libc rather than glibc2, you probably will encounter some difficulties with hostname resolution and getpwnam(). This happens because glibc unfortunately depends on some external libraries to implement hostname resolution and getpwent(), even when compiled with -static). These problems manifest themselves in two ways:
You probably will see the following error message when you run mysql_install_db:
Sorry, the host 'xxxx' could not be looked up
You can deal with this by executing mysql_install_db --force, which will not execute the resolveip test in mysql_install_db. The downside is that you can't use hostnames in the grant tables: Except for localhost, you must use IP numbers instead. If you are using an old version of MySQL that doesn't support --force, you must manually remove the resolveip test in mysql_install using an editor.
You also may see the following error when you try to run mysqld with the --user option:
getpwnam: No such file or directory
To work around this, start mysqld with su rather than by specifying the --user option. This causes the system itself to change the user ID of the mysqld process so that mysqld need not do so.
Another solution, which solves both problems, is to not use a binary distribution. Get a MySQL source distribution (an RPM or the tar.gz distribution) and install that instead.
On some Linux 2.2 versions, you may get the error Resource temporarily unavailable when clients make a lot of new connections to a mysqld server over TCP/IP. The problem is that Linux has a delay between the time that you close a TCP/IP socket and the time that the system actually frees it. There is only room for a finite number of TCP/IP slots, so you will encounter the resource-unavailable error if clients attempt too many new TCP/IP connections during a short time. For example, you may see the error when you run the MySQL test-connect benchmark over TCP/IP.
We have inquired about this problem a few times on different Linux mailing lists but have never been able to find a suitable resolution. The only known ``fix'' is for the clients to use persistent connections, or, if you are running the database server and clients on the same machine, to use Unix socket file connections rather than TCP/IP connections.
The following notes regarding glibc apply only to the situation when you build MySQL yourself. If you are running Linux on an x86 machine, in most cases it is much better for you to just use our binary. We link our binaries against the best patched version of glibc we can come up with and with the best compiler options, in an attempt to make it suitable for a high-load server. For a typical user, even for setups with a lot of concurrent connections or tables exceeding the 2G limit, our binary is the best choice in most cases. After reading the following text, if you are in doubt about what to do, try our binary first to see whether it meets your needs. If you discover that our binary is not good enough, then you may want to try your own build. In that case, we would appreciate a note about it, so we can build a better binary next time.
MySQL uses LinuxThreads on Linux. If you are using an old Linux version that doesn't have glibc2, you must install LinuxThreads before trying to compile MySQL. You can get LinuxThreads at http://www.mysql.com/downloads/os-linux.html.
Note that glibc versions before and including Version 2.1.1 have a fatal bug in pthread_mutex_timedwait() handling, which is used when you issue INSERT DELAYED statements. We recommend that you not use INSERT DELAYED before upgrading glibc.
Note that Linux kernel and the LinuxThread library can by default only have 1024 threads. If you plan to have more than 1000 concurrent connections, you will need to make some changes to LinuxThreads:
Increase PTHREAD_THREADS_MAX in sysdeps/unix/sysv/linux/bits/local_lim.h to 4096 and decrease STACK_SIZE in linuxthreads/internals.h to 256 KB. The paths are relative to the root of glibc. (Note that MySQL will not be stable with around 600-1000 connections if STACK_SIZE is the default of 2 MB.)
Recompile LinuxThreads to produce a new libpthread.a library, and relink MySQL against it.
The page http://www.volano.com/linuxnotes.html contains additional information about circumventing thread limits in LinuxThreads.
There is another issue that greatly hurts MySQL performance, especially on SMP systems. The mutex implementation in LinuxThreads in glibc 2.1 is very bad for programs with many threads that hold the mutex only for a short time. This produces a paradoxical result: If you link MySQL against an unmodified LinuxThreads, removing processors from an SMP actually improves MySQL performance in many cases. We have made a patch available for glibc 2.1.3 to correct this behavior (http://www.mysql.com/Downloads/Linux/linuxthreads-2.1-patch).
With glibc 2.2.2, MySQL version 3.23.36 will use the adaptive mutex, which is much better than even the patched one in glibc 2.1.3. Be warned, however, that under some conditions, the current mutex code in glibc 2.2.2 overspins, which hurts MySQL performance. The likelihood that this condition will occur can be reduced by renicing the mysqld process to the highest priority. We have also been able to correct the overspin behavior with a patch, available at http://www.mysql.com/Downloads/Linux/linuxthreads-2.2.2.patch. It combines the correction of overspin, maximum number of threads, and stack spacing all in one. You will need to apply it in the linuxthreads directory with patch -p0 </tmp/linuxthreads-2.2.2.patch. We hope it will be included in some form in future releases of glibc 2.2. In any case, if you link against glibc 2.2.2, you still need to correct STACK_SIZE and PTHREAD_THREADS_MAX. We hope that the defaults will be corrected to some more acceptable values for high-load MySQL setup in the future, so that the commands needed to produce your own build can be reduced to ./configure; make; make install.
We recommend that you use the above patches to build a special static version of libpthread.a and use it only for statically linking against MySQL. We know that the patches are safe for MySQL and significantly improve its performance, but we cannot say anything about other applications. If you link other applications that require LinuxThreads against the patched static version of the library, or build a patched shared version and install it on your system, you are doing it at your own risk.
If you experience any strange problems during the installation of MySQL, or with some common utilities hanging, it is very likely that they are either library or compiler related. If this is the case, using our binary will resolve them.
If you link your own MySQL client programs, you may see the following error at runtime:
ld.so.1: fatal: libmysqlclient.so.#: open failed: No such file or directory
This problem can be avoided by one of the following methods:
Link clients with the -Wl,r/full-path-to-libmysqlclient.so flag rather than with -Lpath).
Copy libmysqclient.so to /usr/lib.
Add the pathname of the directory where libmysqlclient.so is located to the LD_RUN_PATH environment variable before running your client.
If you are using the Fujitsu compiler (fcc/FCC), you will have some problems compiling MySQL because the Linux header files are very gcc oriented. The following configure line should work with fcc/FCC:
CC=fcc CFLAGS="-O -K fast -K lib -K omitfp -Kpreex -D_GNU_SOURCE \ -DCONST=const -DNO_STRTOLL_PROTO" \ CXX=FCC CXXFLAGS="-O -K fast -K lib \ -K omitfp -K preex --no_exceptions --no_rtti -D_GNU_SOURCE \ -DCONST=const -Dalloca=__builtin_alloca -DNO_STRTOLL_PROTO \ '-D_EXTERN_INLINE=static __inline'" \ ./configure \ --prefix=/usr/local/mysql --enable-assembler \ --with-mysqld-ldflags=-all-static --disable-shared \ --with-low-memory
mysql.server can be found in the share/mysql directory under the MySQL installation directory or in the support-files directory of the MySQL source tree. You can install it as /etc/init.d/mysql for automatic MySQL startup and shutdown. See Automatic start.
If MySQL can't open enough files or connections, it may be that you haven't configured Linux to handle enough files.
In Linux 2.2 and onward, you can check the number of allocated file handles as follows:
shell> cat /proc/sys/fs/file-max shell> cat /proc/sys/fs/dquot-max shell> cat /proc/sys/fs/super-max
If you have more than 16 MB of memory, you should add something like the following to your init scripts (for example, /etc/init.d/boot.local on SuSE Linux):
echo 65536 > /proc/sys/fs/file-max echo 8192 > /proc/sys/fs/dquot-max echo 1024 > /proc/sys/fs/super-max
You can also run the echo commands from the command line as root, but these settings will be lost the next time your computer reboots.
Alternatively, you can set these parameters on bootup by using the sysctl tool, which is used by many Linux distributions (SuSE has added it as well, beginning with SuSE Linux 8.0). Just put the following values into a file named /etc/sysctl.conf:
# Increase some values for MySQL fs.file-max = 65536 fs.dquot-max = 8192 fs.super-max = 1024
You should also add the following to /etc/my.cnf:
[mysqld_safe] open-files-limit=8192
This should allow the server a limit of 8192 for the combined number of connections and open files.
The STACK_SIZE constant in LinuxThreads controls the spacing of thread stacks in the address space. It needs to be large enough so that there will be plenty of room for the stack of each individual thread, but small enough to keep the stack of some threads from running into the global mysqld data. Unfortunately, as we have experimentally discovered, the Linux implementation of mmap() will successfully unmap an already mapped region if you ask it to map out an address already in use, zeroing out the data on the entire page, instead of returning an error. So, the safety of mysqld or any other threaded application depends on ``gentlemanly'' behavior of the code that creates threads. The user must take measures to make sure the number of running threads at any time is sufficiently low for thread stacks to stay away from the global heap. With mysqld, you should enforce this behavior by setting a reasonable value for the max_connections variable.
If you build MySQL yourself, you can patch LinuxThreads for better stack use. See Source notes-Linux. If you do not want to patch LinuxThreads, you should set max_connections to a value no higher than 500. It should be even less if you have a large key buffer, large heap tables, or some other things that make mysqld allocate a lot of memory, or if you are running a 2.2 kernel with a 2G patch. If you are using our binary or RPM version 3.23.25 or later, you can safely set max_connections at 1500, assuming no large key buffer or heap tables with lots of data. The more you reduce STACK_SIZE in LinuxThreads the more threads you can safely create. We recommend values between 128K and 256K.
If you use a lot of concurrent connections, you may suffer from a ``feature'' in the 2.2 kernel that attempts to prevent fork bomb attacks by penalizing a process for forking or cloning a child. This causes MySQL not to scale well as you increase the number of concurrent clients. On single-CPU systems, we have seen this manifested as very slow thread creation: It may take a long time to connect to MySQL (as long as 1 minute), and it may take just as long to shut it down. On multiple-CPU systems, we have observed a gradual drop in query speed as the number of clients increases. In the process of trying to find a solution, we have received a kernel patch from one of our users who claimed it made a lot of difference for his site. The patch is available at http://www.mysql.com/Downloads/Patches/linux-fork.patch. We have now done rather extensive testing of this patch on both development and production systems. It has significantly improved MySQL performance without causing any problems and we now recommend it to our users who still run high-load servers on 2.2 kernels.
This issue has been fixed in the 2.4 kernel, so if you are not satisfied with the current performance of your system, rather than patching your 2.2 kernel, it might be easier to upgrade to 2.4. On SMP systems, upgrading also will give you a nice SMP boost in addition to fixing the fairness bug.
We have tested MySQL on the 2.4 kernel on a 2-CPU machine and found MySQL scales much better. There was virtually no slowdown on query throughput all the way up to 1000 clients, and the MySQL scaling factor (computed as the ratio of maximum throughput to the throughput for one client) was 180%. We have observed similar results on a 4-CPU system: Virtually no slowdown as the number of clients was increased up to 1000, and a 300% scaling factor. Based on these results, for a high-load SMP server using a 2.2 kernel, we definitely recommend upgrading to the 2.4 kernel at this point.
We have discovered that it is essential to run mysqld process with the highest possible priority on the 2.4 kernel to achieve maximum performance. This can be done by adding a renice -20 $$ command to mysqld_safe. In our testing on a 4-CPU machine, increasing the priority gave 60% throughput increase with 400 clients.
We are currently also trying to collect more information on how well MySQL performs on 2.4 kernel on 4-way and 8-way systems. If you have access such a system and have done some benchmarks, please send an email message to <benchmarks@mysql.com> with the results. We will review them for inclusion in the manual.
If you see a dead mysqld server process with ps, this usually means that you have found a bug in MySQL or you have a corrupted table. See Crashing.
To get a core dump on Linux if mysqld dies with a SIGSEGV signal, you can start mysqld with the --core-file option. Note that you also probably need to raise the core file size by adding ulimit -c 1000000 to mysqld_safe or starting mysqld_safe with --core-file-size=1000000. See mysqld_safe.
MySQL requires libc Version 5.4.12 or newer. It's known to work with libc 5.4.46. glibc Version 2.0.6 and later should also work. There have been some problems with the glibc RPMs from Red Hat, so if you have problems, check whether there are any updates. The glibc 2.0.7-19 and 2.0.7-29 RPMs are known to work.
If you are using Red Hat 8.0 or a new glibc 2.2.x library, you may see mysqld die in gethostbyaddr(). This happens because the new glibc library requires a stack size greater than 128K for this call. To fix the problem, start mysqld with the --thread-stack=192K option. (Use -O thread_stack=192K before MySQL 4.) This stack size is now the default on MySQL 4.0.10 and above, so you should not see the problem.
If you are using gcc 3.0 and above to compile MySQL, you must install the libstdc++v3 library before compiling MySQL; if you don't do this, you will get an error about a missing __cxa_pure_virtual symbol during linking.
On some older Linux distributions, configure may produce an error like this:
Syntax error in sched.h. Change _P to __P in the /usr/include/sched.h file. See the Installation chapter in the Reference Manual.
Just do what the error message says. Add an extra underscore to the _P macro name that has only one underscore, then try again.
You may get some warnings when compiling. Those shown here can be ignored:
mysqld.cc -o objs-thread/mysqld.o mysqld.cc: In function `void init_signals()': mysqld.cc:315: warning: assignment of negative value `-1' to `long unsigned int' mysqld.cc: In function `void * signal_hand(void *)': mysqld.cc:346: warning: assignment of negative value `-1' to `long unsigned int'
If mysqld always dumps core when it starts, the problem may be that you have an old /lib/libc.a. Try renaming it, then remove sql/mysqld and do a new make install and try again. This problem has been reported on some Slackware installations.
If you get the following error when linking mysqld, it means that your libg++.a is not installed correctly:
/usr/lib/libc.a(putc.o): In function `_IO_putc': putc.o(.text+0x0): multiple definition of `_IO_putc'
You can avoid using libg++.a by running configure like this:
shell> CXX=gcc ./configure
In some implementations, readdir_r() is broken. The symptom is that the SHOW DATABASES statement always returns an empty set. This can be fixed by removing HAVE_READDIR_R from config.h after configuring and before compiling.
MySQL Version 3.23.12 is the first MySQL version that is tested on Linux-Alpha. If you plan to use MySQL on Linux-Alpha, you should ensure that you have this version or newer.
We have tested MySQL on Alpha with our benchmarks and test suite, and it appears to work nicely.
We currently build the MySQL binary packages on SuSE Linux 7.0 for AXP, kernel 2.4.4-SMP, Compaq C compiler (V6.2-505) and Compaq C++ compiler (V6.3-006) on a Compaq DS20 machine with an Alpha EV6 processor.
You can find the above compilers at http://www.support.compaq.com/alpha-tools/. By using these compilers rather than gcc, we get about 9-14% better MySQL performance.
Note that until MySQL version 3.23.52 and 4.0.2, we optimized the binary for the current CPU only (by using the -fast compile option). This means that for older versions, you can use our Alpha binaries only if you have an Alpha EV6 processor.
For all following releases, we added the -arch generic flag to our compile options, which makes sure the binary runs on all Alpha processors. We also compile statically to avoid library problems. The configure command looks like this:
CC=ccc CFLAGS="-fast -arch generic" CXX=cxx \ CXXFLAGS="-fast -arch generic -noexceptions -nortti" \ ./configure --prefix=/usr/local/mysql --disable-shared \ --with-extra-charsets=complex --enable-thread-safe-client \ --with-mysqld-ldflags=-non_shared --with-client-ldflags=-non_shared
If you want to use egcs, the following configure line worked for us:
CFLAGS="-O3 -fomit-frame-pointer" CXX=gcc \ CXXFLAGS="-O3 -fomit-frame-pointer -felide-constructors \ -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql --disable-shared
Some known problems when running MySQL on Linux-Alpha:
Debugging threaded applications like MySQL will not work with gdb 4.18. You should use gdb 5.1 instead!
If you try linking mysqld statically when using gcc, the resulting image will dump core at startup time. In other words, don't use --with-mysqld-ldflags=-all-static with gcc.
MySQL should work on MkLinux with the newest glibc package (tested with glibc 2.0.7).
To get MySQL to work on Qube2 (Linux Mips), you need the newest glibc libraries. glibc-2.0.7-29C2 is known to work. You must also use the egcs C++ compiler (egcs-1.0.2-9, gcc 2.95.2 or newer).
To get MySQL to compile on Linux IA-64, we use the following configure command for building with gcc 2.96:
CC=gcc \ CFLAGS="-O3 -fno-omit-frame-pointer" \ CXX=gcc \ CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors \ -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql \ "--with-comment=Official MySQL binary" \ --with-extra-charsets=complex
On IA-64, the MySQL client binaries use shared libraries. This means that if you install our binary distribution at a location other than /usr/local/mysql, you need to add the path of the directory where you have libmysqlclient.so installed either to the /etc/ld.so.conf file or to the value of your LD_LIBRARY_PATH environment variable.
See Link errors.
On Mac OS X, tar cannot handle long filenames. If you need to unpack a .tar.gz distribution, use gnutar instead.
MySQL should work without any problems on Mac OS X 10.x (Darwin).
Our binary for Mac OS X is compiled on Darwin 6.3 with the following configure line:
CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc \ CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors \ -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql \ --with-extra-charsets=complex --enable-thread-safe-client \ --enable-local-infile --disable-shared
For current versions of Mac OS X Server, no operating system changes are necessary before compiling MySQL. Compiling for the Server platform is the same as for the client version of Mac OS X. (However, note that MySQL comes preinstalled on Mac OS X Server, so you need not build it yourself.)
For older versions (Mac OS X Server 1.2, a.k.a. Rhapsody), you must first install a pthread package before trying to configure MySQL.
On Solaris, you may run into trouble even before you get the MySQL distribution unpacked! Solaris tar can't handle long file names, so you may see an error like this when you unpack MySQL:
x mysql-3.22.12-beta/bench/Results/ATIS-mysql_odbc-NT_4.0-cmp-db2,\ informix,ms-sql,mysql,oracle,solid,sybase, 0 bytes, 0 tape blocks tar: directory checksum error
In this case, you must use GNU tar (gtar) to unpack the distribution. You can find a precompiled copy for Solaris at http://www.mysql.com/downloads/os-solaris.html.
Sun native threads only work on Solaris 2.5 and higher. For Version 2.4 and earlier, MySQL will automatically use MIT-pthreads. See MIT-pthreads.
If you get the following error from configure, it means that you have something wrong with your compiler installation:
checking for restartable system calls... configure: error can not run test programs while cross compiling
In this case you should upgrade your compiler to a newer version. You may also be able to solve this problem by inserting the following row into the config.cache file:
ac_cv_sys_restartable_syscalls=${ac_cv_sys_restartable_syscalls='no'}
If you are using Solaris on a SPARC, the recommended compiler is gcc 2.95.2 or 3.2. You can find this at http://gcc.gnu.org/. Note that egcs 1.1.1 and gcc 2.8.1 don't work reliably on SPARC!
The recommended configure line when using gcc 2.95.2 is:
CC=gcc CFLAGS="-O3" \ CXX=gcc CXXFLAGS="-O3 -felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql --with-low-memory \ --enable-assembler
If you have an UltraSPARC system, you can get 4% better performance by adding -mcpu=v8 -Wa,-xarch=v8plusa to the CFLAGS and CXXFLAGS environment variables.
If you have Sun's Forte 5.0 (or newer) compiler, you can run configure like this:
CC=cc CFLAGS="-Xa -fast -native -xstrconst -mt" \ CXX=CC CXXFLAGS="-noex -mt" \ ./configure --prefix=/usr/local/mysql --enable-assembler
To create a 64-bit binary with Sun's Forte compiler, use the following configuration options:
CC=cc CFLAGS="-Xa -fast -native -xstrconst -mt -xarch=v9" \ CXX=CC CXXFLAGS="-noex -mt -xarch=v9" ASFLAGS="-xarch=v9" \ ./configure --prefix=/usr/local/mysql --enable-assembler
To create a 64bit Solaris binary using gcc, add -m64 to CFLAGS and CXXFLAGS. Note that this works only with MySQL 4.0 and up - MySQL 3.23 does not include the required modifications to support this.
In the MySQL benchmarks, we got a 4% speedup on an UltraSPARC when using Forte 5.0 in 32-bit mode compared to using gcc 3.2 with -mcpu flags.
If you create a 64-bit mysqld binary, it is 4% slower than the 32-bit binary, but can handle more threads and memory.
If you get a problem with fdatasync or sched_yield, you can fix this by adding LIBS=-lrt to the configure line
For older compilers than WorkShop 5.3, you may have to edit the configure script to change this line:
#if !defined(__STDC__) || __STDC__ != 1
To this:
#if !defined(__STDC__)
If you turn on __STDC__ with the -Xc option, the Sun compiler can't compile with the Solaris pthread.h header file. This is a Sun bug (broken compiler or broken include file).
If mysqld issues the following error message when you run it, you have tried to compile MySQL with the Sun compiler without enabling the multi-thread option (-mt):
libc internal error: _rmutex_unlock: rmutex not held
Add -mt to CFLAGS and CXXFLAGS and recompile.
If you are using the SFW version of gcc (which comes with Solaris 8), you must add /opt/sfw/lib to the environment variable LD_LIBRARY_PATH before running configure.
If you are using the gcc available from sunfreeware.com, you may have many problems. To avoid this, you should recompile gcc and GNU binutils on the machine where you will be running them.
If you get the following error when compiling MySQL with gcc, it means that your gcc is not configured for your version of Solaris:
shell> gcc -O3 -g -O2 -DDBUG_OFF -o thr_alarm ... ./thr_alarm.c: In function `signal_hand': ./thr_alarm.c:556: too many arguments to function `sigwait'
The proper thing to do in this case is to get the newest version of gcc and compile it with your current gcc compiler! At least for Solaris 2.5, almost all binary versions of gcc have old, unusable include files that will break all programs that use threads, and possibly other programs!
Solaris doesn't provide static versions of all system libraries (libpthreads and libdl), so you can't compile MySQL with --static. If you try to do so, you will get one of the following errors:
ld: fatal: library -ldl: not found undefined reference to `dlopen' cannot find -lrt
If you link your own MySQL client programs, you may see the following error at runtime:
ld.so.1: fatal: libmysqlclient.so.#: open failed: No such file or directory
This problem can be avoided by one of the following methods:
Link clients with the -Wl,r/full-path-to-libmysqlclient.so flag rather than with -Lpath).
Copy libmysqclient.so to /usr/lib.
Add the pathname of the directory where libmysqlclient.so is located to the LD_RUN_PATH environment variable before running your client.
If you have problems with configure trying to link with -lz when you don't have zlib installed, you have two options:
If you want to be able to use the compressed communication protocol, you need to get and install zlib from ftp.gnu.org.
Run configure with the --with-named-z-libs=no option when building MySQL.
If you are using gcc and have problems with loading user-defined functions (UDFs) into MySQL, try adding -lgcc to the link line for the UDF.
If you would like MySQL to start automatically, you can copy support-files/mysql.server to /etc/init.d and create a symbolic link to it named /etc/rc3.d/S99mysql.server.
If too many processes try to connect very rapidly to mysqld, you will see this error in the MySQL log:
Error in accept: Protocol error
You might try starting the server with the --back_log=50 option as a workaround for this. (Use -O back_log=50 before MySQL 4.)
Solaris doesn't support core files for setuid() applications, so you can't get a core file from mysqld if you are using the --user option.
You can normally use a Solaris 2.6 binary on Solaris 2.7 and 2.8. Most of the Solaris 2.6 issues also apply for Solaris 2.7 and 2.8.
MySQL Version 3.23.4 and above should be able to detect new versions of Solaris automatically and enable workarounds for the following problems!
Solaris 2.7 / 2.8 has some bugs in the include files. You may see the following error when you use gcc:
/usr/include/widec.h:42: warning: `getwc' redefined /usr/include/wchar.h:326: warning: this is the location of the previous definition
If this occurs, you can fix the problem by copying /usr/include/widec.h to .../lib/gcc-lib/os/gcc-version/include and changing line 41 from this:
#if !defined(lint) && !defined(__lint)
To this:
#if !defined(lint) && !defined(__lint) && !defined(getwc)
Alternatively, you can edit /usr/include/widec.h directly. Either way, after you make the fix, you should remove config.cache and run configure again!
If you get the following errors when you run make, it's because configure didn't detect the curses.h file (probably because of the error in /usr/include/widec.h):
In file included from mysql.cc:50: /usr/include/term.h:1060: syntax error before `,' /usr/include/term.h:1081: syntax error before `;'
The solution to this is to do one of the following:
Configure with CFLAGS=-DHAVE_CURSES_H CXXFLAGS=-DHAVE_CURSES_H ./configure.
Edit /usr/include/widec.h as indicated above and re-run configure.
Remove the #define HAVE_TERM line from the config.h file and run make again.
If your linker can't find -lz when linking client programs, the problem is probably that your libz.so file is installed in /usr/local/lib. You can fix this by one of the following methods:
Add /usr/local/lib to LD_LIBRARY_PATH.
Add a link to libz.so from /lib.
If you are using Solaris 8, you can install the optional zlib from your Solaris 8 CD distribution.
Run configure with the --with-named-z-libs=no option when building MySQL.
On Solaris 8 on x86, mysqld will dump core if you remove the debug symbols using strip.
If you are using gcc or egcs on Solaris x86 and you experience problems with core dumps under load, you should use the following configure command:
CC=gcc CFLAGS="-O3 -fomit-frame-pointer -DHAVE_CURSES_H" \ CXX=gcc \ CXXFLAGS="-O3 -fomit-frame-pointer -felide-constructors \ -fno-exceptions -fno-rtti -DHAVE_CURSES_H" \ ./configure --prefix=/usr/local/mysql
This will avoid problems with the libstdc++ library and with C++ exceptions.
If this doesn't help, you should compile a debug version and run it with a trace file or under gdb. See Using gdb on mysqld.
This section provides information about using MySQL on BSD variants.
FreeBSD 4.x or newer is recommended for running MySQL, because the thread package is much more integrated. To get a secure and stable system, you should use only FreeBSD kernels that are marked -RELEASE.
The easiest (and preferred) way to install MySQL is to use the mysql-server and mysql-client ports available at http://www.freebsd.org/. Using these ports gives you the following benefits:
A working MySQL with all optimizations enabled that are known to work on your version of FreeBSD.
Automatic configuration and build.
Startup scripts installed in /usr/local/etc/rc.d.
The ability to use pkg_info -L to see which files are installed.
The ability to use pkg_delete to remove MySQL if you no longer want it on your machine.
It is recommended you use MIT-pthreads on FreeBSD 2.x, and native threads on Versions 3 and up. It is possible to run with native threads on some late 2.2.x versions but you may encounter problems shutting down mysqld.
Unfortunately, certain function calls on FreeBSD are not yet fully thread-safe. Most notably, this includes the gethostbyname() function, which is used by MySQL to convert hostnames into IP addresses. Under certain circumstances, the mysqld process will suddenly cause 100% CPU load and will be unresponsive. If you encounter this problem, try to start up MySQL using the --skip-name-resolve option.
Alternatively, you can link MySQL on FreeBSD 4.x against the LinuxThreads library, which avoids a few of the problems that the native FreeBSD thread implementation has. For a very good comparison of LinuxThreads vs. native threads, see Jeremy Zawodny's article FreeBSD or Linux for your MySQL Server? at http://jeremy.zawodny.com/blog/archives/000697.html.
A known problem when using LinuxThreads on FreeBSD is that wait_timeout is not working (probably a signal handling problem in FreeBSD/LinuxThreads). This is supposed to be fixed in FreeBSD 5.0. The symptom is that persistent connections can hang for a very long time without getting closed down.
The MySQL build process require GNU make (gmake) to work. If GNU make is not available, you must install it first before compiling MySQL.
The recommended way to compile and install MySQL on FreeBSD with gcc (2.95.2 and up) is:
shell> CC=gcc CFLAGS="-O2 -fno-strength-reduce" \ CXX=gcc CXXFLAGS="-O2 -fno-rtti -fno-exceptions \ -felide-constructors -fno-strength-reduce" \ ./configure --prefix=/usr/local/mysql --enable-assembler shell> gmake shell> gmake install shell> cd /usr/local/mysql shell> bin/mysql_install_db shell> bin/mysqld_safe &
If you notice that configure will use MIT-pthreads, you should read the MIT-pthreads notes. See MIT-pthreads.
If you get an error from make install that it can't find /usr/include/pthreads, configure didn't detect that you need MIT-pthreads. To fix this problem, remove config.cache, then re-run configure with the --with-mit-threads option.
Be sure your name resolver setup is correct. Otherwise, you may experience resolver delays or failures when connecting to mysqld. Also make sure that the localhost entry in the /etc/hosts file is correct. The file should start with a line similar to this:
127.0.0.1 localhost localhost.your.domain
FreeBSD is known to have a very low default file handle limit. See Not enough file handles. Start the server by using the --open-files-limit option for mysqld_safe, or raise the limits for the mysqld user in /etc/login.conf and rebuild it with cap_mkdb /etc/login.conf. Also be sure you set the appropriate class for this user in the password file if you are not using the default (use chpass mysqld-user-name). See mysqld_safe.
If you have a lot of memory, you should consider rebuilding the kernel to allow MySQL to use more than 512M of RAM. Take a look at option MAXDSIZ in the LINT config file for more information.
If you get problems with the current date in MySQL, setting the TZ variable will probably help. See Environment variables.
To compile on NetBSD you need GNU make. Otherwise, the build process will fail when make tries to run lint on C++ files.
On OpenBSD Version 2.5, you can compile MySQL with native threads with the following options:
CFLAGS=-pthread CXXFLAGS=-pthread ./configure --with-mit-threads=no
Our users have reported that OpenBSD 2.8 has a threading bug which causes problems with MySQL. The OpenBSD Developers have fixed the problem, but as of January 25th, 2001, it's only available in the ``-current'' branch. The symptoms of this threading bug are: slow response, high load, high CPU usage, and crashes.
If you get an error like Error in accept:: Bad file descriptor or error 9 when trying to open tables or directories, the problem is probably that you haven't allocated enough file descriptors for MySQL.
In this case, try starting mysqld_safe as root with the following options:
shell> mysqld_safe --user=mysql --open-files-limit=2048 &
If you get the following error when compiling MySQL, your ulimit value for virtual memory is too low:
item_func.h: In method `Item_func_ge::Item_func_ge(const Item_func_ge &)': item_func.h:28: virtual memory exhausted make[2]: *** [item_func.o] Error 1
Try using ulimit -v 80000 and run make again. If this doesn't work and you are using bash, try switching to csh or sh; some BSDI users have reported problems with bash and ulimit.
If you are using gcc, you may also use have to use the --with-low-memory flag for configure to be able to compile sql_yacc.cc.
If you get problems with the current date in MySQL, setting the TZ variable will probably help. See Environment variables.
Upgrade to BSD/OS Version 3.1. If that is not possible, install BSDIpatch M300-038.
Use the following command when configuring MySQL:
shell> env CXX=shlicc++ CC=shlicc2 \ ./configure \ --prefix=/usr/local/mysql \ --localstatedir=/var/mysql \ --without-perl \ --with-unix-socket-path=/var/mysql/mysql.sock
The following is also known to work:
shell> env CC=gcc CXX=gcc CXXFLAGS=-O3 \ ./configure \ --prefix=/usr/local/mysql \ --with-unix-socket-path=/var/mysql/mysql.sock
You can change the directory locations if you wish, or just use the defaults by not specifying any locations.
If you have problems with performance under heavy load, try using the --skip-thread-priority option to mysqld! This will run all threads with the same priority; on BSDI Version 3.1, this gives better performance (at least until BSDI fixes their thread scheduler).
If you get the error virtual memory exhausted while compiling, you should try using ulimit -v 80000 and run make again. If this doesn't work and you are using bash, try switching to csh or sh; some BSDI users have reported problems with bash and ulimit.
BSDI Version 4.x has some thread-related bugs. If you want to use MySQL on this, you should install all thread-related patches. At least M400-023 should be installed.
On some BSDI Version 4.x systems, you may get problems with shared libraries. The symptom is that you can't execute any client programs, for example, mysqladmin. In this case you need to reconfigure not to use shared libraries with the --disable-shared option to configure.
Some customers have had problems on BSDI 4.0.1 that the mysqld binary after a while can't open tables. This is because some library/system related bug causes mysqld to change current directory without asking for this!
The fix is to either upgrade MySQL to at least version 3.23.34 or, after running configure, remove the line #define HAVE_REALPATH from config.h before running make.
Note that the above means that you can't symbolic link a database directories to another database directory or symbolic link a table to another database on BSDI! (Making a symbolic link to another disk is okay).
There are a couple of small problems when compiling MySQL on HP-UX. We recommend that you use gcc instead of the HP-UX native compiler, because gcc produces better code!
We recommend using gcc 2.95 on HP-UX. Don't use high optimization flags (like -O6) as they may not be safe on HP-UX.
The following configure line should work with gcc 2.95:
CFLAGS="-I/opt/dce/include -fpic" \ CXXFLAGS="-I/opt/dce/include -felide-constructors -fno-exceptions \ -fno-rtti" \ CXX=gcc \ ./configure --with-pthread \ --with-named-thread-libs='-ldce' \ --prefix=/usr/local/mysql --disable-shared
The following configure line should work with gcc 3.1:
CFLAGS="-DHPUX -I/opt/dce/include -O3 -fPIC" CXX=gcc \ CXXFLAGS="-DHPUX -I/opt/dce/include -felide-constructors \ -fno-exceptions -fno-rtti -O3 -fPIC" \ ./configure --prefix=/usr/local/mysql \ --with-extra-charsets=complex --enable-thread-safe-client \ --enable-local-infile --with-pthread \ --with-named-thread-libs=-ldce --with-lib-ccflags=-fPIC --disable-shared
For HP-UX Version 11.x, we recommend MySQL Version 3.23.15 or later.
Because of some critical bugs in the standard HP-UX libraries, you should install the following patches before trying to run MySQL on HP-UX 11.0:
PHKL_22840 Streams cumulative PHNE_22397 ARPA cumulative
This will solve the problem of getting EWOULDBLOCK from recv() and EBADF from accept() in threaded applications.
If you are using gcc 2.95.1 on an unpatched HP-UX 11.x system, you will get the error:
In file included from /usr/include/unistd.h:11, from ../include/global.h:125, from mysql_priv.h:15, from item.cc:19: /usr/include/sys/unistd.h:184: declaration of C function ... /usr/include/sys/pthread.h:440: previous declaration ... In file included from item.h:306, from mysql_priv.h:158, from item.cc:19:
The problem is that HP-UX doesn't define pthreads_atfork() consistently. It has conflicting prototypes in /usr/include/sys/unistd.h:184 and /usr/include/sys/pthread.h:440 (details below).
One solution is to copy /usr/include/sys/unistd.h into mysql/include and edit unistd.h and change it to match the definition in pthread.h. Here's the diff:
183,184c183,184 < extern int pthread_atfork(void (*prepare)(), void (*parent)(), < void (*child)()); --- > extern int pthread_atfork(void (*prepare)(void), void (*parent)(void), > void (*child)(void));
After this, the following configure line should work:
CFLAGS="-fomit-frame-pointer -O3 -fpic" CXX=gcc \ CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti -O3" \ ./configure --prefix=/usr/local/mysql --disable-shared
If you are using MySQL 4.0.5 with the HP-UX compiler, you can use the following command (which has been tested with cc B.11.11.04):
CC=cc CXX=aCC CFLAGS=+DD64 CXXFLAGS=+DD64 ./configure \ --with-extra-character-set=complex
You can ignore any errors of the following type:
aCC: warning 901: unknown option: `-3': use +help for online documentation
If you get the following error from configure, check that you don't have the path to the K&R compiler before the path to the HP-UX C and C++ compiler:
checking for cc option to accept ANSI C... no configure: error: MySQL requires a ANSI C compiler (and a C++ compiler). Try gcc. See the Installation chapter in the Reference Manual.
Another reason for not being able to compile is that you didn't define the +DD64 flags above.
Another possibility for HP-UX 11 is to use MySQL binaries for HP-UX 10.20. We have received reports from some users that these binaries work fine on HP-UX 11.00. If you encounter problems, be sure to check your HP-UX patch level.
Automatic detection of xlC is missing from Autoconf, so a number of variables need to be set before running configure. The following example uses the IBM compiler:
export CC="xlc_r -ma -O3 -qstrict -qoptimize=3 -qmaxmem=8192 " export CXX="xlC_r -ma -O3 -qstrict -qoptimize=3 -qmaxmem=8192" export CFLAGS="-I /usr/local/include" export LDFLAGS="-L /usr/local/lib" export CPPFLAGS=$CFLAGS export CXXFLAGS=$CFLAGS ./configure --prefix=/usr/local \ --localstatedir=/var/mysql \ --sysconfdir=/etc/mysql \ --sbindir='/usr/local/bin' \ --libexecdir='/usr/local/bin' \ --enable-thread-safe-client \ --enable-large-files
Above are the options used to compile the MySQL distribution that can be found at http://www-frec.bull.com/.
If you change the -O3 to -O2 in the preceding configure line, you must also remove the -qstrict option (this is a limitation in the IBM C compiler).
If you are using gcc or egcs to compile MySQL, you must use the -fno-exceptions flag, because the exception handling in gcc/egcs is not thread-safe! (This is tested with egcs 1.1.) There are also some known problems with IBM's assembler that may cause it to generate bad code when used with gcc.
We recommend the following configure line with egcs and gcc 2.95 on AIX:
CC="gcc -pipe -mcpu=power -Wa,-many" \ CXX="gcc -pipe -mcpu=power -Wa,-many" \ CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql --with-low-memory
The -Wa,-many is necessary for the compile to be successful. IBM is aware of this problem but is in to hurry to fix it because of the workaround available. We don't know if the -fno-exceptions is required with gcc 2.95, but as MySQL doesn't use exceptions and the above option generates faster code, we recommend that you should always use this option with egcs / gcc.
If you get a problem with assembler code, try changing the -mcpu=xxx option to match your CPU. Typically power2, power, or powerpc may need to be used. Alternatively, you might need to use 604 or 604e. We are not positive but suspect that power would likely be safe most of the time, even on a power2 machine.
If you don't know what your CPU is, execute a uname -m command. It will produce a string that looks like 000514676700, with a format of xxyyyyyymmss where xx and ss are always 00, yyyyyy is a unique system ID and mm is the ID of the CPU Planar. A chart of these values can be found at http://publib.boulder.ibm.com/doc_link/en_US/a_doc_lib/cmds/aixcmds5/uname.htm. This will give you a machine type and a machine model you can use to determine what type of CPU you have.
If you have problems with signals (MySQL dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell MySQL not to use signals by configuring with:
shell> CFLAGS=-DDONT_USE_THR_ALARM CXX=gcc \ CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti \ -DDONT_USE_THR_ALARM" \ ./configure --prefix=/usr/local/mysql --with-debug \ --with-low-memory
This doesn't affect the performance of MySQL, but has the side effect that you can't kill clients that are ``sleeping'' on a connection with mysqladmin kill or mysqladmin shutdown. Instead, the client will die when it issues its next command.
On some versions of AIX, linking with libbind.a makes getservbyname core dump. This is an AIX bug and should be reported to IBM.
For AIX 4.2.1 and gcc, you have to make the following changes.
After configuring, edit config.h and include/my_config.h and change the line that says this:
#define HAVE_SNPRINTF 1
to this:
#undef HAVE_SNPRINTF
And finally, in mysqld.cc you need to add a prototype for initgoups.
#ifdef _AIX41 extern "C" int initgroups(const char *,int); #endif
If you need to allocate a lot of memory to the mysqld process, it's not enough to just use ulimit -d unlimited. You may also have to modify mysqld_safe to add a line something like this:
export LDR_CNTRL='MAXDATA=0x80000000'
You can find more about using a lot of memory at: http://publib16.boulder.ibm.com/pseries/en_US/aixprggd/genprogc/lrg_prg_support.htm.
On SunOS 4, MIT-pthreads is needed to compile MySQL. This in turn means you will need GNU make.
Some SunOS 4 systems have problems with dynamic libraries and libtool. You can use the following configure line to avoid this problem:
shell> ./configure --disable-shared --with-mysqld-ldflags=-all-static
When compiling readline, you may get warnings about duplicate defines. These may be ignored.
When compiling mysqld, there will be some implicit declaration of function warnings. These may be ignored.
If you are using egcs 1.1.2 on Digital Unix, you should upgrade to gcc 2.95.2, because egcs on DEC has some serious bugs!
When compiling threaded programs under Digital Unix, the documentation recommends using the -pthread option for cc and cxx and the -lmach -lexc libraries (in addition to -lpthread). You should run configure something like this:
CC="cc -pthread" CXX="cxx -pthread -O" \ ./configure --with-named-thread-libs="-lpthread -lmach -lexc -lc"
When compiling mysqld, you may see a couple of warnings like this:
mysqld.cc: In function void handle_connections()': mysqld.cc:626: passing long unsigned int *' as argument 3 of accept(int,sockadddr *, int *)'
You can safely ignore these warnings. They occur because configure can detect only errors, not warnings.
If you start the server directly from the command-line, you may have problems with it dying when you log out. (When you log out, your outstanding processes receive a SIGHUP signal.) If so, try starting the server like this:
shell> nohup mysqld [options] &
nohup causes the command following it to ignore any SIGHUP signal sent from the terminal. Alternatively, start the server by running mysqld_safe, which invokes mysqld using nohup for you. See mysqld_safe.
If you get a problem when compiling mysys/get_opt.c, just remove the #define _NO_PROTO line from the start of that file!
If you are using Compaq's CC compiler, the following configure line should work:
CC="cc -pthread" CFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed all -arch host" CXX="cxx -pthread" CXXFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed all \ -arch host -noexceptions -nortti" export CC CFLAGS CXX CXXFLAGS ./configure \ --prefix=/usr/local/mysql \ --with-low-memory \ --enable-large-files \ --enable-shared=yes \ --with-named-thread-libs="-lpthread -lmach -lexc -lc" gnumake
If you get a problem with libtool, when compiling with shared libraries as above, when linking mysql, you should be able to get around this by issuing:
cd mysql /bin/sh ../libtool --mode=link cxx -pthread -O3 -DDBUG_OFF \ -O4 -ansi_alias -ansi_args -fast -inline speed \ -speculate all \ -arch host -DUNDEF_HAVE_GETHOSTBYNAME_R \ -o mysql mysql.o readline.o sql_string.o completion_hash.o \ ../readline/libreadline.a -lcurses \ ../libmysql/.libs/libmysqlclient.so -lm cd .. gnumake gnumake install scripts/mysql_install_db
If you have problems compiling and have DEC CC and gcc installed, try running configure like this:
CC=cc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql
If you get problems with the c_asm.h file, you can create and use a 'dummy' c_asm.h file with:
touch include/c_asm.h CC=gcc CFLAGS=-I./include \ CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql
Note that the following problems with the ld program can be fixed by downloading the latest DEC (Compaq) patch kit from: http://ftp.support.compaq.com/public/unix/.
On OSF/1 V4.0D and compiler "DEC C V5.6-071 on Digital Unix V4.0 (Rev. 878)" the compiler had some strange behavior (undefined asm symbols). /bin/ld also appears to be broken (problems with _exit undefined errors occurring while linking mysqld). On this system, we have managed to compile MySQL with the following configure line, after replacing /bin/ld with the version from OSF 4.0C:
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
With the Digital compiler "C++ V6.1-029", the following should work:
CC=cc -pthread CFLAGS=-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all \ -arch host CXX=cxx -pthread CXXFLAGS=-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all \ -arch host -noexceptions -nortti export CC CFLAGS CXX CXXFLAGS ./configure --prefix=/usr/mysql/mysql --with-mysqld-ldflags=-all-static \ --disable-shared --with-named-thread-libs="-lmach -lexc -lc"
In some versions of OSF/1, the alloca() function is broken. Fix this by removing the line in config.h that defines 'HAVE_ALLOCA'.
The alloca() function also may have an incorrect prototype in /usr/include/alloca.h. This warning resulting from this can be ignored.
configure will use the following thread libraries automatically: --with-named-thread-libs="-lpthread -lmach -lexc -lc".
When using gcc, you can also try running configure like this:
shell> CFLAGS=-D_PTHREAD_USE_D4 CXX=gcc CXXFLAGS=-O3 ./configure ...
If you have problems with signals (MySQL dies unexpectedly under high load), you may have found an OS bug with threads and signals. In this case you can tell MySQL not to use signals by configuring with:
shell> CFLAGS=-DDONT_USE_THR_ALARM \ CXXFLAGS=-DDONT_USE_THR_ALARM \ ./configure ...
This doesn't affect the performance of MySQL, but has the side effect that you can't kill clients that are ``sleeping'' on a connection with mysqladmin kill or mysqladmin shutdown. Instead, the client will die when it issues its next command.
With gcc 2.95.2, you will probably run into the following compile error:
sql_acl.cc:1456: Internal compiler error in `scan_region', at except.c:2566 Please submit a full bug report.
To fix this you should change to the sql directory and do a ``cut and paste'' of the last gcc line, but change -O3 to -O0 (or add -O0 immediately after gcc if you don't have any -O option on your compile line). After this is done you can just change back to the top-level directly and run make again.
If you are using Irix Version 6.5.3 or newer mysqld will be able to create threads only if you run it as a user with CAP_SCHED_MGT privileges (like root) or give the mysqld server this privilege with the following shell command:
shell> chcap "CAP_SCHED_MGT+epi" /opt/mysql/libexec/mysqld
You may have to undefine some symbols in config.h after running configure and before compiling.
In some Irix implementations, the alloca() function is broken. If the mysqld server dies on some SELECT statements, remove the lines from config.h that define HAVE_ALLOC and HAVE_ALLOCA_H. If mysqladmin create doesn't work, remove the line from config.h that defines HAVE_READDIR_R. You may have to remove the HAVE_TERM_H line as well.
SGI recommends that you install all of the patches on this page as a set: http://support.sgi.com/surfzone/patches/patchset/6.2_indigo.rps.html
At the very minimum, you should install the latest kernel rollup, the latest rld rollup, and the latest libc rollup.
You definitely need all the POSIX patches on this page, for pthreads support:
http://support.sgi.com/surfzone/patches/patchset/6.2_posix.rps.html
If you get the something like the following error when compiling mysql.cc:
"/usr/include/curses.h", line 82: error(1084): invalid combination of type
Type the following in the top-level directory of your MySQL source tree:
shell> extra/replace bool curses_bool < /usr/include/curses.h \ > include/curses.h shell> make
There have also been reports of scheduling problems. If only one thread is running, performance is slow. Avoid this by starting another client. This may lead to a 2-to-10-fold increase in execution speed thereafter for the other thread. This is a poorly understood problem with Irix threads; you may have to improvise to find solutions until this can be fixed.
If you are compiling with gcc, you can use the following configure command:
CC=gcc CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql --enable-thread-safe-client \ --with-named-thread-libs=-lpthread
On Irix 6.5.11 with native Irix C and C++ compilers ver. 7.3.1.2, the following is reported to work
CC=cc CXX=CC CFLAGS='-O3 -n32 -TARG:platform=IP22 -I/usr/local/include \ -L/usr/local/lib' CXXFLAGS='-O3 -n32 -TARG:platform=IP22 \ -I/usr/local/include -L/usr/local/lib' \ ./configure --prefix=/usr/local/mysql --with-innodb --with-berkeley-db \ --with-libwrap=/usr/local \ --with-named-curses-libs=/usr/local/lib/libncurses.a
The current port is tested only on ``sco3.2v5.0.5'', ``sco3.2v5.0.6'' and ``sco3.2v5.0.7'' systems. There has also been a lot of progress on a port to ``sco 3.2v4.2''.
For the moment the recommended compiler on OpenServer is gcc 2.95.2. With this you should be able to compile MySQL with just:
CC=gcc CXX=gcc ./configure ... (options)
For OpenServer 5.0.x you need to use gcc-2.95.2p1 or newer from the Skunkware. http://www.sco.com/skunkware/ and choose browser OpenServer packages or by ftp to ftp2.caldera.com in the pub/skunkware/osr5/devtools/gcc directory.
You need the port of GCC 2.5.x for this product and the Development system. They are required on this version of SCO Unix. You cannot just use the GCC Dev system.
You should get the FSU Pthreads package and install it first. This can be found at http://moss.csc.ncsu.edu/~mueller/ftp/pub/PART/pthreads.tar.gz. You can also get a precompiled package from http://www.mysql.com/Downloads/SCO/FSU-threads-3.5c.tar.gz.
FSU Pthreads can be compiled with SCO Unix 4.2 with tcpip. Or OpenServer 3.0 or Open Desktop 3.0 (OS 3.0 ODT 3.0), with the SCO Development System installed using a good port of GCC 2.5.x ODT or OS 3.0 you will need a good port of GCC 2.5.x There are a lot of problems without a good port. The port for this product requires the SCO Unix Development system. Without it, you are missing the libraries and the linker that is needed.
To build FSU Pthreads on your system, do the following:
Run ./configure in the threads/src directory and select the SCO OpenServer option. This command copies Makefile.SCO5 to Makefile.
Run make.
To install in the default /usr/include directory, login as root, then cd to the thread/src directory, and run make install.
Remember to use GNU make when making MySQL.
If you don't start mysqld_safe as root, you probably will get only the default 110 open files per process. mysqld will write a note about this in the log file.
With SCO 3.2V5.0.5, you should use FSU Pthreads version 3.5c or newer. You should also use gcc 2.95.2 or newer!
The following configure command should work:
shell> ./configure --prefix=/usr/local/mysql --disable-shared
With SCO 3.2V4.2, you should use FSU Pthreads version 3.5c or newer. The following configure command should work:
shell> CFLAGS="-D_XOPEN_XPG4" CXX=gcc CXXFLAGS="-D_XOPEN_XPG4" \ ./configure \ --prefix=/usr/local/mysql \ --with-named-thread-libs="-lgthreads -lsocket -lgen -lgthreads" \ --with-named-curses-libs="-lcurses"
You may get some problems with some include files. In this case, you can find new SCO-specific include files at http://www.mysql.com/Downloads/SCO/SCO-3.2v4.2-includes.tar.gz. You should unpack this file in the include directory of your MySQL source tree.
SCO development notes:
MySQL should automatically detect FSU Pthreads and link mysqld with -lgthreads -lsocket -lgthreads.
The SCO development libraries are re-entrant in FSU Pthreads. SCO claims that its libraries' functions are re-entrant, so they must be re-entrant with FSU Pthreads. FSU Pthreads on OpenServer tries to use the SCO scheme to make re-entrant libraries.
FSU Pthreads (at least the version at http://www.mysql.com/) comes linked with GNU malloc. If you encounter problems with memory usage, make sure that gmalloc.o is included in libgthreads.a and libgthreads.so.
In FSU Pthreads, the following system calls are pthreads-aware: read(), write(), getmsg(), connect(), accept(), select(), and wait().
The CSSA-2001-SCO.35.2 (the patch is listed in custom as erg711905-dscr_remap security patch (version 2.0.0) breaks FSU threads and makes mysqld unstable. You have to remove this one if you want to run mysqld on an OpenServer 5.0.6 machine.
SCO provides Operating Systems Patches at ftp://ftp.sco.com/pub/openserver5 for OpenServer 5.0.x
SCO provides security fixes and libsocket.so.2 at ftp://ftp.sco.com/pub/security/OpenServer and ftp://ftp.sco.com/pub/security/sse for OpenServer 5.0.x
pre-OSR506 security fixes. Also, the telnetd fix at ftp://stage.caldera.com/pub/security/openserver/ or ftp://stage.caldera.com/pub/security/openserver/CSSA-2001-SCO.10/ as both libsocket.so.2 and libresolv.so.1 with instructions for installing on pre-OSR506 systems.
It's probably a good idea to install the above patches before trying to compile/use MySQL.
On UnixWare 7.1.0, you must use a version of MySQL at least as recent as 3.22.13 to get fixes for some portability and OS problems.
We have been able to compile MySQL with the following configure command on UnixWare Version 7.1.x:
CC=cc CXX=CC ./configure --prefix=/usr/local/mysql
If you want to use gcc, you must use gcc 2.95.2 or newer.
CC=gcc CXX=g++ ./configure --prefix=/usr/local/mysql
SCO provides Operating Systems Patches at ftp://ftp.sco.com/pub/unixware7 for UnixWare 7.1.1 and 7.1.3 and at ftp://ftp.sco.com/pub/openunix8 for OpenUNIX 8.0.0.
SCO provides information about Security Fixes at ftp://ftp.sco.com/pub/security/OpenUNIX for OpenUNIX and at ftp://ftp.sco.com/pub/security/UnixWare for UnixWare.
MySQL uses quite a few open files. Because of this, you should add something like the following to your CONFIG.SYS file:
SET EMXOPT=-c -n -h1024
If you don't do this, you will probably run into the following error:
File 'xxxx' not found (Errcode: 24)
When using MySQL with OS/2 Warp 3, FixPack 29 or above is required. With OS/2 Warp 4, FixPack 4 or above is required. This is a requirement of the Pthreads library. MySQL must be installed on a partition with a type that supports long filenames, such as HPFS, FAT32, etc.
The INSTALL.CMD script must be run from OS/2's own CMD.EXE and may not work with replacement shells such as 4OS2.EXE.
The scripts/mysql-install-db script has been renamed. It is now called install.cmd and is a REXX script, which will set up the default MySQL security settings and create the WorkPlace Shell icons for MySQL.
Dynamic module support is compiled in but not fully tested. Dynamic modules should be compiled using the Pthreads run-time library.
gcc -Zdll -Zmt -Zcrtdll=pthrdrtl -I../include -I../regex -I.. \ -o example udf_example.cc -L../lib -lmysqlclient udf_example.def mv example.dll example.udf
Note: Due to limitations in OS/2, UDF module name stems must not exceed 8 characters. Modules are stored in the /mysql2/udf directory; the safe-mysqld.cmd script will put this directory in the BEGINLIBPATH environment variable. When using UDF modules, specified extensions are ignored---it is assumed to be .udf. For example, in Unix, the shared module might be named example.so and you would load a function from it like this:
mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "example.so";
In OS/2, the module would be named example.udf, but you would not specify the module extension:
mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "example";
Table of Contents
Perl support for MySQL is provided by means of the DBI/DBD client interface. The interface requires Perl Version 5.6.0 or later. It will not work if you have an older version of Perl.
If you want to use transactions with Perl DBI, you need to have DBD::mysql version 1.2216 or newer. Version 2.9003 or newer is recommended.
As of Version 3.22.8, Perl support is no longer included with MySQL distributions. You can obtain the necessary modules from http://search.cpan.org for Unix, or using the ActiveState ppm program on Windows. The following sections describe how to do this.
Perl support for MySQL must be installed if you want to run the MySQL benchmark scripts. See MySQL Benchmarks.
MySQL Perl support requires that you've installed MySQL client programming support (libraries and header files). Most installation methods install the necesssary files. However, if you installed MySQL from RPM files on Linux, be sure that you've installed the developer RPM. The client programs are in the client RPM, but client programming support is in the developer RPM.
If you want to install Perl support, the files you will need can be obtained from the CPAN (Comprehensive Perl Archive Network) at http://search.cpan.org.
The easiest way to install Perl modules on Unix is to use the CPAN module. For example:
shell> perl -MCPAN -e shell cpan> install DBI cpan> install DBD::mysql
The DBD::mysql installation runs a number of tests. These tests require being able to connect to the local MySQL server as the anonymous user with no password. If you have removed anonymous accounts or assigned them passwords, the tests fail. You can use force install DBD::mysql to ignore the failed tests.
DBI requires the Data::Dumper module. It may already be installed; if not, you should install it before installing DBI.
It is also possible to download the module distributions in the form of compressed tar archives and build the modules manually. For example, to unpack and build a DBI distribution, use a procedure such as this:
Unpack the distribution into the current directory:
shell> gunzip < DBI-VERSION.tar.gz | tar xvf -
This command creates a directory named DBI-VERSION.
Change into the top-level directory of the unpacked distribution:
shell> cd DBI-VERSION
Build the distribution and compile everything:
shell> perl Makefile.PL shell> make shell> make test shell> make install
The make test command is important because it verifies that the module is working. Note that when you run that command during the DBD::mysql installation to exercise the interface code, the MySQL server must be running or the test will fail.
It is a good idea to rebuild and reinstall the DBD::mysql distribution whenever you install a new release of MySQL, particularly if you notice symptoms such as that all your DBI scripts fail after you upgrade MySQL.
If you don't have access rights to install Perl modules in the system directory or if you want to install local Perl modules, the following reference may be useful:
http://servers.digitaldaze.com/extensions/perl/modules.html#modules
Look under the heading Installing New Modules that Require Locally Installed Modules.
On Windows, you should do the following to install the MySQL DBD module with ActiveState Perl:
Get ActiveState Perl from http://www.activestate.com/Products/ActivePerl/ and install it.
Open a console window (a ``DOS window'').
If required, set the HTTP_proxy variable. For example, you might try:
set HTTP_proxy=my.proxy.com:3128
Start the PPM program:
C:\> c:\perl\bin\ppm.pl
If you have not already done so, install DBI:
ppm> install DBI
If this succeeds, run the following command:
install \ ftp://ftp.de.uu.net/pub/CPAN/authors/id/JWIED/DBD-mysql-1.2212.x86.ppd
The above should work at least with ActiveState Perl Version 5.6.
If you can't get the above to work, you should instead install the MyODBC driver and connect to the MySQL server through ODBC:
use DBI; $dbh= DBI->connect("DBI:ODBC:$dsn",$user,$password) || die "Got error $DBI::errstr when connecting to $dsn\n";
If Perl reports that it can't find the ../mysql/mysql.so module, then the problem is probably that Perl can't locate the shared library libmysqlclient.so.
You should be able to fix this by one of the following methods:
Compile the DBD::mysql distribution with perl Makefile.PL -static -config rather than perl Makefile.PL.
Copy libmysqlclient.so to the directory where your other shared libraries are located (probably /usr/lib or /lib).
Modify the -L options used to compile DBD::mysql to reflect the actual location of libmysqlclient.so.
On Linux you can add the pathname of the directory where libmysqlclient.so is located to the /etc/ld.so.conf file.
Add the pathname of the directory where libmysqlclient.so is located to the LD_RUN_PATH environment variable. Some systems use LD_LIBRARY_PATH instead.
Note that you may also need to modify the -L options if there are other libraries that the linker fails to find. For example, if the linker cannot find libc because it is in /lib and the link command specifies -L/usr/lib, change the -L option to -L/lib or add -L/lib to the existing link command.
If you get the following errors from DBD::mysql, you are probably using gcc (or using an old binary compiled with gcc):
/usr/bin/perl: can't resolve symbol '__moddi3' /usr/bin/perl: can't resolve symbol '__divdi3'
Add -L/usr/lib/gcc-lib/... -lgcc to the link command when the mysql.so library gets built (check the output from make for mysql.so when you compile the Perl client). The -L option should specify the pathname of the directory where libgcc.a is located on your system.
Another cause of this problem may be that Perl and MySQL aren't both compiled with gcc. In this case, you can solve the mismatch by compiling both with gcc.
You may see the following error from DBD::mysql when you run the tests:
t/00base............install_driver(mysql) failed: Can't load '../blib/arch/auto/DBD/mysql/mysql.so' for module DBD::mysql: ../blib/arch/auto/DBD/mysql/mysql.so: undefined symbol: uncompress at /usr/lib/perl5/5.00503/i586-linux/DynaLoader.pm line 169.
This means that you need to include the -lz compression library on the link line. That can be done by changing the following line in the file lib/DBD/mysql/Install.pm:
$sysliblist .= " -lm";
Change that line to:
$sysliblist .= " -lm -lz";
After this, you must run make realclean and then proceed with the installation from the beginning.
If you want to install DBI on SCO, you have to edit the Makefile in DBI-xxx and each subdirectory.
Note that the following assumes gcc 2.95.2 or newer:
OLD: NEW: CC = cc CC = gcc CCCDLFLAGS = -KPIC -W1,-Bexport CCCDLFLAGS = -fpic CCDLFLAGS = -wl,-Bexport CCDLFLAGS = LD = ld LD = gcc -G -fpic LDDLFLAGS = -G -L/usr/local/lib LDDLFLAGS = -L/usr/local/lib LDFLAGS = -belf -L/usr/local/lib LDFLAGS = -L/usr/local/lib LD = ld LD = gcc -G -fpic OPTIMISE = -Od OPTIMISE = -O1 OLD: CCCFLAGS = -belf -dy -w0 -U M_XENIX -DPERL_SCO5 -I/usr/local/include NEW: CCFLAGS = -U M_XENIX -DPERL_SCO5 -I/usr/local/include
This is because the Perl dynaloader will not load the DBI modules if they were compiled with icc or cc.
If you want to use the Perl module on a system that doesn't support dynamic linking (like SCO) you can generate a static version of Perl that includes DBI and DBD::mysql. The way this works is that you generate a version of Perl with the DBI code linked in and install it on top of your current Perl. Then you use that to build a version of Perl that additionally has the DBD code linked in, and install that.
On SCO, you must have the following environment variables set:
shell> LD_LIBRARY_PATH=/lib:/usr/lib:/usr/local/lib:/usr/progressive/lib or: shell> LD_LIBRARY_PATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:\ /usr/progressive/lib:/usr/skunk/lib shell> LIBPATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:\ /usr/progressive/lib:/usr/skunk/lib shell> MANPATH=scohelp:/usr/man:/usr/local1/man:/usr/local/man:\ /usr/skunk/man:
First, create a Perl that includes a statically linked DBI module by running these commands in the directory where your DBI distribution is located:
shell> perl Makefile.PL -static -config shell> make shell> make install shell> make perl
Then you must install the new Perl. The output of make perl will indicate the exact make command you will need to execute to perform the installation. On SCO, this is make -f Makefile.aperl inst_perl MAP_TARGET=perl.
Next, use the just-created Perl to create another Perl that also includes a statically linked DBD::mysql by running these commands in the directory where your DBD::mysql distribution is located:
shell> perl Makefile.PL -static -config shell> make shell> make install shell> make perl
Finally, you should install this new Perl. Again, the output of make perl indicates the command to use.
Table of Contents
This chapter provides a tutorial introduction to MySQL by showing how to use the mysql client program to create and use a simple database. mysql (sometimes referred to as the ``terminal monitor'' or just ``monitor'') is an interactive program that allows you to connect to a MySQL server, run queries, and view the results. mysql may also be used in batch mode: you place your queries in a file beforehand, then tell mysql to execute the contents of the file. Both ways of using mysql are covered here.
To see a list of options provided by mysql, invoke it with the --help option:
shell> mysql --help
This chapter assumes that mysql is installed on your machine and that a MySQL server is available to which you can connect. If this is not true, contact your MySQL administrator. (If you are the administrator, you will need to consult other sections of this manual.)
This chapter describes the entire process of setting up and using a database. If you are interested only in accessing an already-existing database, you may want to skip over the sections that describe how to create the database and the tables it contains.
Because this chapter is tutorial in nature, many details are necessarily omitted. Consult the relevant sections of the manual for more information on the topics covered here.
To connect to the server, you'll usually need to provide a MySQL username when you invoke mysql and, most likely, a password. If the server runs on a machine other than the one where you log in, you'll also need to specify a hostname. Contact your administrator to find out what connection parameters you should use to connect (that is, what host, username, and password to use). Once you know the proper parameters, you should be able to connect like this:
shell> mysql -h host -u user -p Enter password: ********
host and user represent the hostname where your MySQL server is running and the username of your MySQL account. Substitute appropriate values for your setup. The ******** represents your password; enter it when mysql displays the Enter password: prompt.
If that works, you should see some introductory information followed by a mysql> prompt:
shell> mysql -h host -u user -p Enter password: ******** Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 25338 to server version: 4.0.14-log Type 'help;' or '\h' for help. Type '\c' to clear the buffer. mysql>
The prompt tells you that mysql is ready for you to enter commands.
Some MySQL installations allow users to connect as the anonymous (unnamed) user to the server running on the local host. If this is the case on your machine, you should be able to connect to that server by invoking mysql without any options:
shell> mysql
After you have connected successfully, you can disconnect any time by typing QUIT (or \q) at the mysql> prompt:
mysql> QUIT Bye
On Unix, you can also disconnect by pressing Control-D.
Most examples in the following sections assume you are connected to the server. They indicate this by the mysql> prompt.
Make sure you are connected to the server, as discussed in the previous section. Doing so will not in itself select any database to work with, but that's okay. At this point, it's more important to find out a little about how to issue queries than to jump right in creating tables, loading data into them, and retrieving data from them. This section describes the basic principles of entering commands, using several queries you can try out to familiarise yourself with how mysql works.
Here's a simple command that asks the server to tell you its version number and the current date. Type it in as shown here following the mysql> prompt and press Enter:
mysql> SELECT VERSION(), CURRENT_DATE; +--------------+--------------+ | VERSION() | CURRENT_DATE | +--------------+--------------+ | 3.22.20a-log | 1999-03-19 | +--------------+--------------+ 1 row in set (0.01 sec) mysql>
This query illustrates several things about mysql:
A command normally consists of an SQL statement followed by a semicolon. (There are some exceptions where a semicolon may be omitted. QUIT, mentioned earlier, is one of them. We'll get to others later.)
When you issue a command, mysql sends it to the server for execution and displays the results, then prints another mysql> prompt to indicate that it is ready for another command.
mysql displays query output in tabular form (rows and columns). The first row contains labels for the columns. The rows following are the query results. Normally, column labels are the names of the columns you fetch from database tables. If you're retrieving the value of an expression rather than a table column (as in the example just shown), mysql labels the column using the expression itself.
mysql shows how many rows were returned and how long the query took to execute, which gives you a rough idea of server performance. These values are imprecise because they represent wall clock time (not CPU or machine time), and because they are affected by factors such as server load and network latency. (For brevity, the ``rows in set'' line is not shown in the remaining examples in this chapter.)
Keywords may be entered in any lettercase. The following queries are equivalent:
mysql> SELECT VERSION(), CURRENT_DATE; mysql> select version(), current_date; mysql> SeLeCt vErSiOn(), current_DATE;
Here's another query. It demonstrates that you can use mysql as a simple calculator:
mysql> SELECT SIN(PI()/4), (4+1)*5; +-------------+---------+ | SIN(PI()/4) | (4+1)*5 | +-------------+---------+ | 0.707107 | 25 | +-------------+---------+
The queries shown thus far have been relatively short, single-line statements. You can even enter multiple statements on a single line. Just end each one with a semicolon:
mysql> SELECT VERSION(); SELECT NOW(); +--------------+ | VERSION() | +--------------+ | 3.22.20a-log | +--------------+ +---------------------+ | NOW() | +---------------------+ | 1999-03-19 00:15:33 | +---------------------+
A command need not be given all on a single line, so lengthy commands that require several lines are not a problem. mysql determines where your statement ends by looking for the terminating semicolon, not by looking for the end of the input line. (In other words, mysql accepts free-format input: it collects input lines but does not execute them until it sees the semicolon.)
Here's a simple multiple-line statement:
mysql> SELECT -> USER() -> , -> CURRENT_DATE; +--------------------+--------------+ | USER() | CURRENT_DATE | +--------------------+--------------+ | joesmith@localhost | 1999-03-18 | +--------------------+--------------+
In this example, notice how the prompt changes from mysql> to -> after you enter the first line of a multiple-line query. This is how mysql indicates that it hasn't seen a complete statement and is waiting for the rest. The prompt is your friend, because it provides valuable feedback. If you use that feedback, you will always be aware of what mysql is waiting for.
If you decide you don't want to execute a command that you are in the process of entering, cancel it by typing \c:
mysql> SELECT -> USER() -> \c mysql>
Here, too, notice the prompt. It switches back to mysql> after you type \c, providing feedback to indicate that mysql is ready for a new command.
The following table shows each of the prompts you may see and summarizes what they mean about the state that mysql is in:
Prompt | Meaning |
mysql> | Ready for new command. |
-> | Waiting for next line of multiple-line command. |
'> | Waiting for next line, collecting a string that begins with a single quote ('). |
"> | Waiting for next line, collecting a string that begins with a double quote ("). |
`> | Waiting for next line, collecting an identifier that begins with a backtick (`). |
Multiple-line statements commonly occur by accident when you intend to issue a command on a single line, but forget the terminating semicolon. In this case, mysql waits for more input:
mysql> SELECT USER() ->
If this happens to you (you think you've entered a statement but the only response is a -> prompt), most likely mysql is waiting for the semicolon. If you don't notice what the prompt is telling you, you might sit there for a while before realising what you need to do. Enter a semicolon to complete the statement, and mysql will execute it:
mysql> SELECT USER() -> ; +--------------------+ | USER() | +--------------------+ | joesmith@localhost | +--------------------+
The '> and "> prompts occur during string collection. In MySQL, you can write strings surrounded by either ' or " characters (for example, 'hello' or "goodbye"), and mysql lets you enter strings that span multiple lines. When you see a '> or "> prompt, it means that you've entered a line containing a string that begins with a ' or " quote character, but have not yet entered the matching quote that terminates the string. That's fine if you really are entering a multiple-line string, but how likely is that? Not very. More often, the '> and "> prompts indicate that you've inadvertantly left out a quote character. For example:
mysql> SELECT * FROM my_table WHERE name = "Smith AND age < 30; ">
If you enter this SELECT statement, then press Enter and wait for the result, nothing will happen. Instead of wondering why this query takes so long, notice the clue provided by the "> prompt. It tells you that mysql expects to see the rest of an unterminated string. (Do you see the error in the statement? The string "Smith is missing the second quote.)
At this point, what do you do? The simplest thing is to cancel the command. However, you cannot just type \c in this case, because mysql interprets it as part of the string that it is collecting! Instead, enter the closing quote character (so mysql knows you've finished the string), then type \c:
mysql> SELECT * FROM my_table WHERE name = "Smith AND age < 30; "> "\c mysql>
The prompt changes back to mysql>, indicating that mysql is ready for a new command.
The `> prompt is similar to th '> and "> prompts, but indicates that you have begun but not completed a backtick-quoted identifier.
It's important to know what the '>, ">, and `> prompts signify, because if you mistakenly enter an unterminated string, any further lines you type will appear to be ignored by mysql---including a line containing QUIT! This can be quite confusing, especially if you don't know that you need to supply the terminating quote before you can cancel the current command.
Table of Contents
Now that you know how to enter commands, it's time to access a database.
Suppose you have several pets in your home (your menagerie) and you'd like to keep track of various types of information about them. You can do so by creating tables to hold your data and loading them with the desired information. Then you can answer different sorts of questions about your animals by retrieving data from the tables. This section shows you how to:
Create a database
Create a table
Load data into the table
Retrieve data from the table in various ways
Use multiple tables
The menagerie database will be simple (deliberately), but it is not difficult to think of real-world situations in which a similar type of database might be used. For example, a database like this could be used by a farmer to keep track of livestock, or by a veterinarian to keep track of patient records. A menagerie distribution containing some of the queries and sample data used in the following sections can be obtained from the MySQL web site. It's available in either compressed tar format (http://www.mysql.com/Downloads/Contrib/Examples/menagerie.tar.gz) or Zip format (http://www.mysql.com/Downloads/Contrib/Examples/menagerie.zip).
Use the SHOW statement to find out what databases currently exist on the server:
mysql> SHOW DATABASES; +----------+ | Database | +----------+ | mysql | | test | | tmp | +----------+
The list of databases is probably different on your machine, but the mysql and test databases are likely to be among them. The mysql database is required because it describes user access privileges. The test database is often provided as a workspace for users to try things out.
Note that you may not see all databases if you don't have the SHOW DATABASES privilege. See GRANT.
If the test database exists, try to access it:
mysql> USE test Database changed
Note that USE, like QUIT, does not require a semicolon. (You can terminate such statements with a semicolon if you like; it does no harm.) The USE statement is special in another way, too: it must be given on a single line.
You can use the test database (if you have access to it) for the examples that follow, but anything you create in that database can be removed by anyone else with access to it. For this reason, you should probably ask your MySQL administrator for permission to use a database of your own. Suppose you want to call yours menagerie. The administrator needs to execute a command like this:
mysql> GRANT ALL ON menagerie.* TO 'your_mysql_name'@'your_client_host';
where your_mysql_name is the MySQL username assigned to you and your_client_host is the host from which you connect to the server.
If the administrator creates your database for you when setting up your permissions, you can begin using it. Otherwise, you need to create it yourself:
mysql> CREATE DATABASE menagerie;
Under Unix, database names are case-sensitive (unlike SQL keywords), so you must always refer to your database as menagerie, not as Menagerie, MENAGERIE, or some other variant. This is also true for table names. (Under Windows, this restriction does not apply, although you must refer to databases and tables using the same lettercase throughout a given query.)
Creating a database does not select it for use; you must do that explicitly. To make menagerie the current database, use this command:
mysql> USE menagerie Database changed
Your database needs to be created only once, but you must select it for use each time you begin a mysql session. You can do this by issuing a USE statement as shown in the example. Alternatively, you can select the database on the command-line when you invoke mysql. Just specify its name after any connection parameters that you might need to provide. For example:
shell> mysql -h host -u user -p menagerie Enter password: ********
Note that menagerie is not your password on the command just shown. If you want to supply your password on the command-line after the -p option, you must do so with no intervening space (for example, as -pmypassword, not as -p mypassword). However, putting your password on the command-line is not recommended, because doing so exposes it to snooping by other users logged in on your machine.
Creating the database is the easy part, but at this point it's empty, as SHOW TABLES will tell you:
mysql> SHOW TABLES; Empty set (0.00 sec)
The harder part is deciding what the structure of your database should be: what tables you will need and what columns will be in each of them.
You'll want a table that contains a record for each of your pets. This can be called the pet table, and it should contain, as a bare minimum, each animal's name. Because the name by itself is not very interesting, the table should contain other information. For example, if more than one person in your family keeps pets, you might want to list each animal's owner. You might also want to record some basic descriptive information such as species and sex.
How about age? That might be of interest, but it's not a good thing to store in a database. Age changes as time passes, which means you'd have to update your records often. Instead, it's better to store a fixed value such as date of birth. Then, whenever you need age, you can calculate it as the difference between the current date and the birth date. MySQL provides functions for doing date arithmetic, so this is not difficult. Storing birth date rather than age has other advantages, too:
You can use the database for tasks such as generating reminders for upcoming pet birthdays. (If you think this type of query is somewhat silly, note that it is the same question you might ask in the context of a business database to identify clients to whom you'll soon need to send out birthday greetings, for that computer-assisted personal touch.)
You can calculate age in relation to dates other than the current date. For example, if you store death date in the database, you can easily calculate how old a pet was when it died.
You can probably think of other types of information that would be useful in the pet table, but the ones identified so far are sufficient for now: name, owner, species, sex, birth, and death.
Use a CREATE TABLE statement to specify the layout of your table:
mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20), -> species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);
VARCHAR is a good choice for the name, owner, and species columns because the column values will vary in length. The lengths of those columns need not all be the same, and need not be 20. You can pick any length from 1 to 255, whatever seems most reasonable to you. (If you make a poor choice and it turns out later that you need a longer field, MySQL provides an ALTER TABLE statement.)
Several types of values can be chosen to represent sex in animal records, such as "m" and "f", or perhaps "male" and "female". It's simplest to use the single characters "m" and "f".
The use of the DATE datatype for the birth and death columns is a fairly obvious choice.
Now that you have created a table, SHOW TABLES should produce some output:
mysql> SHOW TABLES; +---------------------+ | Tables in menagerie | +---------------------+ | pet | +---------------------+
To verify that your table was created the way you expected, use a DESCRIBE statement:
mysql> DESCRIBE pet; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | | owner | varchar(20) | YES | | NULL | | | species | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | birth | date | YES | | NULL | | | death | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+
You can use DESCRIBE any time, for example, if you forget the names of the columns in your table or what types they have.
After creating your table, you need to populate it. The LOAD DATA and INSERT statements are useful for this.
Suppose your pet records can be described as shown here. (Observe that MySQL expects dates in 'YYYY-MM-DD' format; this may be different from what you are used to.)
name | owner | species | sex | birth | death |
Fluffy | Harold | cat | f | 1993-02-04 | |
Claws | Gwen | cat | m | 1994-03-17 | |
Buffy | Harold | dog | f | 1989-05-13 | |
Fang | Benny | dog | m | 1990-08-27 | |
Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 |
Chirpy | Gwen | bird | f | 1998-09-11 | |
Whistler | Gwen | bird | 1997-12-09 | ||
Slim | Benny | snake | m | 1996-04-29 |
Because you are beginning with an empty table, an easy way to populate it is to create a text file containing a row for each of your animals, then load the contents of the file into the table with a single statement.
You could create a text file pet.txt containing one record per line, with values separated by tabs, and given in the order in which the columns were listed in the CREATE TABLE statement. For missing values (such as unknown sexes or death dates for animals that are still living), you can use NULL values. To represent these in your text file, use \N (backslash, capital-N). For example, the record for Whistler the bird would look like this (where the whitespace between values is a single tab character):
name | owner | species | sex | birth | death |
Whistler | Gwen | bird | \N | 1997-12-09 | \N |
To load the text file pet.txt into the pet table, use this command:
mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;
Note that if you created the file on Windows with an editor that uses \r\n as a line terminator, you should use:
mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet -> LINES TERMINATED BY '\r\n';
You can specify the column value separator and end of line marker explicitly in the LOAD DATA statement if you wish, but the defaults are tab and linefeed. These are sufficient for the statement to read the file pet.txt properly.
If the statement fails, it is likely that your MySQL installation does not have local file capability enabled by default. See LOAD DATA LOCAL for information on how to change this.
When you want to add new records one at a time, the INSERT statement is useful. In its simplest form, you supply values for each column, in the order in which the columns were listed in the CREATE TABLE statement. Suppose Diane gets a new hamster named Puffball. You could add a new record using an INSERT statement like this:
mysql> INSERT INTO pet -> VALUES ('Puffball','Diane','hamster','f','1999-03-30',NULL);
Note that string and date values are specified as quoted strings here. Also, with INSERT, you can insert NULL directly to represent a missing value. You do not use \N like you do with LOAD DATA.
From this example, you should be able to see that there would be a lot more typing involved to load your records initially using several INSERT statements rather than a single LOAD DATA statement.
The SELECT statement is used to pull information from a table. The general form of the statement is:
SELECT what_to_select FROM which_table WHERE conditions_to_satisfy;
what_to_select indicates what you want to see. This can be a list of columns, or * to indicate ``all columns.'' which_table indicates the table from which you want to retrieve data. The WHERE clause is optional. If it's present, conditions_to_satisfy specifies conditions that rows must satisfy to qualify for retrieval.
The simplest form of SELECT retrieves everything from a table:
mysql> SELECT * FROM pet; +----------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+--------+---------+------+------------+------------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Fang | Benny | dog | m | 1990-08-27 | NULL | | Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 | | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+--------+---------+------+------------+------------+
This form of SELECT is useful if you want to review your entire table, for instance, after you've just loaded it with your initial dataset. For example, you may happen to think that the birth date for Bowser doesn't seem quite right. Consulting your original pedigree papers, you find that the correct birth year should be 1989, not 1979.
There are least a couple of ways to fix this:
Edit the file pet.txt to correct the error, then empty the table and reload it using DELETE and LOAD DATA:
mysql> DELETE FROM pet; mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;
However, if you do this, you must also re-enter the record for Puffball.
Fix only the erroneous record with an UPDATE statement:
mysql> UPDATE pet SET birth = "1989-08-31" WHERE name = "Bowser";
The UPDATE changes only the record in question and does not require you to reload the table.
As shown in the preceding section, it is easy to retrieve an entire table. Just omit the WHERE clause from the SELECT statement. But typically you don't want to see the entire table, particularly when it becomes large. Instead, you're usually more interested in answering a particular question, in which case you specify some constraints on the information you want. Let's look at some selection queries in terms of questions about your pets that they answer.
You can select only particular rows from your table. For example, if you want to verify the change that you made to Bowser's birth date, select Bowser's record like this:
mysql> SELECT * FROM pet WHERE name = "Bowser"; +--------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+-------+---------+------+------------+------------+ | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+-------+---------+------+------------+------------+
The output confirms that the year is correctly recorded now as 1989, not 1979.
String comparisons normally are case-insensitive, so you can specify the name as "bowser", "BOWSER", etc. The query result will be the same.
You can specify conditions on any column, not just name. For example, if you want to know which animals were born after 1998, test the birth column:
mysql> SELECT * FROM pet WHERE birth >= "1998-1-1"; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+-------+---------+------+------------+-------+
You can combine conditions, for example, to locate female dogs:
mysql> SELECT * FROM pet WHERE species = "dog" AND sex = "f"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
The preceding query uses the AND logical operator. There is also an OR operator:
mysql> SELECT * FROM pet WHERE species = "snake" OR species = "bird"; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | +----------+-------+---------+------+------------+-------+
AND and OR may be intermixed, though AND has higher precedence than OR. If you use both operators, it's a good idea to use parentheses to indicate explicitly how conditions should be grouped:
mysql> SELECT * FROM pet WHERE (species = "cat" AND sex = "m") -> OR (species = "dog" AND sex = "f"); +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
If you don't want to see entire rows from your table, just name the columns in which you're interested, separated by commas. For example, if you want to know when your animals were born, select the name and birth columns:
mysql> SELECT name, birth FROM pet; +----------+------------+ | name | birth | +----------+------------+ | Fluffy | 1993-02-04 | | Claws | 1994-03-17 | | Buffy | 1989-05-13 | | Fang | 1990-08-27 | | Bowser | 1989-08-31 | | Chirpy | 1998-09-11 | | Whistler | 1997-12-09 | | Slim | 1996-04-29 | | Puffball | 1999-03-30 | +----------+------------+
To find out who owns pets, use this query:
mysql> SELECT owner FROM pet; +--------+ | owner | +--------+ | Harold | | Gwen | | Harold | | Benny | | Diane | | Gwen | | Gwen | | Benny | | Diane | +--------+
However, notice that the query simply retrieves the owner field from each record, and some of them appear more than once. To minimise the output, retrieve each unique output record just once by adding the keyword DISTINCT:
mysql> SELECT DISTINCT owner FROM pet; +--------+ | owner | +--------+ | Benny | | Diane | | Gwen | | Harold | +--------+
You can use a WHERE clause to combine row selection with column selection. For example, to get birth dates for dogs and cats only, use this query:
mysql> SELECT name, species, birth FROM pet -> WHERE species = "dog" OR species = "cat"; +--------+---------+------------+ | name | species | birth | +--------+---------+------------+ | Fluffy | cat | 1993-02-04 | | Claws | cat | 1994-03-17 | | Buffy | dog | 1989-05-13 | | Fang | dog | 1990-08-27 | | Bowser | dog | 1989-08-31 | +--------+---------+------------+
You may have noticed in the preceding examples that the result rows are displayed in no particular order. It's often easier to examine query output when the rows are sorted in some meaningful way. To sort a result, use an ORDER BY clause.
Here are animal birthdays, sorted by date:
mysql> SELECT name, birth FROM pet ORDER BY birth; +----------+------------+ | name | birth | +----------+------------+ | Buffy | 1989-05-13 | | Bowser | 1989-08-31 | | Fang | 1990-08-27 | | Fluffy | 1993-02-04 | | Claws | 1994-03-17 | | Slim | 1996-04-29 | | Whistler | 1997-12-09 | | Chirpy | 1998-09-11 | | Puffball | 1999-03-30 | +----------+------------+
On character type columns, sorting---like all other comparison operations---is normally performed in a case-insensitive fashion. This means that the order will be undefined for columns that are identical except for their case. You can force a case-sensitive sort for a column by using the BINARY cast: ORDER BY BINARY col_name.
The default sort order is ascending, with smallest values first. To sort in reverse (descending) order, add the DESC keyword to the name of the column you are sorting by:
mysql> SELECT name, birth FROM pet ORDER BY birth DESC; +----------+------------+ | name | birth | +----------+------------+ | Puffball | 1999-03-30 | | Chirpy | 1998-09-11 | | Whistler | 1997-12-09 | | Slim | 1996-04-29 | | Claws | 1994-03-17 | | Fluffy | 1993-02-04 | | Fang | 1990-08-27 | | Bowser | 1989-08-31 | | Buffy | 1989-05-13 | +----------+------------+
You can sort on multiple columns, and you can sort columns in different directions. For example, to sort by type of animal in ascending order, then by birth date within animal type in descending order (youngest animals first), use the following query:
mysql> SELECT name, species, birth FROM pet ORDER BY species, birth DESC; +----------+---------+------------+ | name | species | birth | +----------+---------+------------+ | Chirpy | bird | 1998-09-11 | | Whistler | bird | 1997-12-09 | | Claws | cat | 1994-03-17 | | Fluffy | cat | 1993-02-04 | | Fang | dog | 1990-08-27 | | Bowser | dog | 1989-08-31 | | Buffy | dog | 1989-05-13 | | Puffball | hamster | 1999-03-30 | | Slim | snake | 1996-04-29 | +----------+---------+------------+
Note that the DESC keyword applies only to the column name immediately preceding it (birth); it does not affect the species column sort order.
MySQL provides several functions that you can use to perform calculations on dates, for example, to calculate ages or extract parts of dates.
To determine how many years old each of your pets is, compute the difference in the year part of the current date and the birth date, then subtract one if the current date occurs earlier in the calendar year than the birth date. The following query shows, for each pet, the birth date, the current date, and the age in years.
mysql> SELECT name, birth, CURDATE(), -> (YEAR(CURDATE())-YEAR(birth)) -> - (RIGHT(CURDATE(),5)<RIGHT(birth,5)) -> AS age -> FROM pet; +----------+------------+------------+------+ | name | birth | CURDATE() | age | +----------+------------+------------+------+ | Fluffy | 1993-02-04 | 2003-08-19 | 10 | | Claws | 1994-03-17 | 2003-08-19 | 9 | | Buffy | 1989-05-13 | 2003-08-19 | 14 | | Fang | 1990-08-27 | 2003-08-19 | 12 | | Bowser | 1989-08-31 | 2003-08-19 | 13 | | Chirpy | 1998-09-11 | 2003-08-19 | 4 | | Whistler | 1997-12-09 | 2003-08-19 | 5 | | Slim | 1996-04-29 | 2003-08-19 | 7 | | Puffball | 1999-03-30 | 2003-08-19 | 4 | +----------+------------+------------+------+
Here, YEAR() pulls out the year part of a date and RIGHT() pulls off the rightmost five characters that represent the MM-DD (calendar year) part of the date. The part of the expression that compares the MM-DD values evaluates to 1 or 0, which adjusts the year difference down a year if CURDATE() occurs earlier in the year than birth. The full expression is somewhat ungainly, so an alias (age) is used to make the output column label more meaningful.
The query works, but the result could be scanned more easily if the rows were presented in some order. This can be done by adding an ORDER BY name clause to sort the output by name:
mysql> SELECT name, birth, CURDATE(), -> (YEAR(CURDATE())-YEAR(birth)) -> - (RIGHT(CURDATE(),5)<RIGHT(birth,5)) -> AS age -> FROM pet ORDER BY name; +----------+------------+------------+------+ | name | birth | CURDATE() | age | +----------+------------+------------+------+ | Bowser | 1989-08-31 | 2003-08-19 | 13 | | Buffy | 1989-05-13 | 2003-08-19 | 14 | | Chirpy | 1998-09-11 | 2003-08-19 | 4 | | Claws | 1994-03-17 | 2003-08-19 | 9 | | Fang | 1990-08-27 | 2003-08-19 | 12 | | Fluffy | 1993-02-04 | 2003-08-19 | 10 | | Puffball | 1999-03-30 | 2003-08-19 | 4 | | Slim | 1996-04-29 | 2003-08-19 | 7 | | Whistler | 1997-12-09 | 2003-08-19 | 5 | +----------+------------+------------+------+
To sort the output by age rather than name, just use a different ORDER BY clause:
mysql> SELECT name, birth, CURDATE(), -> (YEAR(CURDATE())-YEAR(birth)) -> - (RIGHT(CURDATE(),5)<RIGHT(birth,5)) -> AS age -> FROM pet ORDER BY age; +----------+------------+------------+------+ | name | birth | CURDATE() | age | +----------+------------+------------+------+ | Chirpy | 1998-09-11 | 2003-08-19 | 4 | | Puffball | 1999-03-30 | 2003-08-19 | 4 | | Whistler | 1997-12-09 | 2003-08-19 | 5 | | Slim | 1996-04-29 | 2003-08-19 | 7 | | Claws | 1994-03-17 | 2003-08-19 | 9 | | Fluffy | 1993-02-04 | 2003-08-19 | 10 | | Fang | 1990-08-27 | 2003-08-19 | 12 | | Bowser | 1989-08-31 | 2003-08-19 | 13 | | Buffy | 1989-05-13 | 2003-08-19 | 14 | +----------+------------+------------+------+
A similar query can be used to determine age at death for animals that have died. You determine which animals these are by checking whether the death value is NULL. Then, for those with non-NULL values, compute the difference between the death and birth values:
mysql> SELECT name, birth, death, -> (YEAR(death)-YEAR(birth)) - (RIGHT(death,5)<RIGHT(birth,5)) -> AS age -> FROM pet WHERE death IS NOT NULL ORDER BY age; +--------+------------+------------+------+ | name | birth | death | age | +--------+------------+------------+------+ | Bowser | 1989-08-31 | 1995-07-29 | 5 | +--------+------------+------------+------+
The query uses death IS NOT NULL rather than death <> NULL because NULL is a special value that cannot be compared using the usual comparison operators. This is discussed later. See Working with NULL.
What if you want to know which animals have birthdays next month? For this type of calculation, year and day are irrelevant; you simply want to extract the month part of the birth column. MySQL provides several date-part extraction functions, such as YEAR(), MONTH(), and DAYOFMONTH(). MONTH() is the appropriate function here. To see how it works, run a simple query that displays the value of both birth and MONTH(birth):
mysql> SELECT name, birth, MONTH(birth) FROM pet; +----------+------------+--------------+ | name | birth | MONTH(birth) | +----------+------------+--------------+ | Fluffy | 1993-02-04 | 2 | | Claws | 1994-03-17 | 3 | | Buffy | 1989-05-13 | 5 | | Fang | 1990-08-27 | 8 | | Bowser | 1989-08-31 | 8 | | Chirpy | 1998-09-11 | 9 | | Whistler | 1997-12-09 | 12 | | Slim | 1996-04-29 | 4 | | Puffball | 1999-03-30 | 3 | +----------+------------+--------------+
Finding animals with birthdays in the upcoming month is easy, too. Suppose the current month is April. Then the month value is 4 and you look for animals born in May (month 5) like this:
mysql> SELECT name, birth FROM pet WHERE MONTH(birth) = 5; +-------+------------+ | name | birth | +-------+------------+ | Buffy | 1989-05-13 | +-------+------------+
There is a small complication if the current month is December. You don't just add one to the month number (12) and look for animals born in month 13, because there is no such month. Instead, you look for animals born in January (month 1).
You can even write the query so that it works no matter what the current month is. That way you don't have to use a particular month number in the query. DATE_ADD() allows you to add a time interval to a given date. If you add a month to the value of CURDATE(), then extract the month part with MONTH(), the result produces the month in which to look for birthdays:
mysql> SELECT name, birth FROM pet -> WHERE MONTH(birth) = MONTH(DATE_ADD(CURDATE(), INTERVAL 1 MONTH));
A different way to accomplish the same task is to add 1 to get the next month after the current one (after using the modulo function (MOD) to wrap around the month value to 0 if it is currently 12):
mysql> SELECT name, birth FROM pet -> WHERE MONTH(birth) = MOD(MONTH(CURDATE()), 12) + 1;
Note that MONTH returns a number between 1 and 12. And MOD(something,12) returns a number between 0 and 11. So the addition has to be after the MOD(), otherwise we would go from November (11) to January (1).
The NULL value can be surprising until you get used to it. Conceptually, NULL means missing value or unknown value and it is treated somewhat differently than other values. To test for NULL, you cannot use the arithmetic comparison operators such as =, <, or <>. To demonstrate this for yourself, try the following query:
mysql> SELECT 1 = NULL, 1 <> NULL, 1 < NULL, 1 > NULL; +----------+-----------+----------+----------+ | 1 = NULL | 1 <> NULL | 1 < NULL | 1 > NULL | +----------+-----------+----------+----------+ | NULL | NULL | NULL | NULL | +----------+-----------+----------+----------+
Clearly you get no meaningful results from these comparisons. Use the IS NULL and IS NOT NULL operators instead:
mysql> SELECT 1 IS NULL, 1 IS NOT NULL; +-----------+---------------+ | 1 IS NULL | 1 IS NOT NULL | +-----------+---------------+ | 0 | 1 | +-----------+---------------+
Note that in MySQL, 0 or NULL means false and anything else means true. The default truth value from a boolean operation is 1.
This special treatment of NULL is why, in the previous section, it was necessary to determine which animals are no longer alive using death IS NOT NULL instead of death <> NULL.
Two NULL values are regarded as equal in a GROUP BY.
When doing an ORDER BY, NULL values are presented first if you do ORDER BY ... ASC and last if you do ORDER BY ... DESC.
Note that MySQL 4.0.2 to 4.0.10 incorrectly always sorts NULL values first regardless of the sort direction.
MySQL provides standard SQL pattern matching as well as a form of pattern matching based on extended regular expressions similar to those used by Unix utilities such as vi, grep, and sed.
SQL pattern matching allows you to use _ to match any single character and % to match an arbitrary number of characters (including zero characters). In MySQL, SQL patterns are case-insensitive by default. Some examples are shown here. Note that you do not use = or <> when you use SQL patterns; use the LIKE or NOT LIKE comparison operators instead.
To find names beginning with b:
mysql> SELECT * FROM pet WHERE name LIKE "b%"; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+
To find names ending with fy:
mysql> SELECT * FROM pet WHERE name LIKE "%fy"; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+
To find names containing a w:
mysql> SELECT * FROM pet WHERE name LIKE "%w%"; +----------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | +----------+-------+---------+------+------------+------------+
To find names containing exactly five characters, use fives instances of the _ pattern character:
mysql> SELECT * FROM pet WHERE name LIKE "_____"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
The other type of pattern matching provided by MySQL uses extended regular expressions. When you test for a match for this type of pattern, use the REGEXP and NOT REGEXP operators (or RLIKE and NOT RLIKE, which are synonyms).
Some characteristics of extended regular expressions are:
. matches any single character.
A character class [...] matches any character within the brackets. For example, [abc] matches a, b, or c. To name a range of characters, use a dash. [a-z] matches any letter, whereas [0-9] matches any digit.
* matches zero or more instances of the thing preceding it. For example, x* matches any number of x characters, [0-9]* matches any number of digits, and .* matches any number of anything.
A REGEXP pattern match succeed if the pattern matches anywhere in the value being tested. (This differs from a LIKE pattern match, which succeeds only if the pattern matches the entire value.)
To anchor a pattern so that it must match the beginning or end of the value being tested, use ^ at the beginning or $ at the end of the pattern.
To demonstrate how extended regular expressions work, the LIKE queries shown previously are rewritten here to use REGEXP.
To find names beginning with b, use ^ to match the beginning of the name:
mysql> SELECT * FROM pet WHERE name REGEXP "^b"; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+
Prior to MySQL Version 3.23.4, REGEXP is case-sensitive, and the previous query will return no rows. In this case, to match either lowercase or uppercase b, use this query instead:
mysql> SELECT * FROM pet WHERE name REGEXP "^[bB]";
From MySQL 3.23.4 on, if you really want to force a REGEXP comparison to be case-sensitive, use the BINARY keyword to make one of the strings a binary string. This query will match only lowercase b at the beginning of a name:
mysql> SELECT * FROM pet WHERE name REGEXP BINARY "^b";
To find names ending with fy, use $ to match the end of the name:
mysql> SELECT * FROM pet WHERE name REGEXP "fy$"; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+
To find names containing a w, use this query:
mysql> SELECT * FROM pet WHERE name REGEXP "w"; +----------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | +----------+-------+---------+------+------------+------------+
Because a regular expression pattern matches if it occurs anywhere in the value, it is not necessary in the previous query to put a wildcard on either side of the pattern to get it to match the entire value like it would be if you used an SQL pattern.
To find names containing exactly five characters, use ^ and $ to match the beginning and end of the name, and five instances of . in between:
mysql> SELECT * FROM pet WHERE name REGEXP "^.....$"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
You could also write the previous query using the {n} ``repeat-n-times'' operator:
mysql> SELECT * FROM pet WHERE name REGEXP "^.{5}$"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
Databases are often used to answer the question, ``How often does a certain type of data occur in a table?'' For example, you might want to know how many pets you have, or how many pets each owner has, or you might want to perform various kinds of census operations on your animals.
Counting the total number of animals you have is the same question as ``How many rows are in the pet table?'' because there is one record per pet. COUNT(*) counts the number of rows, so the query to count your animals looks like this:
mysql> SELECT COUNT(*) FROM pet; +----------+ | COUNT(*) | +----------+ | 9 | +----------+
Earlier, you retrieved the names of the people who owned pets. You can use COUNT() if you want to find out how many pets each owner has:
mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner; +--------+----------+ | owner | COUNT(*) | +--------+----------+ | Benny | 2 | | Diane | 2 | | Gwen | 3 | | Harold | 2 | +--------+----------+
Note the use of GROUP BY to group together all records for each owner. Without it, all you get is an error message:
mysql> SELECT owner, COUNT(*) FROM pet; ERROR 1140: Mixing of GROUP columns (MIN(),MAX(),COUNT()...) with no GROUP columns is illegal if there is no GROUP BY clause
COUNT() and GROUP BY are useful for characterising your data in various ways. The following examples show different ways to perform animal census operations.
Number of animals per species:
mysql> SELECT species, COUNT(*) FROM pet GROUP BY species; +---------+----------+ | species | COUNT(*) | +---------+----------+ | bird | 2 | | cat | 2 | | dog | 3 | | hamster | 1 | | snake | 1 | +---------+----------+
Number of animals per sex:
mysql> SELECT sex, COUNT(*) FROM pet GROUP BY sex; +------+----------+ | sex | COUNT(*) | +------+----------+ | NULL | 1 | | f | 4 | | m | 4 | +------+----------+
(In this output, NULL indicates that the sex is unknown.)
Number of animals per combination of species and sex:
mysql> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex; +---------+------+----------+ | species | sex | COUNT(*) | +---------+------+----------+ | bird | NULL | 1 | | bird | f | 1 | | cat | f | 1 | | cat | m | 1 | | dog | f | 1 | | dog | m | 2 | | hamster | f | 1 | | snake | m | 1 | +---------+------+----------+
You need not retrieve an entire table when you use COUNT(). For example, the previous query, when performed just on dogs and cats, looks like this:
mysql> SELECT species, sex, COUNT(*) FROM pet -> WHERE species = "dog" OR species = "cat" -> GROUP BY species, sex; +---------+------+----------+ | species | sex | COUNT(*) | +---------+------+----------+ | cat | f | 1 | | cat | m | 1 | | dog | f | 1 | | dog | m | 2 | +---------+------+----------+
Or, if you wanted the number of animals per sex only for known-sex animals:
mysql> SELECT species, sex, COUNT(*) FROM pet -> WHERE sex IS NOT NULL -> GROUP BY species, sex; +---------+------+----------+ | species | sex | COUNT(*) | +---------+------+----------+ | bird | f | 1 | | cat | f | 1 | | cat | m | 1 | | dog | f | 1 | | dog | m | 2 | | hamster | f | 1 | | snake | m | 1 | +---------+------+----------+
The pet table keeps track of which pets you have. If you want to record other information about them, such as events in their lives like visits to the vet or when litters are born, you need another table. What should this table look like? It needs:
To contain the pet name so you know which animal each event pertains to.
A date so you know when the event occurred.
A field to describe the event.
An event type field, if you want to be able to categorise events.
Given these considerations, the CREATE TABLE statement for the event table might look like this:
mysql> CREATE TABLE event (name VARCHAR(20), date DATE, -> type VARCHAR(15), remark VARCHAR(255));
As with the pet table, it's easiest to load the initial records by creating a tab-delimited text file containing the information:
name | date | type | remark |
Fluffy | 1995-05-15 | litter | 4 kittens, 3 female, 1 male |
Buffy | 1993-06-23 | litter | 5 puppies, 2 female, 3 male |
Buffy | 1994-06-19 | litter | 3 puppies, 3 female |
Chirpy | 1999-03-21 | vet | needed beak straightened |
Slim | 1997-08-03 | vet | broken rib |
Bowser | 1991-10-12 | kennel | |
Fang | 1991-10-12 | kennel | |
Fang | 1998-08-28 | birthday | Gave him a new chew toy |
Claws | 1998-03-17 | birthday | Gave him a new flea collar |
Whistler | 1998-12-09 | birthday | First birthday |
Load the records like this:
mysql> LOAD DATA LOCAL INFILE "event.txt" INTO TABLE event;
Based on what you've learned from the queries you've run on the pet table, you should be able to perform retrievals on the records in the event table; the principles are the same. But when is the event table by itself insufficient to answer questions you might ask?
Suppose you want to find out the ages at which each pet had its litters. We saw earlier how to calculate ages from two dates. The litter date of the mother is in the event table, but to calculate her age on that date you need her birth date, which is stored in the pet table. This means the query requires both tables:
mysql> SELECT pet.name, -> (YEAR(date)-YEAR(birth)) - (RIGHT(date,5)<RIGHT(birth,5)) AS age, -> remark -> FROM pet, event -> WHERE pet.name = event.name AND type = "litter"; +--------+------+-----------------------------+ | name | age | remark | +--------+------+-----------------------------+ | Fluffy | 2 | 4 kittens, 3 female, 1 male | | Buffy | 4 | 5 puppies, 2 female, 3 male | | Buffy | 5 | 3 puppies, 3 female | +--------+------+-----------------------------+
There are several things to note about this query:
The FROM clause lists two tables because the query needs to pull information from both of them.
When combining (joining) information from multiple tables, you need to specify how records in one table can be matched to records in the other. This is easy because they both have a name column. The query uses WHERE clause to match up records in the two tables based on the name values.
Because the name column occurs in both tables, you must be specific about which table you mean when referring to the column. This is done by prepending the table name to the column name.
You need not have two different tables to perform a join. Sometimes it is useful to join a table to itself, if you want to compare records in a table to other records in that same table. For example, to find breeding pairs among your pets, you can join the pet table with itself to produce candidate pairs of males and females of like species:
mysql> SELECT p1.name, p1.sex, p2.name, p2.sex, p1.species -> FROM pet AS p1, pet AS p2 -> WHERE p1.species = p2.species AND p1.sex = "f" AND p2.sex = "m"; +--------+------+--------+------+---------+ | name | sex | name | sex | species | +--------+------+--------+------+---------+ | Fluffy | f | Claws | m | cat | | Buffy | f | Fang | m | dog | | Buffy | f | Bowser | m | dog | +--------+------+--------+------+---------+
In this query, we specify aliases for the table name in order to refer to the columns and keep straight which instance of the table each column reference is associated with.
What if you forget the name of a database or table, or what the structure of a given table is (for example, what its columns are called)? MySQL addresses this problem through several statements that provide information about the databases and tables it supports.
You have already seen SHOW DATABASES, which lists the databases managed by the server. To find out which database is currently selected, use the DATABASE() function:
mysql> SELECT DATABASE(); +------------+ | DATABASE() | +------------+ | menagerie | +------------+
If you haven't selected any database yet, the result is NULL (or the empty string before MySQL 4.1.1).
To find out what tables the current database contains (for example, when you're not sure about the name of a table), use this command:
mysql> SHOW TABLES; +---------------------+ | Tables in menagerie | +---------------------+ | event | | pet | +---------------------+
If you want to find out about the structure of a table, the DESCRIBE command is useful; it displays information about each of a table's columns:
mysql> DESCRIBE pet; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | | owner | varchar(20) | YES | | NULL | | | species | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | birth | date | YES | | NULL | | | death | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+
Field indicates the column name, Type is the datatype for the column, NULL indicates whether the column can contain NULL values, Key indicates whether the column is indexed, and Default specifies the column's default value.
If you have indexes on a table, SHOW INDEX FROM tbl_name produces information about them.
In the previous sections, you used mysql interactively to enter queries and view the results. You can also run mysql in batch mode. To do this, put the commands you want to run in a file, then tell mysql to read its input from the file:
shell> mysql < batch-file
If you are running mysql under Windows and have some special characters in the file that cause problems, you can do this:
dos> mysql -e "source batch-file"
If you need to specify connection parameters on the command line, the command might look like this:
shell> mysql -h host -u user -p < batch-file Enter password: ********
When you use mysql this way, you are creating a script file, then executing the script.
If you want the script to continue even if some of the statements in it produce errors, you should use the --force command-line option.
Why use a script? Here are a few reasons:
If you run a query repeatedly (say, every day or every week), making it a script allows you to avoid retyping it each time you execute it.
You can generate new queries from existing ones that are similar by copying and editing script files.
Batch mode can also be useful while you're developing a query, particularly for multiple-line commands or multiple-statement sequences of commands. If you make a mistake, you don't have to retype everything. Just edit your script to correct the error, then tell mysql to execute it again.
If you have a query that produces a lot of output, you can run the output through a pager rather than watching it scroll off the top of your screen:
shell> mysql < batch-file | more
You can catch the output in a file for further processing:
shell> mysql < batch-file > mysql.out
You can distribute your script to other people so they can run the commands, too.
Some situations do not allow for interactive use, for example, when you run a query from a cron job. In this case, you must use batch mode.
The default output format is different (more concise) when you run mysql in batch mode than when you use it interactively. For example, the output of SELECT DISTINCT species FROM pet looks like this when mysql is run interactively:
+---------+ | species | +---------+ | bird | | cat | | dog | | hamster | | snake | +---------+
In batch mode, the output looks like this instead:
species bird cat dog hamster snake
If you want to get the interactive output format in batch mode, use mysql -t. To echo to the output the commands that are executed, use mysql -vvv.
You can also use scripts from the mysql prompt by using the source command:
mysql> source filename;
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Here are examples of how to solve some common problems with MySQL.
Some of the examples use the table shop to hold the price of each article (item number) for certain traders (dealers). Supposing that each trader has a single fixed price per article, then (article, dealer) is a primary key for the records.
Start the command-line tool mysql and select a database:
shell> mysql your-database-name
(In most MySQL installations, you can use the database name test).
You can create and populate the example table with these statements:
mysql> CREATE TABLE shop ( -> article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL, -> dealer CHAR(20) DEFAULT '' NOT NULL, -> price DOUBLE(16,2) DEFAULT '0.00' NOT NULL, -> PRIMARY KEY(article, dealer)); mysql> INSERT INTO shop VALUES -> (1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),(3,'C',1.69), -> (3,'D',1.25),(4,'D',19.95);
After issuing the statements, the table should have the following contents:
mysql> SELECT * FROM shop; +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0001 | A | 3.45 | | 0001 | B | 3.99 | | 0002 | A | 10.99 | | 0003 | B | 1.45 | | 0003 | C | 1.69 | | 0003 | D | 1.25 | | 0004 | D | 19.95 | +---------+--------+-------+
``What's the highest item number?''
SELECT MAX(article) AS article FROM shop; +---------+ | article | +---------+ | 4 | +---------+
``Find number, dealer, and price of the most expensive article.''
In SQL-99 (and MySQL Version 4.1) this is easily done with a subquery:
SELECT article, dealer, price FROM shop WHERE price=(SELECT MAX(price) FROM shop);
In MySQL versions prior to 4.1, just do it in two steps:
Get the maximum price value from the table with a SELECT statement.
mysql> SELECT MAX(price) FROM shop; +------------+ | MAX(price) | +------------+ | 19.95 | +------------+
Using the value 19.95 shown by the previous query to be the maximum article price, write a query to locate and display the corresponding record:
mysql> SELECT article, dealer, price -> FROM shop -> WHERE price=19.95; +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0004 | D | 19.95 | +---------+--------+-------+
Another solution is to sort all rows descending by price and only get the first row using the MySQL-specific LIMIT clause:
SELECT article, dealer, price FROM shop ORDER BY price DESC LIMIT 1;
NOTE: If there were several most expensive articles, each with a price of 19.95, the LIMIT solution would show only one of them!
``What's the highest price per article?''
SELECT article, MAX(price) AS price FROM shop GROUP BY article +---------+-------+ | article | price | +---------+-------+ | 0001 | 3.99 | | 0002 | 10.99 | | 0003 | 1.69 | | 0004 | 19.95 | +---------+-------+
``For each article, find the dealer or dealers with the most expensive price.''
In SQL-99 (and MySQL Version 4.1 or greater), the problem can be solved with a subquery like this:
SELECT article, dealer, price FROM shop s1 WHERE price=(SELECT MAX(s2.price) FROM shop s2 WHERE s1.article = s2.article);
In MySQL versions prior to 4.1, it's best do it in several steps:
Get the list of (article,maxprice) pairs.
For each article, get the corresponding rows that have the stored maximum price.
This can easily be done with a temporary table and a join:
CREATE TEMPORARY TABLE tmp ( article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL, price DOUBLE(16,2) DEFAULT '0.00' NOT NULL); LOCK TABLES shop READ; INSERT INTO tmp SELECT article, MAX(price) FROM shop GROUP BY article; SELECT shop.article, dealer, shop.price FROM shop, tmp WHERE shop.article=tmp.article AND shop.price=tmp.price; UNLOCK TABLES; DROP TABLE tmp;
If you don't use a TEMPORARY table, you must also lock the tmp table.
``Can it be done with a single query?''
Yes, but only by using a quite inefficient trick called the ``MAX-CONCAT trick'':
SELECT article, SUBSTRING( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 7) AS dealer, 0.00+LEFT( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 6) AS price FROM shop GROUP BY article; +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0001 | B | 3.99 | | 0002 | A | 10.99 | | 0003 | C | 1.69 | | 0004 | D | 19.95 | +---------+--------+-------+
The last example can be made a bit more efficient by doing the splitting of the concatenated column in the client.
You can use MySQL user variables to remember results without having to store them in temporary variables in the client. See Variables.
For example, to find the articles with the highest and lowest price you can do this:
mysql> SELECT @min_price:=MIN(price),@max_price:=MAX(price) FROM shop; mysql> SELECT * FROM shop WHERE price=@min_price OR price=@max_price; +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0003 | D | 1.25 | | 0004 | D | 19.95 | +---------+--------+-------+
In MySQL 3.23.44 and up, InnoDB tables support checking of foreign key constraints. See InnoDB. See also ANSI diff Foreign Keys.
You don't actually need foreign keys to join two tables. For table types other than InnoDB), the only things MySQL currently doesn't do are 1) CHECK to make sure that the keys you use really exist in the table or tables you're referencing and 2) automatically delete rows from a table with a foreign key definition. Using your keys to join tables will work just fine:
CREATE TABLE person ( id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT, name CHAR(60) NOT NULL, PRIMARY KEY (id) ); CREATE TABLE shirt ( id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT, style ENUM('t-shirt', 'polo', 'dress') NOT NULL, color ENUM('red', 'blue', 'orange', 'white', 'black') NOT NULL, owner SMALLINT UNSIGNED NOT NULL REFERENCES person(id), PRIMARY KEY (id) ); INSERT INTO person VALUES (NULL, 'Antonio Paz'); INSERT INTO shirt VALUES (NULL, 'polo', 'blue', LAST_INSERT_ID()), (NULL, 'dress', 'white', LAST_INSERT_ID()), (NULL, 't-shirt', 'blue', LAST_INSERT_ID()); INSERT INTO person VALUES (NULL, 'Lilliana Angelovska'); INSERT INTO shirt VALUES (NULL, 'dress', 'orange', LAST_INSERT_ID()), (NULL, 'polo', 'red', LAST_INSERT_ID()), (NULL, 'dress', 'blue', LAST_INSERT_ID()), (NULL, 't-shirt', 'white', LAST_INSERT_ID()); SELECT * FROM person; +----+---------------------+ | id | name | +----+---------------------+ | 1 | Antonio Paz | | 2 | Lilliana Angelovska | +----+---------------------+ SELECT * FROM shirt; +----+---------+--------+-------+ | id | style | color | owner | +----+---------+--------+-------+ | 1 | polo | blue | 1 | | 2 | dress | white | 1 | | 3 | t-shirt | blue | 1 | | 4 | dress | orange | 2 | | 5 | polo | red | 2 | | 6 | dress | blue | 2 | | 7 | t-shirt | white | 2 | +----+---------+--------+-------+ SELECT s.* FROM person p, shirt s WHERE p.name LIKE 'Lilliana%' AND s.owner = p.id AND s.color <> 'white'; +----+-------+--------+-------+ | id | style | color | owner | +----+-------+--------+-------+ | 4 | dress | orange | 2 | | 5 | polo | red | 2 | | 6 | dress | blue | 2 | +----+-------+--------+-------+
MySQL doesn't yet optimize when you search on two different keys combined with OR (searching on one key with different OR parts is optimized quite well):
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1' OR field2_index = '1'
The reason is that we haven't yet had time to come up with an efficient way to handle this in the general case. (The AND handling is, in comparison, now completely general and works very well.)
In MySQL 4.0 and up, you can solve this problem efficiently by using a UNION that combines the output of two separate SELECT statements. See UNION. Each SELECT searches only one key and can be optimized:
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1' UNION SELECT field1_index, field2_index FROM test_table WHERE field2_index = '1';
Prior to MySQL 4.0, you can achieve the same effect by using a TEMPORARY table and separate SELECT statements. This type of optimization is also very good if you are using very complicated queries where the SQL server does the optimizations in the wrong order.
CREATE TEMPORARY TABLE tmp SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1'; INSERT INTO tmp SELECT field1_index, field2_index FROM test_table WHERE field2_index = '1'; SELECT * from tmp; DROP TABLE tmp;
The above way to solve this query is in effect a UNION of two queries.
The following example shows how you can use the bit group functions to calculate the number of days per month a user has visited a web page.
CREATE TABLE t1 (year YEAR(4), month INT(2) UNSIGNED ZEROFILL, day INT(2) UNSIGNED ZEROFILL); INSERT INTO t1 VALUES(2000,1,1),(2000,1,20),(2000,1,30),(2000,2,2), (2000,2,23),(2000,2,23);
The example table contains year-month-day values representing visits by users to the page. To determine how many different days in each month these visits occur, use this query:
SELECT year,month,BIT_COUNT(BIT_OR(1<<day)) AS days FROM t1 GROUP BY year,month;
Which returns:
+------+-------+------+ | year | month | days | +------+-------+------+ | 2000 | 01 | 3 | | 2000 | 02 | 2 | +------+-------+------+
The query calculates how many different days appear in the table for each year/month combination, with automatic removal of duplicate entries.
The AUTO_INCREMENT attribute can be used to generate a unique identity for new rows:
CREATE TABLE animals ( id MEDIUMINT NOT NULL AUTO_INCREMENT, name CHAR(30) NOT NULL, PRIMARY KEY (id) ); INSERT INTO animals (name) VALUES ("dog"),("cat"),("penguin"), ("lax"),("whale"),("ostrich"); SELECT * FROM animals;
Which returns:
+----+---------+ | id | name | +----+---------+ | 1 | dog | | 2 | cat | | 3 | penguin | | 4 | lax | | 5 | whale | | 6 | ostrich | +----+---------+
You can retrieve the most recent AUTO_INCREMENT value with the LAST_INSERT_ID() SQL function or the mysql_insert_id() C API function. Note: For a multiple-row insert, LAST_INSERT_ID()/mysql_insert_id() will actually return the AUTO_INCREMENT key from the first of the inserted rows. This allows multiple-row inserts to be reproduced correctly on other servers in a replication setup.
For MyISAM and BDB tables you can specify AUTO_INCREMENT on a secondary column in a multiple-column index. In this case, the generated value for the AUTO_INCREMENT column is calculated as MAX(auto_increment_column)+1) WHERE prefix=given-prefix. This is useful when you want to put data into ordered groups.
CREATE TABLE animals ( grp ENUM('fish','mammal','bird') NOT NULL, id MEDIUMINT NOT NULL AUTO_INCREMENT, name CHAR(30) NOT NULL, PRIMARY KEY (grp,id) ); INSERT INTO animals (grp,name) VALUES("mammal","dog"),("mammal","cat"), ("bird","penguin"),("fish","lax"),("mammal","whale"), ("bird","ostrich"); SELECT * FROM animals ORDER BY grp,id;
Which returns:
+--------+----+---------+ | grp | id | name | +--------+----+---------+ | fish | 1 | lax | | mammal | 1 | dog | | mammal | 2 | cat | | mammal | 3 | whale | | bird | 1 | penguin | | bird | 2 | ostrich | +--------+----+---------+
Note that in this case (when the AUTO_INCREMENT column is part of a multiple-column index), AUTO_INCREMENT values will be reused if you delete the row with the biggest AUTO_INCREMENT value in any group. This happens even for MyISAM tables, for which AUTO_INCREMENT values normally are not reused.)
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At Analytikerna and Lentus, we have been doing the systems and field work for a big research project. This project is a collaboration between the Institute of Environmental Medicine at Karolinska Institutet Stockholm and the Section on Clinical Research in Aging and Psychology at the University of Southern California.
The project involves a screening part where all twins in Sweden older than 65 years are interviewed by telephone. Twins who meet certain criteria are passed on to the next stage. In this latter stage, twins who want to participate are visited by a doctor/nurse team. Some of the examinations include physical and neuropsychological examination, laboratory testing, neuroimaging, psychological status assessment, and family history collection. In addition, data are collected on medical and environmental risk factors.
More information about Twin studies can be found at: http://www.mep.ki.se/twinreg/index_en.html
The latter part of the project is administered with a web interface written using Perl and MySQL.
Each night all data from the interviews is moved into a MySQL database.
The following query is used to determine who goes into the second part of the project:
SELECT CONCAT(p1.id, p1.tvab) + 0 AS tvid, CONCAT(p1.christian_name, " ", p1.surname) AS Name, p1.postal_code AS Code, p1.city AS City, pg.abrev AS Area, IF(td.participation = "Aborted", "A", " ") AS A, p1.dead AS dead1, l.event AS event1, td.suspect AS tsuspect1, id.suspect AS isuspect1, td.severe AS tsevere1, id.severe AS isevere1, p2.dead AS dead2, l2.event AS event2, h2.nurse AS nurse2, h2.doctor AS doctor2, td2.suspect AS tsuspect2, id2.suspect AS isuspect2, td2.severe AS tsevere2, id2.severe AS isevere2, l.finish_date FROM twin_project AS tp /* For Twin 1 */ LEFT JOIN twin_data AS td ON tp.id = td.id AND tp.tvab = td.tvab LEFT JOIN informant_data AS id ON tp.id = id.id AND tp.tvab = id.tvab LEFT JOIN harmony AS h ON tp.id = h.id AND tp.tvab = h.tvab LEFT JOIN lentus AS l ON tp.id = l.id AND tp.tvab = l.tvab /* For Twin 2 */ LEFT JOIN twin_data AS td2 ON p2.id = td2.id AND p2.tvab = td2.tvab LEFT JOIN informant_data AS id2 ON p2.id = id2.id AND p2.tvab = id2.tvab LEFT JOIN harmony AS h2 ON p2.id = h2.id AND p2.tvab = h2.tvab LEFT JOIN lentus AS l2 ON p2.id = l2.id AND p2.tvab = l2.tvab, person_data AS p1, person_data AS p2, postal_groups AS pg WHERE /* p1 gets main twin and p2 gets his/her twin. */ /* ptvab is a field inverted from tvab */ p1.id = tp.id AND p1.tvab = tp.tvab AND p2.id = p1.id AND p2.ptvab = p1.tvab AND /* Just the sceening survey */ tp.survey_no = 5 AND /* Skip if partner died before 65 but allow emigration (dead=9) */ (p2.dead = 0 OR p2.dead = 9 OR (p2.dead = 1 AND (p2.death_date = 0 OR (((TO_DAYS(p2.death_date) - TO_DAYS(p2.birthday)) / 365) >= 65)))) AND ( /* Twin is suspect */ (td.future_contact = 'Yes' AND td.suspect = 2) OR /* Twin is suspect - Informant is Blessed */ (td.future_contact = 'Yes' AND td.suspect = 1 AND id.suspect = 1) OR /* No twin - Informant is Blessed */ (ISNULL(td.suspect) AND id.suspect = 1 AND id.future_contact = 'Yes') OR /* Twin broken off - Informant is Blessed */ (td.participation = 'Aborted' AND id.suspect = 1 AND id.future_contact = 'Yes') OR /* Twin broken off - No inform - Have partner */ (td.participation = 'Aborted' AND ISNULL(id.suspect) AND p2.dead = 0)) AND l.event = 'Finished' /* Get at area code */ AND SUBSTRING(p1.postal_code, 1, 2) = pg.code /* Not already distributed */ AND (h.nurse IS NULL OR h.nurse=00 OR h.doctor=00) /* Has not refused or been aborted */ AND NOT (h.status = 'Refused' OR h.status = 'Aborted' OR h.status = 'Died' OR h.status = 'Other') ORDER BY tvid;
Some explanations:
CONCAT(p1.id, p1.tvab) + 0 AS tvid | We want to sort on the concatenated id and tvab in numerical order. Adding 0 to the result causes MySQL to treat the result as a number. |
column id | This identifies a pair of twins. It is a key in all tables. |
column tvab | This identifies a twin in a pair. It has a value of 1 or 2. |
column ptvab | This is an inverse of tvab. When tvab is 1 this is 2, and vice versa. It exists to save typing and to make it easier for MySQL to optimize the query. |
This query demonstrates, among other things, how to do lookups on a table from the same table with a join (p1 and p2). In the example, this is used to check whether a twin's partner died before the age of 65. If so, the row is not returned.
All of the above exist in all tables with twin-related information. We have a key on both id,tvab (all tables), and id,ptvab (person_data) to make queries faster.
On our production machine (A 200MHz UltraSPARC), this query returns about 150-200 rows and takes less than one second.
The current number of records in the tables used above:
Table | Rows |
person_data | 71074 |
lentus | 5291 |
twin_project | 5286 |
twin_data | 2012 |
informant_data | 663 |
harmony | 381 |
postal_groups | 100 |
Each interview ends with a status code called event. The query shown here is used to display a table over all twin pairs combined by event. This indicates in how many pairs both twins are finished, in how many pairs one twin is finished and the other refused, and so on.
SELECT t1.event, t2.event, COUNT(*) FROM lentus AS t1, lentus AS t2, twin_project AS tp WHERE /* We are looking at one pair at a time */ t1.id = tp.id AND t1.tvab=tp.tvab AND t1.id = t2.id /* Just the sceening survey */ AND tp.survey_no = 5 /* This makes each pair only appear once */ AND t1.tvab='1' AND t2.tvab='2' GROUP BY t1.event, t2.event;
There are programs that let you authenticate your users from a MySQL database and also let you write your log files into a MySQL table.
You can change the Apache logging format to be easily readable by MySQL by putting the following into the Apache configuration file:
LogFormat \ "\"%h\",%{%Y%m%d%H%M%S}t,%>s,\"%b\",\"%{Content-Type}o\", \ \"%U\",\"%{Referer}i\",\"%{User-Agent}i\""
To load a log file in that format into MySQL, you can use a statement something like this:
LOAD DATA INFILE '/local/access_log' INTO TABLE table_name FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' ESCAPED BY '\\'
The named table should be created to have columns that correspond to those that the LogFormat line writes to the log file.
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This chapter provides a brief overview of the programs provided by MySQL AB and discusses how to specify options when you run these programs. Most programs have options that are specific to their own operation, but the syntax for specifying options is similar for all of them. Later chapters provide more detailed descriptions of individual programs, including which options they recognize.
MySQL AB provides several types of programs:
The MYSQL server and server startup scripts: |
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Client programs that access the server: |
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Utility programs that operate independently of the server: |
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More information on running the server may be found in Database Administration. Client and utility programs are described in more detail in Client-Side Scripts.
Most MySQL distribution formats include all of these programs, except for those programs that are platform-specific. (For example, the server startup scripts are not used on Windows.) The exception is that RPM distributions are more specialized. There is one RPM for the server, another for the client programs, and so forth. If you appear to be missing one or more programs, see Installing for information on distributions and what they contain. It may be that you need to install something else.
To invoke a MySQL program at the command line (that is, from your shell or command prompt), enter the program name followed by any options or other arguments needed to instruct the program what you want it to do. The following commands show some sample program invocations. ``shell>'' represents your command prompt; it is not part of what you type.
shell> mysql test shell> mysqldump --quote-names personnel shell> mysqladmin extended-status variables shell> mysqlshow --help
Arguments that begin with a dash are option arguments. They typically specify the type of connection a program should make to the server or affect its operational mode. Options have a syntax that is described in Program Options.
Non-option arguments (arguments with no leading dash) provide additional information to the program. For example, the mysql program interprets the first non-option argument as a database name, so the command mysql test indicates that you want to use the test database.
Later sections that describe individual programs indicate which options a program understands and describe the meaning of any additional non-option arguments.
Some options are common to a number of programs. The most common of these are the --host, --user, and --password options that specify connection parameters. They indicate the host where the MySQL server is running, and the username and password of your MySQL account. All MySQL client programs understand these options; they allow you to specify which server to connect to and the account to use on that server.
Note that you may find it necessary to invoke MySQL programs using the pathname to the bin directory in which they are installed. This is likely to be the case if you get a ``program not found'' error whenever you attempt to run a MySQL program from any directory other than the bin directory. To make it more convenient to use MySQL, you can add the pathname of the bin directory to your PATH environment variable setting. Then to run a program you need only type its name, not its entire pathname.
Consult the documentation for your command interpreter for instructions on setting your PATH; the syntax for setting environment variables is interpreter-specific.
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You can provide options for MySQL programs in several ways:
On the command line following the program name. This is most common for options that apply to a specific invocation of the program.
In an option file that the program reads when it starts. This is common for options that you want the program to use each time it runs.
In environment variables. These are useful for options that you want to apply each time the program runs, though in practice option files are used more commonly for this purpose. (Multiple Unix servers discusses one situation in which environment variables can be very helpful. It describes a handy technique that uses such variables to specify the TCP/IP port and Unix socket file for both the server and client programs.)
MySQL programs determine which options are given by examining environment variables first, then option files, then the command line. If an option is specified multiple times, the last occurrence takes precedence. This means that environment variables have the lowest precedence and command-line options the highest.
You can take advantage of the way that MySQL programs process options by specifying the default value for a program's options in an option file. Then you need not type them each time you run the program, but can override the defaults if necessary by using command-line options.
Program options specified on the command line follow these rules:
Options are given after the command name.
An option argument begins with one dash or two dashes, depending on whether it has a short name or a long name. Many options have both forms. For example, -? and --help are the short and long forms of the option that instructs a MySQL program to display a help message.
Option names are case sensitive. -v and -V are both legal and have different meanings. (They are the corresponding short forms of the --verbose and --version options.)
Some options take a value following the option name. For example, -h localhost or --host=localhost indicate the MySQL server host to a client program. The option value tells the program the name of the host where the MySQL server is running.
For a long option that takes a value, separate the option name and the value by an = sign. For a short option that takes a value, the option value can immediately follow the option letter, or there can be a space between. (-hlocalhost and -h localhost are equivalent.) An exception to this rule is the option for specifying your MySQL password. This option can be given in long form as --password=pass_val or as --password. In the latter case (with no password value given), the program will prompt you for the password. The password option also may be given in short form as -ppass_val or as -p. However, for the short form, if the password value is given, it must follow the option letter with no intervening space. The reason for this is that if a space follows the option letter, the program has no way to tell whether a following argument is supposed to be the password value or some other kind of argument. Consequently, the following two commands have two completely different meanings:
shell> mysql -ptest shell> mysql -p test
The first command instructs mysql to use a password value of test, but specifies no default database. The second instructs mysql to prompt for the password value and to use test as the default database.
MySQL 4.0 introduced some additional flexibility in the way you specify options. These changes were made in MySQL 4.0.2. Some of them relate to the way you specify options that have ``enabled'' and ``disabled'' states, and to the use of options that may be present in one version of MySQL but not another. Those capabilities are discussed here. Another change pertains to the way you use options to set program variables. Program variables discusses that topic further.
Some options control behavior that can be turned on or off. For example, the mysql client supports a --column-names option that determines whether or not to display a row of column names at the beginning of query results. By default, this option is enabled. However, you may want to disable it in some instances, such as when sending the output of mysql into another program that expects to see only data and not an initial header line.
To disable column names, you can specify the option using any of these forms:
--disable-column-names --skip-column-names --column-names=0
The --disable and --skip prefixes and the =0 suffix all have the same effect of turning the option off.
The ``enabled'' form of the option may be specified as:
--column-names --enable-column-names --column-names=1
Another change to option processing introduced in MySQL 4.0 is that you can use the --loose prefix for command-line options. If an option is prefixed by --loose, the program will not exit with an error if it does not recognize the option, but instead will issue only a warning:
shell> mysql --loose-no-such-option mysql: WARNING: unknown option '--no-such-option'
The --loose prefix can be useful when you run programs from multiple installations of MySQL on the same machine, at least if all the versions are as recent as 4.0.2. This prefix is particularly useful when you list options in an option file. An option that may not be recognized by all versions of a program can be given using the --loose prefix (or loose in an option file). Versions of the program that do not recognize the option will issue a warning and ignore it. Note that this strategy works only if all versions involved are 4.0.2 or later, because earlier versions know nothing of the --loose convention.
MySQL programs can read startup options from option files (also sometimes called configuration files). Option files provide a convenient way to specify commonly used options so they need not be entered on the command line each time you run a program. Option file capability is available from MySQL 3.22 on.
The following programs support option files: mysql, mysqladmin, mysqld, mysqld_safe, mysql.server, mysqldump, mysqlimport, mysqlshow, mysqlcheck, mysqlhotcopy, myisamchk, and myisampack.
On Windows, MySQL programs read startup options from the following files:
Filename | Purpose |
windows-dir\my.ini | Global options |
C:\my.cnf | Global options |
windows-dir represents the location of your Windows directory. This is commonly C:\Windows or C:\WinNT. Check the value of the WINDIR environment vairable to see where this directory is located on your system.
On Unix, MySQL programs read startup options from the following files:
Filename | Purpose |
/etc/my.cnf | Global options |
DATADIR/my.cnf | Server-specific options |
defaults-extra-file | The file specified with --defaults-extra-file=path, if any |
~/.my.cnf | User-specific options |
DATADIR represents the location of the MySQL data directory. Typically this is /usr/local/mysql/data for a binary installation or /usr/local/var for a source installation. Note that this is the data directory location that was specified at configuration time, not the one specified with --datadir when mysqld starts! Use of --datadir at runtime has no effect on where the server looks for option files, because it looks for them before processing any command-line arguments.
MySQL looks for option files in the order listed above and reads any that exist. If multiple option files exist, an option specified in a file read later takes precedence over the same option specified in a file read earlier.
Any long option that may be given on the command-line when running a MySQL program can be given in an option file as well. To get the list of available options for a program, run it with the --help option.
The syntax for specifying options in an option file is similar to command-line syntax, except that you omit the leading two dashes. For example, --quick or --host=localhost on the command line are specified as quick or host=localhost in an option file. To specify an option of the form --loose-opt_name in an option file, write it as loose-opt_name.
Empty lines in option files are ignored. Non-empty lines can take any of the following forms:
#comment , ;comment | Comment lines start with # or ;. As of MySQL 4.0.14, a #-comment can start in the middle of a line as well. |
[group] | group is the name of the program or group for which you want to set options. After a group line, any option or set-variable lines apply to the named group until the end of the option file or another group line is given. |
opt_name | This is equivalent to --opt_name on the command-line. |
opt_name=value | This is equivalent to --opt_name=value on the command-line. In an option file, you can have spaces around the = character, something that is not true on the command line. As of MySQL 4.0.16, you can quote the value with double quotes or single quotes. This is useful if the value contains a comment character or whitespace. |
set-variable = var_name=value | Set the program variable var_name to the given value. This is equivalent to --set-variable=var_name=value on the command-line. Spaces are allowed around the first = character but not around the second. This syntax is deprecated as of MySQL 4.0. See Program variables for more information on setting program variables. |
Note that for options and values, all leading and trailing blanks are automatically deleted. You may use the escape sequences \b, \t, \n, \r, \\, and \s in option values to represent the backspace, tab, newline, carriage return, and space characters.
On Windows, if an option value represents a pathname, you should specify the value using / rather than \ as the pathname separator. If you use \, you must double it as \\, because \ is the escape character in MySQL.
If an option group name is the same as a program name, options in the group apply specifically to that program.
The [client] option group is read by all client programs (but not by mysqld). This allows you to specify options that apply to every client. For example, [client] is the perfect group to use to specify the password that you use to connect to the server. (But make sure the option file is readable and writable only by yourself, so that other people cannot find out your password.) Be sure not to put an option in the [client] group unless it is recognized by all client programs.
As of MySQL 4.0.14, if you want to create options that should only be read by one specific mysqld server release series, you can do this with [mysqld-4.0], [mysqld-4.1], and so forth:
[mysqld-4.0] new
The above new option will be used only with MySQL server versions 4.0.x.
Here is a typical global option file:
[client] port=3306 socket=/tmp/mysql.sock [mysqld] port=3306 socket=/tmp/mysql.sock key_buffer_size=16M max_allowed_packet=1M [mysqldump] quick
Here is a typical user option file:
[client] # The following password will be sent to all standard MySQL clients password="my_password" [mysql] no-auto-rehash set-variable = connect_timeout=2 [mysqlhotcopy] interactive-timeout
If you have a source distribution, you will find sample option files named my-xxxx.cnf in the support-files directory. If you have a binary distribution, look in the support-files directory under your MySQL installation directory (typically C:\mysql on Windows or /usr/local/mysql on Unix). Currently there are sample option files for small, medium, large, and very large systems. To experiment with one of these files, copy it to C:\my.cnf on Windows or to .my.cnf in your home directory on Unix.
All MySQL programs that support option files support the following command-line options:
--no-defaults | Don't read any option files. |
--print-defaults | Print the program name and all options that it will get from option files. |
--defaults-file=path_name | Use only the given option file. path_name is the full pathname to the file. |
--defaults-extra-file=path_name | Read this option file after the global option file but before the user option file. path_name is the full pathname to the file. |
Note that to work properly, each of these options must immediately follow the command name on the command line, with the exception that --print-defaults may be used immediately after --defaults-file or --defaults-extra-file.
In shell scripts, you can use the my_print_defaults program to parse the option files. The following example shows the output that my_print_defaults might produce when asked to show the options found in the [client] and [mysql] groups:
shell> my_print_defaults client mysql --port=3306 --socket=/tmp/mysql.sock --no-auto-rehash
Note for developers: Option file handling is implemented in the C client library simply by processing all matching options (that is, options in the appropriate group) before any command-line arguments. This works nicely for programs that use the last instance of an option that is specified multiple times. If you have a C or C++ program that handles multiply specified options this way but doesn't read option files, you need add only two lines to give it that capability. Check the source code of any of the standard MySQL clients to see how to do this.
Several other language interfaces to MySQL are based on the C client library, and some of them provide a way to access option file contents. These include Perl and Python. See the documentation for your preferred interface for details.
To specify an option using an environment variable, set the variable using the syntax appropriate for your comment processor. For example, on Windows or NetWare, you can set the USER variable to specify your MySQL account name. To do so, use this syntax:
SET USER=your_name
The syntax on Unix depends on your shell. Suppose you want to specify the TCP/IP port number using the MYSQL_TCP_PORT variable. The syntax for Bourne shell and variants (sh, bash, zsh, etc.) is:
MYSQL_TCP_PORT=3306
For csh and tcsh, use this syntax:
setenv MYSQL_TCP_PORT 3306
The commands to set environment variables can be executed at your command prompt to take effect immediately. These settings persist until you log out. To have the settings take effect each time you log in, place the appropriate command or commands in a startup file that your command interpreter reads each time it starts. Typical startup files are AUTOEXEC.BAT for Windows, .bash_profile for bash, or .tcshrc for tcsh. Consult the documentation for your command interpreter for specific details.
Environment variables lists all environment variables that affect MySQL program operation.
Many MySQL programs have internal variables that can be set at runtime. As of MySQL 4.0.2, program variables are set the same way as any other long option that takes a value. For example, mysql has a max_allowed_packet variable that controls the maximum size of its communication buffer. To set the max_allowed_packet variable for mysql to a value of 64 MB, use either of the following commands:
shell> mysql --max_allowed_packet=6710740 shell> mysql --max_allowed_packet=64M
The first command specifies the value in bytes. The second specifies the value in megabytes. Variable values can have a suffix of K, M, or G (either uppercase or lowercase) to indicate units of kilobytes, megabytes, or gigabytes.
In an option file, the variable setting is given without the leading dashes:
[mysql] max_allowed_packet=6710740
Or:
[mysql] max_allowed_packet=64M
If you like, underscores in a variable name can be specified as dashes.
Prior to MySQL 4.0.2, program variable names are not recognized as option names. Instead, use the --set-variable option to assign a value to a variable:
shell> mysql --set-variable=max_allowed_packet=6710740 shell> mysql --set-variable=max_allowed_packet=64M
In an option file, omit the leading dashes:
[mysql] set-variable = max_allowed_packet=6710740
Or:
[mysql] set-variable = max_allowed_packet=64M
With --set-variable, underscores in variable names may not be given as dashes for versions of MySQL older than 4.0.2.
The --set-variable option is still recognized in MySQL 4.0.2 and up, but is deprecated.
Table of Contents
This chapter covers topics that deal with administering a MySQL installation, such as configuring the server, managing user accounts, and performing backups.
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The MySQL server, mysqld, is the main program that does most of the work in a MySQL installation. The server is accompanied by several related scripts that perform setup operations when you install MySQL or that are helper programs to assist you in starting and stopping the server.
All MySQL programs take many different options. However, every MySQL program provides a --help option that you can use to get a description of the program's options. For example, try mysqld --help.
You can override default options for all standard programs by specifying options on the command line or in an option file. Program Options.
The following list briefly describes the server-related MySQL programs:
There are several other programs that also are run on the server host:
myisamchk | A utility to describe, check, optimize, and repair MySQL tables. myisamchk is described in Table maintenance. |
make_binary_distribution | This program makes a binary release of a compiled MySQL. This could be sent by FTP to /pub/mysql/Incoming on support.mysql.com for the convenience of other MySQL users. |
mysqlbug | The MySQL bug reporting script. It can be be used to send a bug report to the MySQL list. (You can also visit http://bugs.mysql.com/ to file a bug report online.) |
A MySQL-Max server is a version of the mysqld MySQL server that is configured to include additional features.
You can find the MySQL-Max binaries at http://www.mysql.com/downloads/mysql-max-4.0.html.
The MySQL binary distributions Windows include both the standard server (named mysqld.exe) and the MySQL-Max server (named mysqld-max.exe). http://www.mysql.com/downloads/mysql-4.0.html. See Windows installation.
If you install MySQL on Linux using RPM distributions, install the MySQL-server RPM first, and then the MySQL-Max RPM. The latter presupposes that you have already installed the regular server RPM. This process installs a standard server named mysqld and a MySQL-Max server named mysqld-max.
All other MySQL-Max distributions contain a single server that is named mysqld but that has the additional features.
MySQL-Max servers are built by using the following configure options:
Option | Comment |
--with-server-suffix=-max | Add a -max suffix to the mysqld version string |
--with-innodb | Support for InnoDB tables (MySQL 3.23 only) |
--with-bdb | Support for Berkeley DB (BDB) tables |
CFLAGS=-DUSE_SYMDIR | Symbolic link support for Windows |
MySQL-Max binary distributions are a convenience for those who wish to install precompiled programs. If you build MySQL using a source distribution, you can build your own Max-like server by enabling the same features at configuration time that the MySQL-Max binary distributions are built with.
MySQL-Max servers always include the InnoDB storage engine. The --with-innodb option for enabling InnoDB support is needed only in MySQL 3.23. (In MySQL 4 and up, InnoDB is included by default. so you do not need a MySQL-Max server to obtain InnoDB support.)
MySQL-Max servers include the BerkeleyDB (BDB) storage engine whenever possible, but not all platforms support BDB. The following table shows which platforms allow MySQL-Max binaries to include BDB:
System | BDB |
Windows/NT | Y |
AIX 4.3 | N |
HP-UX 11.0 | N |
Linux-Alpha | N |
Linux-Intel | Y |
Linux-IA-64 | N |
Solaris-Intel | N |
Solaris-SPARC | Y |
SCO OSR5 | Y |
UnixWare | Y |
Mac OS X | N |
As of Version 3.23, all MySQL servers support MyISAM tables, because MyISAM is the default storage engine. To find out which storage engines your server supports, issue the following statement:
mysql> SHOW VARIABLES LIKE "have_%"; +------------------+----------+ | Variable_name | Value | +------------------+----------+ | have_bdb | NO | | have_crypt | YES | | have_innodb | YES | | have_isam | NO | | have_raid | NO | | have_symlink | DISABLED | | have_openssl | NO | | have_query_cache | YES | +------------------+----------+
The values in the second column indicate the server's level of support for each feature:
Value | Meaning |
YES | The feature is supported and is active. |
NO | The feature is not supported. |
DISABLED | The feature is supported but has been disabled. |
A value of NO means that the server was compiled without support for the feature, so it cannot be activated at runtime.
A value of DISABLED occurs either because the server was started with an option that disables the feature, or because not all options required to enable it were given. In the latter case, the hostname.err file should contain a reason indicating why the option is disabled.
One situation in which you might see DISABLED occurs with MySQL 3.23 when the InnoDB storage engine is compiled in. In MySQL 3.23, you must supply at least the innodb_data_file_path option at runtime to set up the InnoDB tablespace. Without the options, InnoDB disables itself. See InnoDB in MySQL 3.23. (You can specify configuration options for the BDB storage engine, too, but BDB will not disable itself without them. See BDB start.)
You may also see DISABLED for the InnoDB, BDB, or ISAM storage engines if the server was compiled to support them, but was started with the --skip-innodb, --skip-bdb, or --skip-isam options at runtime.
mysqld_safe is the recommended way to start a mysqld server on Unix. mysqld_safe adds some safety features such as restarting the server when an error occurs and logging run-time information to a log file.
Note: Before MySQL 4.0, mysqld_safe is named safe_mysqld. To preserve backward compatibility, MySQL binary distributions for some time will include safe_mysqld as a symbolic link to mysqld_safe.
If you don't use --mysqld=# or --mysqld-version=# mysqld_safe will use an executable named mysqld-max if it exists. If not, mysqld_safe will start mysqld.
On Linux, the MySQL-Max RPM uses this mysqld_safe feature. (It just installs the mysqld-max executable, so mysqld_safe automatically uses this executable when mysqld_safe is restarted.)
The preference of mysqld_safe for mysqld-max over mysqld makes it very easy to test a new mysqld binary in an existing installation. Just run configure with the options you want and then install the new mysqld binary as mysqld-max in the same directory where your existing mysqld binary is located.
On the other hand, this behavior means that if you install a MySQL-Max distribution that includes a server named mysqld-max, then upgrade later to a non-Max version of MySQL, mysqld_safe will still attempt to run the old mysqld-max server. If you perform such an upgrade, manually remove the old mysqld-max server to ensure that mysqld_safe runs the new mysqld server.
Normally, you should never edit the mysqld_safe script. Instead, put the options to mysqld_safe in the [mysqld_safe] section in a my.cnf option file. See Option files. mysqld_safe reads all options from the [mysqld], [server] and [mysqld_safe] sections from the option files. (For backward compatibility, it also reads the [safe_mysqld] sections, though you should rename such sections to [mysqld_safe] once you begin using MySQL 4.0 or later.)
Note that all options specified to mysqld_safe on the command-line are passed to mysqld. If you wants to use any options for mysqld_safe that mysqld doesn't support, you must specify them in the option file.
Many of the options to mysqld_safe are the same as the options to mysqld. See Server options.
mysqld_safe supports the following options:
--basedir=path | The path to the installation directory. |
--core-file-size=# | The size of the core file mysqld should be able to create. Passed to ulimit -c. |
--datadir=path | The path to the data directory. |
--defaults-extra-file=path | The name of an option file to be read in addition to the usual option files. |
--defaults-file=path | The name of an option file to be read instead of the usual option files. |
--err-log=path | Old form of the --log-error option, to be used before MySQL 4.0. |
--log-error=path | Write the error log to the above file. See Error log. |
--ledir=path | The path to the directory containing the mysqld program. Use this option to explicitly indicate the location of the server. |
--log=path , --mysqld=prog_name | The name of the server program (in the ledir directory) that you want to start. |
--mysqld-version=suffix | Similar to --mysqld= but here you only give the suffix for the server program name. The base name is assumed to be mysqld. For example, if you use --mysqld-version=max, mysqld_safe will start the mysqld-max program in the ledir directory. If the argument to --mysqld-version is empty, mysqld in the ledir directory is used. |
--nice=# | Use the nice program to set the server's scheduling priority to the given value. This option was added in MySQL 4.0.14. |
--no-defaults | Do not read any option files. |
--open-files-limit=# | The number of files mysqld should be able to open. Passed to ulimit -n. Note that you need to start mysqld_safe as root for this to work properly! |
--pid-file=path | The path to the process ID file. |
--port=# | The TCP/IP port number. |
--socket=path | The Unix socket file path. |
--timezone=# | Set the time zone (the TZ) variable to the value of this parameter. |
--user=# |
The mysqld_safe script is written so that it normally is able to start a server that was installed from either a source or a binary distribution of MySQL, even those these normally install the server in slightly different locations. See Installation layouts. mysqld_safe expects one of the following conditions to be true:
The server and databases can be found relative to the directory from which mysqld_safe is invoked. mysqld_safe looks under its working directory for bin and data directories (for binary distributions) or for libexec and var directories (for source distributions). This condition should be met if you execute mysqld_safe from your MySQL installation directory (for example, /usr/local/mysql for a binary distribution).
If the server and databases cannot be found relative to the working directory, mysqld_safe attempts to locate them by absolute pathnames. Typical locations are /usr/local/libexec and /usr/local/var. The actual locations are determined from the values configured into the distribution at the time it was built. They should be correct if MySQL is installed in the location specified at configuration time.
Because mysqld_safe will try to find the server and databases relative to its own working directory, you can install a binary distribution of MySQL anywhere, as long as you start mysqld_safe from the MySQL installation directory:
shell> cd mysql_installation_directory shell> bin/mysqld_safe &
If mysqld_safe fails, even when invoked from the MySQL installation directory, you can specify the --ledir and --datadir options to indicate the directories in which the server and databases are located on your system.
In rare cases, it may be necessary to edit mysqld_safe to get it to start the server properly. If you do this, note that if you upgrade MySQL in the future, your modified version of mysqld_safe will be overwritten, so you should make a copy of your edited version that you can reinstall.
MySQL distributions on Unix include a script named mysql.server. It can be used on systems such as Linux and Solaris that use System V-style run directories to start and stop system services.
On Linux systems, the server RPM distribution installs mysql.server in /etc/init.d automatically under the name mysql.
If you install MySQL on Linux using another distribution format, or on a System V-style system, you can install the script manually by copying it to the /etc/init.d directory with the name mysql. Make sure the script is executable. (Use chmod +x mysql.)
The commands needed to activate the script depend on your operating system. On Linux, you can use chkconfig:
shell> chkconfig --add mysql
For other systems, consult your operating system documentation to see how to install startup scripts.
mysqld_multi is meant for managing several mysqld processes that listen for connections on different Unix socket files and TCP/IP ports. It can start or stop servers, or report their current status.
The program searches for groups named [mysqld#] in my.cnf (or in the file named by the --config-file=... option on the command line). # can be any positive integer. This number is referred to in the following discussion as the option group number, or GNR. Group numbers distinquish option groups from one another and are used as arguments to mysqld_multi to specify which servers you want to start, stop, or obtain the status of. Options listed in these groups are the same as you would use in the usual [mysqld] group used for starting mysqld. (See, for example, Automatic start.) However, when using multiple servers it is necessary that each one use its own value for options such as the Unix socket file and TCP/IP port number. For more information on which options should be specified in a multiple-server environment, see Multiple servers.
To invoke mysqld_multi, use the following syntax:
shell> mysqld_multi [OPTIONS] {start|stop|report} [GNR[,GNR]...]
start, stop, and report indicate the operation you want to perform. You can perform the operation on a single server or multiple servers, depending on the GNR list that follows the option name. If there is no list, mysqld_multi performs the operation for all servers in the option file.
Each GNR value represents an option group number or range of group numbers. The value should be the number at the end of the group name in the option file. For example, the GNR for a group named [mysqld17] is 17. To specify a range of numbers, separate the first and last numbers by a dash. The GNR value 10-13 represents groups [mysqld10] through [mysqld13]. Multiple groups or group ranges can be specified on the command line, separated by commas. There must be no whitespace characters (spaces or tabs) in the GNR list. (Anything after a whitespace character is ignored.)
This command starts a single server using option group [mysqld17]:
shell> mysqld_multi start 17
This command stops serveral servers, using option groups [mysql8] and [mysqld10] through [mysqld13]:
shell> mysqld_multi start 8,10-13
For an example of how you might set up an option file, use this command:
shell> mysqld_multi --example
mysqld_multi supports the following options:
Some notes about mysqld_multi:
Make sure that the MySQL user who is stopping the mysqld services (using the mysqladmin program) has the same password and username for all the data directories accessed (to the mysql database). And make sure that the user has the SHUTDOWN privilege! If you have many data directories and many different mysql databases with different passwords for the MySQL root user, you may want to create a common multi_admin user for each using the same password (see below). Example how to do it:
shell> mysql -u root -S /tmp/mysql.sock -proot_password -e "GRANT SHUTDOWN ON *.* TO multi_admin@localhost IDENTIFIED BY 'multipass'"
See Privileges. You will have to do the above for each mysqld running in each data directory, that you have (just change the socket, -S=...).
pid-file is very important, if you are using mysqld_safe to start mysqld (for example, --mysqld=mysqld_safe) Every mysqld should have its own pid-file. The advantage using mysqld_safe instead of mysqld directly here is, that mysqld_safe ``guards'' every mysqld process and will restart it, if a mysqld process terminates due to a signal sent using kill -9, or for other reasons such as a segmentation fault. Please note that the mysqld_safe script may require that you start it from a certain place. This means that you may have to cd to a certain directory, before you start the mysqld_multi. If you have problems starting, please see the mysqld_safe script. Check especially the lines:
-------------------------------------------------------------------------- MY_PWD=`pwd` # Check if we are starting this relative (for the binary release) if test -d $MY_PWD/data/mysql -a -f ./share/mysql/english/errmsg.sys -a \ -x ./bin/mysqld --------------------------------------------------------------------------
See mysqld_safe. The above test should be successful, or you may encounter problems.
Beware of the dangers of using multiple mysqld servers with the same data directory. Use separate data directories, unless you know what you are doing! See Multiple servers.
The Unix socket file and the TCP/IP port must be different for every mysqld.
You may want to use option --user for mysqld, but in order to do this you need to run the mysqld_multi script as the Unix root user. Having the option in the config file doesn't matter; you will just get a warning, if you are not the superuser and the mysqlds are started under your Unix account. Important: Make sure that the pid-file and the data directory are read+write(+execute for the latter one) accessible for that Unix user, who the specific mysqld process is started as. Do not use the Unix root account for this, unless you know what you are doing!
Most important: Before using mysqld_multi be sure that you understand the meanings of the options that are passed to the mysqld servers and why you would want to have separate mysqld processes. Starting multiple servers with the same data directory will not give you extra performance in a threaded system! See Multiple servers.
The following example shows how you might set up an option file for use with mysqld_multi. The first and fifth [mysqld#] group were intentionally left out from the example. You may have ``gaps'' in the option file. This gives you more flexibility. The order in which the mysqld programs are started or stopped depends on the order in which they appear in the option file.
# This file should probably be in your home dir (~/.my.cnf) # or /etc/my.cnf # Version 2.1 by Jani Tolonen [mysqld_multi] mysqld = /usr/local/bin/mysqld_safe mysqladmin = /usr/local/bin/mysqladmin user = multi_admin password = multipass [mysqld2] socket = /tmp/mysql.sock2 port = 3307 pid-file = /usr/local/mysql/var2/hostname.pid2 datadir = /usr/local/mysql/var2 language = /usr/local/share/mysql/english user = john [mysqld3] socket = /tmp/mysql.sock3 port = 3308 pid-file = /usr/local/mysql/var3/hostname.pid3 datadir = /usr/local/mysql/var3 language = /usr/local/share/mysql/swedish user = monty [mysqld4] socket = /tmp/mysql.sock4 port = 3309 pid-file = /usr/local/mysql/var4/hostname.pid4 datadir = /usr/local/mysql/var4 language = /usr/local/share/mysql/estonia user = tonu [mysqld6] socket = /tmp/mysql.sock6 port = 3311 pid-file = /usr/local/mysql/var6/hostname.pid6 datadir = /usr/local/mysql/var6 language = /usr/local/share/mysql/japanese user = jani
See Option files.
Table of Contents
This section discusses MySQL server configuration topics:
Startup options that the server supports.
How to set the server SQL mode.
When you start the mysqld server, you specify program options using any of the methods described in Program Options. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure the server uses the same options each time it runs. The best way to ensure this is to specify server options in an option file. See Option files.
mysqld reads options from the [mysqld] and [server] groups. mysqld_safe reads options from the [mysqld], [server], [mysqld_safe] and [safe_mysqld] groups. mysql.server reads options from the [mysqld] and [mysql.server] groups. An embedded MySQL server usually reads options from the [server], [embedded] and [xxxxx_SERVER] groups, where xxxxx is the name of the application into which the server is embedded.
mysqld accepts many command-line options. For a list, execute mysqld --help. Before MySQL 4.1.1, --help prints the full help message. As of 4.1.1, it prints a brief message; to see the full list, use mysqld --help --verbose.
The following list shows some of the most common server options. Options used for replication are listed in a separate section, see Replication Options.
--ansi | Use SQL-99 syntax instead of MySQL syntax. See ANSI mode. For more precise control over the server SQL mode, use the --sql-mode option instead. | |||||||||||
--basedir=path, -b path | The path to the installation directory. All paths are usually resolved relative to this. | |||||||||||
--big-tables | Allow large result sets by saving all temporary sets on file. This option prevents most ``table full'' errors, but also slows down queries for which in-memory tables would suffice. Since Version 3.23.2, MySQL is able to handle large result sets automatically by using memory for small temporary tables and switching to disk tables where necessary. | |||||||||||
--bind-address=IP | The IP address to bind to. | |||||||||||
--console | Write the error log messages to stderr/stdout even if --log-error is specified. On Windows, mysqld will not close the console screen if this option is used. | |||||||||||
--character-sets-dir=path | The directory where character sets are installed. See Character sets. | |||||||||||
--chroot=path | Put the mysqld server in a closed environment during startup by using the chroot() system call. This is a recommended security measure as of MySQL 4.0. (MySQL 3.23 is not able to provide a chroot() jail that is 100% closed.) Note that use of this option somewhat limits LOAD DATA INFILE and SELECT ... INTO OUTFILE. | |||||||||||
--core-file | Write a core file if mysqld dies. For some systems, you must also specify the --core-file-size option to mysqld_safe. See mysqld_safe. Note that on some systems, such as Solaris, you will not get a core file if you are also using the --user option. | |||||||||||
--datadir=path, -h path | The path to the data directory. | |||||||||||
--debug[=...] | If MySQL is configured with --with-debug, you can use this option to get a trace file of what mysqld is doing. See Making trace files. | |||||||||||
--default-character-set=charset | Set the default character set. See Character sets. | |||||||||||
--default-table-type=type | Set the default table type for tables. See Table types. | |||||||||||
--delay-key-write[= OFF | ON | ALL] | How the DELAYED KEYS option should be used. Delayed key writing causes key buffers not to be flushed between writes for MyISAM tables. OFF disables delayed key writes. ON enables delayed key writes for those tables that were created with the DELAYED KEYS option. ALL delays key writes for all MyISAM tables. Available as of MySQL 4.0.3. See Server parameters. | |||||||||||
--delay-key-write-for-all-tables | Old form of --delay-key-write=ALL for use prior to MySQL 4.0.3. As of 4.0.3, use --delay-key-write instead. | |||||||||||
--des-key-file=filename | Read the default keys used by DES_ENCRYPT() and DES_DECRYPT() from this file. | |||||||||||
--enable-external-locking | Enable system locking. Note that if you use this option on a system on which lockd does not fully work (as on Linux), you will easily get mysqld to deadlock. This option used to be named --enable-locking. | |||||||||||
--enable-named-pipe | Enable support for named pipes. This option applies only on Windows NT, 2000, and XP systems, and may be used only with the mysqld-nt and mysqld-max-nt servers that support named pipe connections. | |||||||||||
--exit-info, -T | This is a bit mask of different flags you can use for debugging the mysqld server. Do not use this option unless you know exactly what it does! | |||||||||||
--flush | Flush all changes to disk after each SQL statement. Normally MySQL only does a write of all changes to disk after each SQL statement and lets the operating system handle the syncing to disk. See Crashing. | |||||||||||
--help, -? | Display a short help message and exit. Prior to MySQL 4.1.1, --help displays the full help message. As of 4.1.1, it displays an abbreviated message only. Use both the --verbose and --help options to see the full message. | |||||||||||
--init-file=file | Read SQL statements from this file at startup. | |||||||||||
--language=lang_name, -L lang_name | Client error messages in given language. lang_name may be given as the language name or as the full pathname to the directory where the language files are installed. See Languages. | |||||||||||
--log[=file], -l [file] | Log connections and queries to this file. See Query log. If you don't specify a file name, MySQL will use hostname.log as filename. | |||||||||||
--log-bin=[file] | Log all queries that change data to this file. Used for backup and replication. See Binary log. If you don't specify a file name, MySQL will use hostname-bin as filename. | |||||||||||
--log-bin-index[=file] | The index file for binary log file names. See Binary log. If you don't specify file name, MySQL will use hostname-bin.index as filename. | |||||||||||
--log-error[=file] | Log errors and startup messages to this file. See Error log. If you don't specify file name, MySQL will use hostname.err as filename. | |||||||||||
--log-isam[=file] | Log all ISAM/MyISAM changes to this file (used only when debugging ISAM/MyISAM). | |||||||||||
--log-long-format | Log some extra information to the log files (update log, binary update log, and slow queries log, whatever log has been activated). For example, username and timestamp are logged for queries. If you are using --log-slow-queries and --log-long-format, then queries that are not using indexes also are logged to the slow query log. Note that --log-long-format is deprecated as of MySQL version 4.1, when --log-short-format was introduced (the long log format is the default setting since version 4.1). Also note that starting with MySQL 4.1 the --log-queries-not-using-indexes option is available for the purpose of logging queries that do not use indexes to the slow queries log. | |||||||||||
--log-queries-not-using-indexes | If you are using this option with --log-slow-queries, then also queries that are not using indexes are logged to the slow query log. This option is available as of MySQL 4.1. See Slow query log. | |||||||||||
--log-short-format | Log less information to the log files (update log, binary update log, and slow queries log, whatever log has been activated). For example, username and timestamp are not logged for queries. This options was introduced in MySQL 4.1. | |||||||||||
--log-slow-queries[=file] | Log all queries that have taken more than long_query_time seconds to execute to file. Note that the default for the amount of information logged has changed in MySQL 4.1. See the --log-long-format and --log-long-format options for details. See Slow query log. | |||||||||||
--log-update[=file] | Log updates to file.# where # is a unique number if not given. See Update log. The update log is deprecated and is removed in MySQL 5.0.0; you should use the binary log instead (--log-bin). See Binary log. Starting from version 5.0.0, using --log-update will just turn on the binlog instead (see News-5.0.0). | |||||||||||
--log-warnings, -W | Print out warnings like Aborted connection... to the .err file. Enabling this option is recommended, for example, if you use replication (you will get more information about what is happening, such as messages about network failures and reconnections). See Communication errors. This option used to be called --warnings. | |||||||||||
--low-priority-updates | Table-modifying operations (INSERT/DELETE/UPDATE) will have lower priority than selects. It can also be done via {INSERT | REPLACE | UPDATE | DELETE} LOW_PRIORITY ... to lower the priority of only one query, or by SET LOW_PRIORITY_UPDATES=1 to change the priority in one thread. See Table locking. | |||||||||||
--memlock | Lock the mysqld process in memory. This works on systems such as Solaris that support the mlockall() system call. This may help if you have a problem where the operating system is causing mysqld to swap on disk. Note that use of this option requires that you run the server as root, which is normally not a good idea for security reasons. | |||||||||||
--myisam-recover [=option[,option...]]] | Set the MyISAM storage engine recovery mode. The option value is any combination of the values of DEFAULT, BACKUP, FORCE or QUICK. If you specify multiple values, seprate them by commas. You can also use a value of "" to disable this option. If this option is used, mysqld will on open check if the table is marked as crashed or if the table wasn't closed properly. (The last option works only if you are running with --skip-external-locking.) If this is the case mysqld will run check on the table. If the table was corrupted, mysqld will attempt to repair it. The following options affects how the repair works. |
| ||||||||||
--new |
From version 4.0.12, the --new option can be used to make the server
behave as 4.1 in certain respects, easing a 4.0 to 4.1 upgrade:
| |||||||||||
--pid-file=path | The path to pid file used by mysqld_safe. | |||||||||||
--port=num, -P num | The port number to listen for TCP/IP connections. | |||||||||||
--old-protocol, -o | Use the 3.20 protocol for compatibility with some very old clients. See Upgrading-from-3.20. | |||||||||||
--one-thread | Only use one thread (for debugging under Linux). This option is available only if the server is built with debugging enabled. See Debugging server. | |||||||||||
--open-files-limit= | To change the number of file descriptors available to mysqld. If this is not set or set to 0, then mysqld will use this value to reserve file descriptors to use with setrlimit(). If this value is 0 then mysqld will reserve max_connections*5 or max_connections + table_cache*2 (whichever is larger) number of files. You should try increasing this if mysqld gives you the error 'Too many open files'. | |||||||||||
--set-variable=name=value, -O value | Assign a value to a system variable. Use --help to list the variables. You can find a full description for all variables in the SHOW VARIABLES section in this manual. See SHOW VARIABLES. The section on tuning server parameters includes information on how to optimize them. See Server parameters. Please note that --set-variable=name=value and -O name=value syntax is deprecated as of MySQL 4.0.2. In 4.0.2, you can set variables directly using --variable-name=value syntax, and --set-variable is no longer needed. If you want to restrict the maximum value a startup option can be set to with SET, you can define this by using the --maximum-variable-name command line option. See SET OPTION. Note that when setting a variable to a value, MySQL may automatically correct it to stay within a given range, or adjust the value to the closest allowable value if only certain values are allowed. | |||||||||||
--safe-mode | Skip some optimize stages. | |||||||||||
--safe-show-database | With this option, the SHOW DATABASES statement returns only those databases for which the user has some kind of privilege. From version 4.0.2 this option is deprecated and doesn't do anything (the option is enabled by default) as we now have the SHOW DATABASES privilege. See GRANT. | |||||||||||
--safe-user-create | If this is enabled, a user can't create new users with the GRANT statement, if the user doesn't have INSERT privilege to the mysql.user table or any column in this table. | |||||||||||
--skip-bdb | Disable the BDB storage engine. This saves memory and may speed up some operations. Do not use this operation if you require BDB tables. | |||||||||||
--skip-concurrent-insert | Turn off the ability to select and insert at the same time on MyISAM tables. (This is only to be used if you think you have found a bug in this feature.) | |||||||||||
--skip-delay-key-write | Ignore the DELAY_KEY_WRITE option for all tables. As of MySQL 4.0.3, you should use --delay-key-write=OFF instead. See Server parameters. | |||||||||||
--skip-external-locking | Don't use system locking. To use isamchk or myisamchk you must shut down the server. See Stability. Note that in MySQL Version 3.23, you can use CHECK TABLE and REPAIR TABLE to check and repairMyISAM tables. This option used to be named --skip-locking. | |||||||||||
--skip-grant-tables | This option causes the server not to use the privilege system at all. This gives everyone full access to all databases! (You can tell a running server to start using the grant tables again by executing a mysqladmin flush-privileges or mysqladmin reload command, or by issuing a FLUSH PRIVILEGES statement.) | |||||||||||
--skip-host-cache | Do not use the internal hostname cache for faster name-IP resolution. Instead, query the DNS server every time a client connects. See DNS. | |||||||||||
--skip-innodb | Disable the InnoDB storage engine. This saves memory and disk space and may speed up some operations. Do not use this operation if you require InnoDB tables. | |||||||||||
--skip-isam | Disable the ISAM storage engine. As of MySQL 4.1, ISAM is disabled by default, so this option applies only if the server was configured with support for ISAM. This option was added in MySQL 4.1.1. | |||||||||||
--skip-name-resolve | Do not resolve hostnames when checking client connections. Use only IP numbers. If you use this option, all Host column values in the grant tables must be IP numbers or localhost. See DNS. | |||||||||||
--skip-networking | Don't listen for TCP/IP connections at all. All interaction with mysqld must be made via named pipes (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are allowed. See DNS. | |||||||||||
--skip-new | Don't use new, possibly wrong routines. | |||||||||||
--skip-symlink | This is the old form of --skip-symbolic-links, for use before MySQL 4.0.13. | |||||||||||
--symbolic-links, --skip-symbolic-links |
Enable or disable symbolic link support. This option has different effects on
Windows and Unix:
| |||||||||||
--skip-safemalloc | If MySQL is configured with --with-debug=full, all MySQL programs checks for memory overruns during each memory allocation and memory freeing operation. This checking is very slow, so for the server you can avoid it when you don't need it by using the --skip-safemalloc option. | |||||||||||
--skip-show-database | Don't allow the SHOW DATABASES statement, unless the user has the SHOW DATABASES privilege. | |||||||||||
--skip-stack-trace | Don't write stack traces. This option is useful when you are running mysqld under a debugger. On some systems, you also must use this option to get a core file. See Debugging server. | |||||||||||
--skip-thread-priority | Disable using thread priorities for faster response time. | |||||||||||
--socket=path | On Unix, this option specifies the Unix socket file to use for local connections. The default value is /tmp/mysql.sock. On Windows, the option specifies the pipe name to use for local connections that use a named pipe. The default value is MySQL. | |||||||||||
--sql-mode=value[,value[,value...]] | Set the SQL mode for MySQL. See SQL mode. This option was added in 3.23.41. | |||||||||||
--temp-pool | This option causes most temporary files created by the server to use a small set of names, rather than a unique name for each new file. This works around a problem in the Linux kernel dealing with creating many new files with different names. With the old behavior, Linux seems to ``leak'' memory, as it's being allocated to the directory entry cache rather than to the disk cache. | |||||||||||
--transaction-isolation=level | Sets the default transaction isolation level, which may be READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE. See SET TRANSACTION. | |||||||||||
--tmpdir=path, -t path | The path of the directory to use for creating temporary files. It may be useful if your default /tmp directory resides on a partition that is too small to hold temporary tables. Starting from MySQL 4.1, this option accepts several paths that are used in round-robin fashion. Paths should be separated by colon characters (:) on Unix and semicolon characters (;) on Windows. It is possible to set tmpdir to point to a memory-based filesystem, except if the MySQL server is a slave replication server. If it is a slave, some of its temporary files are needed to survive a machine's reboot. (For example, to replicate temporary tables or LOAD DATA INFILE statements). In this case, a memory-based tmpdir that is cleared when the machine reboots is not suitable; a disk-based tmpdir is necessary. | |||||||||||
--user={user_name | user_id}, -u {user_name | user_id} | Run the mysqld server as the user having the name user_name or the numeric user ID user_id. (``User'' in this context refers to a system login account, not a MySQL user listed in the grant tables.) This option is mandatory when starting mysqld as root. The server will change its user ID during its startup sequence, causing it to run as that particular user rather than as root. See Security guidelines. Starting from MySQL 3.23.56 and 4.0.12: To avoid a possible security hole where a user adds a --user=root option to some my.cnf file (thus causing the server to run as root), mysqld uses only the first --user option specified and produces a warning if there are multiple --user options. Options in /etc/my.cnf and datadir/my.cnf are processed before command-line options, so it is recommended that you put a --user option in /etc/my.cnf and specify a value other than root. The option in /etc/my.cnf will be found before any other --user options, which ensures that the server runs as a user other than root, and that a warning results if any other --user option is found. | |||||||||||
--version, -V | Display version information and exit. |
You can change the values of most system variables for a running server with the SET statement. See SET OPTION.
The MySQL server can operate in different SQL modes, and (as of MySQL 4.1) can apply these modes differentially for different clients. This allows applications to tailor server operation to their own requirements.
Modes define what SQL syntax MySQL should support and what kind of data validation checks it should perform. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers.
You can set the default SQL mode by starting mysqld with the --sql-mode="modes" option. Beginning with MySQL 4.1, you can also change the mode after startup time by setting the sql_mode variable with a SET [SESSION|GLOBAL] sql_mode="modes" statement. Setting the GLOBAL variable affects the operation of all clients that connect from that time on. Setting the SESSION variable affects only the current client. modes is a list of different modes separated by comma (,) characters. You can retrieve the current mode by issuing a SELECT @@sql_mode statement. The default value is empty (no modes set).
The value also can be empty (--sql-mode="") if you want to reset it.
The following table lists the supported modes. The Version column indicates when each mode value was implemented.
Value | Version | Meaning |
ANSI_QUOTES | 4.0.0 | Treat " as an identifier quote character (like the MySQL Server ` quote character) and not as a string quote character. You can still use ` to quote identifers in ANSI mode. With ANSI_QUOTES enabled, you cannot use double quotes to quote a literal string, because it will be intepreted as an identifier. |
IGNORE_SPACE | 4.0.0 | Allow spaces between a function name and the ( character. This forces all function names to be treated as reserved words. As a result, if you want to access any database, table, or column name that is a reserved word, you must quote it. For example, because there is a USER() function, the name of the user table in the mysql database and the User column in that table become reserved, so you must quote them:
SELECT "User" FROM mysql."user"; |
NO_AUTO_VALUE_ON_ZERO | 4.1.1 | NO_AUTO_VALUE_ON_ZERO affects handling of AUTO_INCREMENT columns. Normally, you generate the next sequence number for the column by inserting either NULL or 0 into it. NO_AUTO_VALUE_ON_ZERO suppresses this behavior for 0 so that only NULL generates the next sequence number. This mode can be useful if 0 has been stored in a table's AUTO_INCREMENT column. (This is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, normally MySQL will generate new sequence numbers when it encounters the 0 values, resulting in a table with different contents than the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. (As of MySQL 4.1.1, mysqldump automatically includes statements in the dump output to enable NO_AUTO_VALUE_ON_ZERO.) |
NO_DIR_IN_CREATE | 4.0.15 | When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY directives. This option is useful on slave replication servers. |
NO_FIELD_OPTIONS | 4.1.1 | Don't print MySQL field-specific options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. |
NO_KEY_OPTIONS | 4.1.1 | Don't print MySQL index-specific options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. |
NO_TABLE_OPTIONS | 4.1.1 | Don't print MySQL table-specific options (such as ENGINE) in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode. |
NO_UNSIGNED_SUBTRACTION | 4.0.2 | In subtraction operations, don't mark the result as UNSIGNED if one of the operands is unsigned. Note that this makes UNSIGNED BIGINT not 100% usable in all contexts. See Cast Functions. |
ONLY_FULL_GROUP_BY | 4.0.0 | Don't allow queries which in the GROUP BY part refers to a not selected column. |
PIPES_AS_CONCAT | 4.0.0 | Treat || as a string concatenation operator (same as CONCAT()) rather than as a synonym for OR. |
REAL_AS_FLOAT | 4.0.0 | Treat REAL as a synonym for FLOAT rather than as a synonym for DOUBLE. |
The following special modes are provided as shorthand for combinations of mode values from the preceding table:
Value | Version | Meaning |
ANSI | 4.1.1 | REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ONLY_FULL_GROUP_BY. See ANSI mode. |
DB2 | 4.1.1 | PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS |
DB2 | 4.1.1 | PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS |
MAXDB | 4.1.1 | PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS |
MSSQL | 4.1.1 | PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS |
MYSQL323 | 4.1.1 | NO_FIELD_OPTIONS |
MYSQL40 | 4.1.1 | NO_FIELD_OPTIONS |
ORACLE | 4.1.1 | PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS |
POSTGRESQL | 4.1.1 | PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS |
Table of Contents
This section describes some general security issues to be aware of and what you can do to make your MySQL installation more secure against attack or misuse. For information specifically about the access control system that MySQL uses for setting up user accounts and checking database access, see Privilege system.
Anyone using MySQL on a computer connected to the Internet should read this section to avoid the most common security mistakes.
In discussing security, we emphasize the necessity of fully protecting the entire server host (not just the MySQL server) against all types of applicable attacks: eavesdropping, altering, playback, and denial of service. We do not cover all aspects of availability and fault tolerance here.
MySQL uses security based on Access Control Lists (ACLs) for all connections, queries, and other operations that users may attempt to perform. There is also some support for SSL-encrypted connections between MySQL clients and servers. Many of the concepts discussed here are not specific to MySQL at all; the same general ideas apply to almost all applications.
When running MySQL, follow these guidelines whenever possible:
Do not ever give anyone (except MySQL root accounts) access to the user table in the mysql database! This is critical. The encrypted password is the real password in MySQL. Anyone who knows the password which is listed in the user table and has access to the host listed for the account can easily log in as that user.
Learn the MySQL access privilege system. The GRANT and REVOKE statements are used for controlling access to MySQL. Do not grant any more privileges than necessary. Never grant privileges to all hosts.
Checklist:
Try mysql -u root. If you are able to connect successfully to the server without being asked for a password, you have problems. Anyone can connect to your MySQL server as the MySQL root user with full privileges! Review the MySQL installation instructions, paying particular attention to the item about setting a root password.
Use the SHOW GRANTS statement and check to see who has access to what. Then use the REVOKE statement to remove those privileges that are not necessary.
Do not store any plain-text passwords in your database. If your computer becomes compromised, the intruder can take the full list of passwords and use them. Instead, use MD5(), SHA1() or some other one-way hashing function.
Do not choose passwords from dictionaries. There are special programs to break them. Even passwords like ``xfish98'' are very bad. Much better is ``duag98'' which contains the same word ``fish'' but typed one key to the left on a standard QWERTY keyboard. Another method is to use ``Mhall'' which is taken from the first characters of each word in the sentence ``Mary had a little lamb.'' This is easy to remember and type, but difficult to guess for someone who does not know it.
Invest in a firewall. This protects you from at least 50% of all types of exploits in any software. Put MySQL behind the firewall or in a demilitarized zone (DMZ).
Checklist:
Try to scan your ports from the Internet using a tool such as nmap. MySQL uses port 3306 by default. This port should not be accessible from untrusted hosts. Another simple way to check whether or not your MySQL port is open is to try the following command from some remote machine, where server_host is the host where your MySQL server runs:
shell> telnet server_host 3306
If you get a connection and some garbage characters, the port is open, and should be closed on your firewall or router, unless you really have a good reason to keep it open. If telnet just hangs or the connection is refused, everything is OK; the port is blocked.
Do not trust any data entered by users of your applications. They can try to trick your code by entering special or escaped character sequences in web forms, URLs, or whatever application you have built. Be sure that your application remains secure if a user enters something like ``; DROP DATABASE mysql;''. This is an extreme example, but large security leaks and data loss may occur as a result of hackers using similar techniques, if you do not prepare for them.
A common mistake is to protect only string data values. Remember to check numeric data as well. If an application generates a query such as SELECT * FROM table WHERE ID=234 when a user enters the value 234, the user can enter the value 234 OR 1=1 to cause the application to generate the query SELECT * FROM table WHERE ID=234 OR 1=1. As a result, the server retrieves every record in the table. This exposes every record and causes excessive server load. The simplest way to protect from this type of attack is to use apostrophes around the numeric constants: SELECT * FROM table WHERE ID="234". If the user enters extra information, it all becomes part of the string. In numeric context, MySQL automatically converts this string to a number and strips any trailing non-numeric characters from it.
Sometimes people think that if a database contains only publicly available data, it need not be protected. This is incorrect. Even if it is allowable to display any record in the database, you should still protect against denial of service attacks (for example, those that are based on the technique in the preceding paragraph that causes the server to waste resources). Otherwise, your server becomes unresponsive to legitimate users.
Checklist:
Try to enter ' and " in all your web forms. If you get any kind of MySQL error, investigate the problem right away.
Try to modify any dynamic URLs by adding %22 ("), %23 (#), and %27 (') in the URL.
Try to modify datatypes in dynamic URLs from numeric ones to character ones containing characters from previous examples. Your application should be safe against this and similar attacks.
Try to enter characters, spaces, and special symbols rather than numbers in numeric fields. Your application should remove them before passing them to MySQL or else generate an error. Passing unchecked values to MySQL is very dangerous!
Check data sizes before passing them to MySQL.
Consider having your application connect to the database using a different username than the one you use for administrative purposes. Do not give your applications any access privileges they do not need.
Many application programming interfaces provide the means of escaping special characters in data values. Properly used, this prevents application users from entering values that cause the application to generate statements that have a different effect than you intend:
Users of PHP: Use the mysql_escape_string() function, which is based on the function of the same name in the MySQL C API. Prior to PHP 4.0.3, use addslashes() instead.
Users of MySQL C API: Use the mysql_real_escape_string() API call.
Users of MySQL++: Use the escape and quote modifiers for query streams.
Users of Perl DBI: Use the quote() method or use placeholders.
Users of Java JDBC: Use a PreparedStatement object and placeholders.
Other programming interfaces may have similar capabilities.
Do not transmit plain (unencrypted) data over the Internet. This information is accessible to everyone who has the time and ability to intercept it and use it for their own purposes. Instead, use an encrypted protocol such as SSL or SSH. MySQL supports internal SSL connections as of Version 4.0.0. SSH port-forwarding can be used to create an encrypted (and compressed) tunnel for the communication.
Learn to use the tcpdump and strings utilities. For most cases, you can check whether MySQL data streams are unencrypted by issuing a command like the following:
shell> tcpdump -l -i eth0 -w - src or dst port 3306 | strings
(This works under Linux and should work with small modifications under other systems.) Warning: If you do not see plaintext data, this doesn't always mean that the information actually is encrypted. If you need high security, you should consult with a security expert.
When you connect to a MySQL server, you should use a password. The password is not transmitted in clear text over the connection. Password handling during the client connection sequence was upgraded in MySQL 4.1.1 to be very secure. If you are using an older version of MySQL, or are still using pre-4.1.1-style passwords, the encryption algorithm is less strong and with some effort a clever attacker that can sniff the traffic between the client and the server can crack the password. (See Password hashing for a discussion of the different password handling methods.) If the connection between the client and the server goes through an untrusted network, you should use an SSH tunnel to encrypt the communication.
All other information is transferred as text that can be read by anyone who is able to watch the connection. If you are concerned about this, you can use the compressed protocol (in MySQL Version 3.22 and above) to make traffic much more difficult to decipher. To make the connection even more secure, you should use SSH to get an encrypted TCP/IP connection between a MySQL server and a MySQL client. You can find an Open Source SSH client at http://www.openssh.org/, and a commercial SSH client at http://www.ssh.com/.
If you are using MySQL 4.0 or newer, you can also use internal OpenSSL support. See Secure connections.
To make a MySQL system secure, you should strongly consider the following suggestions:
Use passwords for all MySQL users. A client program does not necessarily know the identify of the person running it. It is common for client/server applications that the user may specify any username to the client program. For example, anyone can use the mysql program to connect as any other person simply by invoking it as mysql -u other_user db_name if other_user has no password. If all users have a password, connecting using another user's account becomes much more difficult.
To change the password for a user, use the SET PASSWORD statement. It is also possible to update the user table in the mysql database directly. For example, to change the password of all MySQL accounts that have a username of root, do this:
shell> mysql -u root mysql mysql> UPDATE user SET Password=PASSWORD('new_password') -> WHERE user='root'; mysql> FLUSH PRIVILEGES;
Don't run the MySQL server as the Unix root user. This is very dangerous, because any user with the FILE privilege will be able to create files as root (for example, ~root/.bashrc). To prevent this, mysqld refuses to run as root unless that is specified explicitly using a --user=root option.
mysqld can be run as an ordinary unprivileged user instead. You can also create a separate Unix account named mysql to make everything even more secure (use the account only for administering MySQL). To start mysqld as another Unix user, add a user option that specifies the username to the [mysqld] group of the /etc/my.cnf option file or the my.cnf option file in the server's data directory. For example:
[mysqld] user=mysql
This causes the server to start as the designated user whether you start it manually or by using mysqld_safe or mysql.server. For more details, see Changing MySQL user.
Note that running mysql as a Unix user other than root does not mean that you need to change the root username in the user table. Usernames for MySQL accounts have nothing to do with usernames for Unix accounts.
Don't allow the use of symlinks to tables. (This can be disabled with the --skip-symlink option.) This is especially important if you run mysqld as root, because anyone that has write access to the server's data directory could then delete any file in the system! See Symbolic links to tables.
Make sure that the only Unix user with read or write privileges in the database directories is the user that mysqld runs as.
Don't grant the PROCESS privilege to non-administrative users. The output of mysqladmin processlist shows the text of the currently executing queries, so any user who is allowed to execute that command might be able to see if another user issues an UPDATE user SET password=PASSWORD('not_secure') query.
mysqld reserves an extra connection for users who have the PROCESS privilege, so that a MySQL root user can log in and check server activity even if all normal connections are in use.
Don't grant the SUPER privilege to non-administrative users. It can be used to terminate client connections, change server operation by changing the value of system variables, and control replication servers.
Don't grant the FILE privilege to non-administrative users. Any user that has this privilege can write a file anywhere in the filesystem with the privileges of the mysqld daemon! To make this a bit safer, files generated with SELECT ... INTO OUTFILE will not overwrite existing files and are writable by everyone.
The FILE privilege may also be used to read any file that is world-readable or accessible to the Unix user that the server runs as. With this privilege, you can read any file into a database table. This could be abused, for example, by using LOAD DATA to load /etc/passwd into a table, which then can be displayed with SELECT.
If you don't trust your DNS, you should use IP numbers rather than hostnames in the grant tables. In any case, you should be very careful about creating grant table entries using hostname values that contain wildcards!
If you want to restrict the number of connections allowed to a single account, you can do so by setting the max_user_connections variable in mysqld. The GRANT statement also supports resource control options for limiting the extent of server use allowed to an account.
The following mysqld options affect security:
--local-infile[={0|1}] | If you start the server with --local-infile=0, clients cannot use LOCAL in LOAD DATA statements. See LOAD DATA LOCAL. |
--safe-show-database | With this option, the SHOW DATABASES statement displays the names of only those databases for which the user has some kind of privilege. As of version 4.0.2, this option is deprecated and doesn't do anything (it is enabled by default), because there is now a SHOW DATABASES privilege that can be used to control access to database names on a per-account basis. See GRANT. |
--safe-user-create |
If this is enabled, a user cannot create new users with the GRANT
statement unless the user has the INSERT privilege for the
mysql.user table. If you want a user to have the ability to create
new users with those privileges that the user has right to grant, you should
grant the user the following privilege:
mysql> GRANT INSERT(user) ON mysql.user TO 'user'@'hostname';This will ensure that the user can't change any privilege columns directly, but has to use the GRANT statement to give privileges to other users. |
--skip-grant-tables | This option causes the server not to use the privilege system at all. This gives everyone full access to all databases! (You can tell a running server to start using the grant tables again by executing a mysqladmin flush-privileges or mysqladmin reload command, or by issuing a FLUSH PRIVILEGES statement.) |
--skip-name-resolve | Hostnames are not resolved. All Host column values in the grant tables must be IP numbers or localhost. |
--skip-networking | Don't allow TCP/IP connections over the network. All connections to mysqld must be made via Unix socket files. This option is unsuitable when using a MySQL version prior to 3.23.27 with the MIT-pthreads package, because Unix socket files were not supported by MIT-pthreads at that time. |
--skip-show-database | Don't allow the SHOW DATABASES statement, unless the user has the SHOW DATABASES privilege. As of version 4.0.2, you should no longer need this option. Access now can be granted to specific accounts with the SHOW DATABASES privilege. |
The LOAD DATA statement can load a file that is located on the server host, or, when the LOCAL keyword is specified, a file that is located on the client host.
There are two possible problems with supporting the LOCAL version of LOAD DATA statements:
The reading of the file is initiated from the server, so one could theoretically create a patched MySQL server that could tell the client program to read any file on the client machine that the current user has read access to, when the client issues a query against the table.
In a web environment where the clients are connecting from a web server, a user could use LOAD DATA LOCAL to read any files that the web server process has read access to (assuming a user could run any command against the SQL server). In this environment, the client with respect to the MySQL server actually is the web server, not the program being run by the user connecting to the web server.
To deal with these potential security issues, we changed how LOAD DATA LOCAL is handled as of MySQL 3.23.49 and MySQL 4.0.2 (4.0.13 on Windows):
By default, all MySQL clients and libraries in binary distributions are compiled with the --enable-local-infile option, to be compatible with MySQL 3.23.48 and before.
If you build MySQL from source but don't use the --enable-local-infile option to configure, LOAD DATA LOCAL cannot be used by any client unless it is written explicitly to invoke mysql_options(... MYSQL_OPT_LOCAL_INFILE, 0). See mysql_options().
You can disable all LOAD DATA LOCAL commands from the server side by starting mysqld with --local-infile=0.
For the mysql command-line client, LOAD DATA LOCAL can be enabled by specifying the --local-infile[=1] option, or disabled with the --local-infile=0 option. Similarly, for mysqlimport, the --local or -L option enable local datafile loading. In any case, successful use of a local loading operation requires that the server is enabled to allow it.
If LOAD DATA LOCAL INFILE is disabled, either in the server or the client, a client that attempts to issue such a statement receives the following error message:
ERROR 1148: The used command is not allowed with this MySQL version
Table of Contents
MySQL has an advanced but non-standard security/privilege system. This section describes how it works.
An upgrade to MySQL 4.1 can cause a compatibility issue for applications that use PASSWORD() to generate passwords for their own purposes. (Applications really should not do this, because PASSWORD() should be used only to manage passwords for MySQL accounts. But some applications use PASSWORD() for their own purposes anyway.) If you upgrade to 4.1 and run the server under conditions where it generates long password hashes, an application that uses PASSWORD() for its own passwords will break. The recommended course of action is to modify the application to use another function such as SHA1() or MD5() to produce hashed values. If that is not possible, you can use the OLD_PASSWORD() function, which is provided to generate short hashes in the old format. (But note that OLD_PASSWORD() may one day no longer be supported.)
If the server is running under circumstances where it generates short hashes, OLD_PASSWORD() is available but is equivalent to PASSWORD().
Password hashing in MySQL 4.1.0 differs from hashing in 4.1.1 and up. The 4.1.0 differences are:
Password hashes are 45 bytes long rather than 41 bytes.
The PASSWORD() function is non-repeatable. That is, with a given argument X, successive calls to PASSWORD(X) generate different results.
The primary function of the MySQL privilege system is to authenticate a user connecting from a given host, and to associate that user with privileges on a database such as SELECT, INSERT, UPDATE and DELETE.
Additional functionality includes the ability to have an anonymous user and to grant privileges for MySQL-specific functions such as LOAD DATA INFILE and administrative operations.
The MySQL privilege system ensures that all users may perform only the operations allowed to them. As a user, when you connect to a MySQL server, your identity is determined by the host from which you connect and the username you specify. The system grants privileges according to your identity and what you want to do.
MySQL considers both your hostname and username in identifying you because there is little reason to assume that a given username belongs to the same person everywhere on the Internet. For example, the user joe who connects from office.com need not be the same person as the user joe who connects from elsewhere.com. MySQL handles this by allowing you to distinguish users on different hosts that happen to have the same name: you can grant joe one set of privileges for connections from office.com, and a different set of privileges for connections from elsewhere.com.
MySQL access control involves two stages:
Stage 1: The server checks whether you are even allowed to connect.
Stage 2: Assuming you can connect, the server checks each request you issue to see whether you have sufficient privileges to perform it. For example, if you try to select rows from a table in a database or drop a table from the database, the server makes sure you have the SELECT privilege for the table or the DROP privilege for the database.
Note that if your privileges are changed (either by yourself or someone else) while you are connected, those changes will not necessarily take effect with your next query or queries. See Privilege changes for details.
The server uses the user, db, and host tables in the mysql database at both stages of access control. The columns in these grant tables are shown here:
Table name | user | db | host |
Scope columns | Host | Host | Host |
User | Db | Db | |
Password | User | ||
Privilege columns | Select_priv | Select_priv | Select_priv |
Insert_priv | Insert_priv | Insert_priv | |
Update_priv | Update_priv | Update_priv | |
Delete_priv | Delete_priv | Delete_priv | |
Index_priv | Index_priv | Index_priv | |
Alter_priv | Alter_priv | Alter_priv | |
Create_priv | Create_priv | Create_priv | |
Drop_priv | Drop_priv | Drop_priv | |
Grant_priv | Grant_priv | Grant_priv | |
References_priv | References_priv | References_priv | |
Reload_priv | |||
Shutdown_priv | |||
Process_priv | |||
File_priv | |||
Show_db_priv | |||
Super_priv | |||
Create_tmp_table_priv | Create_tmp_table_priv | Create_tmp_table_priv | |
Lock_tables_priv | Lock_tables_priv | Lock_tables_priv | |
Execute_priv | |||
Repl_slave_priv | |||
Repl_client_priv | |||
ssl_type | |||
ssl_cypher | |||
x509_issuer | |||
x509_cubject | |||
max_questions | |||
max_updates | |||
max_connections |
During the second stage of access control (request verification), the server may, if the request involves tables, additionally consult the tables_priv and columns_priv tables that provide finer control at the table and column levels. The columns in these tables are shown here:
Table name | tables_priv | columns_priv |
Scope columns | Host | Host |
Db | Db | |
User | User | |
Table_name | Table_name | |
Column_name | ||
Privilege columns | Table_priv | Column_priv |
Column_priv | ||
Other columns | Timestamp | Timestamp |
Grantor |
Each grant table contains scope columns and privilege columns.
Scope columns determine the scope of each entry (row) in the tables, that is, the context in which the entry applies. For example, a user table entry with Host and User values of 'thomas.loc.gov' and 'bob' would be used for authenticating connections made to the server from the host thomas.loc.gov by a client that specifies a username of bob. Similarly, a db table entry with Host, User, and Db column values of 'thomas.loc.gov', 'bob' and 'reports' would be used when bob connects from the host thomas.loc.gov to access the reports database. The tables_priv and columns_priv tables contain scope columns indicating tables or table/column combinations to which each entry applies.
For access-checking purposes, comparisons of Host values are case-insensitive. User, Password, Db, and Table_name values are case-sensitive. Column_name values are case-insensitive in MySQL Version 3.22.12 or later.
Privilege columns indicate the privileges granted by a table entry, that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. The rules used to do this are described in Request access.
Scope columns contain strings. They are declared as shown here; the default value for each is the empty string:
Column name | Type |
Host | CHAR(60) |
User | CHAR(16) |
Password | CHAR(16) |
Db | CHAR(64) |
Table_name | CHAR(60) |
Column_name | CHAR(60) |
Before MySQL 3.23, the Db column was CHAR(32) in some tables and CHAR(60) in others.
In the user, db and host tables, each privilege is listed in a separate column. Each privilege column is declared as ENUM('N','Y') and can have a value of 'N' or 'Y'; the default value is 'N'.
In the tables_priv and columns_priv tables, the privilege columns are declared as SET columns. Values in these columns can contain any combination of the privileges controlled by the table:
Table name | Column name | Possible set elements |
tables_priv | Table_priv | 'Select', 'Insert', 'Update', 'Delete', 'Create', 'Drop', 'Grant', 'References', 'Index', 'Alter' |
tables_priv | Column_priv | 'Select', 'Insert', 'Update', 'References' |
columns_priv | Column_priv | 'Select', 'Insert', 'Update', 'References' |
Briefly, the server uses the grant tables like this:
The user table scope columns determine whether to allow or reject incoming connections. For allowed connections, any privileges granted in the user table indicate the user's global (superuser) privileges. These privileges apply to all databases on the server.
The db and host tables are used together:
The db table scope columns determine which users can access which databases from which hosts. The privilege columns determine which operations are allowed.
The host table is used as an extension of the db table when you want a given db table entry to apply to several hosts. For example, if you want a user to be able to use a database from several hosts in your network, leave the Host value empty in the user's db table entry, then populate the host table with an entry for each of those hosts. This mechanism is described more detail in Request access. Note that the host table is not affected by the GRANT and REVOKE statements. Most MySQL installations need not use this table at all.
The tables_priv and columns_priv tables are similar to the db table, but are more fine-grained: they apply at the table and column levels rather than at the database level.
Administrative privileges (such as RELOAD or SHUTDOWN) are specified only in the user table. This is because administrative operations are operations on the server itself and are not database-specific, so there is no reason to list these privileges in the other grant tables. In fact, to determine whether you can perform an administrative operation, the server need consult only the user table.
The FILE privilege also is specified only in the user table. It is not an administrative privilege as such, but your ability to read or write files on the server host is independent of the database you are accessing.
The mysqld server reads the contents of the grant tables once, when it starts. Changes to the grant tables take effect as indicated in Privilege changes.
When you modify the contents of the grant tables, it is a good idea to make sure that your changes set up privileges the way you want. For help in diagnosing problems, see Access denied. For advice on general security issues, see Security.
A useful diagnostic tool is the mysqlaccess script, which Yves Carlier has provided for the MySQL distribution. Invoke mysqlaccess with the --help option to find out how it works. Note that mysqlaccess checks access using only the user, db and host tables. It does not check table or column privileges in the tables_priv or columns_priv tables.
Information about user privileges is stored in the user, db, host, tables_priv, and columns_priv tables in the mysql database (that is, in the database named mysql). The MySQL server reads the contents of these tables when it starts and under the circumstances indicated in Privilege changes.
The names used in this manual to refer to the privileges provided by MySQL version 4.0.2 are shown here, along with the table column name associated with each privilege in the grant tables and the context in which the privilege applies. Further information about the meaning of each privilege may be found at GRANT.
Privilege | Column | Context |
ALTER | Alter_priv | tables |
DELETE | Delete_priv | tables |
INDEX | Index_priv | tables |
INSERT | Insert_priv | tables |
SELECT | Select_priv | tables |
UPDATE | Update_priv | tables |
CREATE | Create_priv | databases, tables, or indexes |
DROP | Drop_priv | databases or tables |
GRANT | Grant_priv | databases or tables |
REFERENCES | References_priv | databases or tables |
CREATE TEMPORARY TABLES | Create_tmp_table_priv | server administration |
EXECUTE | Execute_priv | server administration |
FILE | File_priv | file access on server |
LOCK TABLES | Lock_tables_priv | server administration |
PROCESS | Process_priv | server administration |
RELOAD | Reload_priv | server administration |
REPLICATION CLIENT | Repl_client_priv | server administration |
REPLICATION SLAVE | Repl_slave_priv | server administration |
SHOW DATABASES | Show_db_priv | server administration |
SHUTDOWN | Shutdown_priv | server administration |
SUPER | Super_priv | server administration |
The SELECT, INSERT, UPDATE, and DELETE privileges allow you to perform operations on rows in existing tables in a database.
SELECT statements require the SELECT privilege only if they actually retrieve rows from a table. Some SELECT statements do not access tables, so they can be executed even without permission for any of the databases on the server. For example, you can use the mysql client as a simple calculator:
mysql> SELECT 1+1; mysql> SELECT PI()*2;
The INDEX privilege allows you to create or drop (remove) indexes.
The ALTER privilege allows you to use ALTER TABLE.
The CREATE and DROP privileges allow you to create new databases and tables, or to drop (remove) existing databases and tables.
Note that if you grant the DROP privilege for the mysql database to a user, that user can drop the database in which the MySQL access privileges are stored!
The GRANT privilege allows you to give to other users those privileges you yourself possess.
The FILE privilege gives you permission to read and write files on the server using the LOAD DATA INFILE and SELECT ... INTO OUTFILE statements. Any user to whom this privilege is granted can read any world-readable file accessable by the MySQL server and create a new world-readable file in any directory where the MySQL server can write. The user can also read any file in the current database directory. However, the user cannot change any existing file.
The remaining privileges are used for administrative operations. Many of them can be performed by using using the mysqladmin program or by issuing SQL statements. The following table shows which mysqladmin commands each administrative privilege allows you to execute:
Privilege | Commands permitted to privilege holders |
RELOAD | refresh, reload, flush-hosts, flush-logs, flush-privileges, flush-status, flush-threads, and flush-tables |
SHUTDOWN | shutdown |
PROCESS | processlist |
SUPER | kill |
The reload command tells the server to re-read the grant tables. The refresh command flushes all tables and opens and closes the log files. flush-privileges is a synonym for reload. The other flush-* commands perform functions similar to refresh but are more limited in scope, and may be preferable in some instances. For example, if you want to flush just the log files, flush-logs is a better choice than refresh.
The shutdown command shuts down the server. This command can be issued only from mysqladmin. There is no corresponding SQL statement.
The processlist command displays information about the threads executing within the server (that is, about the statements that other clients are executing). The kill command kills server threads. You can always display or kill your own threads, but you need the PROCESS privilege to display threads initiated by other users and and the SUPER privilege to kill them. See KILL.
It is a good idea in general to grant privileges only to those users who need them, but you should exercise particular caution in granting administrative privileges:
The GRANT privilege allows users to give their privileges to other users. Two users with different privileges and with the GRANT privilege are able to combine privileges.
The ALTER privilege may be used to subvert the privilege system by renaming tables.
The FILE privilege can be abused to read into a database table any world-readable file on the server host or any file in the server's data directory. The contents of that table can then be accessed using SELECT.
The SHUTDOWN privilege can be abused to deny service to other users entirely by terminating the server.
The PROCESS privilege can be used to view the plain text of currently executing queries, including queries that set or change passwords.
The SUPER privilege can be used to terminate other clients or change how the server operates.
Privileges granted for the mysql database itself can be used to change passwords and other access privilege information. (Passwords are stored encrypted, so a malicious user cannot simply read them to know the plain text password.) If they can access the mysql.user password column, they can use it to log into the MySQL server for the given user. (With sufficient privileges, the same user can replace a password with a different one.)
There are some things that you cannot do with the MySQL privilege system:
You cannot explicitly specify that a given user should be denied access. That is, you cannot explicitly match a user and then refuse the connection.
You cannot specify that a user has privileges to create or drop tables in a database but not to create or drop the database itself.
MySQL client programs generally require that you specify connection parameters when you want to access a MySQL server: the host you want to connect to, your username, and your password. For example, the mysql client can be started like this, where optional arguments are indicated by [ and ]:
shell> mysql [-h host_name] [-u user_name] [-pyour_pass]
Alternate forms of the -h, -u, and -p options are --host=host_name, --user=user_name, and --password=your_pass. Note that there is no space between -p or --password= and the password following it.
Note: Specifying a password on the command line is not secure! Any user on your system may then find out your password by typing a command like: ps auxww. See Option files.
mysql uses default values for connection parameters that are not given on the command line:
The default hostname is localhost.
The default username is your Unix login name.
No password is supplied if -p is missing.
Thus, for a Unix user joe, the following commands are equivalent:
shell> mysql -h localhost -u joe shell> mysql -h localhost shell> mysql -u joe shell> mysql
Other MySQL clients behave similarly.
On Unix systems, you can specify different default values to be used when you make a connection, so that you need not enter them on the command-line each time you invoke a client program. This can be done in a couple of ways:
You can specify connection parameters in the [client] section of the .my.cnf option file in your home directory. The relevant section of the file might look like this:
[client] host=host_name user=user_name password=your_pass
See Option files.
You can specify connection parameters using environment variables. The host can be specified for mysql using MYSQL_HOST. The MySQL username can be specified using USER (this is for Windows and NetWare only). The password can be specified using MYSQL_PWD (but this is insecure; see the next section). See Environment variables.
When you attempt to connect to a MySQL server, the server accepts or rejects the connection based on your identity and whether you can verify your identity by supplying the correct password. If not, the server denies access to you completely. Otherwise, the server accepts the connection, then enters Stage 2 and waits for requests.
Your identity is based on two pieces of information:
The host from which you connect
Your MySQL username
Identity checking is performed using the three user table scope columns (Host, User, and Password). The server accepts the connection only if a user table entry matches your hostname and user name, and you supply the correct password.
Values in the user table scope columns may be specified as follows:
A Host value may be a hostname or an IP number, or 'localhost' to indicate the local host.
You can use the wildcard characters % and _ in the Host column.
A Host value of '%' matches any hostname.
A blank Host value means that the privilege should be anded with the entry in the host table that matches the given hostname. You can find more information about this in the next chapter.
As of MySQL Version 3.23, for Host values specified as IP numbers, you can specify a netmask indicating how many address bits to use for the network number. For example:
mysql> GRANT ALL PRIVILEGES ON db.* -> TO david@'192.58.197.0/255.255.255.0';
This will allow everyone to connect from an IP where the following is true:
user_ip & netmask = host_ip.
In the above example all IP:s in the interval 192.58.197.0 - 192.58.197.255 can connect to the MySQL server.
Wildcard characters are not allowed in the User column, but you can specify a blank value, which matches any name. If the user table entry that matches an incoming connection has a blank username, the user is considered to be the anonymous user (the user with no name), rather than the name that the client actually specified. This means that a blank username is used for all further access checking for the duration of the connection (that is, during Stage 2).
The Password column can be blank. This does not mean that any password matches, it means the user must connect without specifying a password.
Non-blank Password values represent encrypted passwords. MySQL does not store passwords in plaintext form for anyone to see. Rather, the password supplied by a user who is attempting to connect is encrypted (using the PASSWORD() function). The encrypted password is then used when the client/server is checking if the password is correct. (This is done without the encrypted password ever traveling over the connection.) Note that from MySQL's point of view the encrypted password is the REAL password, so you should not give anyone access to it! In particular, don't give normal users read access to the tables in the mysql database! From version 4.1, MySQL employs a different password and login mechanism that is secure even if TCP/IP packets are sniffed and/or the mysql database is captured.
The examples here show how various combinations of Host and User values in user table entries apply to incoming connections:
Hostvalue | Uservalue | Connections matched by entry |
'thomas.loc.gov' | 'fred' | fred, connecting from thomas.loc.gov |
'thomas.loc.gov' | '' | Any user, connecting from thomas.loc.gov |
'%' | 'fred' | fred, connecting from any host |
'%' | '' | Any user, connecting from any host |
'%.loc.gov' | 'fred' | fred, connecting from any host in the loc.gov domain |
'x.y.%' | 'fred' | fred, connecting from x.y.net, x.y.com,x.y.edu, etc. (this is probably not useful) |
'144.155.166.177' | 'fred' | fred, connecting from the host with IP address 144.155.166.177 |
'144.155.166.%' | 'fred' | fred, connecting from any host in the 144.155.166 class C subnet |
'144.155.166.0/255.255.255.0' | 'fred' | Same as previous example |
Because you can use IP wildcard values in the Host column (for example, '144.155.166.%' to match every host on a subnet), there is the possibility that someone might try to exploit this capability by naming a host 144.155.166.somewhere.com. To foil such attempts, MySQL disallows matching on hostnames that start with digits and a dot. Thus, if you have a host named something like 1.2.foo.com, its name will never match the Host column of the grant tables. Only an IP number can match an IP wildcard value.
An incoming connection may be matched by more than one entry in the user table. For example, a connection from thomas.loc.gov by fred would be matched by several of the entries shown in the preceding table. How does the server choose which entry to use if more than one matches? The server resolves this question by sorting the user table after reading it at startup time, then looking through the entries in sorted order when a user attempts to connect. The first matching entry is the one that is used.
user table sorting works as follows. Suppose the user table looks like this:
+-----------+----------+- | Host | User | ... +-----------+----------+- | % | root | ... | % | jeffrey | ... | localhost | root | ... | localhost | | ... +-----------+----------+-
When the server reads in the table, it orders the entries with the most-specific Host values first ('%' in the Host column means ``any host'' and is least specific). Entries with the same Host value are ordered with the most-specific User values first (a blank User value means ``any user'' and is least specific). The resulting sorted user table looks like this:
+-----------+----------+- | Host | User | ... +-----------+----------+- | localhost | root | ... | localhost | | ... | % | jeffrey | ... | % | root | ... +-----------+----------+-
When a connection is attempted, the server looks through the sorted entries and uses the first match found. For a connection from localhost by jeffrey, the entries with 'localhost' in the Host column match first. Of those, the entry with the blank username matches both the connecting hostname and username. (The '%'/'jeffrey' entry would have matched, too, but it is not the first match in the table.)
Here is another example. Suppose the user table looks like this:
+----------------+----------+- | Host | User | ... +----------------+----------+- | % | jeffrey | ... | thomas.loc.gov | | ... +----------------+----------+-
The sorted table looks like this:
+----------------+----------+- | Host | User | ... +----------------+----------+- | thomas.loc.gov | | ... | % | jeffrey | ... +----------------+----------+-
A connection from thomas.loc.gov by jeffrey is matched by the first entry, whereas a connection from whitehouse.gov by jeffrey is matched by the second.
A common misconception is to think that for a given username, all entries that explicitly name that user will be used first when the server attempts to find a match for the connection. This is simply not true. The previous example illustrates this, where a connection from thomas.loc.gov by jeffrey is first matched not by the entry containing 'jeffrey' as the User column value, but by the entry with no username!
If you have problems connecting to the server, print out the user table and sort it by hand to see where the first match is being made. If connection was successful, but your privileges are not what you expected you may use CURRENT_USER() function (new in version 4.0.6) to see what user/host combination your connection actually matched. See CURRENT_USER().
Once you establish a connection, the server enters Stage 2. For each request that comes in on the connection, the server checks whether you have sufficient privileges to perform it, based on the type of operation you wish to perform. This is where the privilege columns in the grant tables come into play. These privileges can come from any of the user, db, host, tables_priv, or columns_priv tables. The grant tables are manipulated with GRANT and REVOKE commands. See GRANT. (You may find it helpful to refer to Privileges, which lists the columns present in each of the grant tables.)
The user table grants privileges that are assigned to you on a global basis and that apply no matter what the current database is. For example, if the user table grants you the DELETE privilege, you can delete rows from any database on the server host! In other words, user table privileges are superuser privileges. It is wise to grant privileges in the user table only to superusers such as server or database administrators. For other users, you should leave the privileges in the user table set to 'N' and grant privileges on a database-specific basis only, using the db and host tables.
The db and host tables grant database-specific privileges. Values in the scope columns may be specified as follows:
The wildcard characters % and _ can be used in the Host and Db columns of either table. If you wish to use for instance a _ character as part of a database name, specify it as \_ in the GRANT command.
A '%' Host value in the db table means ``any host.'' A blank Host value in the db table means ``consult the host table for further information.''
A '%' or blank Host value in the host table means ``any host.''
A '%' or blank Db value in either table means ``any database.''
A blank User value in either table matches the anonymous user.
The db and host tables are read in and sorted when the server starts (at the same time that it reads the user table). The db table is sorted on the Host, Db, and User scope columns, and the host table is sorted on the Host and Db scope columns. As with the user table, sorting puts the most-specific values first and least-specific values last, and when the server looks for matching entries, it uses the first match that it finds.
The tables_priv and columns_priv tables grant table- and column-specific privileges. Values in the scope columns may be specified as follows:
The wildcard characters % and _ can be used in the Host column of either table.
A '%' or blank Host value in either table means ``any host.''
The Db, Table_name and Column_name columns cannot contain wildcards or be blank in either table.
The tables_priv and columns_priv tables are sorted on the Host, Db, and User columns. This is similar to db table sorting, although the sorting is simpler because only the Host column may contain wildcards.
The request verification process is described here. (If you are familiar with the access-checking source code, you will notice that the description here differs slightly from the algorithm used in the code. The description is equivalent to what the code actually does; it differs only to make the explanation simpler.)
For administrative requests (SHUTDOWN, RELOAD, etc.), the server checks only the user table entry, because that is the only table that specifies administrative privileges. Access is granted if the entry allows the requested operation and denied otherwise. For example, if you want to execute mysqladmin shutdown but your user table entry doesn't grant the SHUTDOWN privilege to you, access is denied without even checking the db or host tables. (They contain no Shutdown_priv column, so there is no need to do so.)
For database-related requests (INSERT, UPDATE, etc.), the server first checks the user's global (superuser) privileges by looking in the user table entry. If the entry allows the requested operation, access is granted. If the global privileges in the user table are insufficient, the server determines the user's database-specific privileges by checking the db and host tables:
The server looks in the db table for a match on the Host, Db, and User columns. The Host and User columns are matched to the connecting user's hostname and MySQL username. The Db column is matched to the database the user wants to access. If there is no entry for the Host and User, access is denied.
If there is a matching db table entry and its Host column is not blank, that entry defines the user's database-specific privileges.
If the matching db table entry's Host column is blank, it signifies that the host table enumerates which hosts should be allowed access to the database. In this case, a further lookup is done in the host table to find a match on the Host and Db columns. If no host table entry matches, access is denied. If there is a match, the user's database-specific privileges are computed as the intersection (not the union!) of the privileges in the db and host table entries, that is, the privileges that are 'Y' in both entries. (This way you can grant general privileges in the db table entry and then selectively restrict them on a host-by-host basis using the host table entries.)
After determining the database-specific privileges granted by the db and host table entries, the server adds them to the global privileges granted by the user table. If the result allows the requested operation, access is granted. Otherwise, the server checks the user's table and column privileges in the tables_priv and columns_priv tables and adds those to the user's privileges. Access is allowed or denied based on the result.
Expressed in boolean terms, the preceding description of how a user's privileges are calculated may be summarized like this:
global privileges OR (database privileges AND host privileges) OR table privileges OR column privileges
It may not be apparent why, if the global user entry privileges are initially found to be insufficient for the requested operation, the server adds those privileges to the database-, table-, and column-specific privileges later. The reason is that a request might require more than one type of privilege. For example, if you execute an INSERT ... SELECT statement, you need both INSERT and SELECT privileges. Your privileges might be such that the user table entry grants one privilege and the db table entry grants the other. In this case, you have the necessary privileges to perform the request, but the server cannot tell that from either table by itself; the privileges granted by the entries in both tables must be combined.
The host table can be used to maintain a list of secure servers.
At TcX, the host table contains a list of all machines on the local network. These are granted all privileges.
You can also use the host table to indicate hosts that are not secure. Suppose you have a machine public.your.domain that is located in a public area that you do not consider secure. You can allow access to all hosts on your network except that machine by using host table entries like this:
+--------------------+----+- | Host | Db | ... +--------------------+----+- | public.your.domain | % | ... (all privileges set to 'N') | %.your.domain | % | ... (all privileges set to 'Y') +--------------------+----+-
Naturally, you should always test your entries in the grant tables (for example, using mysqlaccess) to make sure your access privileges are actually set up the way you think they are.
MySQL user accounts are listed in the user table of the mysql database. Each MySQL account is assigned a password, although what is stored in the Password column of the user table is not the plaintext version of the password, but a hash value computed from it. Password hash values are computed by the PASSWORD() function.
MySQL uses passwords in two phases of client/server communication:
First, when a client attempts to connect to the server, there is an initial authentication step in which the client must present a password that matches the hash value stored in the user table for the account that the client wants to use.
Second, after the client connects, it may set or change the password hashes for accounts listed in the user table (if it has sufficient privileges). The client may do this by using the PASSWORD() function to generate a password hash, or by using the GRANT or SET PASSWORD statements.
In other words, the server uses hash values during authentication when a client first attempts to connect. The server generates hash values if a connected client invokes the PASSWORD() function or uses a GRANT or SET PASSWORD statement to set or change a password.
The password hashing mechanism was updated in MySQL 4.1 to provide better security and to reduce the risk of passwords being stolen. However, this new mechanism is understood only by the 4.1 server and 4.1 clients, which can result in some compatibility problems. A 4.1 client can connect to a pre-4.1 server, because the client understands both the old and new password hashing mechanisms. However, a pre-4.1 client that attempts to connect to a 4.1 server may run into difficulties. For example, a 4.0 mysql client that attempts to connect to a 4.1 server may fail with the following error message:
shell> mysql Client does not support authentication protocol requested by server; consider upgrading MySQL client
The following discussion describes the differences between the old and new password mechanisms, and what you should do if you upgrade your server to 4.1 but need to maintain backward compatibility with pre-4.1 clients.
Note: This discussion contrasts 4.1 behavior with pre-4.1 behavior, but the 4.1 behavior described here actually begins with 4.1.1. MySQL 4.1.0 is an ``odd'' release because it has a slightly different mechanism than that implemented in 4.1.1 and up. Differences between 4.1.0 and more recent versions are described later.
Prior to MySQL 4.1, password hashes computed by the PASSWORD() function are 16 bytes long. Such hashes look like this:
mysql> SELECT PASSWORD('mypass'); +--------------------+ | PASSWORD('mypass') | +--------------------+ | 6f8c114b58f2ce9e | +--------------------+
The Password column of the user table (in which these hashes are stored) also is 16 bytes long before MySQL 4.1.
As of MySQL 4.1, the PASSWORD() function has been modified to produce a longer 41-byte hash value:
mysql> SELECT PASSWORD('mypass'); +-----------------------------------------------+ | PASSWORD('mypass') | +-----------------------------------------------+ | *43c8aa34cdc98eddd3de1fe9a9c2c2a9f92bb2098d75 | +-----------------------------------------------+
Accordingly, the Password column in the user table also must be 41 bytes long to store these values:
If you perform a new installation of MySQL 4.1, the Password column will be made 41 bytes long automatically.
If you upgrade an older installation to 4.1, you should run the mysql_fix_privilege_tables script to update the length of the Password column from 16 to 41 bytes. (The script does not change existing password values, which remain 16 bytes long.)
A widened Password column can store password hashes in both the old and new formats. The format of any given password hash value can be determined two ways:
The obvious difference is the length (16 bytes versus 41 bytes)
A second difference is that password hashes in the new format always begin with a * character, whereas passwords in the old format never do
The longer password hash format has better cryptographic properties, and client authentication based on long hashes is more secure than that based on the older short hashes.
The differences between short and long password hashes are relevant both for how the server uses passwords during authentication and for how it generates password hashes for connected clients that perform password-changing operations.
The way in which the server uses password hashes during authentication is affected by the width of the Password column:
If the column is narrow, only short-hash authentication is used.
If the column is wide, it can hold either short or long hashes, and the server can use either format:
Pre-4.1 clients can connect, though because they know only about the old hashing mechanism, they can authenticate only for accounts that have short hashes.
4.1 clients can authenticate for accounts that have short or long hashes.
For short-hash accounts, the authentication process is actually a bit more secure for 4.1 clients than for older clients. In terms of security, the gradient from least to most secure is:
Pre-4.1 client authenticating for account with short password hash
4.1 client authenticating for account with short password hash
4.1 client authenticating for account with long password hash
The way in which the server generates password hashes for connected clients is affected by the width of the Password column and by the --old-passwords option. A 4.1 server generates long hashes only if certain conditions are met: The Password column must be wide enough to hold long values and the --old-passwords option must not be given. These conditions apply as follows:
The Password column must be wide enough to hold long hashes (41 bytes). If the column has not been updated and still has the pre-4.1 width (16 bytes), the server notices that long hashes cannot fit into it and generates only short hashes when a client performs password-changing operations using PASSWORD(), GRANT, or SET PASSWORD. (This behavior occurs if you have upgraded to 4.1 but have not run the mysql_fix_privilege_tables script to widen the Password column.)
If the Password column is wide, it can store either short or long password hashes. In this case, PASSWORD(), GRANT, and SET PASSWORD will generate long hashes unless the server was started with the --old-passwords option. This option forces the server to generate short passsword hashes instead.
The purpose of the --old-passwords option is to allow you to maintain backward compatibility with pre-4.1 clients under circumstances where the server would otherwise generate long password hashes. It doesn't affect authentication (4.1 clients can still use accounts that have long password hashes), but it does prevent creation of a long password hash in the user table as the result of a password-changing operation. Were that to occur, the account no longer could be used by pre-4.1 clients. Without the --old-passwords option, the following scenario is possible:
An old client connects to an account that has a short password hash.
The client changes the account's password. Without --old-passwords, this results in the account having a long password hash.
The next time the old client attempts to connect to the account, it cannot, because the account now requires the new hashing mechanism during authentication. (Once an account has a long password hash in the user table, only 4.1 clients can authenticate for it, because pre-4.1 clients do not understand long hashes.)
This scenario illustrates that it is dangerous to run a 4.1 server without using the --old-passwords option if you must support older pre-4.1 clients. By running the server with --old-passwords, password-changing operations will not generate long password hashes and thus do not cause accounts to become inaccessible to older clients. (Those clients cannot inadvertently lock themselves out by changing their password and ending up with a long password hash.)
The downside of the --old-passwords option is that any passwords you create or change will use short hashes, even for 4.1 clients. Thus, you lose the additional security provided by long password hashes. If you want to create an account that has a long hash (for example, for use by 4.1 clients), you must do so while running the server without --old-passwords.
The following scenarios are possible for running a 4.1 server:
Scenario 1) Narrow Password column in user table
Only short hashes can be stored in the Password column.
The server uses only short hashes during client authentication.
For connected clients, password hash-generating operations involving PASSWORD(), GRANT, or SET PASSWORD use short hashes exclusively. Any change to an account's password results in that account having a short password hash.
The --old-passwords option can be used but is superfluous because with a narrow Password column, the server will be generating short password hashes anyway.
Scenario 2) Long Password column; server not started with --old-passwords option
Short or long hashes can be stored in the Password column.
4.1 clients can authenticate for accounts that have short or long hashes.
Pre-4.1 clients can authenticate only for accounts that have short hashes.
For connected clients, password hash-generating operations involving PASSWORD(), GRANT, or SET PASSWORD use long hashes exclusively. Any change to an account's password results in that account having a long password hash.
OLD_PASSWORD() may be used to explicitly generate a short hash. For example, to assign an account a short password, use UPDATE as follows:
mysql> UPDATE user SET Password = OLD_PASSWORD('mypass') -> WHERE Host = 'some_host' AND User = 'some_user'; mysql> FLUSH PRIVILEGES;
As indicated earlier, a danger in this scenario is that it is possible for accounts that have a short password hash to become inaccessible to pre-4.1 clients. Any change to such an account's password made via GRANT, SET PASSWORD, or PASSWORD() results in the account being given a long password hash, and from that point on, no pre-4.1 client can authenticate to that account until the client upgrades to 4.1.
Scenario 3) Long Password column; server started with --old-passwords option
Short or long hashes can be stored in the Password column.
4.1 clients can authenticate for accounts that have short or long hashes (but note that it is possible to create long hashes only when the server is started without --old-passwords).
Pre-4.1 clients can authenticate only for accounts that have short hashes.
For connected clients, password hash-generating operations involving PASSWORD(), GRANT, or SET PASSWORD use short hashes exclusively. Any change to an account's password results in that account having a short password hash.
In this scenario, you cannot create accounts that have long password hashes, because --old-passwords prevents generation of long hashes. Also, if you create an account with a long hash before using the --old-passwords option, changing the account's password while --old-passwords is in effect results in the account being given a short password, causing it to lose the security benefits of a longer hash.
The disadvantages for these scenarios may be summarized as follows:
Scenario 1) You cannot take advantage of longer hashes that provide more secure authentication.
Scenario 2) Accounts with short hashes become inaccessible to pre-4.1 clients if you change their passwords without explicitly using OLD_PASSWORD().
Scenario 3) --old-passwords prevents accounts with short hashes from becoming inaccessible, but password-changing operations cause accounts with long hashes to revert to short hashes, and you cannot change them back to long hashes while --old-passwords is in effect.
If you encounter Access denied errors when you try to connect to the MySQL server, the following list indicates some courses of action you can take to correct the problem:
After installing MySQL, did you run the mysql_install_db script to set up the initial grant table contents? If not, do so. See Default privileges. Test the initial privileges by executing this command:
shell> mysql -u root test
The server should let you connect without error. You should also make sure you have a file user.MYD in the MySQL database directory. Ordinarily, this is PATH/var/mysql/user.MYD, where PATH is the pathname to the MySQL installation root.
After a fresh installation, you should connect to the server and set up your users and their access permissions:
shell> mysql -u root mysql
The server should let you connect because the MySQL root user has no password initially. That is also a security risk, so setting the root password is something you should do while you're setting up your other MySQL users.
If you try to connect as root and get this error:
Access denied for user: '@unknown' to database mysql
this means that you don't have an entry in the user table with a User column value of 'root' and that mysqld cannot resolve the hostname for your client. In this case, you must restart the server with the --skip-grant-tables option and edit your /etc/hosts or \windows\hosts file to add an entry for your host.
If you get an error like the following:
shell> mysqladmin -u root -pxxxx ver Access denied for user: 'root@localhost' (Using password: YES)
It means that you are using an incorrect password. See Passwords.
If you have forgot the root password, you can restart mysqld with --skip-grant-tables to change the password. See Resetting permissions.
If you get the above error even if you haven't specified a password, this means that you have an incorrect password in some my.ini file. See Option files. You can avoid using option files with the --no-defaults option, as follows:
shell> mysqladmin --no-defaults -u root ver
If you updated an existing MySQL installation from a version earlier than Version 3.22.11 to Version 3.22.11 or later, did you run the mysql_fix_privilege_tables script? If not, do so. The structure of the grant tables changed with MySQL Version 3.22.11 when the GRANT statement became functional. See Upgrading-grant-tables.
If your privileges seem to have changed in the middle of a session, it may be that a superuser has changed them. Reloading the grant tables affects new client connections, but it also affects existing connections as indicated in Privilege changes.
If you can't get your password to work, remember that you must use the PASSWORD() function if you set the password with the INSERT, UPDATE, or SET PASSWORD statements. The PASSWORD() function is unnecessary if you specify the password using the GRANT ... IDENTIFIED BY statement or the mysqladmin password command. See Passwords.
localhost is a synonym for your local hostname, and is also the default host to which clients try to connect if you specify no host explicitly. However, connections to localhost do not work if you are using a MySQL version prior to 3.23.27 that uses MIT-pthreads (localhost connections are made using Unix socket files, which were not supported by MIT-pthreads at that time). To avoid this problem on such systems, you should use the --host option to name the server host explicitly. This will make a TCP/IP connection to the mysqld server. In this case, you must have your real hostname in user table entries on the server host. (This is true even if you are running a client program on the same host as the server.)
If you get an Access denied error when trying to connect to the database with mysql -u user_name db_name, you may have a problem with the user table. Check this by executing mysql -u root mysql and issuing this SQL statement:
mysql> SELECT * FROM user;
The result should include an entry with the Host and User columns matching your computer's hostname and your MySQL username.
The Access denied error message will tell you who you are trying to log in as, the host from which you are trying to connect, and whether or not you were using a password. Normally, you should have one entry in the user table that exactly matches the hostname and username that were given in the error message. For example if you get an error message that contains Using password: NO, this means that you tried to log in without an password.
If you get the following error when you try to connect from a different host than the one on which the MySQL server is running, then there is no row in the user table that matches that host:
Host ... is not allowed to connect to this MySQL server
You can fix this by using the command-line tool mysql (on the server host!) to add a row to the user, db, or host table for the user/hostname combination from which you are trying to connect and then execute mysqladmin flush-privileges. If you are not running MySQL Version 3.22 and you don't know the IP number or hostname of the machine from which you are connecting, you should put an entry with '%' as the Host column value in the user table and restart mysqld with the --log option on the server machine. After trying to connect from the client machine, the information in the MySQL log will indicate how you really did connect. (Then replace the '%' in the user table entry with the actual hostname that shows up in the log. Otherwise, you'll have a system that is insecure.)
Another reason for this error on Linux is that you are using a binary MySQL version that is compiled with a different glibc version than the one you are using. In this case you should either upgrade your OS/glibc or download the source MySQL version and compile this yourself. A source RPM is normally trivial to compile and install, so this isn't a big problem.
If you get an error message where the hostname is not shown or where the hostname is an IP, even if you try to connect with a hostname:
shell> mysqladmin -u root -pxxxx -h some-hostname ver Access denied for user: 'root@' (Using password: YES)
This means that MySQL got some error when trying to resolve the IP to a hostname. In this case you can execute mysqladmin flush-hosts to reset the internal DNS cache. See DNS.
Some permanent solutions are:
Try to find out what is wrong with your DNS server and fix this.
Specify IPs instead of hostnames in the MySQL privilege tables.
Start mysqld with --skip-name-resolve.
Start mysqld with --skip-host-cache.
Connect to localhost if you are running the server and the client on the same machine.
Put the client machine names in /etc/hosts.
If mysql -u root test works but mysql -h your_hostname -u root test results in Access denied, then you may not have the correct name for your host in the user table. A common problem here is that the Host value in the user table entry specifies an unqualified hostname, but your system's name resolution routines return a fully qualified domain name (or vice-versa). For example, if you have an entry with host 'tcx' in the user table, but your DNS tells MySQL that your hostname is 'tcx.subnet.se', the entry will not work. Try adding an entry to the user table that contains the IP number of your host as the Host column value. (Alternatively, you could add an entry to the user table with a Host value that contains a wildcard---for example, 'tcx.%'. However, use of hostnames ending with % is insecure and is not recommended!)
If mysql -u user_name test works but mysql -u user_name other_db_name doesn't work, you don't have an entry for other_db_name listed in the db table.
If mysql -u user_name db_name works when executed on the server machine, but mysql -h host_name -u user_name db_name doesn't work when executed on another client machine, you don't have the client machine listed in the user table or the db table.
If you can't figure out why you get Access denied, remove from the user table all entries that have Host values containing wildcards (entries that contain % or _). A very common error is to insert a new entry with Host='%' and User='some user', thinking that this will allow you to specify localhost to connect from the same machine. The reason that this doesn't work is that the default privileges include an entry with Host='localhost' and User=''. Because that entry has a Host value 'localhost' that is more specific than '%', it is used in preference to the new entry when connecting from localhost! The correct procedure is to insert a second entry with Host='localhost' and User='some_user', or to remove the entry with Host='localhost' and User=''.
If you get the following error, you may have a problem with the db or host table:
Access to database denied
If the entry selected from the db table has an empty value in the Host column, make sure there are one or more corresponding entries in the host table specifying which hosts the db table entry applies to.
If you get the error when using the SQL commands SELECT ... INTO OUTFILE or LOAD DATA INFILE, your entry in the user table probably doesn't have the FILE privilege enabled.
Remember that client programs will use connection parameters specified in configuration files or environment variables. See Environment variables. If a client seems to be sending the wrong default connection parameters when you don't specify them on the command-line, check your environment and the .my.cnf file in your home directory. You might also check the system-wide MySQL configuration files, though it is far less likely that client connection parameters will be specified there. If you get Access denied when you run a client without any options, make sure you haven't specified an old password in any of your option files! See Option files.
If you make changes to the grant tables directly (using an INSERT or UPDATE statement) and your changes seem to be ignored, remember that you must issue a FLUSH PRIVILEGES statement or execute a mysqladmin flush-privileges command to cause the server to re-read the privilege tables. Otherwise, your changes have no effect until the next time the server is restarted. Remember that after you set the root password with an UPDATE command, you won't need to specify it until after you flush the privileges, because the server won't know you've changed the password yet!
If you have access problems with a Perl, PHP, Python, or ODBC program, try to connect to the server with mysql -u user_name db_name or mysql -u user_name -pyour_pass db_name. If you are able to connect using the mysql client, there is a problem with your program and not with the access privileges. (Note that there is no space between -p and the password; you can also use the --password=your_pass syntax to specify the password. If you use the -p option alone, MySQL will prompt you for the password.)
For testing, start the mysqld daemon with the --skip-grant-tables option. Then you can change the MySQL grant tables and use the mysqlaccess script to check whether your modifications have the desired effect. When you are satisfied with your changes, execute mysqladmin flush-privileges to tell the mysqld server to start using the new grant tables. Note: Reloading the grant tables overrides the --skip-grant-tables option. This allows you to tell the server to begin using the grant tables again without bringing it down and restarting it.
If everything else fails, start the mysqld daemon with a debugging option (for example, --debug=d,general,query). This will print host and user information about attempted connections, as well as information about each command issued. See Making trace files.
If you have any other problems with the MySQL grant tables and feel you must post the problem to the mailing list, always provide a dump of the MySQL grant tables. You can dump the tables with the mysqldump mysql command. As always, post your problem using the mysqlbug script. See Bug reports. In some cases you may need to restart mysqld with --skip-grant-tables to run mysqldump.
Table of Contents
There are several distinctions between the way usernames and passwords are used by MySQL and the way they are used by Unix or Windows:
Usernames, as used by MySQL for authentication purposes, have nothing to do with Unix usernames (login names) or Windows usernames. Most MySQL clients by default try to log in using the current Unix user name as the MySQL username, but that is for convenience only. Client programs allow a different name to be specified with the -u or --user options. This means that you can't make a database secure in any way unless all MySQL usernames have passwords. Anyone may attempt to connect to the server using any name, and they will succeed if they specify any name that doesn't have a password.
MySQL usernames can be up to 16 characters long; Unix usernames typically are limited to 8 characters.
MySQL passwords have nothing to do with Unix passwords. There is no necessary connection between the password you use to log in to a Unix machine and the password you use to access a database on that machine.
MySQL encrypts passwords using a different algorithm than the one used during the Unix login process. See the descriptions of the PASSWORD() and ENCRYPT() functions in Encryption functions. Note that even if the password is stored 'scrambled', and knowing your 'scrambled' password is enough to be able to connect to the MySQL server! From version 4.1, MySQL employs a different password and login mechanism that is secure even if TCP/IP packets are sniffed and/or the mysql database is captured.
MySQL users and their privileges are normally created with the GRANT command. See GRANT.
When you login to a MySQL server with a command-line client you should specify the password with --password=your-password. See Connecting.
mysql --user=monty --password=guess database_name
If you want the client to prompt for a password, you should use --password without any argument
mysql --user=monty --password database_name
or the short form:
mysql -u monty -p database_name
Note that in the last example the password is not 'database_name'.
If you want to use the -p option to supply a password you should do so like this:
mysql -u monty -pguess database_name
On some systems, the library call that MySQL uses to prompt for a password will automatically cut the password to 8 characters. Internally MySQL doesn't have any limit for the length of the password.
When mysqld starts, all grant table contents are read into memory and become effective at that point.
Modifications to the grant tables that you perform using GRANT, REVOKE, or SET PASSWORD are noticed by the server immediately.
If you modify the grant tables manually (using INSERT, UPDATE, etc.), you should execute a FLUSH PRIVILEGES statement or run mysqladmin flush-privileges or mysqladmin reload to tell the server to reload the grant tables. Otherwise, your changes will have no effect until you restart the server. If you change the grant tables manually but forget to reload the privileges, you will be wondering why your changes don't seem to make any difference!
When the server notices that the grant tables have been changed, existing client connections are affected as follows:
Table and column privilege changes take effect with the client's next request.
Database privilege changes take effect at the next USE db_name command.
Global privilege changes and password changes take effect the next time the client connects.
After installing MySQL, you set up the initial access privileges by running scripts/mysql_install_db. See Quick install. The mysql_install_db script starts the mysqld server, then initializes the grant tables to contain the following set of privileges:
The MySQL root user is created as a superuser who can do anything. Connections must be made from the local host.
Note: The initial root password is empty, so anyone can connect as root without a password and be granted all privileges.
An anonymous user is created that can do anything with databases that have a name of 'test' or starting with 'test_'. Connections must be made from the local host. This means any local user can connect without a password and be treated as the anonymous user.
Other privileges are denied. For example, normal users can't use mysqladmin shutdown or mysqladmin processlist.
Note: The default privileges are different for Windows. See Windows running.
Because your installation is initially wide open, one of the first things you should do is specify a password for the MySQL root user. You can do this as follows (note that you specify the password using the PASSWORD() function):
shell> mysql -u root mysql mysql> SET PASSWORD FOR root@localhost=PASSWORD('new_password');
Replace 'new_password' with the password that you want to use.
If you know what you are doing, you can also directly manipulate the privilege tables:
shell> mysql -u root mysql mysql> UPDATE user SET Password=PASSWORD('new_password') -> WHERE user='root'; mysql> FLUSH PRIVILEGES;
Another way to set the password is by using the mysqladmin command:
shell> mysqladmin -u root password new_password
Only users with write/update access to the mysql database can change the password for other users. All normal users (not anonymous ones) can only change their own password with either of the above commands or with SET PASSWORD=PASSWORD('new_password').
Note that if you update the password in the user table directly using UPDATE, you must tell the server to re-read the grant tables (with FLUSH PRIVILEGES), because the change will go unnoticed otherwise.
Once the root password has been set, thereafter you must supply that password when you connect to the server as root.
You may wish to leave the root password blank so that you don't need to specify it while you perform additional setup or testing. However, be sure to set it before using your installation for any real production work.
See the scripts/mysql_install_db script to see how it sets up the default privileges. You can use this as a basis to see how to add other users.
If you want the initial privileges to be different from those just described above, you can modify mysql_install_db before you run it.
To re-create the grant tables completely, remove all the .frm, .MYI, and .MYD files in the directory containing the mysql database. (This is the directory named mysql under the database directory, which is listed when you run mysqld --help.) Then run the mysql_install_db script, possibly after editing it first to have the privileges you want.
Note: For MySQL versions older than Version 3.22.10, you should not delete the .frm files. If you accidentally do this, you should copy them back from your MySQL distribution before running mysql_install_db.
You can add users two different ways: by using GRANT statements or by manipulating the MySQL grant tables directly. The preferred method is to use GRANT statements, because they are more concise and less error-prone. See GRANT.
There are also several contributed programs (such as phpMyAdmin) that can be used to create and administer users.
The following examples show how to use the mysql client to set up new users. These examples assume that privileges are set up according to the defaults described in the previous section. This means that to make changes, you must be on the same machine where mysqld is running, you must connect as the MySQL root user, and the root user must have the INSERT privilege for the mysql database and the RELOAD administrative privilege. Also, if you have changed the root user password, you must specify it for the mysql commands here.
First, use the mysql program to connect to the server as the MySQL root user:
shell> mysql --user=root mysql
Then you can add new users by issuing GRANT statements:
mysql> GRANT ALL PRIVILEGES ON *.* TO monty@localhost -> IDENTIFIED BY 'some_pass' WITH GRANT OPTION; mysql> GRANT ALL PRIVILEGES ON *.* TO monty@'%' -> IDENTIFIED BY 'some_pass' WITH GRANT OPTION; mysql> GRANT RELOAD,PROCESS ON *.* TO admin@localhost; mysql> GRANT USAGE ON *.* TO dummy@localhost;
These GRANT statements set up three new users:
monty | A full superuser who can connect to the server from anywhere, but who must use a password 'some_pass' to do so. Note that we must issue GRANT statements for both monty@localhost and monty@"%". If we don't add the entry with localhost, the anonymous user entry for localhost that is created by mysql_install_db takes precedence when we connect from the local host, because it has a more specific Host column value and thus comes earlier in the user table sort order. |
admin | A user who can connect from localhost without a password and who is granted the RELOAD and PROCESS administrative privileges. This allows the user to execute the mysqladmin reload, mysqladmin refresh, and mysqladmin flush-* commands, as well as mysqladmin processlist . No database-level privileges are granted. (They can be granted later by issuing additional GRANT statements.) |
dummy | A user who can connect without a password, but only from the local host. No privileges are granted---the USAGE privilege type allows you to create a user with no privileges. It has the effect of setting all the global privileges to 'N'. It is assumed that you will grant specific privileges to the account later. |
You can also add the same user access information directly by issuing INSERT statements and then telling the server to reload the grant tables:
shell> mysql --user=root mysql mysql> INSERT INTO user VALUES('localhost','monty',PASSWORD('some_pass'), -> 'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y'); mysql> INSERT INTO user VALUES('%','monty',PASSWORD('some_pass'), -> 'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y'); mysql> INSERT INTO user SET Host='localhost',User='admin', -> Reload_priv='Y', Process_priv='Y'; mysql> INSERT INTO user (Host,User,Password) -> VALUES('localhost','dummy',''); mysql> FLUSH PRIVILEGES;
Depending on your MySQL version, you may have to use a different number of 'Y' values above. (Versions prior to Version 3.22.11 have fewer privilege columns, and versions from 4.0.2 on have more.) For the admin user, the more readable extended INSERT syntax using SET that is available starting with Version 3.22.11 is used.
Note that to set up a superuser, you need only create a user table entry with the privilege columns set to 'Y'. No db or host table entries are necessary.
In the last INSERT statement (for the dummy user), only the Host, User, and Password columns in the user table record are assigned values. None of the privilege columns are set explicitly, so MySQL assigns them all the default value of 'N'. This is the same thing that GRANT USAGE does.
The following example adds a user custom who can access the bankaccount database only from the local host, the expenses database only from the host whitehouse.gov, and the customer database only from the host server.domain. He wants to use the password obscure from all three hosts.
To set up this user's privileges using GRANT statements, run these commands:
shell> mysql --user=root mysql mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP -> ON bankaccount.* -> TO custom@localhost -> IDENTIFIED BY 'obscure'; mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP -> ON expenses.* -> TO custom@'whitehouse.gov' -> IDENTIFIED BY 'obscure'; mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP -> ON customer.* -> TO custom@'server.domain' -> IDENTIFIED BY 'obscure';
To set up the user's privileges by modifying the grant tables directly, run these commands (note the FLUSH PRIVILEGES at the end):
shell> mysql --user=root mysql mysql> INSERT INTO user (Host,User,Password) -> VALUES('localhost','custom',PASSWORD('obscure')); mysql> INSERT INTO user (Host,User,Password) -> VALUES('whitehouse.gov','custom',PASSWORD('obscure')); mysql> INSERT INTO user (Host,User,Password) -> VALUES('server.domain','custom',PASSWORD('obscure')); mysql> INSERT INTO db -> (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, -> Create_priv,Drop_priv) -> VALUES -> ('localhost','bankaccount','custom','Y','Y','Y','Y','Y','Y'); mysql> INSERT INTO db -> (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, -> Create_priv,Drop_priv) -> VALUES -> ('whitehouse.gov','expenses','custom','Y','Y','Y','Y','Y','Y'); mysql> INSERT INTO db -> (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, -> Create_priv,Drop_priv) -> VALUES('server.domain','customer','custom','Y','Y','Y','Y','Y','Y'); mysql> FLUSH PRIVILEGES;
As in the preceding example that used INSERT statements, you may need to use a different number of 'Y' values, depending on your version of MySQL.
The first three INSERT statements add user table entries that allow user custom to connect from the various hosts with the given password, but grant no permissions (all privileges are set to the default value of 'N'). The next three INSERT statements add db table entries that grant privileges to custom for the bankaccount, expenses, and customer databases, but only when accessed from the proper hosts. As usual, after you modify the grant tables directly , you must tell the server to reload them (with FLUSH PRIVILEGES) so that the privilege changes take effect.
If you want to give a specific user access from any machine in a given domain (for example, mydomain.com), you can issue a GRANT statement like the following:
mysql> GRANT ... -> ON *.* -> TO myusername@'%.mydomain.com' -> IDENTIFIED BY 'mypassword';
To do the same thing by modifying the grant tables directly, do this:
mysql> INSERT INTO user VALUES ('%.mydomain.com', 'myusername', -> PASSWORD('mypassword'),...); mysql> FLUSH PRIVILEGES;
DROP USER user_name
This command was added to MySQL 4.1.1.
It deletes a user that doesn't have any privileges.
To delete a user from MySQL, you should use the following procedure, performing the steps in the order shown:
Check which privileges the user has with SHOW PRIVILEGES. See SHOW PRIVILEGES.
Delete all privileges from the user with REVOKE. See GRANT.
Delete the user with DROP USER.
If you are using and older MySQL version you should first revoke the privileges and then delete the user with:
DELETE FROM mysql.user WHERE user='username' and host='hostname'; FLUSH PRIVILEGES;
Starting from MySQL 4.0.2 one can limit certain resources per user.
So far, the only available method of limiting usage of MySQL server resources has been setting the max_user_connections startup variable to a non-zero value. But this method is strictly global and does not allow for management of individual users, which could be of particular interest to Internet Service Providers.
Therefore, management of three resources is introduced on the individual user level:
Number of all queries per hour: All commands that could be run by a user.
Number of all updates per hour: Any command that changes any table or database.
Number of connections made per hour: New connections opened per hour.
A user in the aforementioned context is a single entry in the user table, which is uniquely identified by its user and host columns.
All users are by default not limited in using the above resources, unless the limits are granted to them. These limits can be granted only via global GRANT (*.*), using this syntax:
GRANT ... WITH MAX_QUERIES_PER_HOUR N1 MAX_UPDATES_PER_HOUR N2 MAX_CONNECTIONS_PER_HOUR N3;
One can specify any combination of the above resources. N1, N2, and N3 are integers and represent counts per hour.
If a user reaches the limit on number of connections within one hour, no further connections will be accepted until that hour is up. Similarly, if the user reaches the limit on number of queries or updates, further queries or updates will be rejected until the hour is up. In all cases, an appropriate error message shall be issued.
Current usage values for a particular user can be flushed (set to zero) by issuing a GRANT statement with any of the above clauses, including a GRANT statement with the current values.
Also, current values for all users will be flushed if privileges are reloaded (in the server or using mysqladmin reload) or if the FLUSH USER_RESOURCES command is issued.
The feature is enabled as soon as a single user is granted with any of the limiting GRANT clauses.
As a prerequisite for enabling this feature, the user table in the mysql database must contain the additional columns, as defined in the table creation scripts mysql_install_db and mysql_install_db.sh in scripts subdirectory.
In most cases you should use GRANT to set up your users/passwords, so the following only applies for advanced users. See GRANT.
The examples in the preceding sections illustrate an important principle: when you store a non-empty password using INSERT or UPDATE statements, you must use the PASSWORD() function to encrypt it. This is because the user table stores passwords in encrypted form, not as plaintext. If you forget that fact, you are likely to attempt to set passwords like this:
shell> mysql -u root mysql mysql> INSERT INTO user (Host,User,Password) -> VALUES('%','jeffrey','biscuit'); mysql> FLUSH PRIVILEGES;
The result is that the plaintext value 'biscuit' is stored as the password in the user table. When the user jeffrey attempts to connect to the server using this password, the mysql client encrypts it with PASSWORD(), generates an authentication vector based on encrypted password and a random number, obtained from server, and sends the result to the server. The server uses the password value in the user table (that is not encrypted value 'biscuit') to perform the same calculations, and compares results. The comparison fails and the server rejects the connection:
shell> mysql -u jeffrey -pbiscuit test Access denied
Passwords must be encrypted when they are inserted in the user table, so the INSERT statement should have been specified like this instead:
mysql> INSERT INTO user (Host,User,Password) -> VALUES('%','jeffrey',PASSWORD('biscuit'));
You must also use the PASSWORD() function when you use SET PASSWORD statements:
mysql> SET PASSWORD FOR jeffrey@"%" = PASSWORD('biscuit');
If you set passwords using the GRANT ... IDENTIFIED BY statement or the mysqladmin password command, the PASSWORD() function is unnecessary. They both take care of encrypting the password for you, so you would specify a password of 'biscuit' like this:
mysql> GRANT USAGE ON *.* TO jeffrey@"%" IDENTIFIED BY 'biscuit';
or:
shell> mysqladmin -u jeffrey password biscuit
Note: PASSWORD() is different from Unix password encryption. See User names.
It is inadvisable to specify your password in a way that exposes it to discovery by other users. The methods you can use to specify your password when you run client programs are listed here, along with an assessment of the risks of each method:
Never give a normal user access to the mysql.user table. Knowing the encrypted password for a user makes it possible to log in as this user. The passwords are only scrambled so that one shouldn't be able to see the real password you used (if you happen to use a similar password with your other applications).
Use a -pyour_pass or --password=your_pass option on the command line. This is convenient but insecure, because your password becomes visible to system status programs (such as ps) that may be invoked by other users to display command-lines. (MySQL clients typically overwrite the command-line argument with zeroes during their initialization sequence, but there is still a brief interval during which the value is visible.)
Use a -p or --password option (with no your_pass value specified). In this case, the client program solicits the password from the terminal:
shell> mysql -u user_name -p Enter password: ********
The * characters represent your password.
It is more secure to enter your password this way than to specify it on the command-line because it is not visible to other users. However, this method of entering a password is suitable only for programs that you run interactively. If you want to invoke a client from a script that runs non-interactively, there is no opportunity to enter the password from the terminal. On some systems, you may even find that the first line of your script is read and interpreted (incorrectly) as your password!
Store your password in a configuration file. For example, you can list your password in the [client] section of the .my.cnf file in your home directory:
[client] password=your_pass
If you store your password in .my.cnf, the file should not be group or world-readable or -writable. Make sure the file's access mode is 400 or 600.
See Option files.
You can store your password in the MYSQL_PWD environment variable, but this method must be considered extremely insecure and should not be used. Some versions of ps include an option to display the environment of running processes; your password will be in plain sight for all to see if you set MYSQL_PWD. Even on systems without such a version of ps, it is unwise to assume there is no other method to observe process environments. See Environment variables.
All in all, the safest methods are to have the client program prompt for the password or to specify the password in a properly protected .my.cnf file.
This section describes how to set up secure connections between MySQL clients and the server using the Secure Sockets Layer (SSL) protocol. It also decribes a way to set up SSH on Windows.
Beginning with version 4.0.0, MySQL has support for SSL encrypted connections. To understand how MySQL uses SSL, it's necessary to explain some basic SSL and X509 concepts. People who are already familiar with them can skip this part.
By default, MySQL uses unencrypted connections between the client and the server. This means that someone could watch all your traffic and look at the data being sent or received. They could even change the data while it is in transit between client and server. Sometimes you need to move information over public networks in a secure fashion; in such cases, using an unencrypted connection is unacceptable.
SSL is a protocol that uses different encryption algorithms to ensure that data received over a public network can be trusted. It has mechanisms to detect any change, loss or replay of data. SSL also incorporates algorithms to recognize and provide identity verification using the X509 standard.
Encryption is the way to make any kind of data unreadable. In fact, today's practice requires many additional security elements from encryption algorithms. They should resist many kind of known attacks like just messing with the order of encrypted messages or replaying data twice.
X509 is a standard that makes it possible to identify someone on the Internet. It is most commonly used in e-commerce applications. In basic terms, there should be some company (called a ``Certificate Authority'') that assigns electronic certificates to anyone who needs them. Certificates rely on asymmetric encryption algorithms that have two encryption keys (a public key and a secret key). A certificate owner can prove his identity by showing his certificate to other party. A certificate consists of its owner's public key. Any data encrypted with this public key can be decrypted only using the corresponding secret key, which is held by the owner of the certificate.
MySQL doesn't use encrypted connections by default, because doing so would make the client/server protocol much slower. Any kind of additional functionality requires the computer to do additional work and encrypting data is a CPU-intensive operation that requires time and can delay MySQL main tasks. By default MySQL is tuned to be fast as possible.
If you need more information about SSL, X509, or encryption, you should use your favorite Internet search engine and search for keywords in which you are interested.
To get secure connections to work with MySQL you must do the following:
Install the OpenSSL library. We have tested MySQL with OpenSSL 0.9.6. http://www.openssl.org/.
Configure MySQL with --with-vio --with-openssl.
If you are using an old MySQL installation, you have to update your mysql.user table with some new SSL-related columns. This is necessary if your grant tables date from a version prior to MySQL 4.0.0. The procedure is described in Upgrading-grant-tables.
You can check if a running mysqld server supports OpenSSL by examining if SHOW VARIABLES LIKE 'have_openssl' returns YES.
Here is an example for setting up SSL certificates for MySQL:
DIR=`pwd`/openssl PRIV=$DIR/private mkdir $DIR $PRIV $DIR/newcerts cp /usr/share/ssl/openssl.cnf $DIR replace ./demoCA $DIR -- $DIR/openssl.cnf # Create necessary files: $database, $serial and $new_certs_dir # directory (optional) touch $DIR/index.txt echo "01" > $DIR/serial # # Generation of Certificate Authority(CA) # openssl req -new -x509 -keyout $PRIV/cakey.pem -out $DIR/cacert.pem \ -config $DIR/openssl.cnf # Sample output: # Using configuration from /home/monty/openssl/openssl.cnf # Generating a 1024 bit RSA private key # ................++++++ # .........++++++ # writing new private key to '/home/monty/openssl/private/cakey.pem' # Enter PEM pass phrase: # Verifying password - Enter PEM pass phrase: # ----- # You are about to be asked to enter information that will be incorporated # into your certificate request. # What you are about to enter is what is called a Distinguished Name or a DN. # There are quite a few fields but you can leave some blank # For some fields there will be a default value, # If you enter '.', the field will be left blank. # ----- # Country Name (2 letter code) [AU]:FI # State or Province Name (full name) [Some-State]:. # Locality Name (eg, city) []: # Organization Name (eg, company) [Internet Widgits Pty Ltd]:MySQL AB # Organizational Unit Name (eg, section) []: # Common Name (eg, YOUR name) []:MySQL admin # Email Address []: # # Create server request and key # openssl req -new -keyout $DIR/server-key.pem -out \ $DIR/server-req.pem -days 3600 -config $DIR/openssl.cnf # Sample output: # Using configuration from /home/monty/openssl/openssl.cnf # Generating a 1024 bit RSA private key # ..++++++ # ..........++++++ # writing new private key to '/home/monty/openssl/server-key.pem' # Enter PEM pass phrase: # Verifying password - Enter PEM pass phrase: # ----- # You are about to be asked to enter information that will be incorporated # into your certificate request. # What you are about to enter is what is called a Distinguished Name or a DN. # There are quite a few fields but you can leave some blank # For some fields there will be a default value, # If you enter '.', the field will be left blank. # ----- # Country Name (2 letter code) [AU]:FI # State or Province Name (full name) [Some-State]:. # Locality Name (eg, city) []: # Organization Name (eg, company) [Internet Widgits Pty Ltd]:MySQL AB # Organizational Unit Name (eg, section) []: # Common Name (eg, YOUR name) []:MySQL server # Email Address []: # # Please enter the following 'extra' attributes # to be sent with your certificate request # A challenge password []: # An optional company name []: # # Remove the passphrase from the key (optional) # openssl rsa -in $DIR/server-key.pem -out $DIR/server-key.pem # # Sign server cert # openssl ca -policy policy_anything -out $DIR/server-cert.pem \ -config $DIR/openssl.cnf -infiles $DIR/server-req.pem # Sample output: # Using configuration from /home/monty/openssl/openssl.cnf # Enter PEM pass phrase: # Check that the request matches the signature # Signature ok # The Subjects Distinguished Name is as follows # countryName :PRINTABLE:'FI' # organizationName :PRINTABLE:'MySQL AB' # commonName :PRINTABLE:'MySQL admin' # Certificate is to be certified until Sep 13 14:22:46 2003 GMT (365 days) # Sign the certificate? [y/n]:y # # # 1 out of 1 certificate requests certified, commit? [y/n]y # Write out database with 1 new entries # Data Base Updated # # Create client request and key # openssl req -new -keyout $DIR/client-key.pem -out \ $DIR/client-req.pem -days 3600 -config $DIR/openssl.cnf # Sample output: # Using configuration from /home/monty/openssl/openssl.cnf # Generating a 1024 bit RSA private key # .....................................++++++ # .............................................++++++ # writing new private key to '/home/monty/openssl/client-key.pem' # Enter PEM pass phrase: # Verifying password - Enter PEM pass phrase: # ----- # You are about to be asked to enter information that will be incorporated # into your certificate request. # What you are about to enter is what is called a Distinguished Name or a DN. # There are quite a few fields but you can leave some blank # For some fields there will be a default value, # If you enter '.', the field will be left blank. # ----- # Country Name (2 letter code) [AU]:FI # State or Province Name (full name) [Some-State]:. # Locality Name (eg, city) []: # Organization Name (eg, company) [Internet Widgits Pty Ltd]:MySQL AB # Organizational Unit Name (eg, section) []: # Common Name (eg, YOUR name) []:MySQL user # Email Address []: # # Please enter the following 'extra' attributes # to be sent with your certificate request # A challenge password []: # An optional company name []: # # Remove a passphrase from the key (optional) # openssl rsa -in $DIR/client-key.pem -out $DIR/client-key.pem # # Sign client cert # openssl ca -policy policy_anything -out $DIR/client-cert.pem \ -config $DIR/openssl.cnf -infiles $DIR/client-req.pem # Sample output: # Using configuration from /home/monty/openssl/openssl.cnf # Enter PEM pass phrase: # Check that the request matches the signature # Signature ok # The Subjects Distinguished Name is as follows # countryName :PRINTABLE:'FI' # organizationName :PRINTABLE:'MySQL AB' # commonName :PRINTABLE:'MySQL user' # Certificate is to be certified until Sep 13 16:45:17 2003 GMT (365 days) # Sign the certificate? [y/n]:y # # # 1 out of 1 certificate requests certified, commit? [y/n]y # Write out database with 1 new entries # Data Base Updated # # Create a my.cnf file that you can use to test the certificates # cnf="" cnf="$cnf [client]" cnf="$cnf ssl-ca=$DIR/cacert.pem" cnf="$cnf ssl-cert=$DIR/client-cert.pem" cnf="$cnf ssl-key=$DIR/client-key.pem" cnf="$cnf [mysqld]" cnf="$cnf ssl-ca=$DIR/cacert.pem" cnf="$cnf ssl-cert=$DIR/server-cert.pem" cnf="$cnf ssl-key=$DIR/server-key.pem" echo $cnf | replace " " ' ' > $DIR/my.cnf # # To test MySQL mysqld --defaults-file=$DIR/my.cnf & mysql --defaults-file=$DIR/my.cnf
You can also test your setup by modifying the above my.cnf file to refer to the demo certificates in the mysql-source-dist/SSL direcory.
MySQL can check X509 certificate attributes in addition to the normal username/password scheme. All the usual options are still required (username, password, IP address mask, database/table name).
There are different possibilities to limit connections:
Without any SSL or X509 options, all kind of encrypted/unencrypted connections are allowed if the username and password are valid.
REQUIRE SSL option limits the server to allow only SSL encrypted connections. Note that this option can be omitted if there are any ACL records which allow non-SSL connections.
mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost -> IDENTIFIED BY 'goodsecret' REQUIRE SSL;
REQUIRE X509 means that the client should have a valid certificate but we do not care about the exact certificate, issuer or subject. The only restriction is that it should be possible to verify its signature with one of the CA certificates.
mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost -> IDENTIFIED BY 'goodsecret' REQUIRE X509;
REQUIRE ISSUER 'issuer' places a restriction on connection attempts: The client must present a valid X509 certificate issued by CA 'issuer'. Using X509 certificates always implies encryption, so the SSL option is unneccessary.
mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost -> IDENTIFIED BY 'goodsecret' -> REQUIRE ISSUER 'C=FI, ST=Some-State, L=Helsinki, '> O=MySQL Finland AB, CN=Tonu Samuel/Email=tonu@mysql.com';
REQUIRE SUBJECT 'subject' requires clients to have valid X509 certificate with subject 'subject' on it. If the client presents a certificate that is valid but has a different 'subject', the connection is disallowed.
mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost -> IDENTIFIED BY 'goodsecret' -> REQUIRE SUBJECT 'C=EE, ST=Some-State, L=Tallinn, '> O=MySQL demo client certificate, '> CN=Tonu Samuel/Email=tonu@mysql.com';
REQUIRE CIPHER 'cipher' is needed to assure enough strong ciphers and keylengths will be used. SSL itself can be weak if old algorithms with short encryption keys are used. Using this option, we can ask for some exact cipher method to allow a connection.
mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost -> IDENTIFIED BY 'goodsecret' -> REQUIRE CIPHER 'EDH-RSA-DES-CBC3-SHA';
The SUBJECT, ISSUER, and CIPHER options can be combined in the REQUIRE clause like this:
mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost -> IDENTIFIED BY 'goodsecret' -> REQUIRE SUBJECT 'C=EE, ST=Some-State, L=Tallinn, '> O=MySQL demo client certificate, '> CN=Tonu Samuel/Email=tonu@mysql.com' -> AND ISSUER 'C=FI, ST=Some-State, L=Helsinki, '> O=MySQL Finland AB, CN=Tonu Samuel/Email=tonu@mysql.com' -> AND CIPHER 'EDH-RSA-DES-CBC3-SHA';
Starting from MySQL 4.0.4 the AND keyword is optional between REQUIRE options.
The order of the options does not matter, but no option can be specified twice.
The following table lists options that are used for specifying the use of SSL, certificate files, and key files. These options are available beginning with MySQL 4.0. They may be given on the command line or in option files.
--ssl | For the server, specifies that the server allows SSL connections. For a client program, allows the client to connect to the server using SSL. This option itself is not sufficient to cause an SSL connection to be used. You must also specify the --ssl-ca, --ssl-cert, and --ssl-key options. Note that this option doesn't require an SSL connection. For example, if the server or client are compiled without SSL support, a normal unencrypted connection will be used. The secure way to ensure that a SSL connection will be used is to create an account on the server that includes a REQUIRE SSL clause in the GRANT statement. Then use this account to connect to the server, with both a server and client that have SSL support enabled. You can use this option to indicate that the connection should not use SSL. Do this by specifying the option as --skip-ssl or --ssl=0. |
--ssl-ca=file_name | The path to a file with a list of trusted SSL CAs. |
--ssl-capath=directory_name | The path to a directory that contains trusted SSL CA certificates in pem format. |
--ssl-cert=file_name | The name of the SSL certificate file to use used for establishing a secure connection. |
--ssl-cipher=cipher_list | A list of allowable ciphers to use for SSL encryption. cipher_list has the same format as the openssl ciphers command. Example: --ssl-cipher=ALL:-AES:-EXP |
--ssl-key=file_name | The name of the SSL key file to use used for establishing a secure connection. |
Here is a note about how to connect to get a secure connection to remote MySQL server with SSH (by David Carlson <dcarlson@mplcomm.com>):
Install an SSH client on your Windows machine. As a user, the best non-free one I've found is from SecureCRT from http://www.vandyke.com/. Another option is f-secure from http://www.f-secure.com/. You can also find some free ones on Google at http://directory.google.com/Top/Computers/Security/Products_and_Tools/Cryptography/SSH/Clients/Windows/.
Start your Windows SSH client. Set Host_Name = yourmysqlserver_URL_or_IP. Set userid=your_userid to log in to your server. This userid value may not be the same as the username of your MySQL account.
Set up port forwarding. Either do a remote forward (Set local_port: 3306, remote_host: yourmysqlservername_or_ip, remote_port: 3306 ) or a local forward (Set port: 3306, host: localhost, remote port: 3306).
Save everything, otherwise you'll have to redo it the next time.
Log in to your server with the SSH session you just created.
On your Windows machine, start some ODBC application (such as Access).
Create a new file in Windows and link to MySQL using the ODBC driver the same way you normally do, except type in localhost for the MySQL host server---not yourmysqlservername.
You should now have an ODBC connection to MySQL, encrypted using SSH.
Table of Contents
This section discusses how to make database backups and how to perform table maintenance. The syntax of the SQL statements described here is given in Database Administration.
Because MySQL tables are stored as files, it is easy to do a backup. To get a consistent backup, do a LOCK TABLES on the relevant tables followed by FLUSH TABLES for the tables. See LOCK TABLES. See FLUSH. You only need a read lock; this allows other threads to continue to query the tables while you are making a copy of the files in the database directory. The FLUSH TABLE is needed to ensure that the all active index pages is written to disk before you start the backup.
Starting from 3.23.56 and 4.0.12 BACKUP TABLE will not allow you to overwrite existing files as this would be a security risk.
If you want to make an SQL level backup of a table, you can use SELECT INTO OUTFILE or BACKUP TABLE. See SELECT. See BACKUP TABLE.
Another way to back up a database is to use the mysqldump program or the mysqlhotcopy script. See mysqldump. See mysqlhotcopy.
Do a full backup of your database:
shell> mysqldump --tab=/path/to/some/dir --opt db_name
or:
shell> mysqlhotcopy db_name /path/to/some/dir
You can also simply copy all table files (*.frm, *.MYD, and *.MYI files) as long as the server isn't updating anything. The script mysqlhotcopy does use this method. (But note that these methods will not work if your database contains InnoDB tables. InnoDB does not store table contents in database directories, and mysqlhotcopy works only for MyISAM and ISAM tables.)
Stop mysqld if it's running, then start it with the --log-bin[=file_name] option. See Binary log. The binary log files provide you with the information you need to replicate changes to the database that are made subsequent to the point at which you executed mysqldump.
If your MySQL server is a slave, whatever backup method you choose, when you backup your slave's data, you should also backup the master.info and relay-log.info files which are always needed to resume replication after you restore the slave's data. If your slave is subject to replicating LOAD DATA INFILE commands, you should also backup the SQL_LOAD-* files which may exist in the directory specified by the --slave-load-tmpdir option. (This location defaults to the value of the tmpdir variable if not specified.) The slave will need these files to resume replication of any interrupted LOAD DATA INFILE operations.
If you have to restore something, try to recover your tables using REPAIR TABLE or myisamchk -r first. That should work in 99.9% of all cases. If myisamchk fails, try the following procedure (this will work only if you have started MySQL with --log-bin, see Binary log):
Restore the original mysqldump backup, or binary backup.
Execute the following command to re-run the updates in the binary log:
shell> mysqlbinlog hostname-bin.[0-9]* | mysql
In your case you may want to re-run only certain binlogs, from certain positions (usually you want to re-run all binlogs from the date of the restored backup, possibly excepted some wrong queries). See mysqlbinlog for more information on the mysqlbinlog utility and how to use it.
If you are using the update log (which is removed in MySQL 5.0.0) you can execute the content of the update log like this:
shell> ls -1 -t -r hostname.[0-9]* | xargs cat | mysql
ls is used to get all the update log files in the right order.
You can also do selective backups with SELECT * INTO OUTFILE 'file_name' FROM tbl_name and restore with LOAD DATA INFILE 'file_name' REPLACE ... To avoid duplicate records, you need a PRIMARY KEY or a UNIQUE key in the table. The REPLACE keyword causes old records to be replaced with new ones when a new record duplicates an old record on a unique key value.
If you get performance problems in making backups on your system, you can solve this by setting up replication and do the backups on the slave instead of on the master. See Replication Intro.
If you are using a Veritas filesystem, you can do:
From a client (or Perl), execute: FLUSH TABLES WITH READ LOCK.
From another shell, execute: mount vxfs snapshot.
From the first client, execute: UNLOCK TABLES.
Copy files from snapshot.
Unmount snapshot.
Starting with MySQL Version 3.23.13, you can check MyISAM tables with the CHECK TABLE command. See CHECK TABLE. You can repair tables with the REPAIR TABLE command. See REPAIR TABLE.
To check/repair MyISAM tables (.MYI and .MYD) you should use the myisamchk utility. To check/repair ISAM tables (.ISM and .ISD) you should use the isamchk utility. See Table types.
In the following text we will talk about myisamchk, but everything also applies to the old isamchk.
You can use the myisamchk utility to get information about your database tables, check and repair them, or optimize them. The following sections describe how to invoke myisamchk (including a description of its options), how to set up a table maintenance schedule, and how to use myisamchk to perform its various functions.
You can, in most cases, also use the command OPTIMIZE TABLES to optimize and repair tables, but this is not as fast or reliable (in case of real fatal errors) as myisamchk. On the other hand, OPTIMIZE TABLE is easier to use and you don't have to worry about flushing tables. See OPTIMIZE TABLE.
Even though the repair in myisamchk is quite secure, it's always a good idea to make a backup before doing a repair (or anything that could make a lot of changes to a table)
myisamchk is invoked like this:
shell> myisamchk [options] tbl_name
The options specify what you want myisamchk to do. They are described here. (You can also get a list of options by invoking myisamchk --help.) With no options, myisamchk simply checks your table. To get more information or to tell myisamchk to take corrective action, specify options as described here and in the following sections.
tbl_name is the database table you want to check/repair. If you run myisamchk somewhere other than in the database directory, you must specify the path to the file, because myisamchk has no idea where your database is located. Actually, myisamchk doesn't care whether the files you are working on are located in a database directory; you can copy the files that correspond to a database table into another location and perform recovery operations on them there.
You can name several tables on the myisamchk command-line if you wish. You can also specify a name as an index file name (with the .MYI suffix), which allows you to specify all tables in a directory by using the pattern *.MYI. For example, if you are in a database directory, you can check all the tables in the directory like this:
shell> myisamchk *.MYI
If you are not in the database directory, you can check all the tables there by specifying the path to the directory:
shell> myisamchk /path/to/database_dir/*.MYI
You can even check all tables in all databases by specifying a wildcard with the path to the MySQL data directory:
shell> myisamchk /path/to/datadir/*/*.MYI
The recommended way to quickly check all tables is:
myisamchk --silent --fast /path/to/datadir/*/*.MYI isamchk --silent /path/to/datadir/*/*.ISM
If you want to check all tables and repair all tables that are corrupted, you can use the following line:
myisamchk --silent --force --fast --update-state -O key_buffer=64M \ -O sort_buffer=64M -O read_buffer=1M -O write_buffer=1M \ /path/to/datadir/*/*.MYI isamchk --silent --force -O key_buffer=64M -O sort_buffer=64M \ -O read_buffer=1M -O write_buffer=1M /path/to/datadir/*/*.ISM
The above assumes that you have more than 64 M free.
Note that if you get an error like:
myisamchk: warning: 1 clients is using or hasn't closed the table properly
This means that you are trying to check a table that has been updated by another program (like the mysqld server) that hasn't yet closed the file or that has died without closing the file properly.
If mysqld is running, you must force a sync/close of all tables with FLUSH TABLES and ensure that no one is using the tables while you are running myisamchk. In MySQL Version 3.23 the easiest way to avoid this problem is to use CHECK TABLE instead of myisamchk to check tables.
myisamchk supports the following options.
-# or --debug=debug_options | Output debug log. The debug_options string often is 'd:t:o,filename'. | |||||||||||||||
-? or --help | Display a help message and exit. | |||||||||||||||
-O name=value, --set-variable=name=value | Set the value of a variable. Please note that --set-variable=name=value and -O name=value syntax is deprecated as of MySQL 4.0. Use --name=value instead. The possible variables and their default values for myisamchk can be examined with myisamchk --help: |
| ||||||||||||||
-s or --silent | Silent mode. Write output only when errors occur. You can use -s twice (-ss) to make myisamchk very silent. | |||||||||||||||
-v or --verbose | Verbose mode. Print more information. This can be used with -d and -e. Use -v multiple times (-vv, -vvv) for more verbosity! | |||||||||||||||
-V or --version | Print the myisamchk version and exit. | |||||||||||||||
-w or, --wait | Instead of giving an error if the table is locked, wait until the table is unlocked before continuing. Note that if you are running mysqld on the table with --skip-external-locking, the table can only be locked by another myisamchk command. |
-c or --check | Check table for errors. This is the default operation if you are not giving myisamchk any options that override this. |
-e or --extend-check | Check the table very thoroughly (which is quite slow if you have many indexes). This option should only be used in extreme cases. Normally, myisamchk or myisamchk --medium-check should, in most cases, be able to find out if there are any errors in the table. If you are using --extended-check and have much memory, you should increase the value of key_buffer_size a lot! |
-F or --fast | Check only tables that haven't been closed properly. |
-C or --check-only-changed | Check only tables that have changed since the last check. |
-f or --force | Restart myisamchk with -r (repair) on the table, if myisamchk finds any errors in the table. |
-i or --information | Print informational statistics about the table that is checked. |
-m or --medium-check | Faster than extended-check, but only finds 99.99% of all errors. Should, however, be good enough for most cases. |
-U or --update-state | Store in the .MYI file when the table was checked and if the table crashed. This should be used to get full benefit of the --check-only-changed option, but you shouldn't use this option if the mysqld server is using the table and you are running mysqld with --skip-external-locking. |
-T or --read-only | Don't mark table as checked. This is useful if you use myisamchk to check a table that is in use by some other application that doesn't use locking (like mysqld --skip-external-locking). |
The following options are used if you start myisamchk with -r or -o:
-B or --backup | Make a backup of the .MYD file as filename-time.BAK |
--correct-checksum | Correct checksum information for table. |
-D # or --data-file-length=# | Max length of datafile (when re-creating datafile when it's 'full'). |
-e or --extend-check | Try to recover every possible row from the datafile. Normally this will also find a lot of garbage rows. Don't use this option if you are not totally desperate. |
-f or --force | Overwrite old temporary files (table_name.TMD) instead of aborting. |
-k # or --keys-used=# | If you are using ISAM, tells the ISAM storage engine to update only the first # indexes. If you are using MyISAM, tells which keys to use, where each binary bit stands for one key (first key is bit 0). This can be used to get faster inserts! Deactivated indexes can be reactivated by using myisamchk -r. |
-l or --no-symlinks | Do not follow symbolic links. Normally myisamchk repairs the table a symlink points at. This option doesn't exist in MySQL 4.0, as MySQL 4.0 will not remove symlinks during repair. |
-p or --parallel-recover | Uses the same technique as -r and -n, but creates all the keys in parallel, in different threads. This option was added in MySQL 4.0.2. This is alpha code. Use at your own risk! |
-r or --recover | Can fix almost anything except unique keys that aren't unique (which is an extremely unlikely error with ISAM/MyISAM tables). If you want to recover a table, this is the option to try first. Only if myisamchk reports that the table can't be recovered by -r, you should then try -o. (Note that in the unlikely case that -r fails, the datafile is still intact.) If you have lots of memory, you should increase the size of sort_buffer_size! |
-o or --safe-recover | Uses an old recovery method (reads through all rows in order and updates all index trees based on the found rows); this is an order of magnitude slower than -r, but can handle a couple of very unlikely cases that -r cannot handle. This recovery method also uses much less disk space than -r. Normally one should always first repair with -r, and only if this fails use -o. If you have lots of memory, you should increase the size of key_buffer_size! |
-n or --sort-recover | Force myisamchk to use sorting to resolve the keys even if the temporary files should be very big. |
--character-sets-dir=... | Directory where character sets are stored. |
--set-character-set=name | Change the character set used by the index |
-t or --tmpdir=path | Path for storing temporary files. If this is not set, myisamchk will use the environment variable TMPDIR for this. Starting from MySQL 4.1, tmpdir can be set to a list of paths separated by colon : (semicolon ; on Windows). They will be used in round-robin fashion. |
-q or --quick | Faster repair by not modifying the datafile. One can give a second -q to force myisamchk to modify the original datafile in case of duplicate keys |
-u or --unpack | Unpack file packed with myisampack. |
Other actions that myisamchk can do, besides repair and check tables:
-a or --analyze | Analyze the distribution of keys. This improves join performance by enabling the join optimizer to better choose in which order it should join the tables and which keys it should use: myisamchk --describe --verbose table_name' or using SHOW KEYS in MySQL. |
-d or --description | Prints some information about table. |
-A or --set-auto-increment[=value] | Force AUTO_INCREMENT to start at this or higher value. If no value is given, then sets the next AUTO_INCREMENT value to the highest used value for the auto key + 1. |
-S or --sort-index | Sort the index tree blocks in high-low order. This will optimize seeks and will make table scanning by key faster. |
-R or --sort-records=# | Sorts records according to an index. This makes your data much more localized and may speed up ranged SELECT and ORDER BY operations on this index. (It may be very slow to do a sort the first time!) To find out a table's index numbers, use SHOW INDEX, which shows a table's indexes in the same order that myisamchk sees them. Indexes are numbered beginning with 1. |
Memory allocation is important when you run myisamchk. myisamchk uses no more memory than you specify with the -O options. If you are going to use myisamchk on very large files, you should first decide how much memory you want it to use. The default is to use only about 3M to perform repairs. By using larger values, you can get myisamchk to operate faster. For example, if you have more than 32M RAM, you could use options such as these (in addition to any other options you might specify):
shell> myisamchk -O sort=16M -O key=16M -O read=1M -O write=1M ...
Using -O sort=16M should probably be enough for most cases.
Be aware that myisamchk uses temporary files in TMPDIR. If TMPDIR points to a memory filesystem, you may easily get out of memory errors. If this happens, set TMPDIR to point at some directory with more space and restart myisamchk.
When repairing, myisamchk will also need a lot of disk space:
Double the size of the record file (the original one and a copy). This space is not needed if one does a repair with --quick, as in this case only the index file will be re-created. This space is needed on the same disk as the original record file!
Space for the new index file that replaces the old one. The old index file is truncated at start, so one usually ignore this space. This space is needed on the same disk as the original index file!
When using --recover or --sort-recover (but not when using --safe-recover), you will need space for a sort buffer for: (largest_key + row_pointer_length)*number_of_rows * 2. You can check the length of the keys and the row_pointer_length with myisamchk -dv table. This space is allocated on the temporary disk (specified by TMPDIR or --tmpdir=#).
If you have a problem with disk space during repair, you can try to use --safe-recover instead of --recover.
If you run mysqld with --skip-external-locking (which is the default on some systems, like Linux), you can't reliably use myisamchk to check a table when mysqld is using the same table. If you can be sure that no one is accessing the tables through mysqld while you run myisamchk, you only have to do mysqladmin flush-tables before you start checking the tables. If you can't guarantee the above, then you must take down mysqld while you check the tables. If you run myisamchk while mysqld is updating the tables, you may get a warning that a table is corrupt even if it isn't.
If you are not using --skip-external-locking, you can use myisamchk to check tables at any time. While you do this, all clients that try to update the table will wait until myisamchk is ready before continuing.
If you use myisamchk to repair or optimize tables, you must always ensure that the mysqld server is not using the table (this also applies if you are using --skip-external-locking). If you don't take down mysqld you should at least do a mysqladmin flush-tables before you run myisamchk. Your tables may be corrupted if the server and myisamchk access the tables simultaneously.
This section describes how to check for and deal with data corruption in MySQL databases. If your tables get corrupted frequently you should try to find the reason for this! See Crashing.
The MyISAM table section contains reason for why a table could be corrupted. See MyISAM table problems.
When performing crash recovery, it is important to understand that each table tbl_name in a database corresponds to three files in the database directory:
File | Purpose |
tbl_name.frm | Table definition (form) file |
tbl_name.MYD | Datafile |
tbl_name.MYI | Index file |
Each of these three file types is subject to corruption in various ways, but problems occur most often in datafiles and index files.
myisamchk works by creating a copy of the .MYD (data) file row by row. It ends the repair stage by removing the old .MYD file and renaming the new file to the original file name. If you use --quick, myisamchk does not create a temporary .MYD file, but instead assumes that the .MYD file is correct and only generates a new index file without touching the .MYD file. This is safe, because myisamchk automatically detects if the .MYD file is corrupt and aborts the repair in this case. You can also give two --quick options to myisamchk. In this case, myisamchk does not abort on some errors (like duplicate key) but instead tries to resolve them by modifying the .MYD file. Normally the use of two --quick options is useful only if you have too little free disk space to perform a normal repair. In this case you should at least make a backup before running myisamchk.
In the following section we only talk about using myisamchk on MyISAM tables (extensions .MYI and .MYD). If you are using ISAM tables (extensions .ISM and .ISD), you should use isamchk instead.
Starting with MySQL Version 3.23.14, you can repair MyISAM tables with the REPAIR TABLE command. See REPAIR TABLE.
The symptoms of a corrupted table include queries that abort unexpectedly and observable errors such as these:
tbl_name.frm is locked against change
Can't find file tbl_name.MYI (Errcode: ###)
Unexpected end of file
Record file is crashed
Got error ### from table handler
To get more information about the error you can run perror ###. Here is the most common errors that indicates a problem with the table:
shell> perror 126 127 132 134 135 136 141 144 145 126 = Index file is crashed / Wrong file format 127 = Record-file is crashed 132 = Old database file 134 = Record was already deleted (or record file crashed) 135 = No more room in record file 136 = No more room in index file 141 = Duplicate unique key or constraint on write or update 144 = Table is crashed and last repair failed 145 = Table was marked as crashed and should be repaired
Note that error 135 (no more room in record file), is not an error that can be fixed by a simple repair. In this case you have to do:
ALTER TABLE table MAX_ROWS=xxx AVG_ROW_LENGTH=yyy;
You can also use this technique for error 136 (no more room in index file).
In the other cases, you must repair your tables. myisamchk can usually detect and fix most problems that occur.
The repair process involves up to four stages, described here. Before you begin, you should cd to the database directory and check the permissions of the table files. Make sure they are readable by the Unix user that mysqld runs as (and to you, because you need to access the files you are checking). If it turns out you need to modify files, they must also be writable by you.
If you are using MySQL Version 3.23.16 and above, you can (and should) use the CHECK and REPAIR commands to check and repair MyISAM tables. See CHECK TABLE. See REPAIR TABLE.
The manual section about table maintenance includes the options to isamchk/myisamchk. See Table maintenance.
The following section is for the cases where the above command fails or if you want to use the extended features that isamchk/myisamchk provides.
If you are going to repair a table from the command-line, you must first take down the mysqld server. Note that when you do mysqladmin shutdown on a remote server, the mysqld server will still be alive for a while after mysqladmin returns, until all queries are stopped and all keys have been flushed to disk.
Stage 1: Checking your tables
Run myisamchk *.MYI or myisamchk -e *.MYI if you have more time. Use the -s (silent) option to suppress unnecessary information.
If the mysqld server is done you should use the --update option to tell myisamchk to mark the table as 'checked'.
You have to repair only those tables for which myisamchk announces an error. For such tables, proceed to Stage 2.
If you get weird errors when checking (such as out of memory errors), or if myisamchk crashes, go to Stage 3.
Stage 2: Easy safe repair
Note: If you want repairing to go much faster, you should add: -O sort_buffer=# -O key_buffer=# (where # is about 1/4 of the available memory) to all isamchk/myisamchk commands.
First, try myisamchk -r -q tbl_name (-r -q means ``quick recovery mode''). This will attempt to repair the index file without touching the datafile. If the datafile contains everything that it should and the delete links point at the correct locations within the datafile, this should work, and the table is fixed. Start repairing the next table. Otherwise, use the following procedure:
Make a backup of the datafile before continuing.
Use myisamchk -r tbl_name (-r means ``recovery mode''). This will remove incorrect records and deleted records from the datafile and reconstruct the index file.
If the preceding step fails, use myisamchk --safe-recover tbl_name. Safe recovery mode uses an old recovery method that handles a few cases that regular recovery mode doesn't (but is slower).
If you get weird errors when repairing (such as out of memory errors), or if myisamchk crashes, go to Stage 3.
Stage 3: Difficult repair
You should only reach this stage if the first 16K block in the index file is destroyed or contains incorrect information, or if the index file is missing. In this case, it's necessary to create a new index file. Do so as follows:
Move the datafile to some safe place.
Use the table description file to create new (empty) data and index files:
shell> mysql db_name mysql> SET AUTOCOMMIT=1; mysql> TRUNCATE TABLE table_name; mysql> quit
If your SQL version doesn't have TRUNCATE TABLE, use DELETE FROM table_name instead.
Copy the old datafile back onto the newly created datafile. (Don't just move the old file back onto the new file; you want to retain a copy in case something goes wrong.)
Go back to Stage 2. myisamchk -r -q should work now. (This shouldn't be an endless loop.)
As of MySQL 4.0.2 you can also use REPAIR ... USE_FRM which performs the whole procedure automatically.
Stage 4: Very difficult repair
You should reach this stage only if the description file has also crashed. That should never happen, because the description file isn't changed after the table is created:
Restore the description file from a backup and go back to Stage 3. You can also restore the index file and go back to Stage 2. In the latter case, you should start with myisamchk -r.
If you don't have a backup but know exactly how the table was created, create a copy of the table in another database. Remove the new datafile, then move the description and index files from the other database to your crashed database. This gives you new description and index files, but leaves the datafile alone. Go back to Stage 2 and attempt to reconstruct the index file.
To coalesce fragmented records and eliminate wasted space resulting from deleting or updating records, run myisamchk in recovery mode:
shell> myisamchk -r tbl_name
You can optimize a table in the same way using the SQL OPTIMIZE TABLE statement. OPTIMIZE TABLE does a repair of the table and a key analysis, and also sorts the index tree to give faster key lookups. There is also no possibility of unwanted interaction between a utility and the server, because the server does all the work when you use OPTIMIZE TABLE. See OPTIMIZE TABLE.
myisamchk also has a number of other options you can use to improve the performance of a table:
-S, --sort-index
-R index_num, --sort-records=index_num
-a, --analyze
For a full description of the option. See myisamchk syntax.
Starting with MySQL Version 3.23.13, you can check MyISAM tables with the CHECK TABLE command. See CHECK TABLE. You can repair tables with the REPAIR TABLE command. See REPAIR TABLE.
It is a good idea to perform table checks on a regular basis rather than waiting for problems to occur. For maintenance purposes, you can use myisamchk -s to check tables. The -s option (short for --silent) causes myisamchk to run in silent mode, printing messages only when errors occur.
It's also a good idea to check tables when the server starts. For example, whenever the machine has done a reboot in the middle of an update, you usually need to check all the tables that could have been affected. (This is an ``expected crashed table''.) You could add a test to mysqld_safe that runs myisamchk to check all tables that have been modified during the last 24 hours if there is an old .pid (process ID) file left after a reboot. (The .pid file is created by mysqld when it starts and removed when it terminates normally. The presence of a .pid file at system startup time indicates that mysqld terminated abnormally.)
An even better test would be to check any table whose last-modified time is more recent than that of the .pid file.
You should also check your tables regularly during normal system operation. At MySQL AB, we run a cron job to check all our important tables once a week, using a line like this in a crontab file:
35 0 * * 0 /path/to/myisamchk --fast --silent /path/to/datadir/*/*.MYI
This prints out information about crashed tables so we can examine and repair them when needed.
As we haven't had any unexpectedly crashed tables (tables that become corrupted for reasons other than hardware trouble) for a couple of years now (this is really true), once a week is more than enough for us.
We recommend that to start with, you execute myisamchk -s each night on all tables that have been updated during the last 24 hours, until you come to trust MySQL as much as we do.
Normally you don't need to maintain MySQL tables that much. If you are changing tables with dynamic size rows (tables with VARCHAR, BLOB or TEXT columns) or have tables with many deleted rows you may want to from time to time (once a month?) defragment/reclaim space from the tables.
You can do this by using OPTIMIZE TABLE on the tables in question or if you can take down the mysqld server for a while do:
isamchk -r --silent --sort-index -O sort_buffer_size=16M */*.ISM myisamchk -r --silent --sort-index -O sort_buffer_size=16M */*.MYI
To get a description of a table or statistics about it, use the commands shown here. We explain some of the information in more detail later:
myisamchk -d tbl_name Runs myisamchk in ``describe mode'' to produce a description of your table. If you start the MySQL server using the --skip-external-locking option, myisamchk may report an error for a table that is updated while it runs. However, because myisamchk doesn't change the table in describe mode, there isn't any risk of destroying data.
myisamchk -d -v tbl_name To produce more information about what myisamchk is doing, add -v to tell it to run in verbose mode.
myisamchk -eis tbl_name Shows only the most important information from a table. It is slow because it must read the whole table.
myisamchk -eiv tbl_name This is like -eis, but tells you what is being done.
Example of myisamchk -d output:
MyISAM file: company.MYI Record format: Fixed length Data records: 1403698 Deleted blocks: 0 Recordlength: 226 table description: Key Start Len Index Type 1 2 8 unique double 2 15 10 multip. text packed stripped 3 219 8 multip. double 4 63 10 multip. text packed stripped 5 167 2 multip. unsigned short 6 177 4 multip. unsigned long 7 155 4 multip. text 8 138 4 multip. unsigned long 9 177 4 multip. unsigned long 193 1 text
Example of myisamchk -d -v output:
MyISAM file: company Record format: Fixed length File-version: 1 Creation time: 1999-10-30 12:12:51 Recover time: 1999-10-31 19:13:01 Status: checked Data records: 1403698 Deleted blocks: 0 Datafile parts: 1403698 Deleted data: 0 Datafilepointer (bytes): 3 Keyfile pointer (bytes): 3 Max datafile length: 3791650815 Max keyfile length: 4294967294 Recordlength: 226 table description: Key Start Len Index Type Rec/key Root Blocksize 1 2 8 unique double 1 15845376 1024 2 15 10 multip. text packed stripped 2 25062400 1024 3 219 8 multip. double 73 40907776 1024 4 63 10 multip. text packed stripped 5 48097280 1024 5 167 2 multip. unsigned short 4840 55200768 1024 6 177 4 multip. unsigned long 1346 65145856 1024 7 155 4 multip. text 4995 75090944 1024 8 138 4 multip. unsigned long 87 85036032 1024 9 177 4 multip. unsigned long 178 96481280 1024 193 1 text
Example of myisamchk -eis output:
Checking MyISAM file: company Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 98% Packed: 17% Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Record blocks: 1403698 Delete blocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1626.51, System time 232.36 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 627, Swaps 0 Blocks in 0 out 0, Messages in 0 out 0, Signals 0 Voluntary context switches 639, Involuntary context switches 28966
Example of myisamchk -eiv output:
Checking MyISAM file: company Data records: 1403698 Deleted blocks: 0 - check file-size - check delete-chain block_size 1024: index 1: index 2: index 3: index 4: index 5: index 6: index 7: index 8: index 9: No recordlinks - check index reference - check data record references index: 1 Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 2 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 - check data record references index: 3 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 - check data record references index: 5 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 6 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 7 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 8 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 9 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 9% Packed: 17% - check records and index references [LOTS OF ROW NUMBERS DELETED] Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Record blocks: 1403698 Delete blocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1639.63, System time 251.61 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 10580, Swaps 0 Blocks in 4 out 0, Messages in 0 out 0, Signals 0 Voluntary context switches 10604, Involuntary context switches 122798
Here are the sizes of the data and index files for the table used in the preceding examples:
-rw-rw-r-- 1 monty tcx 317235748 Jan 12 17:30 company.MYD -rw-rw-r-- 1 davida tcx 96482304 Jan 12 18:35 company.MYM
Explanations for the types of information myisamchk produces are given here. The ``keyfile'' is the index file. ``Record'' and ``row'' are synonymous:
ISAM file Name of the ISAM (index) file.
Isam-version Version of ISAM format. Currently always 2.
Creation time When the datafile was created.
Recover time When the index/datafile was last reconstructed.
Data records How many records are in the table.
Deleted blocks How many deleted blocks still have reserved space. You can optimize your table to minimise this space. See Optimisation.
Data file: Parts For dynamic record format, this indicates how many data blocks there are. For an optimized table without fragmented records, this is the same as Data records.
Deleted data How many bytes of non-reclaimed deleted data there are. You can optimize your table to minimise this space. See Optimisation.
Data file pointer The size of the datafile pointer, in bytes. It is usually 2, 3, 4, or 5 bytes. Most tables manage with 2 bytes, but this cannot be controlled from MySQL yet. For fixed tables, this is a record address. For dynamic tables, this is a byte address.
Keyfile pointer The size of the index file pointer, in bytes. It is usually 1, 2, or 3 bytes. Most tables manage with 2 bytes, but this is calculated automatically by MySQL. It is always a block address.
Max datafile length How long the table's datafile (.MYD file) can become, in bytes.
Max keyfile length How long the table's key file (.MYI file) can become, in bytes.
Recordlength How much space each record takes, in bytes.
Record format The format used to store table rows. The preceding examples use Fixed length. Other possible values are Compressed and Packed.
table description A list of all keys in the table. For each key, some low-level information is presented:
Key This key's number.
Start Where in the record this index part starts.
Len How long this index part is. For packed numbers, this should always be the full length of the column. For strings, it may be shorter than the full length of the indexed column, because you can index a prefix of a string column.
Index unique or multip. (multiple). Indicates whether one value can exist multiple times in this index.
Type What data-type this index part has. This is an ISAM data-type with the options packed, stripped or empty.
Root Address of the root index block.
Blocksize The size of each index block. By default this is 1024, but the value may be changed at compile time.
Rec/key This is a statistical value used by the optimizer. It tells how many records there are per value for this key. A unique key always has a value of 1. This may be updated after a table is loaded (or greatly changed) with myisamchk -a. If this is not updated at all, a default value of 30 is given.
In the first example above, the 9th key is a multi-part key with two parts.
Keyblocks used What percentage of the keyblocks are used. Because the table used in the examples had just been reorganized with myisamchk, the values are very high (very near the theoretical maximum).
Packed MySQL tries to pack keys with a common suffix. This can only be used for CHAR/VARCHAR/DECIMAL keys. For long strings like names, this can significantly reduce the space used. In the third example above, the 4th key is 10 characters long and a 60% reduction in space is achieved.
Max levels How deep the B-tree for this key is. Large tables with long keys get high values.
Records How many rows are in the table.
M.recordlength The average record length. For tables with fixed-length records, this is the exact record length.
Packed MySQL strips spaces from the end of strings. The Packed value indicates the percentage of savings achieved by doing this.
Recordspace used What percentage of the datafile is used.
Empty space What percentage of the datafile is unused.
Blocks/Record Average number of blocks per record (that is, how many links a fragmented record is composed of). This is always 1.0 for fixed-format tables. This value should stay as close to 1.0 as possible. If it gets too big, you can reorganize the table with myisamchk. See Optimisation.
Recordblocks How many blocks (links) are used. For fixed format, this is the same as the number of records.
Deleteblocks How many blocks (links) are deleted.
Recorddata How many bytes in the datafile are used.
Deleted data How many bytes in the datafile are deleted (unused).
Lost space If a record is updated to a shorter length, some space is lost. This is the sum of all such losses, in bytes.
Linkdata When the dynamic table format is used, record fragments are linked with pointers (4 to 7 bytes each). Linkdata is the sum of the amount of storage used by all such pointers.
If a table has been compressed with myisampack, myisamchk -d prints additional information about each table column. See myisampack, for an example of this information and a description of what it means.
Table of Contents
By default, MySQL uses the ISO-8859-1 (Latin1) character set with sorting according to Swedish/Finnish rules. These defaults are suitable for the USA and most of western Europe.
All standard MySQL binaries are compiled with --with-extra-charsets=complex. This will add code to all standard programs to be able to handle latin1 and all multi-byte character sets within the binary. Other character sets will be loaded from a character-set definition file when needed.
The character set determines what characters are allowed in names and how strings are sorted by the ORDER BY and GROUP BY clauses of the SELECT statement.
You can change the character set with the --default-character-set option when you start the server. The character sets available depend on the --with-charset=charset and --with-extra-charsets= list-of-charset | complex | all | none options to configure, and the character set configuration files listed in SHAREDIR/charsets/Index. See configure options.
If you change the character set when running MySQL (which may also change the sort order), you must run myisamchk -r -q --set-character-set=charset on all tables. Otherwise, your indexes may not be ordered correctly.
When a client connects to a MySQL server, the server sends the default character set in use to the client. The client will switch to use this character set for this connection.
One should use mysql_real_escape_string() when escaping strings for an SQL query. mysql_real_escape_string() is identical to the old mysql_escape_string() function, except that it takes the MYSQL connection handle as the first parameter.
If the client is compiled with different paths than where the server is installed and the user who configured MySQL didn't include all character sets in the MySQL binary, one must specify for the client where it can find the additional character sets it will need if the server runs with a different character set than the client.
One can specify this by putting in a MySQL option file:
[client] character-sets-dir=/usr/local/mysql/share/mysql/charsets
where the path points to the directory in which the dynamic MySQL character sets are stored.
One can force the client to use specific character set by specifying:
[client] default-character-set=character-set-name
but normally this is never needed.
To get German sorting order, you should start mysqld with --default-character-set=latin1_de. This will give you the following characteristics.
When sorting and comparing strings, the following mapping is done on the strings before doing the comparison:
ä -> ae ö -> oe ü -> ue ß -> ss
All accented characters, are converted to their un-accented uppercase counterpart. All letters are converted to uppercase.
When comparing strings with LIKE the one -> two character mapping is not done. All letters are converted to uppercase. Accent are removed from all letters except: Ü, ü, Ö, ö, Ä and ä.
mysqld can issue error messages in the following languages: Czech, Danish, Dutch, English (the default), Estonian, French, German, Greek, Hungarian, Italian, Japanese, Korean, Norwegian, Norwegian-ny, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, and Swedish.
To start mysqld with a particular language, use either the --language=lang or -L lang options. For example:
shell> mysqld --language=swedish
or:
shell> mysqld --language=/usr/local/share/swedish
Note that all language names are specified in lowercase.
The language files are located (by default) in mysql_base_dir/share/LANGUAGE/.
To update the error message file, you should edit the errmsg.txt file and execute the following command to generate the errmsg.sys file:
shell> comp_err errmsg.txt errmsg.sys
If you upgrade to a newer version of MySQL, remember to repeat your changes with the new errmsg.txt file.
To add another character set to MySQL, use the following procedure.
Decide if the set is simple or complex. If the character set does not need to use special string collating routines for sorting and does not need multi-byte character support, it is simple. If it needs either of those features, it is complex.
For example, latin1 and danish are simple charactersets while big5 or czech are complex character sets.
In the following section, we have assumed that you name your character set MYSET.
For a simple character set do the following:
Add MYSET to the end of the sql/share/charsets/Index file Assign a unique number to it.
Create the file sql/share/charsets/MYSET.conf. (You can use sql/share/charsets/latin1.conf as a base for this.)
The syntax for the file is very simple:
Comments start with a '#' character and proceed to the end of the line.
Words are separated by arbitrary amounts of whitespace.
When defining the character set, every word must be a number in hexadecimal format
The ctype array takes up the first 257 words. The to_lower[], to_upper[] and sort_order[] arrays take up 256 words each after that.
See Character arrays.
Add the character set name to the CHARSETS_AVAILABLE and COMPILED_CHARSETS lists in configure.in.
Reconfigure, recompile, and test.
For a complex character set do the following:
Create the file strings/ctype-MYSET.c in the MySQL source distribution.
Add MYSET to the end of the sql/share/charsets/Index file. Assign a unique number to it.
Look at one of the existing ctype-*.c files to see what needs to be defined, for example strings/ctype-big5.c. Note that the arrays in your file must have names like ctype_MYSET, to_lower_MYSET, and so on. This corresponds to the arrays in the simple character set. See Character arrays.
Near the top of the file, place a special comment like this:
/* * This comment is parsed by configure to create ctype.c, * so don't change it unless you know what you are doing. * * .configure. number_MYSET=MYNUMBER * .configure. strxfrm_multiply_MYSET=N * .configure. mbmaxlen_MYSET=N */
The configure program uses this comment to include the character set into the MySQL library automatically.
The strxfrm_multiply and mbmaxlen lines will be explained in the following sections. Only include these if you need the string collating functions or the multi-byte character set functions, respectively.
You should then create some of the following functions:
my_strncoll_MYSET()
my_strcoll_MYSET()
my_strxfrm_MYSET()
my_like_range_MYSET()
See String collating.
Add the character set name to the CHARSETS_AVAILABLE and COMPILED_CHARSETS lists in configure.in.
Reconfigure, recompile, and test.
The file sql/share/charsets/README includes some more instructions.
If you want to have the character set included in the MySQL distribution, mail a patch to the MySQL internals mailing list. See Mailing-list.
to_lower[] and to_upper[] are simple arrays that hold the lowercase and uppercase characters corresponding to each member of the character set. For example:
to_lower['A'] should contain 'a' to_upper['a'] should contain 'A'
sort_order[] is a map indicating how characters should be ordered for comparison and sorting purposes. Quite often (but not for all character sets) this is the same as to_upper[] (which means sorting will be case-insensitive). MySQL will sort characters based on the value of sort_order[character]. For more complicated sorting rules, see the discussion of string collating below. See String collating.
ctype[] is an array of bit values, with one element for one character. (Note that to_lower[], to_upper[], and sort_order[] are indexed by character value, but ctype[] is indexed by character value + 1. This is an old legacy to be able to handle EOF.)
You can find the following bitmask definitions in m_ctype.h:
#define _U 01 /* Uppercase */ #define _L 02 /* Lowercase */ #define _N 04 /* Numeral (digit) */ #define _S 010 /* Spacing character */ #define _P 020 /* Punctuation */ #define _C 040 /* Control character */ #define _B 0100 /* Blank */ #define _X 0200 /* heXadecimal digit */
The ctype[] entry for each character should be the union of the applicable bitmask values that describe the character. For example, 'A' is an uppercase character (_U) as well as a hexadecimal digit (_X), so ctype['A'+1] should contain the value:
_U + _X = 01 + 0200 = 0201
If the sorting rules for your language are too complex to be handled with the simple sort_order[] table, you need to use the string collating functions.
Right now the best documentation on this is the character sets that are already implemented. Look at the big5, czech, gbk, sjis, and tis160 character sets for examples.
You must specify the strxfrm_multiply_MYSET=N value in the special comment at the top of the file. N should be set to the maximum ratio the strings may grow during my_strxfrm_MYSET (it must be a positive integer).
If your want to add support for a new character set that includes multi-byte characters, you need to use the multi-byte character functions.
Right now the best documentation on this is the character sets that are already implemented. Look at the euc_kr, gb2312, gbk, sjis, and ujis character sets for examples. These are implemented in the ctype-'charset'.c files in the strings directory.
You must specify the mbmaxlen_MYSET=N value in the special comment at the top of the source file. N should be set to the size in bytes of the largest character in the set.
If you try to use a character set that is not compiled into your binary, you can run into a couple of different problems:
Your program has a wrong path to where the character sets are stored. (Default /usr/local/mysql/share/mysql/charsets). This can be fixed by using the --character-sets-dir option to the program in question.
The character set is a multi-byte character set that can't be loaded dynamically. In this case you have to recompile the program with the support for the character set.
The character set is a dynamic character set, but you don't have a configure file for it. In this case you should install the configure file for the character set from a new MySQL distribution.
Your Index file doesn't contain the name for the character set.
ERROR 1105: File '/usr/local/share/mysql/charsets/?.conf' not found (Errcode: 2)
In this case you should either get a new Index file or add by hand the name of any missing character sets.
For MyISAM tables, you can check the character set name and number for a table with myisamchk -dvv table_name.
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MySQL has several different log files that can help you find out what's going on inside mysqld:
Log file | Description |
The error log | Problems encountering starting, running or stopping mysqld. |
The isam log | Logs all changes to the ISAM tables. Used only for debugging the isam code. |
The query log | Established connections and executed queries. |
The update log | Deprecated: Stores all statements that changes data |
The binary log | Stores all statements that changes something. Used also for replication |
The slow log | Stores all queries that took more than long_query_time seconds to execute or didn't use indexes. |
All logs can be found in the mysqld data directory. You can force mysqld to reopen the log files (or in some cases switch to a new log) by executing FLUSH LOGS. See FLUSH.
The error log file contains information indicating when mysqld was started and stopped and also any critical errors found when running.
If mysqld dies unexpectedly and mysqld_safe needs to restart mysqld, mysqld_safe will write a restarted mysqld row in this file. This log also holds a warning if mysqld notices a table that needs to be automatically checked or repaired.
On some operating systems, the error log will contain a stack trace for where mysqld died. This can be used to find out where mysqld died. See Using stack trace.
Beginning with MySQL 4.0.10 you can specify where mysqld stores the error log file with the option --log-error[=filename]. If no file name is given mysqld will use mysql-data-dir/'hostname'.err on Unix and \mysql\data\mysql.err on Windows. If you execute flush logs the old file will be prefixed with --old and mysqld will create a new empty log file.
In older MySQL versions the error log handling was done by mysqld_safe which redirected the error file to 'hostname'.err. One could change this file name with the option --err-log=filename.
If you don't specify --log-error or if you use the --console option the errors will be written to stderr (the terminal).
On Windows, the output is always written to the .err file if --console is not given.
If you want to know what happens within mysqld, you should start it with --log[=file]. This will log all connections and queries to the log file (by default named 'hostname'.log). This log can be very useful when you suspect an error in a client and want to know exactly what mysqld thought the client sent to it.
Older versions of the mysql.server script (from MySQL 3.23.4 to 3.23.8) pass safe_mysqld a --log option (enable general query log). If you need better performance when you start using MySQL in a production environment, you can remove the --log option from mysql.server or change it to --log-bin. See Binary log.
The entries in this log are written as mysqld receives the questions. This may be different from the order in which the statements are executed. This is in contrast to the update log and the binary log which are written after the query is executed, but before any locks are released.
Note: The update log has been deprecated and replaced by the binary log. See Binary log. The binary log can do anything the old update log could do, and more. The update log is removed starting from MySQL 5.0.0.
When started with the --log-update[=file_name] option, mysqld writes a log file containing all SQL commands that update data. If no filename is given, it defaults to the name of the host machine. If a filename is given, but it doesn't contain a path, the file is written in the data directory. If file_name doesn't have an extension, mysqld will create log file names like so: file_name.###, where ### is a number that is incremented each time you execute mysqladmin refresh, execute mysqladmin flush-logs, execute the FLUSH LOGS statement, or restart the server.
Note: For the above scheme to work, you must not create your own files with the same filename as the update log + some extensions that may be regarded as a number, in the directory used by the update log!
If you use the --log or -l options, mysqld writes a general log with a filename of hostname.log, and restarts and refreshes do not cause a new log file to be generated (although it is closed and reopened). In this case you can copy it (on Unix) by doing:
mv hostname.log hostname-old.log mysqladmin flush-logs cp hostname-old.log to-backup-directory rm hostname-old.log
Update logging is smart because it logs only statements that really update data. So an UPDATE or a DELETE with a WHERE that finds no rows is not written to the log. It even skips UPDATE statements that set a column to the value it already has.
The update logging is done immediately after a query completes but before any locks are released or any commit is done. This ensures that the log will be logged in the execution order.
If you want to update a database from update log files, you could do the following (assuming your update logs have names of the form file_name.###):
shell> ls -1 -t -r file_name.[0-9]* | xargs cat | mysql
ls is used to get all the log files in the right order.
This can be useful if you have to revert to backup files after a crash and you want to redo the updates that occurred between the time of the backup and the crash.
The binary log has replaced the old update log. The update log is removed starting from MySQL 5.0. The binary log contains all information that is available in the update log in a more efficient format and in a manner that is transactionally safe.
The binary log, like the old update log, only logs statements that really update data. So an UPDATE or a DELETE with a WHERE that finds no rows is not written to the log. It even skips UPDATE statements that set a column to the value it already has.
The primary purpose of the binary log is to be able to update the database during a restore operation as fully as possible, as the binary log would contain all updates done after a backup was made.
The binary log is also used when you are replicating a slave from a master. See Replication.
The binary log also contains information about how long each query took that updated the database. It doesn't contain queries that don't modify any data. If you want to log all queries (for example to find a problem query) you should use the general query log. See Query log.
When started with the --log-bin[=file_name] option, mysqld writes a log file containing all SQL commands that update data. If no file name is given, it defaults to the name of the host machine followed by -bin. If file name is given, but it doesn't contain a path, the file is written in the data directory.
If you supply an extension to --log-bin=filename.extension, the extension will be silenty removed.
To the binary log filename mysqld will append an extension that is a number that is incremented each time you execute mysqladmin refresh, execute mysqladmin flush-logs, execute the FLUSH LOGS statement or restart the server. A new binary log will also automatically be created when the current one's size reaches max_binlog_size. Note if you are using transactions: a transaction is written in one chunk to the binary log, hence it is never split between several binary logs. Therefore, if you have big transactions, you may see binlogs bigger than max_binlog_size.
You can delete all binary log files with the RESET MASTER command (see RESET), or only some of them with PURGE MASTER LOGS (see Replication Master SQL).
You can use the following options to mysqld to affect what is logged to the binary log (please make sure to read the notes which follow this table):
Option | Description |
binlog-do-db=database_name | Tells the master that it should log updates to the binary log if the current database (that is, the one selected by USE) database is 'database_name'. All others databases which are not explicitly mentioned are ignored. Note that if you use this you should ensure that you only do updates in the current database. (Example: binlog-do-db=some_database) Example of what does not work as you could expect it: if the server is started with binlog-do-db=sales, and you do USE prices; UPDATE sales.january SET amount=amount+1000;, this query will not be written into the binary log. |
binlog-ignore-db=database_name | Tells the master that updates where the current database (that is, the one selected by USE) is 'database_name' should not be stored in the binary log. Note that if you use this you should ensure that you only do updates in the current database. (Example: binlog-ignore-db=some_database) Example of what does not work as you could expect it: if the server is started with binlog-ignore-db=sales, and you do USE prices; UPDATE sales.january SET amount=amount+1000;, this query will be written into the binary log. |
The rules are evaluated in the following order, to decide if the query should be written to the binary log or not:
Are there binlog-do-db or binlog-ignore-db rules?
No: write the query to the binlog and exit.
Yes: go to step below.
So there are some rules (binlog-do-db or binlog-ignore-db or both). Is there a current database (has any database been selected by USE?)?
No: do NOT write the query, and exit.
Yes: go to step below.
There is a current database. Are there some binlog-do-db rules?
Yes: Does the current database match any of the binlog-do-db rules?
Yes: write the query and exit.
No: do NOT write the query, and exit.
No: go to step below.
There are some binlog-ignore-db rules. Does the current database match any of the binlog-ignore-db rules?
Yes: do not write the query, and exit.
No: write the query and exit.
So for example, a slave running with only binlog-do-db=sales will not write to the binlog any query whose current database is different from sales (in other words, binlog-do-db can sometimes mean ``ignore other databases'').
To be able to know which different binary log files have been used, mysqld will also create a binary log index file that contains the name of all used binary log files. By default this has the same name as the binary log file, with the extension '.index'. You can change the name of the binary log index file with the --log-bin-index=[filename] option. You should not manually edit this file while mysqld is running; doing this would confuse mysqld.
If you are using replication, you should not delete old binary log files until you are sure that no slave will ever need to use them. One way to do this is to do mysqladmin flush-logs once a day and then remove any logs that are more than 3 days old. You can remove them manually, or preferably using PURGE MASTER LOGS (see Replication Master SQL) which will also safely update the binary log index file for you (and which can take a date argument since MySQL 4.1)
A connection with the SUPER privilege can disable the binary logging of its queries using SET SQL_LOG_BIN=0. See Replication Master SQL.
You can examine the binary log file with the mysqlbinlog utility. For example, you can update a MySQL server from the binary log as follows:
shell> mysqlbinlog log-file | mysql -h server_name
See mysqlbinlog for more information on the mysqlbinlog utility and how to use it.
If you are using BEGIN [WORK] or SET AUTOCOMMIT=0, you must use the MySQL binary log for backups instead of the old update log. As of MySQL 5.0.0, the old update log is no longer available.
The binary logging is done immediately after a query completes but before any locks are released or any commit is done. This ensures that the log will be logged in the execution order.
Updates to non-transactional tables are stored in the binary log immediately after execution. For transactional tables such as BDB or InnoDB tables, all updates (UPDATE, DELETE or INSERT) that change tables are cached until a COMMIT command is sent to the server. At this point mysqld writes the whole transaction to the binary log before the COMMIT is executed. Every thread will, on start, allocate a buffer of binlog_cache_size to buffer queries. If a query is bigger than this, the thread will open a temporary file to store the transaction. The temporary file will be deleted when the thread ends.
The max_binlog_cache_size (default 4G) can be used to restrict the total size used to cache a multi-query transaction. If a transaction is bigger than this it will fail and roll back.
If you are using the update or binary log, concurrent inserts will be converted to normal inserts when using CREATE ... SELECT or INSERT ... SELECT. This is to ensure that you can re-create an exact copy of your tables by applying the log on a backup.
The binary log format is different in versions 3.23, 4.0, and 5.0.0. Those format changes were required to enhance replication. MySQL 4.1 has the same binary log format as 4.0.
When started with the --log-slow-queries[=file_name] option, mysqld writes a log file containing all SQL commands that took more than long_query_time seconds to execute. The time to get the initial table locks are not counted as execution time.
The slow query log is logged after the query is executed and after all locks has been released. This may be different from the order in which the statements are executed.
If no file name is given, it defaults to the name of the host machine suffixed with -slow.log. If a filename is given, but doesn't contain a path, the file is written in the data directory.
The slow query log can be used to find queries that take a long time to execute and are thus candidates for optimization. With a large log, that can become a difficult task. You can pipe the slow query log through the mysqldumpslow command to get a summary of the queries which appear in the log.
You are using --log-long-format then also queries that are not using indexes are printed. See Server options.
The MySQL Server can create a number of different log files, which make it easy to see what is going on. See Log Files. However, you must clean up these files regularly, to ensure that the logs don't take up too much disk space.
When using MySQL with log files, you will want to remove/backup old log files from time to time and tell MySQL to start logging to new files. See Backup.
On a Linux (Red Hat) installation, you can use the mysql-log-rotate script for this. If you installed MySQL from an RPM distribution, the script should have been installed automatically. Note that you should be careful with this script if you are using the binary log for replication!
On other systems you must install a short script yourself that you start from cron to handle log files.
You can force MySQL to start using new log files by using mysqladmin flush-logs or by using the SQL command FLUSH LOGS. If you are using MySQL Version 3.21, you must use mysqladmin refresh.
The above command does the following:
If standard logging (--log) or slow query logging (--log-slow-queries) is used, closes and reopens the log file (mysql.log and `hostname`-slow.log as default).
If update logging (--log-update) is used, closes the update log and opens a new log file with a higher sequence number.
If you are using only an update log, you only have to flush the logs and then move away the old update log files to a backup. If you are using the normal logging, you can do something like:
shell> cd mysql-data-directory shell> mv mysql.log mysql.old shell> mysqladmin flush-logs
and then take a backup and remove mysql.old.
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In some cases you might want to run multiple mysqld servers on the same machine. You might want to test a new MySQL release while leaving your existing production setup undisturbed. Or you may want to give different users access to different mysqld servers that they manage themselves. (For example, you might be an Internet service provider that wants to provide independent MySQL installations for different customers.)
To run multiple servers on a single machine, each server must have unique values for several operating parameters. These can be set on the command line or in option files. See Program Options.
At least the following options must be different for each server:
--port=port_num
--socket=path
--shared-memory-base-name=name (Windows only; new in MySQL 4.1)
--pid-file=path (Unix only)
--port controls the port number for TCP/IP connections. --socket controls the socket file path on Unix and the name of the named pipe on Windows. (It's necessary to specify distinct pipe names on Windows only for those servers that support named pipe connections.) --shared-memory-base-name designates the shared memory name used by a Windows server to allow clients to connect via shared memory. --pid-file indicates the name of the file in which a Unix server writes its process ID.
If you use the following options, they must be different for each server:
--log=path
--log-bin=path
--log-update=path
--log-error=path
--log-isam=path
--bdb-logdir=path
If you want more performance, you can also specify the following options differently for each server, to spread load between several physical disks:
--tmpdir=path
--bdb-tmpdir=path
Having different temporary directories like above is also recommended because it will be easier for you in case you want to know to which MySQL server a certain temporary file belongs.
Generally, each server should also use a different data directory, which is specified using the --datadir=path option.
Warning: Normally you should never have two servers that update data in the same databases! This may lead to unpleasant surprises if your operating system doesn't support fault-free system locking! If (despite this warning) you run multiple servers using the same data directory and they have logging enabled, you must use the appropriate options to specify log file names that are unique to each server. Otherwise, the servers will try to log to the same files.
This warning against sharing a data directory among servers also applies in an NFS environment. Allowing multiple MySQL servers to access a common data directory over NFS is a bad idea!
The primary problem is that NFS will become the speed bottleneck. It is not meant for such use.
Another risk with NFS is that you will have to come up with a way to make sure that two or more servers do not interfere with each other. Usually NFS file locking is handled by the lockd daemon, but at the moment there is no platform that will perform locking 100% reliably in every situation.
Make it easy for yourself: Forget about sharing a data directory among servers over NFS. A better solution is to have one computer that contains several CPUs and use an operating system that handles threads efficiently.
If you have multiple MySQL installations in different locations, normally you can specify the base installation directory for each server with the --basedir=path option to cause each server to use a different data directory, log files, and PID file. (The defaults for all these values are determined relative to the base directory.) In that case, the only other options you need to specify are the --socket and --port options. For example, suppose you install different versions of MySQL using .tar file binary distributions. These will install in different locations, so you can start the server for each installation using the command ./bin/mysqld_safe under its corresponding base directory. mysqld_safe will determine the proper --basedir option to pass to mysqld, and you need specify only the --socket and --port options to mysqld_safe.
As discussed in the following sections, it is possible to start additional servers by setting environment variables or by specifying appropriate command-line options. However, if you need to run multiple servers on a more permanent basis, it will be more convenient to use option files to specify for each server those option values that must be unique to it.
You can run multiple servers on Windows by starting them manually from the command line, each with appropriate operating parameters. On Windows NT-based systems, you also have the option of installing several servers as Windows services and running them that way. General instructions for running MySQL servers from the command line or as services are given in Windows installation. This section describes how to make sure you start each server with different values for those startup options that must be unique per server, such as the data directory. (These options are described in Multiple servers.)
To start multiple servers manually from the command line, you can specify the appropriate options on the command line or in an option file. It's more convenient to place the options in an option file, but it's necessary to make sure that each server gets its own set of options. To do this, create an option file for each server and tell the server the filename with a --defaults-file option when you run it.
Suppose you want to run mysqld on port 3307 with a data directory of C:\mydata1, and mysqld-max on port 3308 with a data directory of C:\mydata2. To accomplish this, create two option files. For example, create one file named C:\my-opts1.cnf that looks like this:
[mysqld] datadir = C:/mydata1 port = 3307
Create a second file named C:\my-opts2.cnf that looks like this:
[mysqld] datadir = C:/mydata2 port = 3308
Then start each server with its own option file:
shell> mysqld --defaults-file=C:\my-opts1.cnf shell> mysqld-max --defaults-file=C:\my-opts2.cnf
(On NT, the servers will start in the foreground, so you'll need to issue those two commands in separate console windows.)
To shut down the servers, you must connect to the appropriate port number:
shell> mysqladmin --port=3307 shutdown shell> mysqladmin --port=3308 shutdown
Servers configured as just described will allow clients to connect over TCP/IP. If you also want to allow named pipe connections, use the mysqld-nt or mysqld-max-nt servers and specify options that enable the named pipe and specify its name. (Each server that supports named pipe connections must use a unique pipe name.) For example, the C:\my-opts1.cnf file might be written like this:
[mysqld] datadir = C:/mydata1 port = 3307 enable-named-pipe socket = mypipe1
Then start the server this way:
shell> mysqld-nt --defaults-file=C:\my-opts1.cnf
C:\my-opts2.cnf would be modified similarly for use by the second server.
On NT-based systems, a MySQL server can be run as a Windows service. The procedures for installing, controlling, and removing a single MySQL service are described in NT start.
As of MySQL 4.0.2, you can install multiple servers as services. In this case, you must make sure that each server uses a different service name in addition to all the other parameters that must be unique per server.
For the following instructions, assume that you want to run the mysqld-nt server from two different versions of MySQL that are installed at C:\mysql-4.0.8 and C:\mysql-4.0.17, respectively. (This might be the case if you're running 4.0.8 as your production server, but want to test 4.0.17 before upgrading to it.)
The following principles are relevant when installing a MySQL service with the --install option:
If you specify no service name, the server uses the default service name of MySQL and the server reads options from the [mysqld] group in the standard option files.
If you specify a service name after the --install option, the server ignores the [mysqld] option group and instead reads options from the group that has the same name as the service. The server reads options from the standard option files.
If you specify a --defaults-file option after the service name, the server ignores the standard option files and reads options only from the [mysqld] group of the named file.
These principles also apply if you install a server using the --install-manual option.
Based on the preceding information, you have several ways to set up multiple services. The following instructions describe some examples. Before trying any of them, be sure you shut down and remove any existing MySQL services first.
Specify the options for all services in one of the standard option files. To do this, use a different service name for each server. Suppose you want to run the 4.0.8 mysqld-nt using the service name of mysqld1 and the 4.0.17 mysqld-nt using the service name mysqld2. In this case, you can use the [mysqld1] group for 4.0.8 and the [mysqld2] group for 4.0.17. For example, you can set up C:\my.cnf like this:
# options for mysqld1 service [mysqld1] basedir = C:/mysql-4.0.8 port = 3307 enable-named-pipe socket = mypipe1 # options for mysqld2 service [mysqld2] basedir = C:/mysql-4.0.17 port = 3308 enable-named-pipe socket = mypipe2
Install the services as follows, using the full server pathnames to ensure that Windows registers the correct executable program for each service:
shell> C:\mysql-4.0.8\bin\mysqld-nt --install mysqld1 shell> C:\mysql-4.0.17\bin\mysqld-nt --install mysqld2
To start the services, use the services manager, or use NET START with the appropriate service names:
shell> NET START mysqld1 shell> NET START mysqld2
To stop the services, use the services manager, or use NET STOP with the appropriate service names:
shell> NET STOP mysqld1 shell> NET STOP mysqld2
Note: Before MySQL 4.0.17, only a server installed using the default service name (MySQL) or one installed explicitly with a service name of mysqld will read the [mysqld] group in the standard option files. As of 4.0.17, all servers read the [mysqld group if they read the standard option files, even if they are installed using another service name. This allows you to use the [mysqld] group for options that should be used by all MySQL services, and an option group named after each service for use by the server installed with that service name.
Specify options for each server in separate files and use --defaults-file when you install the services to tell each server what file to use. In this case, each file should list options using a [mysqld] group.
With this approach, to specify options for the 4.0.8 mysqld-nt, create a file C:\my-opts1.cnf that looks like this:
[mysqld] basedir = C:/mysql-4.0.8 port = 3307 enable-named-pipe socket = mypipe1
For the 4.0.17 mysqld-nt, create a file C:\my-opts2.cnf that looks like this:
[mysqld] basedir = C:/mysql-4.0.17 port = 3308 enable-named-pipe socket = mypipe2
Install the services as follows (enter each command on a single line):
shell> C:\mysql-4.0.8\bin\mysqld-nt --install mysqld1 --defaults-file=C:\my-opts1.cnf shell> C:\mysql-4.0.17\bin\mysqld-nt --install mysqld2 --defaults-file=C:\my-opts2.cnf
To use a --defaults-file option when you install a MySQL server as a service, you must precede the option with the service name.
After installing the services, start and stop them the same way as in the preceding example.
To remove multiple services, use mysqld --remove for each one, specifying a service name following the --remove option if the service to remove has a name different than the default.
The easiest way is to run multiple servers on Unix is to compile them with different TCP/IP ports and socket files so that each one is listening on different network interfaces. Also, by compiling in different base directories for each installation, that automatically results in different compiled-in data directory, log file, and PID file locations for each of your servers.
Assume an existing server is configured for the default port number and socket file. To configure a new server to have different operating parameters, use a configure command something like this:
shell> ./configure --with-tcp-port=port_number \ --with-unix-socket-path=file_name \ --prefix=/usr/local/mysql-4.0.17
Here port_number and file_name should be different from the default port number and socket file pathname, and the --prefix value should specify an installation directory different than the one under which the existing MySQL installation is located.
If you have a MySQL server listening on a given port number, you can use the following command to find out what operating parameters it is using for several important configurable variables, including the base directory and socket name:
shell> mysqladmin --host=host_name --port=port_number variables
With the information displayed by that command, you can tell what option values not to use when configuring an additional server.
Note that if you specify ``localhost'' as a hostname, mysqladmin will default to using a Unix socket connection rather than TCP/IP. In MySQL 4.1, you can explicitly specify the connection protocol to use by using the --protocol={TCP | SOCKET | PIPE | MEMORY} option.
You don't have to compile a new MySQL server just to start with a different socket file and TCP/IP port number. It is also possible to specify those values at runtime. One way to do so is by using command-line options:
shell> /path/to/mysqld_safe --socket=file_name --port=port_number
To use another database directory for the second server, pass a --datadir=path option to mysqld_safe.
Another way to achieve a similar effect is to use environment variables to set the socket name and port number:
shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock shell> MYSQL_TCP_PORT=3307 shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT shell> scripts/mysql_install_db shell> bin/mysqld_safe &
This is a quick way of starting a second server to use for testing. The nice thing about this method is that the environment variable settings will apply to any client programs that you invoke from the above shell. Thus, connections for those clients automatically will be directed to the second server!
Environment variables includes a list of other environment variables you can use to affect mysqld.
For automatic server execution, your startup script that is executed at boot time should execute the following command once for each server with an appropriate option file path for each command:
mysqld_safe --defaults-file=path-to-option-file
Each option file should contain option values specific to a given server.
On Unix, the mysqld_multi script is another way to start multiple servers. See mysqld_multi.
When you want to connect with a client program to a MySQL server that is listening to different network interfaces than those compiled into your client, you can use one of the following methods:
Start the client with --host=host_name --port=port_number to connect via TCP/IP to a remote host, or with --host=localhost --socket=file_name to connect to a local host via a Unix socket or a Windows named pipe.
As of MySQL 4.1, start the client with --protocol=tcp to connect via TCP/IP, --protocol=socket to connect via a Unix socket, --protocol=pipe to connect via a named pipe, or --protocol=memory to connect via shared memory. For TCP/IP connections, you may also need to specify --host and --port options. For the other types of connections, you may need to specify a --socket option to specify a socket or named pipe name, or a --shared-memory-base-name option to specify the shared memory name.
On Unix, set the MYSQL_UNIX_PORT and MYSQL_TCP_PORT environment variables to point to the Unix socket and TCP/IP port before you start your clients. If you normally use a specific socket or port, you can place commands to set these environment variables in your .login file so that they apply each time you log in. See Environment variables.
Specify the default socket and TCP/IP port in the [client] group of an option file. For example, you can use C:\my.cnf on Windows, or the .my.cnf file in your home directory on Unix. See Option files.
In a C program, you can specify the port or socket arguments in the mysql_real_connect() call. You can also have the program read option files by calling mysql_options(). See C API functions.
If you are using the Perl DBD::mysql module, you can read the options from the MySQL option files. For example:
$dsn = "DBI:mysql:test;mysql_read_default_group=client;" . "mysql_read_default_file=/usr/local/mysql/data/my.cnf"; $dbh = DBI->connect($dsn, $user, $password);
See Perl.
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Replication capabilities allowing the databases on one MySQL server to be duplicated on another were introduced in MySQL version 3.23.15. This section describes the various replication features in MySQL. It serves as a reference to the options available with replication. You will be introduced to replication and learn how to implement it. Toward that end, there are some frequently asked questions, descriptions of problems, and how to solve them.
For a description of the syntax of replication SQL statements, see Replication SQL.
We suggest that you visit our website at http://www.mysql.com/ often and read updates to this section. Replication is constantly being improved, and we update the manual frequently with the most current information.
Starting in Version 3.23.15, MySQL supports one-way replication internally. One server acts as the master, while one or more other servers act as slaves. The master server keeps a binary log of updates (see Binary log). It also maintains an index file of the binary logs to keep track of log rotation. Each slave, upon connecting, informs the master where it left off since the last successfully propagated update, catches up any updates that have occurred since then, and then blocks and waits for the master to notify it of new updates.
A slave can also serve as a master if you set up chained replication servers.
Note that when you are using replication, all updates to the tables that are replicated should be performed on the master server. Otherwise, you must always be careful to avoid conflicts between updates that users make to tables on the master and updates that they make to tables on the slave.
One-way replication has benefits for robustness, speed, and system administration:
Robustness is increased with a master/slave setup. In the event of problems with the master, you can switch to the slave as a backup.
The extra speed is achieved by splitting the load for processing client queries between the master and slave servers, resulting in better client response time. SELECT queries may be sent to the slave to reduce query processing load of the master. Queries that modify data should still be sent to the master so that the master and slave to not get out of sync. This load-balancing strategy is effective if non-updating queries dominate, but that is the normal case.
Another benefit of using replication is that one can get non-disturbing backups of the system by doing a backup on a slave instead of doing it on the master. See Backup.
MySQL replication is based on the master server keeping track of all changes to your database (updates, deletes, etc) in the binary log (see Binary log). Each slave server receives from the master the saved queries that the master has recorded in its binary log, so that the slave can execute the same queries on its copy of the data.
It is very important to realize that the binary log is simply a record starting from a fixed point in time (the moment you enable binary logging). Any slaves that you set up will need copies of the databases on your master as they existed at the moment you enabled binary logging on the master. If you start your slaves with data that is not the same as what was on the master when the binary log was started, your slaves may fail.
Starting from 4.0.0, you can use LOAD DATA FROM MASTER to set up a slave. Be aware that LOAD DATA FROM MASTER currently works only if all the tables on the master are MyISAM type. Also, this statement acquires a global read lock, so no writes are possible while the tables are being transferred from the master. When we implement lock-free hot table backup (in MySQL 5.0), this global read lock will no longer be necessary.
Due to these limitations, we recommend that at this point you use LOAD DATA FROM MASTER only if the dataset on the master is relatively small, or if a prolonged read lock on the master is acceptable. While the actual speed of LOAD DATA FROM MASTER may vary from system to system, a good rule of thumb for how long it is going to take is 1 second per 1 MB of the datafile. You will get close to the estimate if both master and slave are equivalent to 700 MHz Pentium and are connected through a 100 MBit/s network. Note that this is only a rough estimate.
Once a slave is properly configured and running, it will simply connect to the master and wait for updates to process. If the master goes away or the slave loses connectivity with your master, it will keep trying to connect periodically until it is able to reconnect and resume listening for updates. The retry interval is controlled by the --master-connect-retry option. The default is 60 seconds.
Each slave keeps track of where it left off. The master server has no knowledge of how many slaves there are or which ones are up-to-date at any given time.
Three threads are involved in replication: one on the master and two on the slave. When START SLAVE is issued, the I/O thread is created on the slave. It connects to the master and asks it to send the queries recorded in its binlogs. Then one thread is created on the master to send these binlogs. This thread is identified by Binlog Dump in SHOW PROCESSLIST output on the master. The I/O thread reads what the master Binlog Dump thread sends and simply copies it to some local files in the slave's data directory called relay logs. The last thread, the SQL thread, is created on the slave; it reads the relay logs and executes the queries it contains.
Note that the master has one thread for each currently connected slave server.
With SHOW PROCESSLIST you can know what is happening on the master and on the slave as regards replication.
The following example illustrates how the three threads show up in SHOW PROCESSLIST. The output format is that used by SHOW PROCESSLIST as of MySQL version 4.0.15, when the content of the State column was changed to be more meaningful compared to earlier versions.
On the master server, the output looks like this:
mysql> SHOW PROCESSLIST\G *************************** 1. row *************************** Id: 2 User: root Host: localhost:32931 db: NULL Command: Binlog Dump Time: 94 State: Has sent all binlog to slave; waiting for binlog to be updated Info: NULL
On the slave server, the output looks like this:
mysql> SHOW PROCESSLIST\G *************************** 1. row *************************** Id: 10 User: system user Host: db: NULL Command: Connect Time: 11 State: Waiting for master to send event Info: NULL *************************** 2. row *************************** Id: 11 User: system user Host: db: NULL Command: Connect Time: 11 State: Has read all relay log; waiting for the slave I/O thread to update it Info: NULL
Here thread 2 is on the master. Thread 10 is the I/O thread on the slave. Thread 11 is the SQL thread on the slave; note that the value in the Time column can tell how late the slave is compared to the master (see Replication FAQ).
The following list shows the most common states you will see in the State column for the master's Binlog Dump thread. If you don't see this thread on a master server, replication is not running.
Sending binlog event to slave | Binlogs consist of events, where an event is usually a query plus some other information. The thread has read an event from the binlog and is sending it to the slave. |
Finished reading one binlog; switching to next binlog | The thread has finished reading a binlog file and is opening the next one to send to the slave. |
Has sent all binlog to slave; waiting for binlog to be updated | The thread has read all binary log files and is idle. It is waiting for new events to appear in the binary log as a result of new update queries being executed on the master. |
Waiting to finalize termination | A very brief state that happens as the thread is stopping. |
Here are the most common states you will see in the State column for the I/O thread of a slave server. Beginning with MySQL 4.1.1, this state also appears in the Slave_IO_State column of SHOW SLAVE STATUS output. This means that you can get a good view of what is happening by using only SHOW SLAVE STATUS.
Connecting to master | The thread is attempting to connect to the master. |
Checking master version | A very brief state that happens just after the connection to the master is established. |
Registering slave on master | A very brief state that happens just after the connection to the master is established. |
Requesting binlog dump | A very brief state that happens just after the connection to the master is established. The thread sends to the master a request for the contents of its binlogs, starting from the requested binlog filename and position. |
Waiting to reconnect after a failed binlog dump request | If the binlog dump request failed (due to disconnection), the thread goes into this state while it sleeps. The thread sleeps for master-connect-retry seconds before retrying. |
Reconnecting after a failed binlog dump request | Then the thread tries to reconnect to the master. |
Waiting for master to send event | The thread has connected and is waiting for binlog events to arrive. This can last for a long time if the master is idle. If the wait lasts for slave_read_timeout seconds, a timeout will occur. At that point, the thread will consider the connection to be broken and make an attempt to reconnect. |
Queueing master event to the relay log | The thread has read an event and is copying it to the relay log so the SQL thread can process it. |
Waiting to reconnect after a failed master event read | An error occurred while reading (due to disconnection). The thread is sleeping for master-connect-retry seconds before attempting to reconnect. |
Reconnecting after a failed master event read | Then the thread tries to reconnect. When connection is established again, the state will become Waiting for master to send event. |
Waiting for the slave SQL thread to free enough relay log space | You are using a non-zero relay_log_space_limit value, and the relay logs have grown so much that their combined size exceeds this value. The I/O thread is waiting until the SQL thread frees enough space by processing relay log contents so that it can delete some relay log files. |
Waiting for slave mutex on exit | A very brief state that happens as the thread is stopping. |
Here are the most common states you will see in the State column for the SQL thread of a slave server:
Reading event from the relay log | The thread has read an event from the relay log so that it can process it. |
Has read all relay log; waiting for the slave I/O thread to update it | The thread has processed all events in the relay log files and is waiting for the I/O thread to write new events to the relay log. |
Waiting for slave mutex on exit | A very brief state that happens as the thread is stopping. |
The State column for the I/O thread may also show a query string. This indicates that the thread has read an event from the relay log, extracted the query from it and is executing the query.
Before MySQL 4.0.2, the slave I/O and SQL threads were combined as a single thread, and no relay log files were used. The advantage of using two threads is that it separates query reading and query execution into two independent tasks, so the task of reading queries is not slowed down if query execution is slow. For example, if the slave server has not been running for a while, its I/O thread can quickly fetch all the binlog contents from the master when the slave starts, even if the SQL thread lags far behind and may take hours to catch up. If the slave stops before the SQL thread has executed all the fetched queries, the I/O thread has at least fetched everything so that a safe copy of the queries is locally stored in the slave's relay logs for execution when next the slave starts. This allows the binlogs to be purged on the master, because it no longer need wait for the slave to fetch their contents.
By default, relay logs are named using filenames of the form host_name-relay-bin.nnn, where host_name is the name of the slave server host, and nnn is a sequence number. Successive relay log files are created using successive sequence numbers, beginning with 001. The slave keeps track of relay logs currently in use in an index file. The default relay log index filename is host_name-relay-bin.index. By default these files are created in the slave's data directory. The default filenames may be overridden with the --relay-log and --relay-log-index server options.
Relay logs have the same format as binary logs, so they can be read with mysqlbinlog. A relay log is automatically deleted by the SQL thread as soon as it no longer needs it (that is, as soon as it has executed all its events). There is no command to delete relay logs, because the SQL thread takes care of doing so. However, from MySQL 4.0.14, FLUSH LOGS rotates relay logs, which will influence when the SQL thread deletes them.
A new relay log is created under the following conditions:
The first time the I/O thread starts after the slave server starts. (In MySQL 5.0, a new relay log will be created each time the I/O thread starts, not just the first time.)
A FLUSH LOGS statement is issued (4.0.14 and up only).
The size of the current relay log file becomes too big. The meaning of ``too big'' is determined as follows:
max_relay_log_size, if max_relay_log_size > 0
max_binlog_size, if max_relay_log_size = 0 or MySQL is older than 4.0.14
A slave replication server creates additional two small files in the data directory. These files are named master.info and relay-log.info by default. They contain information like that shown in the output of the SHOW SLAVE STATUS statement (see Replication Slave SQL for a description of this command). As disk files they survive slave's shutdown. The next time the slave starts up, it can read these files to know how far it has proceeded in reading binlogs from the master and in processing its own relay logs.
The master.info file is updated by the I/O thread. The correspondance between the lines in the file and the columns displayed by SHOW SLAVE STATUS is as follows:
Line | Description |
1 | Master_Log_File |
2 | Read_Master_Log_Pos |
3 | Master_Host |
4 | Master_User |
5 | Password (not shown by SHOW SLAVE STATUS) |
6 | Master_Port |
7 | Connect_Retry |
The relay-log.info file is updated by the SQL thread. The correspondance between the lines in the file and the columns displayed by SHOW SLAVE STATUS is as follows:
Line | Description |
1 | Relay_Log_File |
2 | Relay_Log_Pos |
3 | Relay_Master_Log_File |
4 | Exec_Master_Log_Pos |
When you back up your slave's data, you should back up these 2 small files as well, along with the relay log files. because they are needed to resume replication after you restore the slave's data. If you lose the relay logs but still have the relay-log.info file, you can check it to determine how far the SQL thread has executed in the master binlogs. Then you can use CHANGE MASTER TO with the MASTER_RELAY_LOG and MASTER_RELAY_POS options to tell the slave to re-read the binlogs from that point. This requires that the binlogs still exist on the master server.
If your slave is subject to replicating LOAD DATA INFILE statements, you should also backup the SQL_LOAD-* files that may exist in the directory that the slave uses for this purpose. The slave needs these files to resume replication of any interrupted LOAD DATA INFILE statements. The directory location is specified using the --slave-load-tmpdir option. Its default value if not specified is the value of the tmpdir variable.
Here is a quick description of how to set up complete replication on your current MySQL server. It assumes you want to replicate all your databases and have not configured replication before. You will need to shut down your master server briefly to complete the steps outlined here.
The procedure is written in terms of setting up a single slave, but you can use it to set up multiple slaves.
While this method is the most straightforward way to set up a slave, it is not the only one. For example, if you already have a snapshot of the master's data, and the master already has its server ID set and binary logging enabled, you can set up a slave without shutting down the master or even blocking updates to it. For more details, please see Replication FAQ.
If you want to administer a MySQL replication setup, we suggest that you read this entire chapter through and try all commands mentioned in Replication Master SQL ans Replication Slave SQL. You should also familiarise yourself with replication startup options in my.cnf in Replication Options.
Note that this procedure and some of the replication SQL statements in later sections refer to the SUPER privilege. Prior to MySQL 4.0.2, use the PROCESS privilege instead.
Make sure you have a recent version of MySQL installed on the master and and slaves, and that these versions are compatible according to the table shown in Replication Upgrade.
Please do not report bugs until you have verified that the problem is present in the latest release.
Set up an account on the master server that the slave server can use to connnect. This account must be given the REPLICATION SLAVE privilege. (If MySQL versions older than 4.0.2, give the account the FILE privilege instead.) If the account is only for replication (which is recommended), you don't need to grant any additional privileges.
The hostname in the account name should be such that each of the slave servers can use the account to connect to the master. For example, to create a user named repl which can access your master from any host, you might use this command:
mysql> GRANT REPLICATION SLAVE ON *.* TO repl@'%' IDENTIFIED BY '<password>';
For MySQL versions older than 4.0.2, use this command instead:
mysql> GRANT FILE ON *.* TO repl@'%' IDENTIFIED BY '<password>';
If you plan to use the LOAD TABLE FROM MASTER or LOAD DATA FROM MASTER statements from the slave host, you will need to grant this account additional privileges:
Grant to the account the SUPER and RELOAD global privileges.
Grant the SELECT privilege for all tables that you want to load. Any master tables from which the account cannot SELECT will be ignored by LOAD DATA FROM MASTER.
If you are using MyISAM tables, flush all the tables and block write queries by executing FLUSH TABLES WITH READ LOCK command.
mysql> FLUSH TABLES WITH READ LOCK;
and then take a snapshot of the data on your master server.
The easiest way to create a snapshot is to simply use an archiving program (tar on Unix, PowerArchiver, WinRAR, WinZip or any similar software on Windows) to produce an archive of the databases in your master's data directory. For example, to use tar to create an archive that includes all databases, change location into the master server's data directory, then execute this command:
shell> tar -cvf /tmp/mysql-snapshot.tar .
If you want the archive to include only a database called this_db, use this command instead:
shell> tar -cvf /tmp/mysql-snapshot.tar ./this_db
Then copy the archive file to the /tmp directory on the slave server host. On that machine, change location into the slave's data directory, and unpack the archive file using this command:
shell> tar -xvf /tmp/mysql-snapshot.tar
You may not want to replicate the mysql database. If not, you can exclude it from the archive. You also need not include any log files in the archive, or the master.info or relay-log.info files.
While the read lock placed by FLUSH TABLES WITH READ LOCK is in effect, read the value of the current binary log name and offset on the master:
mysql > SHOW MASTER STATUS; +---------------+----------+--------------+------------------+ | File | Position | Binlog_Do_DB | Binlog_Ignore_DB | +---------------+----------+--------------+------------------+ | mysql-bin.003 | 73 | test,bar | foo,manual,mysql | +---------------+----------+--------------+------------------+ 1 row in set (0.06 sec)
The File column shows the name of the log, while Position shows the offset. In the above example, the binary log value is mysql-bin.003 and the offset is 73. Record the values. You will need to use them later when you are setting up the slave.
Once you have taken the snapshot and recorded the log name and offset, you can re-enable write activity on the master:
mysql> UNLOCK TABLES;
If you are using InnoDB tables, ideally you should use the InnoDB Hot Backup tool that is available to those who purchase MySQL commercial licenses, support, or the backup tool itself. It takes a consistent snapshot without acquiring any locks on the master server, and records the log name and offset corresponding to the snapshot to be later used on the slave. More information about the tool is available at http://www.innodb.com/order.php.
Without the Hot Backup tool, the quickest way to take a snapshot of InnoDB tables is to shut down the master server and copy the InnoDB datafiles and logs, and the table definition files (.frm). To record the current log file name and offset, you should do the following before you shut down the server:
mysql> FLUSH TABLES WITH READ LOCK; mysql> SHOW MASTER STATUS;
And then record the log name and the offset from the output of SHOW MASTER STATUS as was shown earlier. Once you have recorded the log name and the offset, shut down the server without unlocking the tables to make sure it goes down with the snapshot corresponding to the current log file and offset:
shell> mysqladmin -uroot shutdown
An alternative for both MyISAM and InnoDB tables is to take an SQL dump of the master instead of a binary copy like above; for this you can use mysqldump --master-data on your master and later run this SQL dump into your slave. However, this is slower than doing a binary copy.
If the master has been previously running without --log-bin enabled, the log name and position values displayed by SHOW MASTER STATUS or mysqldump will be empty. In that case, record empty string ('') for the log name, and 4 for the offset.
Make sure the [mysqld] section of the my.cnf file on the master host includes a log-bin option. The section should also have a server-id=master_id option, where master_id must be an integer value from 1 to 2^32 - 1. For example:
[mysqld] log-bin server-id=1
If those options are not present, add them and restart the server.
Stop the server that is to be used as a slave server and add the following to its my.cnf file:
[mysqld] server-id=slave_id
The slave_id value, like the master_id value, must be an integer value from 1 to 2^32 - 1. In addition, it is very important that the ID of the slave be different than the ID of the master. For example:
[mysqld] server-id=2
If you are setting up multiple slaves, each one must have a server-id value that differs from that of the master and from each of the other slaves. Think of server-id values as something similar to IP addresses: These IDs uniquely identify each server instance in the community of replication partners.
If you don't specify a server-id value, it will be set to 1 if you have not defined master-host, else it will be set to 2. Note that in the case of server-id omission, a master will refuse connections from all slaves, and a slave will refuse to connect to a master. Thus, omitting server-id is only good for backup with a binary log.
If you made a binary backup of the master server's data, copy it to the slave server's data directory before starting the slave. Make sure that the privileges on the files and directories are correct. The user which MySQL runs as needs to be able to read from and write to them, just as on the master.
If you made a backup using mysqldump, start the slave first (see next step).
Start the slave server. If it has been replicating previously, start the slave server with the --skip-slave-start option. You also may want to start the slave server with the --log-warnings option. That way, you will get more messages about problems (for example, network or connection problems).
If you made a backup of the master server's data using mysqldump, load the dump file into the slave server:
shell> mysql -u root -p < dump_file.sql
Execute the following command on the slave, replacing the values within <> with the actual values relevant to your system:
mysql> CHANGE MASTER TO -> MASTER_HOST='<master hostname>', -> MASTER_USER='<replication username>', -> MASTER_PASSWORD='<replication password>', -> MASTER_LOG_FILE='<recorded log file name>', -> MASTER_LOG_POS=<recorded log offset>;
The following table lists the maximum string length for these variables:
MASTER_HOST | 60 |
MASTER_USER | 16 |
MASTER_PASSWORD | 32 |
MASTER_LOG_FILE | 255 |
Start the slave threads:
mysql> START SLAVE;
After you have performed this procedure, the slave should connect to the master and catch up on any updates that have occurred since the snapshot was taken.
If you have forgotten to set server-id for the master, slaves will not be able to connect to it.
If you have forgotten to set server-id for the slave, you will get the following error in its error log:
Warning: one should set server_id to a non-0 value if master_host is set. The server will not act as a slave.
You will also find error messages in the slave's error log if it is not able to replicate for any other reason.
Once a slave is replicating, you will find in its data directory one file called master.info and another called relay-log.info. The slave uses these two files to keep track of how much of the master's binary log it has processed. Do not remove or edit these files, unless you really know what you are doing and understand the implications. Even in that case, it is preferred that you use CHANGE MASTER TO command.
NOTE: The content of master.info overrides some options specified on the command-line or in my.cnf See Replication Options for more details.
Once you have a snapshot, you can use it to set up other slaves by following the slave portion of the procedure just described. You do not need to take another snapshot of the master.
Any MySQL 4.1.x version is identical to MySQL 4.0.3 (and newer 4.0) as far as replication is concerned (same binary log format). So replication between 4.0.3 (and newer 4.0) and any 4.1.x (whatever of the two is the master or slave) is working seamlessly.
Binary log format was changed between MySQL 3.23 and MySQL 4.0, and between MySQL 4.0 (or 4.1, as it's the same binary log format) and MySQL 5.0. This has consequences on how to upgrade a replication setup, which is explained below.
The following table indicates master/slave replication compatibility between different versions of MySQL.
Master | Master | Master | ||
3.23.33 and up | 4.0.3 and up or any 4.1.x | 5.0.0 | ||
Slave | 3.23.33 and up | yes | no | no |
Slave | 4.0.3 and up | yes | yes | no |
Slave | 5.0.0 | yes | yes | yes |
Versions 4.0.0, 4.0.1 and 4.0.2 were very early development versions which should not be used anymore (their compatibility is still documented in the manual included in these versions' distributions).
As a general rule, it's always recommended to use recent MySQL versions, because replication capabilities are continually being improved. We recommend using same version for both the master and the slave.
Upgrading from 3.23 to 4.0 (4.0.3 or newer) or any 4.1.x |
When you upgrade a master from MySQL 3.23 to MySQL 4.0 (or
4.1), you should first ensure that all the slaves of this master are
already 4.0 or 4.1 (if that's not the case, you should first upgrade
your slaves as explained a few lines below).
Once the master is upgraded, you should not restart replication
using old 3.23 binary logs, because this will unfortunately confuse the
4.0 or 4.1 slave. The upgrade
can safely be done this way, assuming you have a 3.23 master to upgrade
and you have 4.0 or 4.1 slaves:
|
Upgrading from 3.23 or 4.0 (4.0.3 or newer) or any 4.1.x to 5.0.0 | First, note that MySQL 5.0.0 is alpha; even if it is supposed to work better than older versions (easier upgrade, replication of some important session variables like sql_mode; see News-5.0.0), it has not been tested a lot yet so, as with any alpha release, we recommend you do not use in critical production environment yet. When you upgrade a master from MySQL 3.23 or 4.0 or 4.1 to 5.0.0, you should first ensure that all the slaves of this master are already 5.0.0 (if that's not the case, you should first upgrade your slaves as explained a few lines below). Then just shut down your master, upgrade it to 5.0.0 and restart it. The 5.0.0 master will be able to read the old binary logs (of before the master upgrade) and to send them to the 5.0.0 slaves which will recognize this old format and handle it. Binary logs created after the master upgrade will be in 5.0.0 format and be recognized by 5.0.0 slaves too. To upgrade the slaves, just shut them down, upgrade them to 5.0.0, and restart them (and restart replication). The 5.0.0 slaves will be able to read the old relay logs (of before the slave upgrade) and execute the statements they contain. Relay logs created after the slave upgrade will be in 5.0.0 format. In other words, there are no measures to take when upgrading to 5.0.0, except that slaves must be 5.0.0 to be able to upgrade the master to 5.0.0. Note that downgrading from 5.0.0 to older versions does not work as automatically; you will have to remove any 5.0.0 binary logs or relay logs before proceeding. |
Here is an explanation of what is supported and what is not:
Replication will be done correctly with AUTO_INCREMENT, LAST_INSERT_ID(), and TIMESTAMP values.
The USER() and LOAD_FILE() functions are replicated without changes and will thus not work reliably on the slave. This is also true for CONNECTION_ID() in slave versions older than 4.1.1. The new PASSWORD() function in MySQL 4.1, is well replicated since 4.1.1 masters; your slaves must be 4.1.0 or above to replicate it. If you have older slaves and need to replicate PASSWORD() from your 4.1.x master, you must start your master with option --old-password.
The SQL_MODE, UNIQUE_CHECKS, SQL_AUTO_IS_NULL variables are replicated only starting from 5.0.0. SQL_SELECT_LIMIT and TABLE_TYPE variables are not replicated yet. FOREIGN_KEY_CHECKS is replicated since version 4.0.14.
You must use the same character set (--default-character-set) on the master and the slave. Otherwise, you may get duplicate key errors on the slave, because a key that is regarded as unique in the master character set may not be unique in the slave character set. Character sets will be replicated in 5.0.x.
If you are using transactional tables on the master and non-transactional tables (for the same tables) on the slave, you will get problems if the slave is stopped in the middle of a BEGIN/COMMIT block, as the slave will later start at the beginning of the BEGIN block. This issue is on our TODO and will be fixed in the near future.
Update queries that use user variables are badly replicated in 3.23 and 4.0. This is fixed in 4.1. Note that user variable names are case insensitive starting from version 5.0, so you should take this into account when setting up replication between 5.0 and a previous version.
The slave can connect to the master using SSL, if the master and slave are both 4.1.1 or newer.
If a DATA DIRECTORY or INDEX DIRECTORY clause was used in a CREATE TABLE on master, then these clauses will be used too on slave. Starting from MySQL 4.0.15 there is a SQL_MODE mode called NO_DIR_IN_CREATE; if the slave server is run in this mode, it will simply cut off the clauses before replicating the CREATE TABLE (so the MyISAM data and index files will be created in the slave's datadir directory).
Though we have never heard of it actually occurring, it is theoretically possible for the data on the master and slave to become different if a query is designed in such a way that the data modification is non-deterministic, that is, left to the will of the query optimizer (which generally is not a good practice, even outside of replication!). For a detailed explanation, see Open bugs.
Before MySQL 4.1.1, FLUSH, ANALYZE, OPTIMIZE, REPAIR commands are not stored in the binary log and thus are not replicated to the slaves. This is not normally a problem as these commands don't change anything. However, it does mean that if you update the MySQL privilege tables directly without using the GRANT statement and you replicate the mysql privilege database, you must do a FLUSH PRIVILEGES on your slaves to put the new privileges into effect. Also if you use FLUSH TABLES when renaming a MyISAM table involved in a MERGE table, you will have to issue FLUSH TABLES manually on the slave. Since MySQL 4.1.1, these commands are written to the binary log (except FLUSH LOGS, FLUSH MASTER, FLUSH SLAVE, FLUSH TABLES WITH READ LOCK) unless you specify NO_WRITE_TO_BINLOG (or its alias LOCAL). For a syntax example, see FLUSH.
MySQL only supports one master and many slaves. Later we will add a voting algorithm to automatically change master if something goes wrong with the current master. We will also introduce ``agent'' processes to help do load balancing by sending SELECT queries to different slaves.
Starting from MySQL 4.0.18, the master notifies the slave of a HEAP table having been emptied by master's shutdown/restart by writing a DELETE FROM to its binary log the first time it uses the table since startup. See HEAP for more details.
Temporary tables are replicated with the exception of the case that you shut down slave server (not just slave thread) and you have some replicated temporary tables that are used in update statements that have not yet been executed on the slave. (If you shut down the slave, the temporary tables needed by those updates no longer are available when the slave starts again.) To avoid this problem, do not shut down the slave while it has temporary tables open. Instead, use this procedure:
Issue a STOP SLAVE statement.
Use SHOW STATUS to check the value of the Slave_open_temp_tables variable.
If the value is 0, issue a mysqladmin shutdown command to shut down the slave.
If the value is not 0, restart the slave threads with START SLAVE.
Repeat the procedure later to see if you have better luck next time.
We have plans to fix this problem in the near future.
It is safe to connect servers in a circular master/slave relationship with log-slave-updates enabled. Note, however, that many queries will not work correctly in this kind of setup unless your client code is written to take care of the potential problems that can happen from updates that occur in different sequence on different servers.
This means that you can do a setup like the following:
A -> B -> C -> A
Server IDs are encoded in the binary log events. A will know when an event it reads had originally been created by A, so A will not execute it and there will be no infinite loop. But this circular setup will work only if you only if you perform no conflicting updates between the tables. In other words, if you insert data in A and C, you should never insert a row in A that may have a conflicting key with a row insert in C. You should also not update the same rows on two servers if the order in which the updates are applied matters.
If a query on the slave gets an error, the slave SQL thread will terminate, and a message will appear in the slave error log. You should then connect to the slave manually, fix the cause of the error (for example, non-existent table), and then run START SLAVE.
If the connection to the master is lost, the slave will try to reconnect immediately. If that fails, the slave will retry every master-connect-retry seconds (default 60). Because of this, it is safe to shut down the master, and then restart it after a while. The slave will also be able to deal with network connectivity outages. However, the slave will notice the network outage only after receiving no data from the master for slave_net_timeout seconds. So if your outages are short, you may want to decrease slave_net_timeout. See SHOW VARIABLES.
Shutting down the slave (cleanly) is also safe, as it keeps track of where it left off. Unclean shutdowns might produce problems, especially if disk cache was not synced before the system died. Your system fault tolerance will be greatly increased if you have a good UPS.
Due to the non-transactional nature of MyISAM tables, it is possible to have a query that will only partially update a table and return an error code. This can happen, for example, on a multi-row insert that has one row violating a key constraint, or if a long update query is killed after updating some of the rows. If that happens on the master, the slave thread will exit and wait for the DBA to decide what to do about it unless the error code is legitimate and the query execution results in the same error code. If this error code validation behavior is not desirable, some (or all) errors can be masked out (ignored) with the --slave-skip-errors option. This option is available starting with MySQL Version 3.23.47.
If you update transactional tables from non-transactional tables inside a BEGIN/COMMIT segment, updates to the binary log may be out of sync if some thread changes the non-transactional table before the transaction commits. This is because the transaction is written to the binary log only when it's commited.
Before version 4.0.15, any update to a non-transactional table is written to the binary log at once when the update is made while transactional updates are written on COMMIT or not written at all if you use ROLLBACK; you have to take this into account when updating both transactional tables and non-transactional tables in the same transaction if you are using binary logging for backups or replication. In version 4.0.15, we changed the logging behavior for transactions that mix updates to transactional and non-transactional tables, which solves the problems (order of queries is good in binlog, and all needed queries are written to the binlog even in case of ROLLBACK). The problem which remains is when a second connection updates the non-transactional table while the first connection's transaction is not finished yet (wrong order can still occur, because the second connection's update will be written immediately after it is done).
The following table lists problems in MySQL 3.23 that are fixed in MySQL 4.0:
LOAD DATA INFILE is handled properly, as long as the data file still resides on the master server at the time of update propagation.
LOAD LOCAL DATA INFILE will be skipped.
In 3.23 RAND() in updates does not replicate properly. Use RAND(some_non_rand_expr) if you are replicating updates with RAND(). You can, for example, use UNIX_TIMESTAMP() for the argument to RAND(). This is fixed in 4.0.
On both the master and the slave you need to use the server-id option to establish a unique replication ID for each server. You should pick a unique integer in the range from 1 to 2^32 - 1 for each master and slave. Example: server-id=3
The options that you can use on the master server for controlling binary logging are all described in Binary log.
The following table describes the options you can use on slave servers. You can specify them on the command line or in an option file.
NOTE: Replication handles the following options in a special way:
--master-host
--master-user
--master-password
--master-port
--master-connect-retry
If no master.info file exists when the slave server starts, it uses values for those options that are specified in option files or on the command line. This will occur when you start the server as a replication slave for the very first time, or you have run RESET SLAVE and shut down and restarted the slave server.
However, if the master.info file exists when the slave server starts, it uses the values in the file and IGNORES any values specified for those options in option files or on the command line.
Suppose you specify this option in your my.cnf file:
[mysqld] master-host=this_host
The first time you start the server as a replication slave, it will read and use that option from the my.cnf file. The server will then record that value in the master.info file. The next time you start the server, it will read the master host value from the master.info file only. If you modify the my.cnf file to specify a different master host, it will have no effect. You must use CHANGE MASTER TO instead.
As of MySQL 4.1.1, the following options also are handled specially:
--master-ssl
--master-ssl-ca
--master-ssl-capath
--master-ssl-cert
--master-ssl-cipher
--master-ssl-key
The master.info file includes the values corresponding to those options. In addition, the 4.1.1 file format includes as its first line the number of lines in the file. If you upgrade an older server to 4.1.1, the master.info will be upgraded to the new format automatically when the new server starts. (If you downgrade a 4.1.1 or newer server to a version older than 4.1.1, you should manually remove the first line before starting the older server for the first time.)
Because the server gives an existing master.info file precedence over the startup options just described, you might prefer not to use startup options for these values at all, and instead specify them by using the CHANGE MASTER TO statement. See CHANGE MASTER TO.
This example shows a more extensive use of startup options to configure a slave server:
[mysqld] server-id=2 master-host=db-master.mycompany.com master-port=3306 master-user=pertinax master-password=freitag master-connect-retry=60 report-host=db-slave.mycompany.com
The following list describes startup options for controlling replication:
--log-slave-updates |
Tells the slave to log the updates performed by its SQL thread to the
slave's own binary log. Off by default.
For this option to have any effect, the slave must be started with
binary logging enabled (--log-bin option).
--log-slave-updates is used when you want to chain replication servers.
For example, you might want a setup like this:
A -> B -> CThat is, A serves as the master for the slave B, and B serves as the master for the slave C. For this to work, where B is both a master and a slave, you must start B with the --log-slave-updates option. A and B must both be started with binary logging enabled. |
--log-warnings | Makes the slave print more messages about what it is doing. For example, it will warn you that it succeeded in reconnecting after a network/connection failure, and warn you about how each slave thread started. This option is not limited to replication use only. It produces warnings across a spectrum of server activities. |
--master-host=host | Specify the hostname or IP address of the master replication server. If this option is not given, the slave thread will not be started. The value in master.info takes precedence if it can be read. Probably a better name for this options would have been something like --bootstrap-master-host, but it is too late to change now. |
--master-user=username | The username of the account that the slave thread uses for authentication when connecting to the master. The account must have the REPLICATION SLAVE privilege (prior to MySQL 4.0.2, it must have the FILE privilege instead). If the master user is not set, user test is assumed. The value in master.info takes precedence if it can be read. |
--master-password=password | The password of the account that the slave thread uses for authentication when connecting to the master. If not set, an empty password is assumed. The value in master.info takes precedence if it can be read. |
--master-port=port_number | The port the master is listening on. If not set, the compiled setting of MYSQL_PORT is assumed. If you have not tinkered with configure options, this should be 3306. The value in master.info takes precedence if it can be read. |
--master-connect-retry=seconds | The number of seconds the slave thread sleeps before retrying to connect to the master in case the master goes down or the connection is lost. Default is 60. The value in master.info takes precedence if it can be read. |
--master-info-file=filename | Specifies the name to use for the file in which the slave records information about the master. The default name is mysql.info in the data directory. |
--master-ssl , --master-ssl-ca=file_name , --master-ssl-capath=directory_name , --master-ssl-cert=file_name , --master-ssl-cipher=cipher_list , --master-ssl-key=file_name | These options are used for setting up a secure replication connection to the master server using SSL. Their meanings are the same as the corresponding --ssl, --ssl-ca, --ssl-capath, --ssl-cert, --ssl-cipher, --ssl-key options described in SSL options. These options are operational as of MySQL 4.1.1. |
--max-relay-log-size=# | To rotate the relay log automatically. See SHOW VARIABLES. |
--relay-log=filename | To specify the location and name that should be used for relay logs. You can use this to have hostname-independant relay log names, or if your relay logs tend to be big (and you don't want to decrease max_relay_log_size) and you need to put them on some area different from the data directory, or if you want to increase speed by balancing load between disks. |
--relay-log-index=filename | To specify the location and name that should be used for the relay logs index file. |
--relay-log-info-file=filename | To give relay-log.info another name and/or to put it in another directory than the data directory. |
--relay-log-purge=0|1 | Disables/enables automatic purging of relay logs as soon as they are not needed any more. This is a global variable that can be dynamically changed with SET GLOBAL RELAY_LOG_PURGE=0|1. The default value is 1. This option is available as of MySQL 4.1.1. |
--relay-log-space-limit=# | To put an upper limit on the total size of all relay logs on the slave (a value of 0 means ``unlimited''). This is useful if you have a small hard disk on your slave machine. When the limit is reached, the I/O thread pauses (does not read the master's binlog) until the SQL thread has caught up and deleted some now unused relay logs. Note that this limit is not absolute: there are cases where the SQL thread needs more events to be able to delete; in that case the I/O thread will overgo the limit until deletion becomes possible. Not doing so would cause a deadlock (which happens before MySQL 4.0.13). Users should not set --relay-log-space-limit to less than twice the value of --max-relay-log-size (or --max-binlog-size if --max-relay-log-size is 0) because in that case there are chances that when the I/O thread waits for free space because --relay-log-space-limit is exceeded, the SQL thread has no relay log to purge and so cannot satisfy the I/O thread, forcing the I/O thread to temporarily ignore --relay-log-space-limit. |
--replicate-do-table=db_name.table_name | Tells the slave thread to restrict replication to the specified table. To specify more than one table, use the directive multiple times, once for each table. This will work for cross-database updates, in contrast to --replicate-do-db. Please read the notes that follow this option list. |
--replicate-ignore-table=db_name.table_name | Tells the slave thread to not replicate any command that updates the specified table (even if any other tables may be update by the same command). To specify more than one table to ignore, use the directive multiple times, once for each table. This will work for cross-database updates, in contrast to --replicate-ignore-db. Please read the notes that follow this option list. |
--replicate-wild-do-table=db_name.table_name | Tells the slave thread to restrict replication to queries where any of the updated tables match the specified wildcard pattern. To specify more than one table, use the directive multiple times, once for each table. This will work for cross-database updates. Please read the notes that follow this option list. Example: --replicate-wild-do-table=foo%.bar% will replicate only updates that uses a table in any databases that start with foo and whose table names start with bar. Note that if you do --replicate-wild-do-table=foo%.% then the rule will be propagated to CREATE DATABASE and DROP DATABASE, that is, these two statements will be replicated if the database name matches the database pattern (foo% here) (this magic is triggered by % being the table pattern). Escaping wildcard characters _ and %: if you want to replicate, for example, all tables of the my_own%db database (this is the exact name of the database), but not replicate tables from the my1ownAABCdb database, you should escape the _ and %: you should use something like this: replicate-wild-do-table=my\_own\%db. And if you are specifying this option from the command-line, depending on your system you may need to escape the \ (for example, with a bash shell, you would need to type --replicate-wild-do-table=my\\_own\\%db). |
--replicate-wild-ignore-table=db_name.table_name | Tells the slave thread to not replicate a query where any table matches the given wildcard pattern. To specify more than one table to ignore, use the directive multiple times, once for each table. This will work for cross-database updates. Please read the notes that follow this option list. Example: --replicate-wild-ignore-table=foo%.bar% will not do updates to tables in databases that start with foo and whose table names start with bar. Note that if you do --replicate-wild-ignore-table=foo%.% then the rule will be propagated to CREATE DATABASE and DROP DATABASE, that is, these two statements will not be replicated if the database name matches the database pattern (foo% here) (this magic is triggered by % being the table pattern). Escaping wildcard characters _ and %: see notes in the description of replicate-wild-do-table just above. |
--replicate-do-db=database_name | Tells the slave to restrict replication to commands where the current database (that is, the one selected by USE) is database_name. To specify more than one database, use the directive multiple times, once for each database. Note that this will not replicate cross-database queries such as UPDATE some_db.some_table SET foo="bar" while having selected a different or no database. If you need cross database updates to work, make sure you have 3.23.28 or later, and use --replicate-wild-do-table=db_name.%. Please read the notes that follow this option list. Example of what does not work as you could expect it: if the slave is started with --replicate-do-db=sales, and you do USE prices; UPDATE sales.january SET amount=amount+1000;, this query will not be replicated. If you need cross database updates to work, use --replicate-wild-do-table=db_name.% instead. The main reason for this ``just-check-the-current-database'' behavior is that it's hard from the command alone to know if a query should be replicated or not; for example if you are using multiple-table-delete or multiple-table-update commands that go across multiple databases. It's also very fast to just check the current database. |
--replicate-ignore-db=database_name | Tells the slave to not replicate any command where the current database (that is, the one selected by USE) is database_name. To specify more than one database to ignore, use the directive multiple times, once for each database. You should not use this directive if you are using cross table updates and you don't want these update to be replicated. Please read the notes that follow this option list. Example of what does not work as you could expect it: if the slave is started with --replicate-ignore-db=sales, and you do USE prices; UPDATE sales.january SET amount=amount+1000;, this query will be replicated. If you need cross database updates to work, use --replicate-wild-ignore-table=db_name.% instead. |
--replicate-rewrite-db=from_name->to_name | Tells the slave to translate the current database (that is, the one selected by USE) to to_name if it was from_name on the master. Only statements involving tables may be affected (CREATE DATABASE, DROP DATABASE won't), and only if from_name was the current database on the master. This will not work for cross-database updates. Note that the translation is done before --replicate-* rules are tested. Example: replicate-rewrite-db=master_db_name->slave_db_name |
--report-host=host | The hostname or IP number of the slave to be reported to the master during slave registration. Will appear in the output of SHOW SLAVE HOSTS. Leave unset if you do not want the slave to register itself with the master. Note that it is not sufficient for the master to simply read the IP number of the slave from the TCP/IP socket once the slave connects. Due to NAT and other routing issues, that IP may not be valid for connecting to the slave from the master or other hosts. This option is available as of MySQL 4.0.0. |
--report-port=port_number | Port for connecting to slave reported to the master during slave registration. Set it only if the slave is listening on a non-default port or if you have a special tunnel from the master or other clients to the slave. If not sure, leave this option unset. This option is available as of MySQL 4.0.0. |
--skip-slave-start | Tells the slave server not to start the slave threads on server startup. The user can start them later with START SLAVE. |
--slave_compressed_protocol=# | If 1, then use compression on the slave/client protocol if both slave and master support this. |
--slave-load-tmpdir=filename | This option is by default equal to the value of the tmpdir variable. When the slave SQL thread replicates a LOAD DATA INFILE command, it extracts the to-be-loaded file from the relay log into temporary files, then loads these into the table. If the file loaded on the master was huge, the temporary files on the slave will be huge, too; therefore you may wish/have to tell the slave to put the temporary files on some large disk different from tmpdir, using this option. In that case, you may also use the --relay-log option, as relay logs will be huge, too. --slave-load-tmpdir should point to a disk-based filesystem; not a memory-based one. Because the slave needs the temporary files used to replicate LOAD DATA INFILE) to survive a machine's reboot. |
--slave-net-timeout=# | Number of seconds to wait for more data from the master before aborting the read, considering the connection broken and retrying to connect. The first retry occurs immediately after timeout. The interval between retries is controlled by the --master-connect-retry option. |
--slave-skip-errors= [err_code1,err_code2,... | all] |
Tells the slave SQL thread to continue
replication when a query returns an error from the provided
list. Normally, replication will discontinue when an error is
encountered, giving the user a chance to resolve the inconsistency in the
data manually. Do not use this option unless you fully understand why
you are getting the errors. If there are no bugs in your
replication setup and client programs, and no bugs in MySQL itself, you
should never get an abort with error. Indiscriminate use of this option
will result in slaves being hopelessly out of sync with the master and
you having no idea how the problem happened.
For error codes, you should use the numbers provided by the error message in
your slave error log and in the output of SHOW SLAVE STATUS. A full list
of error messages can be found in the source distribution in
Docs/mysqld_error.txt.
The server error codes also are listed at Error-returns.
You can (but should not) also use a very non-recommended value of all
which will ignore all error messages and keep barging along regardless.
Needless to say, if you use it, we make no promises regarding your data
integrity. Please do not complain if your data on the slave is not anywhere
close to what it is on the master in this case --- you have been warned.
Examples:
--slave-skip-errors=1062,1053 --slave-skip-errors=all |
Some of these options, like all --replicate-* options, can only be set at the slave server's startup, not on-the-fly. We plan to fix this.
Here is the order of evaluation of the r--eplicate-* rules, to decide if the query is going to be executed by the slave or ignored by it:
Are there some --replicate-do-db or --replicate-ignore-db rules?
Yes: test them like for --binlog-do-db and --binlog-ignore-db (see Binary log). What is the result of the test?
ignore the query: ignore it and exit.
execute the query: don't execute it immediately, defer the decision, go to step below.
No: go to step below.
Are there some --replicate-*-table rules?
No: execute the query and exit.
Yes: go to step below. Only tables which are to be updated will be compared to rules (INSERT INTO sales SELECT * from prices: only sales will be compared to rules). If several tables are to be updated (multiple-table statement), the first matching table (matching ``do'' or ``ignore'') wins (that is, the first table is compared to rules, then if no decision could be taken the second table is compared to rules, etc).
Are there some --replicate-do-table rules?
Yes: does the table match any of them?
Yes: execute the query and exit.
No: go to step below.
No: go to step below.
Are there some --replicate-ignore-table rules?
Yes: does the table match any of them?
Yes: ignore the query and exit.
No: go to step below.
No: go to step below.
Are there some --replicate-wild-do-table rules?
Yes: does the table match any of them?
Yes: execute the query and exit.
No: go to step below.
No: go to step below.
Are there some --replicate-wild-ignore-table rules?
Yes: does the table match any of them?
Yes: ignore the query and exit.
No: go to step below.
No: go to step below.
No --replicate-*-table rule was matched. Is there another table to test against these rules?
Yes: loop.
No: we have tested all tables to be updated, could not match any rule. Are there --replicate-do-table or --replicate-wild-do-table rules ?
Yes: ignore the query and exit.
No: execute the query and exit.
Q: How do I configure a slave if the master is already running and I do not want to stop it?
A: There are several options. If you have taken a backup of the master at some point and recorded the binlog name and offset ( from the output of SHOW MASTER STATUS ) corresponding to the snapshot, do the following:
Make sure the slave is assigned a unique server ID.
Execute the following statement on the slave, filling in appropriate values for each parameter:
mysql> CHANGE MASTER TO -> MASTER_HOST='master_host-name', -> MASTER_USER='master_user_name', -> MASTER_PASSWORD='master_pass', -> MASTER_LOG_FILE='recorded_log_name', -> MASTER_LOG_POS=recorded_log_pos;
Execute START SLAVE on the slave.
If you do not have a backup of the master already, here is a quick way to do it consistently:
FLUSH TABLES WITH READ LOCK
gtar zcf /tmp/backup.tar.gz /var/lib/mysql (or a variation of this)
SHOW MASTER STATUS - make sure to record the output - you will need it later
UNLOCK TABLES
An alternative is taking an SQL dump of the master instead of a binary copy like above; for this you can use mysqldump --master-data on your master and later run this SQL dump into your slave. However, this is slower than makeing a binary copy.
No matter which of the two methods you use, afterwards follow the instructions for the case when you have a snapshot and have recorded the log name and offset. You can use the same snapshot to set up several slaves. As long as the binary logs of the master are left intact, you can wait as long as several days or in some cases maybe a month to set up a slave once you have the snapshot of the master. In theory the waiting gap can be infinite. The two practical limitations is the diskspace of the master getting filled with old logs, and the amount of time it will take the slave to catch up.
You can also use LOAD DATA FROM MASTER. This is a convenient command that takes a snapshot, restores it to the slave, and adjusts the log name and offset on the slave all at once. In the future, LOAD DATA FROM MASTER will be the recommended way to set up a slave. Be warned, howerver, that the read lock may be held for a long time if you use this command. It is not yet implemented as efficiently as we would like to have it. If you have large tables, the preferred method at this time is still with a local tar snapshot after executing FLUSH TABLES WITH READ LOCK.
Q: Does the slave need to be connected to the master all the time?
A: No, it does not. The slave can go down or stay disconnected for hours or even days, then reconnect and catch up on the updates. For example, you can set up a master/slave relationship over a dial-up link where the link is up only sporadically and for short periods of time. The implication of this is that at any given time the slave is not guaranteed to be in sync with the master unless you take some special measures. In the future, we will have the option to block the master until at least one slave is in sync.
Q: How do I know how late a slave is compared to the master? In other words, how do I know the date of the last query replicated by the slave?
A: If the slave is 4.1.1 or newer, read the Seconds_Behind_Master column in SHOW SLAVE STATUS. For older versions, the following applies. This is possible only if the slave SQL thread exists (that is, if it shows up in SHOW PROCESSLIST, see Replication Implementation Details) (in MySQL 3.23: if the slave thread exists, that is, shows up in SHOW PROCESSLIST), and if it has executed at least one event from the master. Indeed, when the slave SQL thread executes an event read from the master, this thread modifies its own time to the event's timestamp (this is why TIMESTAMP is well replicated). So in the Time column in the output of SHOW PROCESSLIST, the number of seconds displayed for the slave SQL thread is the number of seconds between the timestamp of the last replicated event and the real time of the slave machine. You can use this to determine the date of the last replicated event. Note that if your slave has been disconnected from the master for one hour, then reconnects, you may immediately see Time values like 3600 for the slave SQL thread in SHOW PROCESSLIST... This would be because the slave is executing queries that are one hour old.
Q: How do I force the master to block updates until the slave catches up?
A: Use the following procedure:
On the master, execute these commands:
mysql> FLUSH TABLES WITH READ LOCK; mysql> SHOW MASTER STATUS;
Record the log name and the offset from the output of the SHOW statement.
On the slave, issue this command, where the replication coordinates that are the arguments to the MASTER_POS_WAIT() function are the values recorded in the previous step:
mysql> SELECT MASTER_POS_WAIT('log_name', log_offset);
The SELECT statement will block until the slave reaches the specified log file and offset. At that point, the slave will be in sync with the master and the statement will return.
On the master, issue the following statement to allow the master to begin processing updates again:
mysql> UNLOCK TABLES;
Q: What issues should I be aware of when setting up two-way replication?
A: MySQL replication currently does not support any locking protocol between master and slave to guarantee the atomicity of a distributed (cross-server) update. In other words, it is possible for client A to make an update to co-master 1, and in the meantime, before it propagates to co-master 2, client B could make an update to co-master 2 that will make the update of client A work differently than it did on co-master 1. Thus, when the update of client A will make it to co-master 2, it will produce tables that are different than what you have on co-master 1, even after all the updates from co-master 2 have also propagated. So you should not co-chain two servers in a two-way replication relationship, unless you are sure that your updates can safely happen in any order, or unless you take care of mis-ordered updates somehow in the client code.
You must also realize that two-way replication actually does not improve performance very much (if at all), as far as updates are concerned. Both servers need to do the same amount of updates each, as you would have one server do. The only difference is that there will be a little less lock contention, because the updates originating on another server will be serialized in one slave thread. Even so, this benefit might be offset by network delays.
Q: How can I use replication to improve performance of my system?
A: You should set up one server as the master and direct all writes to it. Then configure as many slaves as you have the money and rackspace for, and distribute the reads among the master and the slaves. You can also start the slaves with --skip-bdb, --low-priority-updates and --delay-key-write=ALL to get speed improvements for the slave. In this case the slave will use non-transactional MyISAM tables instead of BDB tables to get more speed.
Q: What should I do to prepare client code in my own applications to use performance-enhancing replication?
A: If the part of your code that is responsible for database access has been properly abstracted/modularised, converting it to run with a replicated setup should be very smooth and easy. Just change the implementation of your database access to send all writes the the master, and to send reads to either the master or a slave. If your code does not have this level of abstraction, setting up a replicated system will give you the opportunity and motivation to it clean up. You should start by creating a wrapper library or module with the following functions:
safe_writer_connect()
safe_reader_connect()
safe_reader_query()
safe_writer_query()
safe_ in each function name means that the function will take care of handling all the error conditions. You can use different names for the functions. The important thing is to have a unified interface for connecting for reads, connecting for writes, doing a read, and doing a write.
You should then convert your client code to use the wrapper library. This may be a painful and scary process at first, but it will pay off in the long run. All applications that use the approach just described will be able to take advantage of a master/slave configuration, even one involving multiple slaves. The code will be a lot easier to maintain, and adding troubleshooting options will be trivial. You will just need to modify one or two functions, for example, to log how long each query took, or which query, among your many thousands, gave you an error.
If you have written a lot of code already, you may want to automate the conversion task by using the replace utility that comes with the standard distribution of MySQL, or just write your own Perl script. Hopefully, your code follows some recognizable pattern. If not, then you are probably better off rewriting it anyway, or at least going through and manually beating it into a pattern.
Q: When and how much can MySQL replication improve the performance of my system?
A: MySQL replication is most beneficial for a system with frequent reads and infrequent writes. In theory, by using a single-master/multiple-slave setup, you can scale the system by adding more slaves until you either run out of network bandwidth, or your update load grows to the point that the master cannot handle it.
In order to determine how many slaves you can get before the added benefits begin to level out, and how much you can improve performance of your site, you need to know your query patterns, and empirically (by benchmarking) determine the relationship between the throughput on reads (reads per second, or max_reads) and on writes (max_writes) on a typical master and a typical slave. The example here will show you a rather simplified calculation of what you can get with replication for a hypothetical system.
Let's say that system load consists of 10% writes and 90% reads, and we have determined max_reads to be 1200 - 2 * max_writes. In other words, the system can do 1200 reads per second with no writes, the average write is twice as slow as average read, and the relationship is linear. Let us suppose that the master and each slave have the same capacity, and that we have 1 master and N slaves. Then we have for each server (master or slave):
reads = 1200 - 2 * writes (from benchmarks)
reads = 9* writes / (N + 1) (reads split, but writes go to all servers)
9*writes/(N+1) + 2 * writes = 1200
writes = 1200/(2 + 9/(N+1)
This analysis yields the following conclusions:
If N = 0 (which means we have no replication), our system can handle 1200/11, about 109 writes per second (which means we will have 9 times as many reads due to the nature of our application).
If N = 1, we can get up to 184 writes per second.
If N = 8, we get up to 400.
If N = 17, 480 writes.
Eventually, as N approaches infinity (and our budget negative infinity), we can get very close to 600 writes per second, increasing system throughput about 5.5 times. However, with only 8 servers, we increased it almost 4 times already.
Note that these computations assume infinite network bandwidth and neglect several other factors that could turn out to be significant on your system. In many cases, you may not be able to perform a computation similar to the one above that will accurately predict what will happen on your system if you add N replication slaves. However, answering the following questions should help you decide whether and how much replication will improve the performance of your system:
What is the read/write ratio on your system?
How much more write load can one server handle if you reduce the reads?
How many slaves do you have bandwidth available for on your network?
Q: How can I use replication to provide redundancy/high availability?
A: With the currently available features, you would have to set up a master and a slave (or several slaves), and write a script that will monitor the master to see whether it is up, and instruct your applications and the slaves of the master change in case of failure. Some suggestions:
To tell a slave to change the master, use the CHANGE MASTER TO command.
A good way to keep your applications informed as to the location of the master is by having a dynamic DNS entry for the master. With bind you can use nsupdate to dynamically update your DNS.
You should run your slaves with the --log-bin option and without --log-slave-updates. This way the slave will be ready to become a master as soon as you issue STOP SLAVE; RESET MASTER, and CHANGE MASTER TO on the other slaves. For example, consider you have the following setup (``M'' means the master, ``S'' the slaves, ``WC'' the clients that issue database writes and reads; clients that issue only database reads are not represented, because they need not switch):
WC \ v WC----> M / | \ / | \ v v v S1 S2 S3
S1 (like S2 and S3) is a slave running with --log-bin and without --log-slave-updates. As the only writes executed on S1 are those replicated from M, the binary log on S1 is empty (remember, S1 runs without --log-slave-updates). Then, for some reason, M becomes unavailable, and you want S1 to become the new master (that is, direct all WC to S1, and make S2 and S3 replicate S1).
Make sure that all slaves have processed any queries in their relay log. On each slave, issue STOP SLAVE IO_THREAD, then check the output of SHOW PROCESSLIST until you see Has read all relay log. When this is true for all slaves, they can be reconfigured to the new setup. Issue STOP SLAVE on all slaves, RESET MASTER on the slave being promoted to master, and CHANGE MASTER on the other slaves.
No WC accesses M. Instruct all WC to direct their queries to S1. From now on, all queries sent by WC to S1 are written to the binary log of S1. The binary log of S1 contains exactly every writing query sent to S1 since M died. On S2 (and S3) do STOP SLAVE, CHANGE MASTER TO MASTER_HOST="S1" (where 'S1' is replaced by the real hostname of S1). To CHANGE MASTER, add all information about how to connect to S1 from S2 or S3 (user, password, port). In CHANGE MASTER, no need to specify the name of S1's binary log or binary log position to read from: we know it is the first binary log, from position 4, and these are the defaults of CHANGE MASTER. Finally do START SLAVE on S2 and S3, and now you have this:
WC / | WC | M(unavailable) \ | \ | v v S1<--S2 S3 ^ | +-------+
When M is up again, you just have to issue on it the same CHANGE MASTER as the one issued on S2 and S3, so that M becomes a slave of S1 and picks all the WC writes it has missed while it was down. Now to make M a master again (because it is the most powerful machine, for example), follow the preceding procedure as if S1 was unavailable and M was to be the new master; then during the procedure don't forget to run RESET MASTER on M before making S1, S2, S3 slaves of M, or they may pick old WC writes from before M's unavailibility.
We are currently working on integrating an automatic master election system into MySQL, but until it is ready, you will have to create your own monitoring tools.
If you have followed the instructions, and your replication setup is not working, first check the following:
Check the error log for messages. Many users have lost time by not doing this early enough.
Is the master logging to the binary log? Check with SHOW MASTER STATUS. If it is, Position will be non-zero. If not, verify that you have given the master log-bin option and have set server-id.
Is the slave running? Do SHOW SLAVE STATUS and check that the Slave_IO_Running and Slave_SQL_Running values are both Yes. If not, verify slave options
If the slave is running, did it establish a connection with the master? Do SHOW PROCESSLIST, find the I/O and SQL threads (see Replication Implementation Details to see how they display), and check their State column. If it says Connecting to master, verify the privileges for the replication user on the master, master hostname, your DNS setup, whether the master is actually running, whether it is reachable from the slave.
If the slave was running before but now has stopped, the reason usually is that some query that succeeded on the master failed on the slave. This should never happen if you have taken a proper snapshot of the master, and never modify the data on the slave outside of the slave thread. If it does, it is a bug; read below on how to report it.
If a query on that succeeded on the master refuses to run on the slave, and it does not feasible to do a full database resync (that is, to delete the slave's database and copy a new snapshot from the master), try the following:
First see if the slave's table was different from the master's. Understand how it happened (it may be a bug: read the Changelogs in the online MySQL manual as http://www.mysql.com/documentation to check if this is a known bug and if it is fixed yet). Then make the slave's table identical to the master's and run START SLAVE.
If the above does not work or does not apply, try to understand if it would be safe to make the update manually (if needed) and then ignore the next query from the master.
If you have decided you can skip the next query, issue the following statements:
mysql> SET GLOBAL SQL_SLAVE_SKIP_COUNTER = n; mysql> START SLAVE;
The value of n should be 1 if the query does not use AUTO_INCREMENT or LAST_INSERT_ID(). Otherwise, the value should be 2. The reason for using a value of 2 for queries that use AUTO_INCREMENT or LAST_INSERT_ID() is that they take two events in the binary log of the master.
Make sure you are not running into an old bug by upgrading to the most recent version.
If you are sure the slave started out perfectly in sync with the master, and no one has updated the tables involved outside of slave thread, report the bug.
When you have determined that there is no user error involved, and replication still either does not work at all or is unstable, it is time to send us a bug report. We need to get as much information as possible from you to be able to track down the bug. Please do spend some time and effort preparing a good bug report.
If you have a repeatable way to demonstrate the bug, please enter it into our bugs database at http://bugs.mysql.com/. If you have a phantom problem (one that you cannot duplicate ``at will''), use the following procedure:
Verify that no user error is involved. For example, if you update the slave outside of the slave thread, the data will go out of sync, and you can have unique key violations on updates. In this case, the slave thread will stop and wait for you to clean up the tables manually to bring them in sync. This is not a replication problem; it is a problem of outside interference that causes replication to fail.
Run the slave with the --log-slave-updates and --log-bin options. They will cause the slave to log the updates that it receives in its own binlogs.
Save all evidence before resetting the replication state. If we have no information or only sketchy information, it will take us longer to track down the problem. The evidence you should collect is:
All binary logs from the master
All binary logs from the slave
The output of SHOW MASTER STATUS from the master at the time you have discovered the problem
The output of SHOW SLAVE STATUS from the master at the time you have discovered the problem
Error logs from the master and on the slave
Use mysqlbinlog to examine the binary logs. The following should be helpful to find the trouble query, for example:
mysqlbinlog -j pos_from_slave_status /path/to/log_from_slave_status | head
Once you have collected the evidence for the phantom problem, try hard to isolate it into a separate test case first. Then enter the problem into our bugs database at http://bugs.mysql.com/ with as much information as possible.
Table of Contents
Optimization is a complicated task because it ultimately requires understanding of the whole system. While it may be possible to perform some local optimizations with small knowledge of your system or application, the more optimal you want your system to become the more you will have to know about it.
This chapter tries to explain and give some examples of different ways to optimize MySQL. Remember, however, that there are always some (increasingly harder) additional ways to make the system even faster.
Table of Contents
The most important factor in making a system fast is the basic design. You also need to know what kinds of things your system will be doing, and what your bottlenecks are.
The most common bottlenecks are:
Disk seeks. It takes time for the disk to find a piece of data. With modern disks in 1999, the mean time for this is usually lower than 10ms, so we can in theory do about 100 seeks a second. This time improves slowly with new disks and is very hard to optimize for a single table. The way to optimize this is to spread the data on more than one disk.
Disk reading/writing. When the disk is at the correct position we need to read the data. With modern disks in 1999, one disk delivers something like 10-20 MB. This is easier to optimize than seeks because you can read in parallel from multiple disks.
CPU cycles. When we have the data in main memory (or if it already were there) we need to process it to get to our result. Having small tables compared to the memory is the most common limiting factor. But then, with small tables speed is usually not the problem.
Memory bandwidth. When the CPU needs more data than can fit in the CPU cache the main memory bandwidth becomes a bottleneck. This is an uncommon bottleneck for most systems, but one should be aware of it.
When using the MyISAM storage engine, MySQL uses extremely fast table locking (multiple readers / single writers). The biggest problem with this table type occurs when you have a mix of a steady stream of updates and slow selects on the same table. If this is a problem with some tables, you can use another table type for these. See Table types.
MySQL can work with both transactional and non-transactional tables. To be able to work smoothly with non-transactional tables (which can't roll back if something goes wrong), MySQL has the following rules:
All columns have default values.
If you insert a 'wrong' value in a column like a NULL in a NOT NULL column or a too big numerical value in a numerical column, MySQL will instead of giving an error instead set the column to the 'best possible value'. For numerical values this is 0, the smallest possible values or the largest possible value. For strings this is either the empty string or the longest possible string that can be in the column.
All calculated expressions returns a value that can be used instead of signaling an error condition. For example 1/0 returns NULL
For more information about this, see See Constraints.
The above means that one should not use MySQL to check fields content, but one should do this in the application.
Because all SQL servers implement different parts of SQL, it takes work to write portable SQL applications. For very simple selects/inserts it is very easy, but the more you need the harder it gets. If you want an application that is fast with many databases it becomes even harder!
To make a complex application portable you need to choose a number of SQL servers that it should work with.
You can use the MySQL crash-me program/web-page http://www.mysql.com/information/crash-me.php to find functions, types, and limits you can use with a selection of database servers. Crash-me now tests far from everything possible, but it is still comprehensive with about 450 things tested.
For example, you shouldn't have column names longer than 18 characters if you want to be able to use Informix or DB2.
Both the MySQL benchmarks and crash-me programs are very database-independent. By taking a look at how we have handled this, you can get a feeling for what you have to do to write your application database-independent. The benchmarks themselves can be found in the sql-bench directory in the MySQL source distribution. They are written in Perl with DBI database interface (which solves the access part of the problem).
See http://www.mysql.com/information/benchmarks.html for the results from this benchmark.
As you can see in these results, all databases have some weak points. That is, they have different design compromises that lead to different behavior.
If you strive for database independence, you need to get a good feeling for each SQL server's bottlenecks. MySQL is very fast in retrieving and updating records, but will have a problem in mixing slow readers/writers on the same table. Oracle, on the other hand, has a big problem when you try to access rows that you have recently updated (until they are flushed to disk). Transaction databases in general are not very good at generating summary tables from log tables, as in this case row locking is almost useless.
To get your application really database-independent, you need to define an easy extendable interface through which you manipulate your data. As C++ is available on most systems, it makes sense to use a C++ classes interface to the databases.
If you use some specific feature for some database (like the REPLACE command in MySQL), you should code a method for the other SQL servers to implement the same feature (but slower). With MySQL you can use the /*! */ syntax to add MySQL-specific keywords to a query. The code inside /**/ will be treated as a comment (ignored) by most other SQL servers.
If high performance is more important than exactness, as in some web applications, it is possibile to create an application layer that caches all results to give you even higher performance. By letting old results 'expire' after a while, you can keep the cache reasonably fresh. This provides a method to handle high load spikes, in which case you can dynamically increase the cache and set the expire timeout higher until things get back to normal.
In this case the table creation information should contain information of the initial size of the cache and how often the table should normally be refreshed.
During MySQL initial development, the features of MySQL were made to fit our largest customer. They handle data warehousing for a couple of the biggest retailers in Sweden.
From all stores, we get weekly summaries of all bonus card transactions, and we are expected to provide useful information for the store owners to help them find how their advertisement campaigns are affecting their customers.
The data is quite huge (about 7 million summary transactions per month), and we have data for 4-10 years that we need to present to the users. We got weekly requests from the customers that they want to get 'instant' access to new reports from this data.
We solved this by storing all information per month in compressed 'transaction' tables. We have a set of simple macros (script) that generates summary tables grouped by different criteria (product group, customer id, store ...) from the transactional tables. The reports are web pages that are dynamically generated by a small Perl script that parses a web page, executes the SQL statements in it, and inserts the results. We would have used PHP or mod_perl instead but they were not available at that time.
For graphical data we wrote a simple tool in C that can produce GIFs based on the result of an SQL query (with some processing of the result). This is also dynamically executed from the Perl script that parses the HTML files.
In most cases a new report can simply be done by copying an existing script and modifying the SQL query in it. In some cases, we will need to add more fields to an existing summary table or generate a new one, but this is also quite simple, as we keep all transactions tables on disk. (Currently we have at least 50G of transactions tables and 200G of other customer data.)
We also let our customers access the summary tables directly with ODBC so that the advanced users can themselves experiment with the data.
We haven't had any problems handling this with quite modest Sun Ultra SPARCstation (2x200 Mhz). We recently upgraded one of our servers to a 2 CPU 400 Mhz UltraSPARC, and we are now planning to start handling transactions on the product level, which would mean a ten-fold increase of data. We think we can keep up with this by just adding more disk to our systems.
We are also experimenting with Intel-Linux to be able to get more CPU power cheaper. Now that we have the binary portable database format (new in Version 3.23), we will start to use this for some parts of the application.
Our initial feelings are that Linux will perform much better on low-to-medium load and Solaris will perform better when you start to get a high load because of extreme disk IO, but we don't yet have anything conclusive about this. After some discussion with a Linux kernel developer, this might be a side effect of Linux allocating so many resources to the batch job that the interactive performance gets very low. This makes the machine feel very slow and unresponsive while big batches are going. Hopefully this will be better handled in future Linux Kernels.
This section should contain a technical description of the MySQL benchmark suite (and crash-me), but that description is not written yet. Currently, you can get a good idea of the benchmark by looking at the code and results in the sql-bench directory in any MySQL source distribution.
This benchmark suite is meant to be a benchmark that will tell any user what operations a given SQL implementation performs well or poorly.
Note that this benchmark is single-threaded, so it measures the minimum time for the operations performed. We plan to add a lot of multi-threaded tests to the benchmark suite in the future.
The following tables show some comparative benchmark results for several database servers when accessed through ODBC on a Windows NT 4.0 machine.
Reading 2000000 rows by index | Seconds | Seconds |
mysql | 367 | 249 |
mysql_odbc | 464 | |
db2_odbc | 1206 | |
informix_odbc | 121126 | |
ms-sql_odbc | 1634 | |
oracle_odbc | 20800 | |
solid_odbc | 877 | |
sybase_odbc | 17614 |
Inserting 350768 rows | Seconds | Seconds |
mysql | 381 | 206 |
mysql_odbc | 619 | |
db2_odbc | 3460 | |
informix_odbc | 2692 | |
ms-sql_odbc | 4012 | |
oracle_odbc | 11291 | |
solid_odbc | 1801 | |
sybase_odbc | 4802 |
For the preceding tests, MySQL was run with an index cache size of 8M.
We have gathered some more benchmark results at http://www.mysql.com/information/benchmarks.html.
Note that Oracle is not included because they asked to be removed. All Oracle benchmarks have to be passed by Oracle! We believe that makes Oracle benchmarks very biased because the above benchmarks are supposed to show what a standard installation can do for a single client.
To use the benchmark suite, the following requirements must be satisified:
The benchmark suite is provided with MySQL source distributions, so you must have a source distribution. You can either download a released distribution from http://www.mysql.com/downloads/, or use the current development source tree (see Installing source tree).
The benchmark scripts are written in Perl and use the Perl DBI module to access database servers, so DBI must be installed. You will also need the server-specific DBD drivers for each of the servers you want to test. For example, to test MySQL, PostgreSQL, and DB2, the DBD::mysql, DBD::Pg, and DBD::DB2 modules must be installed.
The benchmark suite is located in the sql-bench directory of MySQL source distributions. To run the benchmark tests, change location into that directory and execute the run-all-tests script:
shell> cd sql-bench shell> perl run-all-tests --server=server_name
server_name is one of supported servers. You can get a list of all options and supported servers by invoking run-all-tests --help.
crash-me tries to determine what features a database supports and what its capabilities and limitations are by actually running queries. For example, it determines:
What column types are supported
How many indexes are supported
What functions are supported
How big a query can be
How big a VARCHAR column can be
We can find the result from crash-me on a lot of different databases at http://www.mysql.com/information/crash-me.php.
You should definitely benchmark your application and database to find out where the bottlenecks are. By fixing it (or by replacing the bottleneck with a ``dummy module'') you can then easily identify the next bottleneck (and so on). Even if the overall performance for your application currently is acceptable, you should at least make a plan for each bottleneck, and decide how to solve it if someday you really need the extra performance.
For an example of portable benchmark programs, look at the MySQL benchmark suite. See MySQL Benchmarks. You can take any program from this suite and modify it for your needs. By doing this, you can try different solutions to your problem and test which is really fastest for you.
Another free benchmark suite is the Open Source Database Benchmark, available at http://osdb.sourceforge.net/.
It is very common for a problem to occur only when the system is very heavily loaded. We have had many customers who contact us when they have a (tested) system in production and have encountered load problems. In most cases, performance problems turn out to be due to issues of basic database design (table scans are not good at high load) or problems with the operating system or libraries. Most of the time, these problems would be a lot easier to fix if the systems were not already in production.
To avoid problems like this, you should put some effort into benchmarking your whole application under the worst possible load! You can use Super Smack for this. It is available at http://www.mysql.com/Downloads/super-smack/super-smack-1.0.tar.gz. As the name suggests, it can bring your system to its knees if you ask it, so make sure to use it only on your development systems.
Table of Contents
First, one thing that affects all queries: The more complex permission system setup you have, the more overhead you get.
If you do not have any GRANT statements done, MySQL will optimize the permission checking somewhat. So if you have a very high volume it may be worth the time to avoid grants. Otherwise, more permission check results in a larger overhead.
If your problem is with some explicit MySQL function, you can always time this in the MySQL client:
mysql> SELECT BENCHMARK(1000000,1+1); +------------------------+ | BENCHMARK(1000000,1+1) | +------------------------+ | 0 | +------------------------+ 1 row in set (0.32 sec)
The above shows that MySQL can execute 1,000,000 + expressions in 0.32 seconds on a PentiumII 400MHz.
All MySQL functions should be very optimized, but there may be some exceptions, and the BENCHMARK(loop_count,expression) is a great tool to find out if this is a problem with your query.
EXPLAIN tbl_name or EXPLAIN SELECT select_options
EXPLAIN tbl_name is a synonym for DESCRIBE tbl_name or SHOW COLUMNS FROM tbl_name.
When you precede a SELECT statement with the keyword EXPLAIN, MySQL explains how it would process the SELECT, providing information about how tables are joined and in which order.
With the help of EXPLAIN, you can see when you must add indexes to tables to get a faster SELECT that uses indexes to find the records.
You should frequently run ANALYZE TABLE to update table statistics such as cardinality of keys which can affect the choices the optimizer makes. See ANALYZE TABLE.
You can also see if the optimizer joins the tables in an optimal order. To force the optimizer to use a specific join order for a SELECT statement, add a STRAIGHT_JOIN clause.
For non-simple joins, EXPLAIN returns a row of information for each table used in the SELECT statement. The tables are listed in the order they would be read. MySQL resolves all joins using a single-sweep multi-join method. This means that MySQL reads a row from the first table, then finds a matching row in the second table, then in the third table and so on. When all tables are processed, it outputs the selected columns and backtracks through the table list until a table is found for which there are more matching rows. The next row is read from this table and the process continues with the next table.
In MySQL version 4.1 the EXPLAIN output was changed to work better with constructs like UNION statements, subqueries and derived tables. Most notable is the addition of two new columns: id and select_type.
Output from EXPLAIN consists of the following columns:
id | SELECT identifier, the sequential number of this SELECT within the query. | |||||||||||||||||||||
select_type | Type of SELECT clause, which can be any of the following: |
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table | The table to which the row of output refers. | |||||||||||||||||||||
type | The join type. The different join types are listed here, ordered from best to worst type: |
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possible_keys | The possible_keys column indicates which indexes MySQL could use to find the rows in this table. Note that this column is totally independent of the order of the tables. That means that some of the keys in possible_keys may not be usable in practice with the generated table order. If this column is NULL, there are no relevant indexes. In this case, you may be able to improve the performance of your query by examining the WHERE clause to see whether it refers to some column or columns that would be suitable for indexing. If so, create an appropriate index and check the query with EXPLAIN again. See ALTER TABLE. To see what indexes a table has, use SHOW INDEX FROM tbl_name. | |||||||||||||||||||||
key | The key column indicates the key (index) that MySQL actually decided to use. The key is NULL if no index was chosen. To force MySQL to use an key listed in the possible_keys column, use USE KEY/IGNORE KEY in your query. See SELECT. Also, running myisamchk --analyze (see myismchk syntax) or ANALYZE TABLE (see ANALYZE TABLE) on the table will help the optimizer choose better indexes. | |||||||||||||||||||||
key_len | The key_len column indicates the length of the key that MySQL decided to use. The length is NULL if the key is NULL. Note that this tells us how many parts of a multi-part key MySQL will actually use. | |||||||||||||||||||||
ref | The ref column shows which columns or constants are used with the key to select rows from the table. | |||||||||||||||||||||
rows | The rows column indicates the number of rows MySQL believes it must examine to execute the query. | |||||||||||||||||||||
Extra | This column contains additional information of how MySQL will resolve the query. Here is an explanation of the different text strings that can be found in this column: |
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You can get a good indication of how good a join is by multiplying all values in the rows column of the EXPLAIN output. This should tell you roughly how many rows MySQL must examine to execute the query. This number is also used when you restrict queries with the max_join_size variable. See Server parameters.
The following example shows how a JOIN can be optimized progressively using the information provided by EXPLAIN.
Suppose you have the SELECT statement shown here, that you examine using EXPLAIN:
EXPLAIN SELECT tt.TicketNumber, tt.TimeIn, tt.ProjectReference, tt.EstimatedShipDate, tt.ActualShipDate, tt.ClientID, tt.ServiceCodes, tt.RepetitiveID, tt.CurrentProcess, tt.CurrentDPPerson, tt.RecordVolume, tt.DPPrinted, et.COUNTRY, et_1.COUNTRY, do.CUSTNAME FROM tt, et, et AS et_1, do WHERE tt.SubmitTime IS NULL AND tt.ActualPC = et.EMPLOYID AND tt.AssignedPC = et_1.EMPLOYID AND tt.ClientID = do.CUSTNMBR;
For this example, assume that:
The columns being compared have been declared as follows:
Table | Column | Column type |
tt | ActualPC | CHAR(10) |
tt | AssignedPC | CHAR(10) |
tt | ClientID | CHAR(10) |
et | EMPLOYID | CHAR(15) |
do | CUSTNMBR | CHAR(15) |
The tables have the indexes shown here:
Table | Index |
tt | ActualPC |
tt | AssignedPC |
tt | ClientID |
et | EMPLOYID (primary key) |
do | CUSTNMBR (primary key) |
The tt.ActualPC values aren't evenly distributed.
Initially, before any optimizations have been performed, the EXPLAIN statement produces the following information:
table type possible_keys key key_len ref rows Extra et ALL PRIMARY NULL NULL NULL 74 do ALL PRIMARY NULL NULL NULL 2135 et_1 ALL PRIMARY NULL NULL NULL 74 tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 range checked for each record (key map: 35)
Because type is ALL for each table, this output indicates that MySQL is generating a Cartesian product of all the tables! This will take quite a long time, as the product of the number of rows in each table must be examined! For the case at hand, this is 74 * 2135 * 74 * 3872 = 45,268,558,720 rows. If the tables were bigger, you can only imagine how long it would take.
One problem here is that MySQL can't (yet) use indexes on columns efficiently if they are declared differently. In this context, VARCHAR and CHAR are the same unless they are declared as different lengths. Because tt.ActualPC is declared as CHAR(10) and et.EMPLOYID is declared as CHAR(15), there is a length mismatch.
To fix this disparity between column lengths, use ALTER TABLE to lengthen ActualPC from 10 characters to 15 characters:
mysql> ALTER TABLE tt MODIFY ActualPC VARCHAR(15);
Now tt.ActualPC and et.EMPLOYID are both VARCHAR(15). Executing the EXPLAIN statement again produces this result:
table type possible_keys key key_len ref rows Extra tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 Using where do ALL PRIMARY NULL NULL NULL 2135 range checked for each record (key map: 1) et_1 ALL PRIMARY NULL NULL NULL 74 range checked for each record (key map: 1) et eq_ref PRIMARY PRIMARY 15 tt.ActualPC 1
This is not perfect, but is much better (the product of the rows values is now less by a factor of 74). This version is executed in a couple of seconds.
A second alteration can be made to eliminate the column length mismatches for the tt.AssignedPC = et_1.EMPLOYID and tt.ClientID = do.CUSTNMBR comparisons:
mysql> ALTER TABLE tt MODIFY AssignedPC VARCHAR(15), -> MODIFY ClientID VARCHAR(15);
Now EXPLAIN produces the output shown here:
table type possible_keys key key_len ref rows Extra et ALL PRIMARY NULL NULL NULL 74 tt ref AssignedPC, ActualPC 15 et.EMPLOYID 52 Using where ClientID, ActualPC et_1 eq_ref PRIMARY PRIMARY 15 tt.AssignedPC 1 do eq_ref PRIMARY PRIMARY 15 tt.ClientID 1
This is almost as good as it can get.
The remaining problem is that, by default, MySQL assumes that values in the tt.ActualPC column are evenly distributed, and that isn't the case for the tt table. Fortunately, it is easy to tell MySQL about this:
shell> myisamchk --analyze PATH_TO_MYSQL_DATABASE/tt shell> mysqladmin refresh
Now the join is perfect, and EXPLAIN produces this result:
table type possible_keys key key_len ref rows Extra tt ALL AssignedPC NULL NULL NULL 3872 Using where ClientID, ActualPC et eq_ref PRIMARY PRIMARY 15 tt.ActualPC 1 et_1 eq_ref PRIMARY PRIMARY 15 tt.AssignedPC 1 do eq_ref PRIMARY PRIMARY 15 tt.ClientID 1
Note that the rows column in the output from EXPLAIN is an educated guess from the MySQL join optimizer. To optimize a query, you should check if the numbers are even close to the truth. If not, you may get better performance by using STRAIGHT_JOIN in your SELECT statement and trying to list the tables in a different order in the FROM clause.
In most cases you can estimate the performance by counting disk seeks. For small tables, you can usually find the row in 1 disk seek (as the index is probably cached). For bigger tables, you can estimate that (using B++ tree indexes) you will need: log(row_count) / log(index_block_length / 3 * 2 / (index_length + data_pointer_length)) + 1 seeks to find a row.
In MySQL an index block is usually 1024 bytes and the data pointer is usually 4 bytes. A 500,000 row table with an index length of 3 (medium integer) gives you: log(500,000)/log(1024/3*2/(3+4)) + 1 = 4 seeks.
As the above index would require about 500,000 * 7 * 3/2 = 5.2M, (assuming that the index buffers are filled to 2/3, which is typical) you will probably have much of the index in memory and you will probably only need 1-2 calls to read data from the OS to find the row.
For writes, however, you will need 4 seek requests (as above) to find where to place the new index and normally 2 seeks to update the index and write the row.
Note that the above doesn't mean that your application will slowly degenerate by log N! As long as everything is cached by the OS or SQL server, things will go only marginally slower while the table gets bigger. After the data gets too big to be cached, things will start to go much slower until your applications is only bound by disk-seeks (which increase by log N). To avoid this, increase the index cache as the data grows. See Server parameters.
In general, when you want to make a slow SELECT ... WHERE faster, the first thing to check is whether you can add an index. See MySQL indexes. All references between different tables should usually be done with indexes. You can use the EXPLAIN command to determine which indexes are used for a SELECT. See EXPLAIN.
Some general tips:
To help MySQL optimize queries better, run myisamchk --analyze on a table after it has been loaded with relevant data. This updates a value for each index part that indicates the average number of rows that have the same value. (For unique indexes, this is always 1.) MySQL will use this to decide which index to choose when you connect two tables with 'a non-constant expression'. You can check the result from the analyze run by doing SHOW INDEX FROM table_name and examining the Cardinality column.
To sort an index and data according to an index, use myisamchk --sort-index --sort-records=1 (if you want to sort on index 1). If you have a unique index from which you want to read all records in order according to that index, this is a good way to make that faster. Note, however, that this sorting isn't written optimally and will take a long time for a large table!
The WHERE optimizations are put in the SELECT part here because they are mostly used with SELECT, but the same optimizations apply for WHERE in DELETE and UPDATE statements.
Also note that this section is incomplete. MySQL does many optimizations, and we have not had time to document them all.
Some of the optimizations performed by MySQL are listed here:
Removal of unnecessary parentheses:
((a AND b) AND c OR (((a AND b) AND (c AND d)))) -> (a AND b AND c) OR (a AND b AND c AND d)
Constant folding:
(a<b AND b=c) AND a=5 -> b>5 AND b=c AND a=5
Constant condition removal (needed because of constant folding):
(B>=5 AND B=5) OR (B=6 AND 5=5) OR (B=7 AND 5=6) -> B=5 OR B=6
Constant expressions used by indexes are evaluated only once.
COUNT(*) on a single table without a WHERE is retrieved directly from the table information for MyISAM and HEAP tables. This is also done for any NOT NULL expression when used with only one table.
Early detection of invalid constant expressions. MySQL quickly detects that some SELECT statements are impossible and returns no rows.
HAVING is merged with WHERE if you don't use GROUP BY or group functions (COUNT(), MIN()...).
For each sub-join, a simpler WHERE is constructed to get a fast WHERE evaluation for each sub-join and also to skip records as soon as possible.
All constant tables are read first, before any other tables in the query. A constant table is:
An empty table or a table with 1 row.
A table that is used with a WHERE clause on a UNIQUE index, or a PRIMARY KEY, where all index parts are used with constant expressions and the index parts are defined as NOT NULL.
All the following tables are used as constant tables:
mysql> SELECT * FROM t WHERE primary_key=1; mysql> SELECT * FROM t1,t2 -> WHERE t1.primary_key=1 AND t2.primary_key=t1.id;
The best join combination to join the tables is found by trying all possibilities. If all columns in ORDER BY and in GROUP BY come from the same table, then this table is preferred first when joining.
If there is an ORDER BY clause and a different GROUP BY clause, or if the ORDER BY or GROUP BY contains columns from tables other than the first table in the join queue, a temporary table is created.
If you use SQL_SMALL_RESULT, MySQL will use an in-memory temporary table.
Each table index is queried, and the best index that spans fewer than 30% of the rows is used. If no such index can be found, a quick table scan is used.
In some cases, MySQL can read rows from the index without even consulting the datafile. If all columns used from the index are numeric, only the index tree is used to resolve the query.
Before each record is output, those that do not match the HAVING clause are skipped.
Some examples of queries that are very fast:
mysql> SELECT COUNT(*) FROM tbl_name; mysql> SELECT MIN(key_part1),MAX(key_part1) FROM tbl_name; mysql> SELECT MAX(key_part2) FROM tbl_name -> WHERE key_part_1=constant; mysql> SELECT ... FROM tbl_name -> ORDER BY key_part1,key_part2,... LIMIT 10; mysql> SELECT ... FROM tbl_name -> ORDER BY key_part1 DESC,key_part2 DESC,... LIMIT 10;
The following queries are resolved using only the index tree (assuming the indexed columns are numeric):
mysql> SELECT key_part1,key_part2 FROM tbl_name WHERE key_part1=val; mysql> SELECT COUNT(*) FROM tbl_name -> WHERE key_part1=val1 AND key_part2=val2; mysql> SELECT key_part2 FROM tbl_name GROUP BY key_part1;
The following queries use indexing to retrieve the rows in sorted order without a separate sorting pass:
mysql> SELECT ... FROM tbl_name -> ORDER BY key_part1,key_part2,... ; mysql> SELECT ... FROM tbl_name -> ORDER BY key_part1 DESC,key_part2 DESC,... ;
The Merge Index method is used to retrieve rows with several ref, ref_or_null or range scans and merge the results into one. This method is employed when the table condition is a disjunction of conditions for which ref, ref_or_null, or range could be used with different keys. The key column contains a list of used indexes. key_len contains a list of the longest key parts of the used indexes.
Example:
SELECT * FROM table WHERE key1column = 10 OR key2column = 20; SELECT * FROM table WHERE (key1column = 10 OR key2column = 20) AND nonkeycolumn=30; SELECT * FROM t1,t2 WHERE (t1.key1 IN (1,2) OR t1.key2 LIKE 'value%') AND t2.key1=t1.somefield SELECT * FROM t1,t2 WHERE t1.key1=1 AND (t2.key1=t1.somefield OR t2.key2=t1.somefield2)
This ``join'' type optimization is new in MySQL 5.0.0, and represents a significant change in behaviour with regard to indexes since the old rule was that the server is only ever able to use at most one index for each referenced table.
MySQL can do the same optimization on column IS NULL as it can do with column = constant_value. For example, MySQL can use indexes and ranges to search for NULL with IS NULL.
SELECT * FROM table_name WHERE key_col IS NULL; SELECT * FROM table_name WHERE key_col <=> NULL; SELECT * FROM table_name WHERE key_col=# OR key_col=# OR key_col IS NULL
If you use column_name IS NULL on a NOT NULL in a WHERE clause on table that is not used OUTER JOIN that expression will be optimized away.
MySQL 4.1.1 can additionally optimize the combination column = expr AND column IS NULL, an form that is common in resolved sub queries. EXPLAIN will show ref_or_null when this optimization is used.
This optimization can handle one IS NULL for any key part.
Some examples of queries that are optimized (assuming key on t2 (a,b)):
SELECT * FROM t1 WHERE t1.a=expr OR t1.a IS NULL; SELECT * FROM t1,t2 WHERE t1.a=t2.a OR t2.a IS NULL; SELECT * FROM t1,t2 WHERE (t1.a=t2.a OR t2.a IS NULL) AND t2.b=t1.b; SELECT * FROM t1,t2 WHERE t1.a=t2.a AND (t2.b=t1.b OR t2.b IS NULL); SELECT * FROM t1,t2 WHERE (t1.a=t2.a AND t2.a IS NULL AND ...) OR (t1.a=t2.a AND t2.a IS NULL AND ...);
ref_or_null works by first doing a read on the reference key and after that a separate search after rows with NULL key.
Note that the optimization can only handle one IS NULL level.
SELECT * FROM t1,t2 where (t1.a=t2.a AND t2.a IS NULL) OR (t1.b=t2.b AND t2.b IS NULL);
Int the above case MySQL will only use key lookups on the part (t1.a=t2.a AND t2.a IS NULL) and not be able to use the key part on b.
DISTINCT combined with ORDER BY will in many cases need a temporary table.
Note that as DISTINCT may use GROUP BY, you should be aware of how MySQL works with in fields in ORDER BY or HAVING that are not part of the selected fields. See GROUP-BY-hidden-fields.
When combining LIMIT row_count with DISTINCT, MySQL will stop as soon as it finds row_count unique rows.
If you don't use columns from all used tables, MySQL will stop the scanning of the not used tables as soon as it has found the first match.
SELECT DISTINCT t1.a FROM t1,t2 where t1.a=t2.a;
In this case, assuming t1 is used before t2 (check with EXPLAIN), then MySQL will stop reading from t2 (for that particular row in t1) when the first row in t2 is found.
A LEFT JOIN B join_condition in MySQL is implemented as follows:
The table B is set to be dependent on table A and all tables that A is dependent on.
The table A is set to be dependent on all tables (except B) that are used in the LEFT JOIN condition.
The LEFT JOIN condition is used to decide how we should retrieve rows from table B. (In other words, any condition in the WHERE clause is not used).
All standard join optimizations are done, with the exception that a table is always read after all tables it is dependent on. If there is a circular dependence then MySQL will issue an error.
All standard WHERE optimizations are done.
If there is a row in A that matches the WHERE clause, but there wasn't any row in B that matched the ON condition, then an extra B row is generated with all columns set to NULL.
If you use LEFT JOIN to find rows that don't exist in some table and you have the following test: column_name IS NULL in the WHERE part, where column_name is a column that is declared as NOT NULL, then MySQL will stop searching after more rows (for a particular key combination) after it has found one row that matches the LEFT JOIN condition.
RIGHT JOIN is implemented analogously to LEFT JOIN.
The table read order forced by LEFT JOIN and STRAIGHT JOIN will help the join optimizer (which calculates in which order tables should be joined) to do its work much more quickly, as there are fewer table permutations to check.
Note that the above means that if you do a query of type:
SELECT * FROM a,b LEFT JOIN c ON (c.key=a.key) LEFT JOIN d (d.key=a.key) WHERE b.key=d.key
MySQL will do a full scan on b as the LEFT JOIN will force it to be read before d.
The fix in this case is to change the query to:
SELECT * FROM b,a LEFT JOIN c ON (c.key=a.key) LEFT JOIN d (d.key=a.key) WHERE b.key=d.key
Starting from 4.0.14, MySQL does the following LEFT JOIN optimization:
If the WHERE condition is always be false for the generated NULL row, the LEFT JOIN is changed to a normal join.
For example, in the following query the WHERE clause would be false if t2.column would be NULL so it's safe to convert to a normal join.
SELECT * FROM t1 LEFT t2 ON (column) WHERE t2.column2 =5; -> SELECT * FROM t1,t2 WHERE t2.column2=5 AND t1.column=t2.column;
This can be made faster as MySQL can now use table t2 before table t1 if this would result in a better query plan. To force a specific table order, use STRAIGHT JOIN.
In some cases MySQL can uses index to satisfy an ORDER BY or GROUP BY request without doing any extra sorting.
The index can also be used even if the ORDER BY doesn't match the index exactly, as long as all the unused index parts and all the extra are ORDER BY columns are constants in the WHERE clause. The following queries will use the index to resolve the ORDER BY / GROUP BY part:
SELECT * FROM t1 ORDER BY key_part1,key_part2,... SELECT * FROM t1 WHERE key_part1=constant ORDER BY key_part2 SELECT * FROM t1 WHERE key_part1=constant GROUP BY key_part2 SELECT * FROM t1 ORDER BY key_part1 DESC,key_part2 DESC SELECT * FROM t1 WHERE key_part1=1 ORDER BY key_part1 DESC,key_part2 DESC
Some cases where MySQL can not use indexes to resolve the ORDER BY: (Note that MySQL will still use indexes to find the rows that matches the WHERE clause):
You are doing an ORDER BY on different keys:
SELECT * FROM t1 ORDER BY key1,key2
You are doing an ORDER BY using non-consecutive key parts.
SELECT * FROM t1 WHERE key2=constant ORDER BY key_part2
You are mixing ASC and DESC.
SELECT * FROM t1 ORDER BY key_part1 DESC,key_part2 ASC
The key used to fetch the rows are not the same one that is used to do the ORDER BY:
SELECT * FROM t1 WHERE key2=constant ORDER BY key1
You are joining many tables and the columns you are doing an ORDER BY on are not all from the first not-const table that is used to retrieve rows (This is the first table in the EXPLAIN output which doesn't use a const row fetch method).
You have different ORDER BY and GROUP BY expressions.
The used table index is an index type that doesn't store rows in order. (Like the HASH index in HEAP tables).
In the cases where MySQL have to sort the result, it uses the following algorithm:
Read all rows according to key or by table scanning. Rows that don't match the WHERE clause are skipped.
Store the sort-key in a buffer (of size sort_buffer).
When the buffer gets full, run a qsort on it and store the result in a temporary file. Save a pointer to the sorted block. (In the case where all rows fits into the sort buffer, no temporary file is created)
Repeat the above until all rows have been read.
Do a multi-merge of up to MERGEBUFF (7) regions to one block in another temporary file. Repeat until all blocks from the first file are in the second file.
Repeat the following until there is less than MERGEBUFF2 (15) blocks left.
On the last multi-merge, only the pointer to the row (last part of the sort-key) is written to a result file.
Now the code in sql/records.cc will be used to read through them in sorted order by using the row pointers in the result file. To optimize this, we read in a big block of row pointers, sort these and then we read the rows in the sorted order into a row buffer (read_rnd_buffer_size) .
You can with EXPLAIN SELECT ... ORDER BY check if MySQL can use indexes to resolve the query. If you get Using filesort in the extra column, then MySQL can't use indexes to resolve the ORDER BY. See EXPLAIN.
If you want to have a higher ORDER BY speed, you should first see if you can get MySQL to use indexes instead of having to do an extra sorting phase. If this is not possible, then you can do:
Increase the size of the sort_buffer_size variable.
Increase the size of the read_rnd_buffer_size variable.
Change tmpdir to point to a dedicated disk with lots of empty space. If you use MySQL 4.1 or later you can spread load between several physical disks by setting tmpdir to a list of paths separated by colon : (semicolon ; on Windows). They will be used in round-robin fashion. Note: These paths should end up on different physical disks, not different partitions of the same disk.
By default, MySQL sorts all GROUP BY x,y[,...] queries as if you specified ORDER BY x,y[,...] in the query as well. If you include the ORDER BY clause explicitly, MySQL optimizes it away without any speed penalty, though the sorting still occurs. If a query includes GROUP BY but you want to avoid the overhead of sorting the result, you can supress sorting by specifying ORDER BY NULL:
INSERT INTO foo SELECT a,COUNT(*) FROM bar GROUP BY a ORDER BY NULL;
In some cases MySQL will handle the query differently when you are using LIMIT row_count and not using HAVING:
If you are selecting only a few rows with LIMIT, MySQL will use indexes in some cases when it normally would prefer to do a full table scan.
If you use LIMIT row_count with ORDER BY, MySQL will end the sorting as soon as it has found the first row_count lines instead of sorting the whole table.
When combining LIMIT row_count with DISTINCT, MySQL will stop as soon as it finds row_count unique rows.
In some cases a GROUP BY can be resolved by reading the key in order (or do a sort on the key) and then calculate summaries until the key value changes. In this case LIMIT row_count will not calculate any unnecessary GROUP BY values.
As soon as MySQL has sent the first # rows to the client, it will abort the query (if you are not using SQL_CALC_FOUND_ROWS).
LIMIT 0 will always quickly return an empty set. This is useful to check the query and to get the column types of the result columns.
When the server uses temporary tables to resolve the query, the LIMIT row_count is used to calculate how much space is required.
The time to insert a record consists approximately of:
Connect: (3)
Sending query to server: (2)
Parsing query: (2)
Inserting record: (1 x size of record)
Inserting indexes: (1 x number of indexes)
Close: (1)
where the numbers are somewhat proportional to the overall time. This does not take into consideration the initial overhead to open tables (which is done once for each concurrently running query).
The size of the table slows down the insertion of indexes by log N (B-trees).
Some ways to speed up inserts:
If you are inserting many rows from the same client at the same time, use multiple value lists INSERT statements. This is much faster (many times in some cases) than using separate INSERT statements. If you are adding data to non-empty table, you may tune up the bulk_insert_buffer_size variable to make it even faster. See bulk_insert_buffer_size.
If you are inserting a lot of rows from different clients, you can get higher speed by using the INSERT DELAYED statement. See INSERT.
Note that with MyISAM tables you can insert rows at the same time SELECT statements are running if there are no deleted rows in the tables.
When loading a table from a text file, use LOAD DATA INFILE. This is usually 20 times faster than using a lot of INSERT statements. See LOAD DATA.
It is possible with some extra work to make LOAD DATA INFILE run even faster when the table has many indexes. Use the following procedure:
Optionally create the table with CREATE TABLE. For example, using mysql or Perl-DBI.
Execute a FLUSH TABLES statement or the shell command mysqladmin flush-tables.
Use myisamchk --keys-used=0 -rq /path/to/db/tbl_name. This will remove all usage of all indexes from the table.
Insert data into the table with LOAD DATA INFILE. This will not update any indexes and will therefore be very fast.
If you are going to only read the table in the future, run myisampack on it to make it smaller. See Compressed format.
Re-create the indexes with myisamchk -r -q /path/to/db/tbl_name. This will create the index tree in memory before writing it to disk, which is much faster because it avoids lots of disk seeks. The resulting index tree is also perfectly balanced.
Execute a FLUSH TABLES statement or the shell command mysqladmin flush-tables.
Note that LOAD DATA INFILE also does the above optimization if you insert into an empty table; the main difference with the above procedure is that you can let myisamchk allocate much more temporary memory for the index creation that you may want MySQL to allocate for every index recreation.
Since MySQL 4.0 you can also use ALTER TABLE tbl_name DISABLE KEYS instead of myisamchk --keys-used=0 -rq /path/to/db/tbl_name and ALTER TABLE tbl_name ENABLE KEYS instead of myisamchk -r -q /path/to/db/tbl_name. This way you can also skip FLUSH TABLES steps.
You can speed up insertions that are done using multiple statements by locking your tables:
mysql> LOCK TABLES a WRITE; mysql> INSERT INTO a VALUES (1,23),(2,34),(4,33); mysql> INSERT INTO a VALUES (8,26),(6,29); mysql> UNLOCK TABLES;
The main speed difference is that the index buffer is flushed to disk only once, after all INSERT statements have completed. Normally there would be as many index buffer flushes as there are different INSERT statements. Locking is not needed if you can insert all rows with a single statement.
For transactional tables, you should use BEGIN/COMMIT instead of LOCK TABLES to get a speedup.
Locking will also lower the total time of multi-connection tests, but the maximum wait time for some threads will go up (because they wait for locks). For example:
thread 1 does 1000 inserts thread 2, 3, and 4 does 1 insert thread 5 does 1000 inserts
If you don't use locking, 2, 3, and 4 will finish before 1 and 5. If you use locking, 2, 3, and 4 probably will not finish before 1 or 5, but the total time should be about 40% faster.
As INSERT, UPDATE, and DELETE operations are very fast in MySQL, you will obtain better overall performance by adding locks around everything that does more than about 5 inserts or updates in a row. If you do very many inserts in a row, you could do a LOCK TABLES followed by an UNLOCK TABLES once in a while (about each 1000 rows) to allow other threads access to the table. This would still result in a nice performance gain.
LOAD DATA INFILE is much faster for loading data.
To get some more speed for both LOAD DATA INFILE and INSERT, enlarge the key buffer. See Server parameters.
Update queries are optimized as a SELECT query with the additional overhead of a write. The speed of the write is dependent on the size of the data that is being updated and the number of indexes that are updated. Indexes that are not changed will not be updated.
Also, another way to get fast updates is to delay updates and then do many updates in a row later. Doing many updates in a row is much quicker than doing one at a time if you lock the table.
Note that, with dynamic record format, updating a record to a longer total length may split the record. So if you do this often, it is very important to OPTIMIZE TABLE sometimes. See OPTIMIZE TABLE.
If you want to delete all rows in the table, you should use TRUNCATE TABLE table_name. See TRUNCATE.
The time to delete a record is exactly proportional to the number of indexes. To delete records more quickly, you can increase the size of the index cache. See Server parameters.
Unsorted tips for faster systems:
Use persistent connections to the database to avoid the connection overhead. If you can't use persistent connections and you are doing a lot of new connections to the database, you may want to change the value of the thread_cache_size variable. See Server parameters.
Always check that all your queries really use the indexes you have created in the tables. In MySQL you can do this with the EXPLAIN command. See Explain: (manual) Explain.
Try to avoid complex SELECT queries on MyISAM tables that are updated a lot. This is to avoid problems with table locking.
With MyISAM tables that have no deleted rows, you can insert rows at the same time another query is reading from it. If this is important for you, you should consider methods where you don't have to delete rows or run OPTIMIZE TABLE after you have deleted a lot of rows.
Use ALTER TABLE ... ORDER BY expr1,expr2... if you mostly retrieve rows in expr1,expr2... order. By using this option after big changes to the table, you may be able to get higher performance.
In some cases it may make sense to introduce a column that is 'hashed' based on information from other columns. If this column is short and reasonably unique it may be much faster than a big index on many columns. In MySQL it's very easy to use this extra column: SELECT * FROM table_name WHERE hash=MD5(CONCAT(col1,col2)) AND col_1="constant" AND col_2='constant'
For tables that change a lot you should try to avoid all VARCHAR or BLOB columns. You will get dynamic row length as soon as you are using a single VARCHAR or BLOB column. See Table types.
It's not normally useful to split a table into different tables just because the rows gets 'big'. To access a row, the biggest performance hit is the disk seek to find the first byte of the row. After finding the data most new disks can read the whole row fast enough for most applications. The only cases where it really matters to split up a table is if it's a dynamic row size table (see above) that you can change to a fixed row size, or if you very often need to scan the table and don't need most of the columns. See Table types.
If you very often need to calculate things based on information from a lot of rows (like counts of things), it's probably much better to introduce a new table and update the counter in real time. An update of type UPDATE table SET count=count+1 WHERE index_column=constant is very fast!
This is really important when you use MySQL table types like MyISAM and ISAM that only have table locking (multiple readers / single writers). This will also give better performance with most databases, as the row locking manager in this case will have less to do.
If you need to collect statistics from big log tables, use summary tables instead of scanning the whole table. Maintaining the summaries should be much faster than trying to do statistics 'live'. It's much faster to regenerate new summary tables from the logs when things change (depending on business decisions) than to have to change the running application!
If possible, one should classify reports as 'live' or 'statistical', where data needed for statistical reports are only generated based on summary tables that are generated from the actual data.
Take advantage of the fact that columns have default values. Insert values explicitly only when the value to be inserted differs from the default. This reduces the parsing that MySQL need to do and improves the insert speed.
In some cases it's convenient to pack and store data into a blob. In this case you have to add some extra code in your application to pack/unpack things in the blob, but this may save a lot of accesses at some stage. This is practical when you have data that doesn't conform to a static table structure.
Normally you should try to keep all data non-redundant (what is called 3rd normal form in database theory), but you should not be afraid of duplicating things or creating summary tables if you need these to gain more speed.
Stored procedures or UDF (user-defined functions) may be a good way to get more performance. In this case you should, however, always have a way to do this some other (slower) way if you use some database that doesn't support this.
You can always gain something by caching queries/answers in your application and trying to do many inserts/updates at the same time. If your database supports lock tables (like MySQL and Oracle), this should help to ensure that the index cache is only flushed once after all updates.
Use INSERT /*! DELAYED */ when you do not need to know when your data is written. This speeds things up because many records can be written with a single disk write.
Use INSERT /*! LOW_PRIORITY */ when you want your selects to be more important.
Use SELECT /*! HIGH_PRIORITY */ to get selects that jump the queue. That is, the select is done even if there is somebody waiting to do a write.
Use the multi-line INSERT statement to store many rows with one SQL command (many SQL servers supports this).
Use LOAD DATA INFILE to load bigger amounts of data. This is faster than normal inserts and will be even faster when myisamchk is integrated in mysqld.
Use AUTO_INCREMENT columns to make unique values.
Use OPTIMIZE TABLE once in a while to avoid fragmentation when using a dynamic table format. See OPTIMIZE TABLE.
Use HEAP tables to get more speed when possible. See Table types.
When using a normal web server setup, images should be stored as files. That is, store only a file reference in the database. The main reason for this is that a normal web server is much better at caching files than database contents. So it it's much easier to get a fast system if you are using files.
Use in memory tables for non-critical data that are accessed often (like information about the last shown banner for users that don't have cookies).
Columns with identical information in different tables should be declared identical and have identical names. Before Version 3.23 you got slow joins otherwise.
Try to keep the names simple (use name instead of customer_name in the customer table). To make your names portable to other SQL servers you should keep them shorter than 18 characters.
If you need really high speed, you should take a look at the low-level interfaces for data storage that the different SQL servers support! For example, by accessing the MySQL MyISAM directly, you could get a speed increase of 2-5 times compared to using the SQL interface. To be able to do this the data must be on the same server as the application, and usually it should only be accessed by one process (because external file locking is really slow). One could eliminate the above problems by introducing low-level MyISAM commands in the MySQL server (this could be one easy way to get more performance if needed). By carefully designing the database interface, it should be quite easy to support this types of optimization.
In many cases it's faster to access data from a database (using a live connection) than accessing a text file, just because the database is likely to be more compact than the text file (if you are using numerical data), and this will involve fewer disk accesses. You will also save code because you don't have to parse your text files to find line and column boundaries.
You can also use replication to speed things up. See Replication.
Declaring a table with DELAY_KEY_WRITE=1 will make the updating of indexes faster, as these are not logged to disk until the file is closed. The downside is that you should run myisamchk on these tables before you start mysqld to ensure that they are okay if something killed mysqld in the middle. As the key information can always be generated from the data, you should not lose anything by using DELAY_KEY_WRITE.
Table of Contents
You can find a discussion about different locking methods in the appendix. See Locking methods.
All locking in MySQL is deadlock-free, except for InnoDB and BDB type tables. This is managed by always requesting all needed locks at once at the beginning of a query and always locking the tables in the same order.
InnoDB type tables automatically acquire their row locks and BDB type tables their page locks during the processing of SQL statements, not at the start of the transaction.
The locking method MySQL uses for WRITE locks works as follows:
If there are no locks on the table, put a write lock on it.
Otherwise, put the lock request in the write lock queue.
The locking method MySQL uses for READ locks works as follows:
If there are no write locks on the table, put a read lock on it.
Otherwise, put the lock request in the read lock queue.
When a lock is released, the lock is made available to the threads in the write lock queue, then to the threads in the read lock queue.
This means that if you have many updates on a table, SELECT statements will wait until there are no more updates.
To work around this for the case where you want to do many INSERT and SELECT operations on a table, you can insert rows in a temporary table and update the real table with the records from the temporary table once in a while.
This can be done with the following code:
mysql> LOCK TABLES real_table WRITE, insert_table WRITE; mysql> INSERT INTO real_table SELECT * FROM insert_table; mysql> TRUNCATE TABLE insert_table; mysql> UNLOCK TABLES;
You can use the LOW_PRIORITY options with INSERT, UPDATE or DELETE or HIGH_PRIORITY with SELECT if you want to prioritize retrieval in some specific cases. You can also start mysqld with --low-priority-updates to get the same behavior.
Using SQL_BUFFER_RESULT can also help making table locks shorter. See SELECT.
You could also change the locking code in mysys/thr_lock.c to use a single queue. In this case, write locks and read locks would have the same priority, which might help some applications.
The table locking code in MySQL is deadlock free.
MySQL uses table locking (instead of row locking or column locking) on all table types, except InnoDB and BDB tables, to achieve a very high lock speed. For large tables, table locking is much better than row locking for most applications, but there are some pitfalls.
For InnoDB and BDB tables, MySQL only uses table locking if you explicitly lock the table with LOCK TABLES. For these table types we recommend you to not use LOCK TABLES at all, because InnoDB uses automatic row level locking and BDB uses page level locking to ensure transaction isolation.
As of MySQL Version 3.23.7 (3.23.25 for Windows), you can insert rows into MyISAM tables at the same time other threads are reading from the table. Note that currently this works only if there are no holes resulting from deleted rows in the table at the time the insert is made. When all holes has been filled with new data, concurrent inserts will automatically be enabled again.
Table locking enables many threads to read from a table at the same time, but if a thread wants to write to a table, it must first get exclusive access. During the update, all other threads that want to access this particular table will wait until the update is ready.
As updates on tables normally are considered to be more important than SELECT, all statements that update a table have higher priority than statements that retrieve information from a table. This should ensure that updates are not 'starved' because one issues a lot of heavy queries against a specific table. (You can change this by using LOW_PRIORITY with the statement that does the update or HIGH_PRIORITY with the SELECT statement.)
Starting from MySQL Version 3.23.7 one can use the max_write_lock_count variable to force MySQL to temporary give all SELECT statements, that wait for a table, a higher priority after a specific number of inserts on a table.
Table locking is, however, not very good under the following scenario:
A client issues a SELECT that takes a long time to run.
Another client then issues an UPDATE on a used table. This client will wait until the SELECT is finished.
Another client issues another SELECT statement on the same table. As UPDATE has higher priority than SELECT, this SELECT will wait for the UPDATE to finish. It will also wait for the first SELECT to finish!
A thread is waiting for something like full disk, in which case all threads that wants to access the problem table will also be put in a waiting state until more disk space is made available.
Some possible solutions to this problem are:
Try to get the SELECT statements to run faster. You may have to create some summary tables to do this.
Start mysqld with --low-priority-updates. This will give all statements that update (modify) a table lower priority than a SELECT statement. In this case the last SELECT statement in the previous scenario would execute before the INSERT statement.
You can give a specific INSERT, UPDATE, or DELETE statement lower priority with the LOW_PRIORITY attribute.
Start mysqld with a low value for max_write_lock_count to give READ locks after a certain number of WRITE locks.
You can specify that all updates from a specific thread should be done with low priority by using the SQL command: SET LOW_PRIORITY_UPDATES=1. See SET.
You can specify that a specific SELECT is very important with the HIGH_PRIORITY attribute. See SELECT.
If you have problems with INSERT combined with SELECT, switch to use the new MyISAM tables as these support concurrent SELECT and INSERT statements.
If you mainly mix INSERT and SELECT statements, the DELAYED attribute to INSERT will probably solve your problems. See INSERT.
If you have problems with SELECT and DELETE, the LIMIT option to DELETE may help. See DELETE.
Table of Contents
MySQL keeps row data and index data in separate files. Many (almost all) other databases mix row and index data in the same file. We believe that the MySQL choice is better for a very wide range of modern systems.
Another way to store the row data is to keep the information for each column in a separate area (examples are SDBM and Focus). This will cause a performance hit for every query that accesses more than one column. Because this degenerates so quickly when more than one column is accessed, we believe that this model is not good for general purpose databases.
The more common case is that the index and data are stored together (as in Oracle/Sybase et al). In this case you will find the row information at the leaf page of the index. The good thing with this layout is that it, in many cases, depending on how well the index is cached, saves a disk read. The bad things with this layout are:
Table scanning is much slower because you have to read through the indexes to get at the data.
You can't use only the index table to retrieve data for a query.
You lose a lot of space, as you must duplicate indexes from the nodes (as you can't store the row in the nodes).
Deletes will degenerate the table over time (as indexes in nodes are usually not updated on delete).
It's harder to cache only the index data.
One of the most basic optimization is to get your data (and indexes) to take as little space on the disk (and in memory) as possible. This can give huge improvements because disk reads are faster and normally less main memory will be used. Indexing also takes less resources if done on smaller columns.
MySQL supports a lot of different table types and row formats. Choosing the right table format may give you a big performance gain. See Table types.
You can get better performance on a table and minimise storage space using the techniques listed here:
Use the most efficient (smallest) types possible. MySQL has many specialized types that save disk space and memory.
Use the smaller integer types if possible to get smaller tables. For example, MEDIUMINT is often better than INT.
Declare columns to be NOT NULL if possible. It makes everything faster and you save one bit per column. Note that if you really need NULL in your application you should definitely use it. Just avoid having it on all columns by default.
If you don't have any variable-length columns (VARCHAR, TEXT, or BLOB columns), a fixed-size record format is used. This is faster but unfortunately may waste some space. See MyISAM table formats.
The primary index of a table should be as short as possible. This makes identification of one row easy and efficient.
For each table, you have to decide which storage/index method to use. See Table types.
Only create the indexes that you really need. Indexes are good for retrieval but bad when you need to store things fast. If you mostly access a table by searching on a combination of columns, make an index on them. The first index part should be the most used column. If you are always using many columns, you should use the column with more duplicates first to get better compression of the index.
If it's very likely that a column has a unique prefix on the first number of characters, it's better to only index this prefix. MySQL supports an index on a part of a character column. Shorter indexes are faster not only because they take less disk space but also because they will give you more hits in the index cache and thus fewer disk seeks. See Server parameters.
In some circumstances it can be beneficial to split into two a table that is scanned very often. This is especially true if it is a dynamic format table and it is possible to use a smaller static format table that can be used to find the relevant rows when scanning the table.
Indexes are used to find rows with specific column values fast. Without an index MySQL has to start with the first record and then read through the whole table to find the relevant rows. The bigger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly get a position to seek to in the middle of the datafile without having to look at all the data. If a table has 1000 rows, this is at least 100 times faster than reading sequentially. Note that if you need to access almost all 1000 rows, it is faster to read sequentially, because that minimises disk seeks.
All MySQL indexes (PRIMARY KEY, UNIQUE, and INDEX) are stored in B-trees. Strings are automatically prefix- and end-space compressed. See CREATE INDEX.
Indexes are used in the following ways:
To quickly find the rows that match a WHERE clause.
To retrieve rows from other tables when performing joins.
To find the MAX() or MIN() value for a specific indexed column. This is optimized by a preprocessor that checks if you are using WHERE key_part_# = constant on all key parts < N. In this case MySQL will do a single key lookup and replace the MIN() expression with a constant. If all expressions are replaced with constants, the query will return at once:
SELECT MIN(key_part2),MAX(key_part2) FROM table_name where key_part1=10
To sort or group a table if the sorting or grouping is done on a leftmost prefix of a usable key (for example, ORDER BY key_part_1,key_part_2 ). The key is read in reverse order if all key parts are followed by DESC. See ORDER BY optimisation.
In some cases a query can be optimized to retrieve values without consulting the datafile. If all used columns for some table are numeric and form a leftmost prefix for some key, the values may be retrieved from the index tree for greater speed:
SELECT key_part3 FROM table_name WHERE key_part1=1
Suppose you issue the following SELECT statement:
mysql> SELECT * FROM tbl_name WHERE col1=val1 AND col2=val2;
If a multiple-column index exists on col1 and col2, the appropriate rows can be fetched directly. If separate single-column indexes exist on col1 and col2, the optimizer tries to find the most restrictive index by deciding which index will find fewer rows and using that index to fetch the rows.
If the table has a multiple-column index, any leftmost prefix of the index can be used by the optimizer to find rows. For example, if you have a three-column index on (col1, col2, col3), you have indexed search capabilities on (col1), (col1, col2), and (col1, col2, col3).
MySQL can't use a partial index if the columns don't form a leftmost prefix of the index. Suppose you have the SELECT statements shown here:
mysql> SELECT * FROM tbl_name WHERE col1=val1; mysql> SELECT * FROM tbl_name WHERE col2=val2; mysql> SELECT * FROM tbl_name WHERE col2=val2 AND col3=val3;
If an index exists on (col1, col2, col3), only the first of the preceding queries uses the index. The second and third queries do involve indexed columns, but (col2) and (col2, col3) are not leftmost prefixes of (col1, col2, col3).
MySQL also uses indexes for LIKE comparisons if the argument to LIKE is a constant string that doesn't start with a wildcard character. For example, the following SELECT statements use indexes:
mysql> SELECT * FROM tbl_name WHERE key_col LIKE "Patrick%"; mysql> SELECT * FROM tbl_name WHERE key_col LIKE "Pat%_ck%";
In the first statement, only rows with "Patrick" <= key_col < "Patricl" are considered. In the second statement, only rows with "Pat" <= key_col < "Pau" are considered.
The following SELECT statements will not use indexes:
mysql> SELECT * FROM tbl_name WHERE key_col LIKE "%Patrick%"; mysql> SELECT * FROM tbl_name WHERE key_col LIKE other_col;
In the first statement, the LIKE value begins with a wildcard character. In the second statement, the LIKE value is not a constant.
MySQL 4.0 does another optimization on LIKE. If you use ... LIKE "%string%" and string is longer than 3 characters, MySQL will use the Turbo Boyer-Moore algorithm to initialize the pattern for the string and then use this pattern to perform the search quicker.
Searching using column_name IS NULL will use indexes if column_name is an index.
MySQL normally uses the index that finds the smallest number of rows. An index is used for columns that you compare with the following operators: =, >, >=, <, <=, BETWEEN, or a LIKE with a pattern that begins with a non-wildcard prefix like 'something%'.
Any index that doesn't span all AND levels in the WHERE clause is not used to optimize the query. In other words: To be able to use an index, a prefix of the index must be used in every AND group.
The following WHERE clauses use indexes:
... WHERE index_part1=1 AND index_part2=2 AND other_column=3 ... WHERE index=1 OR A=10 AND index=2 /* index = 1 OR index = 2 */ ... WHERE index_part1='hello' AND index_part_3=5 /* optimized like "index_part1='hello'" */ ... WHERE index1=1 AND index2=2 OR index1=3 AND index3=3; /* Can use index on index1 but not on index2 or index 3 */
These WHERE clauses do not use indexes:
... WHERE index_part2=1 AND index_part3=2 /* index_part_1 is not used */ ... WHERE index=1 OR A=10 /* Index is not used in both AND parts */ ... WHERE index_part1=1 OR index_part2=10 /* No index spans all rows */
Note that sometime MySQL will not use an index, even if one is available. One instance of this is when use of the index would require MySQL to access more than 30% of the rows in the table. (In this case a table scan is probably much faster, as it will require many fewer seeks.) However, if such a query uses LIMIT to only retrieve part of the rows, MySQL will use an index anyway, as it can much more quickly find the few rows to return in the result.
All MySQL column types can be indexed. Use of indexes on the relevant columns is the best way to improve the performance of SELECT operations.
The maximum number of indexes per table and the maximum index length is defined per storage engine. See Table types. All storage engines support a minimum of 16 indexes per table and a minimum total index length of 256 bytes.
For CHAR and VARCHAR columns, you can index a prefix of a column. This is much faster and requires less disk space than indexing the whole column. The syntax to use in the CREATE TABLE statement to index a column prefix looks like this:
INDEX index_name (col_name(length))
The example here creates an index for the first 10 characters of the name column:
mysql> CREATE TABLE test ( -> name CHAR(200) NOT NULL, -> INDEX index_name (name(10)));
For BLOB and TEXT columns, you must index a prefix of the column. The prefix may be up to 255 bytes long.
In MySQL Version 3.23.23 or later, you can also create special FULLTEXT indexes. They are used for full-text search. Only the MyISAM table type supports FULLTEXT indexes and only for CHAR, VARCHAR, and TEXT columns. Indexing always happens over the entire column and partial (prefix) indexing is not supported. See Fulltext Search for details.
MySQL can create indexes on multiple columns. An index may consist of up to 15 columns. (On CHAR and VARCHAR columns you can also use a prefix of the column as a part of an index.)
A multiple-column index can be considered a sorted array containing values that are created by concatenating the values of the indexed columns.
MySQL uses multiple-column indexes in such a way that queries are fast when you specify a known quantity for the first column of the index in a WHERE clause, even if you don't specify values for the other columns.
Suppose a table has the following specification:
mysql> CREATE TABLE test ( -> id INT NOT NULL, -> last_name CHAR(30) NOT NULL, -> first_name CHAR(30) NOT NULL, -> PRIMARY KEY (id), -> INDEX name (last_name,first_name));
Then the index name is an index over last_name and first_name. The index can used for queries that specify values in a known range for last_name, or for both last_name and first_name. Therefore, the name index will be used in the following queries:
mysql> SELECT * FROM test WHERE last_name="Widenius"; mysql> SELECT * FROM test WHERE last_name="Widenius" -> AND first_name="Michael"; mysql> SELECT * FROM test WHERE last_name="Widenius" -> AND (first_name="Michael" OR first_name="Monty"); mysql> SELECT * FROM test WHERE last_name="Widenius" -> AND first_name >="M" AND first_name < "N";
However, the name index will not be used in the following queries:
mysql> SELECT * FROM test WHERE first_name="Michael"; mysql> SELECT * FROM test WHERE last_name="Widenius" -> OR first_name="Michael";
For more information on the manner in which MySQL uses indexes to improve query performance, see MySQL indexes.
To minimize disk I/O, the MyISAM storage engine employs a strategy that is used by many database management systems. It exploits a cache mechanism to keep the most frequently accessed table blocks in memory:
For index blocks, a special structure called the key cache (key buffer) is employed. The structure contains a number of block buffers where the most-used index blocks are placed.
For data blocks, MySQL uses no special cache. Instead it relies on the native operating system filesystem cache.
This section first describes the basic operation of the MyISAM key cache. Then it discusses changes made in MySQL 4.1 that improve key cache performance and that allow you control over cache operation:
The key cache access no longer is serialized among threads. Multiple threads can access the cache concurrently.
Multiple key caches can be set up and table indexes assigned to specific caches.
The key cache mechanism also is used for ISAM tables, which use B-tree indexes. However, the significance of this fact is on the wane. ISAM table use has been decreasing since MySQL 3.23 when MyISAM was introduced. MySQL 4.1 carries this trend further; the ISAM storage engine is disabled by default.
You can control the size of the key cache by means of the key_buffer_size system variable. If this variable is set equal to zero, no key cache is used. The key cache also is not used if the key_buffer_size value is too small to allocate the minimal number of block buffers (8).
If the key cache is not used, index files are accessed using only the native filesystem buffering provided by the operating system. (That is, table index blocks are accessed using the same strategy as that employed for table data blocks.)
An index block is a contiguous unit of access to the MyISAM index files. Usually the size of an index block is equal to the size of nodes of the index B-tree. (Indexes are represented on disk using a B-tree data structure. Nodes at the bottom of the tree are leaf nodes. Nodes above the leaf nodes are non-leaf nodes.)
All block buffers in a key cache structure are the same size. This size can be equal to, greater than, or less than the size of a table index block. Usually one these two values is the multiple of the other.
When data from any table index block must be accessed, the server first checks whether it is available in some block buffer of the key cache. If it is, the server accesses data in the key cache rather than on disk. That is, it reads from the cache or writes into it rather than reading from or writing to disk. Otherwise, the server chooses a cache block buffer containing a different table index block (or blocks) and replaces the data there by a copy of required table index block. As soon as the new index block is in the cache, the index data can be accessed.
If it happens that a block selected for replacement has been modified, the block is considered ``dirty.'' In this case, before being replaced, its contents are flushed to the table index from which it came.
Usually the server follows a LRU (Least Recently Used) strategy: When choosing a block for replacement, it selects the least recently used index block. To be able to make such a choice easy, the key cache module maintains a special queue (LRU chain) of all used blocks. When a block is accessed, it is placed at the end of the queue. When blocks need to be replaced, blocks at the beginning of the queue are the least recently used and become the first candidates for eviction.
Prior to MySQL 4.1, access to the key cache is serialized: No two threads can access key cache buffers simultaneously. The server processes a request for an index block only after it has finished processing the previous request. As a result, a request for an index block not present in any key cache buffer blocks access by other threads while a buffer is being updated to contain the requested index block.
Starting from version 4.1.0, the server supports shared access to the key cache:
A buffer that is not being updated can be accessed by multiple threads
A buffer that is being updated causes threads that need to use it to wait until the update is complete
Multiple threads can initiate requests that result in cache block replacements, as long as they do not interfere with each other (that is, as long as they need different index blocks, and thus cause different cache blocks to be replaced).
Shared access to the key cache allows the server to improve throughput significantly.
Shared access to the key cache improves performance but does not eliminate contention among threads entirely. They still compete for control structures that manage access to the key cache buffers. To reduce key cache access contention further, MySQL 4.1.1 offers the feature of multiple key caches. This allows you to assign different table indexes to different key caches.
When there may be multiple key caches, the server must know which cache to use when processing queries for a given MyISAM table. By default, all MyISAM table indexes are cached in the default key cache. To assign table indexes to a specific key cache, use the CACHE INDEX statement.
For example, The following statement assigns indexes from the tables t1, t2, and t3 to the key cache named hot_cache:
mysql> CACHE INDEX t1, t2, t3 IN hot_cache; +---------+--------------------+----------+----------+ | Table | Op | Msg_type | Msg_text | +---------+--------------------+----------+----------+ | test.t1 | assign_to_keycache | status | OK | | test.t2 | assign_to_keycache | status | OK | | test.t3 | assign_to_keycache | status | OK | +---------+--------------------+----------+----------+
Note: If the server has been built with the ISAM storage engine enabled, ISAM tables use the key cache mechanism. However, ISAM indexes use only the default key cache and cannot be reassigned to a different cache.
The key cache referred to in a CACHE INDEX statement can be created by setting its size with a parameter setting statement or in the server parameter settings. For example:
mysql> SET GLOBAL keycache1.key_buffer_size=128*1024;
To destroy a key cache, set its size to zero:
mysql> SET GLOBAL keycache1.key_buffer_size=0;
See Structured System Variables for a description of the syntax used for referring to structured key cache system variables.
By default, table indexes are assigned to the main (default) key cache created at the server start-up. When a key cache is destroyed, all indexes assigned to it become assigned to the default key cache again.
For a busy server, we recommend a strategy that uses three key caches:
A hot key cache that takes up another 20% the space allocated for all key caches. This is used for tables that are heavily used for searches but that are not updated.
A cold key cache that takes up 20% of the space allocated for all key caches. This is used for medium-sized intensively modified tables, such as temporary tables.
A warm key cache that takes up 60% of the key cache space. This is the default key cache, to be used by default for all other tables.
One reason the use of three key caches be beneficial is that access to one key cache structure does not block access to the others. Queries that access tables assigned to one cache do not compete with queries that access tables assigned to another cache. Performance gains occur for other reasons as well:
The hot cache is used only for retrieval queries, so its contents are never modified. Consequently, whenever an index block needs to be pulled in from disk, the contents of the cache block chosen for replacement need not be flushed first.
For an index assigned to the hot cache, if there are no queries requiring an index scan, there is a high probability that the index blocks corresponding to non-leaf nodes of the index B-tree will remain in the cache.
An update operation most frequently executed for temporary tables is performed much faster when the updated node already is in the cache and need not be read in from disk first. If the size of the indexes of the temporary tables are comparable with the size of cold key cache, the probability is very high that the updated node already will be in the cache.
By default, the key cache management system of MySQL 4.1 uses the LRU strategy for choosing key cache blocks to be evicted, but it also supports a more sophisticated method called the midpoint insertion strategy.
When using the midpoint insertion strategy, the LRU chain is divided into two parts: A hot sub-chain and a warm sub-chain. The division point between two parts is not fixed, but the key cache management system takes care that the warm part is not ``too short,'' always containing at least key_cache_division_limit percent of the key cache blocks. The key_cache_division_limit value is a parameter and can be set per key cache.
When an index block is read from a table into the key cache, it is placed at the end of the warm sub-chain. After a certain number of hits (accesses of the block) it is promoted to the hot sub-chain. At present, the number of hits required to promote a block (3) is the same for all index blocks. In the future, we will allow the hit count to depend on the B-tree level of the node corresponding to an index block: Fewer hits will be required for promotion of an index block if it contains a non-leaf node from the upper levels of the index B-tree than if it contains a leaf node.
A block promoted into the hot sub-chain is placed at the end of the chain. The block then circulates within this sub-chain. If the block stays at the beginning of the sub-chain for a long enough time, it is demoted to the warm chain. This time is determined by the key_cache_age_threshold variable of the key cache.
This variable prescribes that, for a key cache containing N blocks, the block at the beginning of the hot sub-chain not accessed within the last N*key_cache_age_threshold/100 hits is to be moved to the beginning of the warm sub-chain. It then becomes the first candidate for eviction, because blocks for replacement always are taken from the beginning of the warm sub-chain.
The midpoint insertion strategy allows you to keep more valued blocks always in the cache. If you prefer to use the plain LRU strategy, leave the key_cache_division_limit variable set to its default value of 100.
The midpoint insertion strategy helps to improve performance when execution of a query that requires an index scan effectively pushes out of the cache all the index blocks corresponding to valuable high level B-tree nodes. To avoid this, you must use a midpoint insertion strategy with the key_cache_division_limit set to much less than 100. Then valuable frequently hit nodes will be preserved in the hot sub-chain during an index scan operation as well.
If there are enough blocks in a key cache to hold blocks of an entire index, or at least the blocks corresponding to its non-leaf nodes, then it makes sense to preload the key cache with index blocks before starting to use it. Preloading allows you to put the table index blocks into a key cache buffer in the most efficient way: By reading the index blocks from disk sequentially.
Without preloading, the blocks still will be placed into the key cache as needed by queries. In this case, however, although the blocks will stay in the cache as there are enough buffers for all of them, they will be fetched from disk in a random order, not sequentially.
To preload an index into a cache, use the LOAD INDEX INTO CACHE statement. For example, the following statement preloads nodes (index blocks) of indexes of the tables t1 and t2:
mysql> LOAD INDEX INTO CACHE t1, t2 IGNORE LEAVES; +---------+--------------+----------+----------+ | Table | Op | Msg_type | Msg_text | +---------+--------------+----------+----------+ | test.t1 | preload_keys | status | OK | | test.t2 | preload_keys | status | OK | +---------+--------------+----------+----------+
The IGNORE LEAVES modifier causes only blocks for the non-leaf nodes of the index to be preloaded. Thus, this statement preloads all index blocks from t1, but only blocks for the non-leaf nodes from t2.
If an index has been assigned to a key cache using a CACHE INDEX statement, preloading places index blocks into that cache. Otherwise, the index is loaded into the default key cache.
MySQL 4.1 introduces a new key_cache_block_size variable on a per-key cache basis. This variable specifies the size of the block buffers for a key cache.
This variable is introduced to allow tuning the performance of I/O operations for index files.
The best performance for I/O operations is achieved when the size of read buffers are equal to the size of the native operating system I/O buffers. But setting the size of key nodes equal to the size of I/O buffer does not always ensure the best overall performance. When reading the big leaf nodes the server pulls in a lot of unnecessary data, effectively preventing reading other leaf nodes.
Currently, you cannot control the size of the index blocks in a table. This size is set by the server when the .MYI index file is created, depending on the size of the keys in the indexes present in the table definition. In most cases, it is set equal to the I/O buffer size. In the future this will be changed and then key_cache_block_size variable will be fully employed.
A key cache can be restructured at any time by updating its parameter values. For example:
mysql> SET GLOBAL cold_cache.key_buffer_size=4*1024*1024;
If you assign to either the key_buffer_size or key_cache_block_size key cache component a value that differs from the component's currrent value, the server destroys the cache's old structure and creates a new one based on the new values. If the cache contains any dirty blocks, the server saves them to disk before destroying and recreating the cache. Restructuring does not occur if you set other key cache parameters.
When restructuring a key cache, the server first flushes the contents of any dirty buffers to disk. After that, the cache contents become unavailable. However, restructuring does not block queries that need to use indexes assigned to the cache. Instead, the server directly accesses the table indexes using native filesystem caching. Filesystem caching is not as efficient as using a key cache, so although queries will execute, a slowdown can be anticipated. Once the cache has been restructured, it becomes available again for caching indexes assigned to it. The use of filesystem caching for the indexes ceases.
When you run mysqladmin status, you'll see something like this:
Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12
The Open tables value of 12 can be somewhat puzzling if you have only 6 tables.
MySQL is multi-threaded, so there may be many clients issuing queries for a given simultaneously. To minimise the problem with two client threads having different states on the same file, the table is opened independently by each concurrent thread. This takes some memory but will normally increase performance. With ISAM and MyISAM tables, one extra file descriptor is required for the datafile for each client that has the table open. With these table types, the index file descriptor is shared between all threads.
You can read more about this topic in the next section. See Table cache.
The table_cache, max_connections, and max_tmp_tables server variables affect the maximum number of files the server keeps open. If you increase one or more of these values, you may run up against a limit imposed by your operating system on the per-process number of open file descriptors. You can increase the open-files limit on many operating systems, though the method varies widely from system to system. Consult your operating system documentation to determine whether it is possible to increase the limit and how to do so.
table_cache is related to max_connections. For example, for 200 concurrent running connections, you should have a table cache size of at least 200 * n, where n is the maximum number of tables in a join. You also need to reserve some extra file descriptors for temporary tables and files.
Make sure that your operating system can handle the number of open file descriptors implied by the table_cache setting. If table_cache is set too high, MySQL may run out of file descriptors and refuse connections, fail to perform queries, and be very unreliable. You also have to take into account that the MyISAM storage engine needs two file descriptors for each unique open table. You can increase the number of file descriptors available for MySQL with the --open-files-limit=# startup option. See Not enough file handles.
The cache of open tables will be kept at a level of table_cache entries. The default value is 64; this can be changed with the -O table_cache=# option to mysqld). Note that MySQL may temporarily open even more tables to be able to execute queries.
A not used table is closed and removed from the table cache under the following circumstances:
When the cache is full and a thread tries to open a table that is not in the cache.
When the cache contains more than table_cache entries and a thread is no longer using a table.
When someone executes mysqladmin refresh or mysqladmin flush-tables.
When someone executes a FLUSH TABLES statement.
When the table cache fills up, the server uses the following procedure to locate a cache entry to use:
Tables that are not currently in use are released, in least-recently-used order.
If the cache is full and no tables can be released, but a new table needs to be opened, the cache is temporarily extended as necessary.
If the cache is in a temporarily extended state and a table goes from in-use to not-in-use state, the table is closed and released from the cache.
A table is opened for each concurrent access. This means the table needs to be opened twice if two threads access the same table or if a thread accesses the table twice in the same query (for example, by joining the table to itself). The first open of any table takes two file descriptors; each additional use of the table takes only one file descriptor. The extra descriptor for the first open is used for the index file; this descriptor is shared among all threads.
If you are opening a table with the HANDLER table_name OPEN statement, a dedicated table object is allocated for the thread. This table object is not shared by other threads and is not closed until the thread calls HANDLER table_name CLOSE or the thread dies. See HANDLER. When this happens, the table is put back in the table cache (if the cache isn't full).
You can check if your table cache is too small by checking the mysqld variable Opened_tables. If this is quite big, even if you haven't done a lot of FLUSH TABLES, you should increase your table cache size. See Opened_tables.
If you have many files in a directory, open, close, and create operations will be slow. If you execute SELECT statements on many different tables, there will be a little overhead when the table cache is full, because for every table that has to be opened, another must be closed. You can reduce this overhead by making the table cache larger.
Table of Contents
We start with the system level factors, because some of these decisions must be made very early. In other cases, a quick look at this section may suffice because it not that important for the big gains. However, it is always nice to have a feeling about how much one could gain by changing things at this level.
The default operating system to use is really important! To get the best use of multiple-CPU machines, you should use Solaris (because its threads implementation works really well) or Linux (because the 2.2 kernel has really good SMP support). Also, older Linux kernels have a 2G file-size limit by default. If you have such a kernel and a desperate need for files larger than 2G, you should get the LFS (large file system) patch for the ext2 filesystem. Other filesystems such as ReiserFS and XFS do not have this 2G limitation.
Because we have not run MySQL in production on that many platforms, we advise you to test your intended platform before choosing it, if possible.
Other tips:
If you have enough RAM, you could remove all swap devices. Some operating systems will use a swap device in some contexts even if you have free memory.
Use the --skip-external-locking MySQL option to avoid external locking. Note that this will not impact MySQL's functionality as long as you only run one server. Just remember to take down the server (or lock and flush the relevant tables) before you run myisamchk. On some systems this option is mandatory, because the external locking does not work in any case.
The --skip-external-locking option is on by default as of MySQL 4.0. Before that, it is on by default when compiling with MIT-pthreads, because flock() isn't fully supported by MIT-pthreads on all platforms. It's also on default for Linux as Linux file locking are not yet safe.
The only case when you can't use --skip-external-locking is if you run multiple MySQL servers (not clients) on the same data, or if you run myisamchk on the table without telling the server to flush and lock the tables first.
You can still use LOCK TABLES/UNLOCK TABLES even if you are using --skip-external-locking.
You can determine the default buffer sizes used by the mysqld server with this command:
shell> mysqld --help
This command produces a list of all mysqld options and configurable variables. The output includes the default variable values and looks something like this:
back_log current value: 5 bdb_cache_size current value: 1048540 binlog_cache_size current value: 32768 connect_timeout current value: 5 delayed_insert_timeout current value: 300 delayed_insert_limit current value: 100 delayed_queue_size current value: 1000 flush_time current value: 0 interactive_timeout current value: 28800 join_buffer_size current value: 131072 key_buffer_size current value: 1048540 lower_case_table_names current value: 0 long_query_time current value: 10 max_allowed_packet current value: 1048576 max_binlog_cache_size current value: 4294967295 max_connections current value: 100 max_connect_errors current value: 10 max_delayed_threads current value: 20 max_heap_table_size current value: 16777216 max_join_size current value: 4294967295 max_sort_length current value: 1024 max_tmp_tables current value: 32 max_write_lock_count current value: 4294967295 myisam_sort_buffer_size current value: 8388608 net_buffer_length current value: 16384 net_retry_count current value: 10 net_read_timeout current value: 30 net_write_timeout current value: 60 read_buffer_size current value: 131072 read_rnd_buffer_size current value: 262144 slow_launch_time current value: 2 sort_buffer current value: 2097116 table_cache current value: 64 thread_concurrency current value: 10 tmp_table_size current value: 1048576 thread_stack current value: 131072 wait_timeout current value: 28800
If there is a mysqld server currently running, you can see what values it actually is using for the variables by issuing this statement:
mysql> SHOW VARIABLES;
You can also see some statistics and status indicators for a running server by issuing this statement:
mysql> SHOW STATUS;
You can find a full description for all variables in the SHOW VARIABLES section in this manual. See SHOW VARIABLES. For information about status variables, see SHOW STATUS.
Server variable and status information also can be obtained using mysqladmin:
shell> mysqladmin variables shell> mysqladmin extended-status
MySQL uses algorithms that are very scalable, so you can usually run with very little memory. However, if you give MySQL more memory, normally you will also get better performance.
When tuning a MySQL server, the two most important variables to use are key_buffer_size and table_cache. You should first feel confident that you have these set appropriately before trying to change any other variables.
The following examples indicate some typical variable values for different runtime configurations. The examples use the mysqld_safe script and use --name=value syntax to set the variable name to the value value. This syntax is available as of MySQL 4.0. For older versions of MySQL, take the following differences into account:
Use safe_mysqld rather than mysqld_safe.
Set variables using --set-variable=name=value or -O name=value syntax.
For variable names that end in _size, you may need to specify them without _size. For example, the old name for sort_buffer_size is sort_buffer. The old name for read_buffer_size is record_buffer. To see which variables your version of the server recognizes, use mysqld --help.
If you have at least 256M of memory and many tables and want maximum performance with a moderate number of clients, you should use something like this:
shell> mysqld_safe --key_buffer_size=64M --table_cache=256 \ --sort_buffer_size=4M --read_buffer_size=1M &
If you have only 128M of memory and only a few tables, but you still do a lot of sorting, you can use something like:
shell> mysqld_safe --key_buffer_size=16M --sort_buffer_size=1M
If you have little memory and lots of connections, use something like this:
shell> mysqld_safe --key_buffer_size=512K --sort_buffer_size=100K \ --read_buffer_size=100K &
Or even this:
shell> mysqld_safe --key_buffer_size=512K --sort_buffer_size=16K \ --table_cache=32 --read_buffer_size=8K -O net_buffer_length=1K &
If you are doing a GROUP BY or ORDER BY on tables that are much larger than your available memory, you should increase the value of read_rnd_buffer_size to speed up the reading of rows after sorting operations.
When you have installed MySQL, the support-files directory will contain some different my.cnf example files, my-huge.cnf, my-large.cnf, my-medium.cnf, and my-small.cnf, you can use as a base to optimize your system.
If there are very many simultaneous connections, swapping problems may occur unless mysqld has been configured to use very little memory for each connection. mysqld performs better if you have enough memory for all connections.
Note that if you specicy an option on the command line for mysqld or mysqld_safe, it remains in effect only for that invocation of the server. To use the option every time the server runs, put it in an option file.
To see the effects of a parameter change, do something like this:
shell> mysqld --key_buffer_size=32m --help
Make sure that the --help option is last; otherwise, the effect of any options listed after it on the command line will not be reflected in the output.
Most of the following tests are done on Linux with the MySQL benchmarks, but they should give some indication for other operating systems and workloads.
You get the fastest executable when you link with -static.
On Linux, you will get the fastest code when compiling with pgcc and -O3. To compile sql_yacc.cc with these options, you need about 200M memory because gcc/pgcc needs a lot of memory to make all functions inline. You should also set CXX=gcc when configuring MySQL to avoid inclusion of the libstdc++ library (it is not needed). Note that with some versions of pgcc, the resulting code will run only on true Pentium processors, even if you use the compiler option that you want the resulting code to be working on all x586 type processors (like AMD).
By just using a better compiler and/or better compiler options you can get a 10-30% speed increase in your application. This is particularly important if you compile the SQL server yourself!
We have tested both the Cygnus CodeFusion and Fujitsu compilers, but when we tested them, neither was sufficiently bug free to allow MySQL to be compiled with optimizations on.
When you compile MySQL you should only include support for the character sets that you are going to use. (Option --with-charset=xxx.) The standard MySQL binary distributions are compiled with support for all character sets.
Here is a list of some measurements that we have done:
If you use pgcc and compile everything with -O6, the mysqld server is 1% faster than with gcc 2.95.2.
If you link dynamically (without -static), the result is 13% slower on Linux. Note that you still can use a dynamic linked MySQL library for your client applications. It is the server that is most critical for performance.
If you strip your mysqld binary with strip libexec/mysqld, the resulting binary can be up to 4% faster.
For a connection from a client to a server running on the same host, if you connect using TCP/IP rather than a Unix socket file, performance is 7.5% slower. (If you connect to the hostname localhost, MySQL uses a socket file by default.)
For TCP/IP connections from a client to a server, connecting to a remote server on another host will be 8-11% slower than connecting to the local server on the same host, even for connections over 100M Ethernet.
When running our benchmark tests using secure connections (all data encrypted with internal SSL support) performance was 55% slower.
If you compile with --with-debug=full, most queries will be 20% slower. Some queries may take substantially longer (for example, the MySQL benchmarks ran 35% slower). If you use --with-debug, the slowdown will be only 15%. For a mysqld version that has been compiled with --with-debug=full, you can disable memory checking at runtime by starting it with the --skip-safemalloc option. The end result in this case should be close to when configuring with --with-debug.
On a Sun UltraSPARC-IIe, Forte 5.0 is 4% faster than gcc 3.2.
On a Sun UltraSPARC-IIe, Forte 5.0 is 4% faster in 32-bit mode than in 64-bit mode.
Compiling with gcc 2.95.2 for UltraSPARC with the option -mcpu=v8 -Wa,-xarch=v8plusa gives 4% more performance.
On Solaris 2.5.1, MIT-pthreads is 8-12% slower than Solaris native threads on a single processor. With more load/CPUs the difference should be larger.
Running with --log-bin makes mysqld 1% slower.
Compiling on Linux-x86 using gcc without frame pointers -fomit-frame-pointer or -fomit-frame-pointer -ffixed-ebp makes mysqld 1-4% faster.
The MySQL-Linux distribution provided by MySQL AB used to be compiled with pgcc, but we had to go back to regular gcc because of a bug in pgcc that would generate the code that does not run on AMD. We will continue using gcc until that bug is resolved. In the meantime, if you have a non-AMD machine, you can get a faster binary by compiling with pgcc. The standard MySQL Linux binary is linked statically to make it faster and more portable.
The following list indicates some of the ways that the mysqld server uses memory. Where applicable, the name of the server variable relevant to the memory use is given:
The key buffer (variable key_buffer_size) is shared by all threads; other buffers used by the server are allocated as needed. See Server parameters.
Each connection uses some thread-specific space: A stack (default 64K, variable thread_stack), a connection buffer (variable net_buffer_length), and a result buffer (variable net_buffer_length). The connection buffer and result buffer are dynamically enlarged up to max_allowed_packet when needed. When a query is running, a copy of the current query string is also allocated.
All threads share the same base memory.
Only compressed ISAM and MyISAM tables are memory mapped. This is because the 32-bit memory space of 4 GB is not large enough for most big tables. When systems with a 64-bit address space become more common we may add general support for memory mapping.
Each request doing a sequential scan over a table allocates a read buffer (variable read_buffer_size).
When reading rows in ``random'' order (for example, after a sort) a random-read buffer is allocated to avoid disk seeks. (variable read_rnd_buffer_size).
All joins are done in one pass, and most joins can be done without even using a temporary table. Most temporary tables are memory-based (HEAP) tables. Temporary tables with a large record length (calculated as the sum of all column lengths) or that contain BLOB columns are stored on disk.
One problem in MySQL before Version 3.23.2 is that if an in-memory HEAP table exceeds the size of tmp_table_size, you get the error The table tbl_name is full. From 3.23.2 on, this is handled automatically by changing the in-memory HEAP table to a disk-based MyISAM table as necessary. To work around this problem, you can increase the temporary table size by setting the tmp_table_size option to mysqld, or by setting the SQL option BIG_TABLES in the client program. See SET Syntax. In MySQL Version 3.20, the maximum size of the temporary table is record_buffer*16; if you are using this version, you have to increase the value of record_buffer. You can also start mysqld with the --big-tables option to always store temporary tables on disk. However, this will affect the speed of many complicated queries.
Most requests that perform a sort allocate a sort buffer and 0 to 2 temporary files depending on the result set size. See Temporary files.
Almost all parsing and calculating is done in a local memory store. No memory overhead is needed for small items and the normal slow memory allocation and freeing is avoided. Memory is allocated only for unexpectedly large strings; this is done with malloc() and free().
Each index file is opened once and the datafile is opened once for each concurrently running thread. For each concurrent thread, a table structure, column structures for each column, and a buffer of size 3 * n is allocated (where n is the maximum row length, not counting BLOB columns). A BLOB column uses 5 to 8 bytes plus the length of the BLOB data. The ISAM and MyISAM storage engines use one extra row buffer for internal usage.
For each table having BLOB columns, a buffer is enlarged dynamically to read in larger BLOB values. If you scan a table, a buffer as large as the largest BLOB value is allocated.
Handler structures for all in-use tables are saved in a cache and managed as a FIFO. Normally the cache has 64 entries. If a table has been used by two running threads at the same time, the cache contains two entries for the table. See Table cache.
A mysqladmin flush-tables command (or FLUSH TABLES statement) closes all tables that are not in use and marks all in-use tables to be closed when the currently executing thread finishes. This will effectively free most in-use memory.
ps and other system status programs may report that mysqld uses a lot of memory. This may be caused by thread-stacks on different memory addresses. For example, the Solaris version of ps counts the unused memory between stacks as used memory. You can verify this by checking available swap with swap -s. We have tested mysqld with commercial memory-leakage detectors, so there should be no memory leaks.
When a new client connects to mysqld, mysqld spawns a new thread to handle the request. This thread first checks if the hostname is in the hostname cache. If not, the thread attempts to resolve the hostname:
If the operating system supports the thread-safe gethostbyaddr_r() and gethostbyname_r() calls, the thread uses them to perform hostname resolution.
If the operating system doesn't support the thread-safe calls, the thread locks a mutex and calls gethostbyaddr() and gethostbyname() instead. Note that in this case no other thread can resolve hostnames that are not in the hostname cache until the first thread unlocks the mutex.
You can disable DNS hostname lookups by starting mysqld with the --skip-name-resolve option. However, in this case you can use only IP numbers in the MySQL grant tables.
If you have a very slow DNS and many hosts, you can get more performance by either disabling DNS lookups with --skip-name-resolve or by increasing the HOST_CACHE_SIZE define (default value: 128) and recompiling mysqld.
You can disable the hostname cache by starting the server with the --skip-host-cache option. To clear the hostname cache, issue a FLUSH HOSTS statement or execute the mysqladmin flush-hosts command.
If you want to disallow TCP/IP connections entirely, start mysqld with the --skip-networking option.
SET [GLOBAL | SESSION] sql_variable=expression, [[GLOBAL | SESSION] sql_variable=expression] ...
SET sets various options that affect the operation of the server or your client.
The following examples shows the different syntaxes one can use to set variables:
In old MySQL versions we allowed the use of the SET OPTION syntax, but this syntax is now deprecated.
In MySQL 4.0.3 we added the GLOBAL and SESSION options and access to most important startup variables.
LOCAL can be used as a synonym for SESSION.
If you set several variables on the same command line, the last used GLOBAL | SESSION mode is used.
SET sort_buffer_size=10000; SET @@local.sort_buffer_size=10000; SET GLOBAL sort_buffer_size=1000000, SESSION sort_buffer_size=1000000; SET @@sort_buffer_size=1000000; SET @@global.sort_buffer_size=1000000, @@local.sort_buffer_size=1000000;
The @@variable_name syntax is supported to make MySQL syntax compatible with some other databases.
The different system variables you can set are described in the system variable section of this manual. See System Variables.
If you are using SESSION (the default), the option you set remains in effect until the current session ends or until you set the option to a different value. If you use GLOBAL, which requires the SUPER privilege, the option is remembered and used for new connections until the server restarts. If you want to make an option permanent, you should set it in an option file. See Option files.
To avoid incorrect usage, MySQL will produce an error if you use SET GLOBAL with a variable that can only be used with SET SESSION or if you are not using SET GLOBAL with a global variable.
If you want to set a SESSION variable to the GLOBAL value or a GLOBAL value to the MySQL default value, you can set it to DEFAULT.
SET max_join_size=DEFAULT;
This is identical to:
SET @@session.max_join_size=@@global.max_join_size;
If you want to restrict the maximum value to which a server variable can be set with the SET command, you can specify this maximum by using the --maximum-variable-name command line option. See Server options.
You can get a list of most variables with SHOW VARIABLES. See SHOW VARIABLES. You can get the value for a specific value with the @@[global.|local.]variable_name syntax:
SHOW VARIABLES like "max_join_size"; SHOW GLOBAL VARIABLES like "max_join_size"; SELECT @@max_join_size, @@global.max_join_size;
Here follows a description of the variables that use a non-standard SET syntax and some of the other variables. The other variable definitions can be found in the system variable section, among the startup options or in the description of SHOW VARIABLES. See System Variables. See Server options. See SHOW VARIABLES.
AUTOCOMMIT= 0 | 1 | If set to 1, all changes to a table will be done at once. To start a multi-command transaction, you have to use the BEGIN statement. See COMMIT. If set to 0 you have to use COMMIT to accept that transaction or ROLLBACK to cancel it. See COMMIT. Note that when you change AUTOCOMMIT mode from 0 to 1, MySQL performs an automatic COMMIT of any open transaction. | |||||||||
BIG_TABLES = 0 | 1 | If set to 1, all temporary tables are stored on disk rather than in memory. This will be a little slower, but you will not get the error The table tbl_name is full for big SELECT operations that require a large temporary table. The default value for a new connection is 0 (that is, use in-memory temporary tables). This variable previously was named SQL_BIG_TABLES. In MySQL 4.0, you should normally never need to set this variable, because MySQL automatically converts in-memory tables to disk-based tables as necessary. | |||||||||
CHARACTER SET character_set_name | DEFAULT | This maps all strings from and to the client with the given mapping. Currently the only option for character_set_name is cp1251_koi8, but you can easily add new mappings by editing the sql/convert.cc file in the MySQL source distribution. The default mapping can be restored by using a character_set_name value of DEFAULT. Note that the syntax for setting the CHARACTER SET option differs from the syntax for setting the other options. | |||||||||
INSERT_ID = # | Set the value to be used by the following INSERT or ALTER TABLE command when inserting an AUTO_INCREMENT value. This is mainly used with the binary log. | |||||||||
LAST_INSERT_ID = # | Set the value to be returned from LAST_INSERT_ID(). This is stored in the binary log when you use LAST_INSERT_ID() in a command that updates a table. Setting this variable does not update mysql_insert_id(). | |||||||||
LOW_PRIORITY_UPDATES = 0 | 1 | If set to 1, all INSERT, UPDATE, DELETE, and LOCK TABLE WRITE statements wait until there is no pending SELECT or LOCK TABLE READ on the affected table. This variable previously was named SQL_LOW_PRIORITY_UPDATES. | |||||||||
MAX_JOIN_SIZE = value | DEFAULT | Don't allow SELECT statements that will probably need to examine more than value row combinations or is likely to do more than value disk seeks. By setting this value, you can catch SELECT statements where keys are not used properly and that would probably take a long time. Setting this to a value other than DEFAULT resets the SQL_BIG_SELECTS value to 0. If you set the SQL_BIG_SELECTS value again, the SQL_MAX_JOIN_SIZE variable will be ignored. You can set a default value for this variable by starting mysqld with the --max_join_size=value option. This variable previously was named SQL_MAX_JOIN_SIZE. Note that if a query result already is in the query cache, no result size check is performed, because the result has already been computed and it will not burden the server to send it to the client. | |||||||||
PASSWORD = PASSWORD('some password') | Set the password for the current user. Any non-anonymous user can change his own password! | |||||||||
PASSWORD FOR user = PASSWORD('some password') |
Set the password for a specific user on the current server host. Only a user
with access to the mysql database can do this. The user should be
given in user@hostname format, where user and hostname
are exactly as they are listed in the User and Host columns of
the mysql.user table entry. For example, if you had an entry with
User and Host fields of 'bob' and '%.loc.gov',
you would write:
mysql> SET PASSWORD FOR 'bob'@'%.loc.gov' = PASSWORD('newpass');Which is equivalent to: mysql> UPDATE mysql.user SET Password=PASSWORD('newpass') -> WHERE User='bob' AND Host='%.loc.gov'; mysql> FLUSH PRIVILEGES; | |||||||||
QUERY_CACHE_TYPE = OFF | ON | DEMAND , QUERY_CACHE_TYPE = 0 | 1 | 2 | Set query cache setting for this thread. |
| ||||||||
SQL_AUTO_IS_NULL = 0 | 1 | If set to 1 (default), you can find the last inserted row for a table that contains an AUTO_INCREMENT column by using the following construct: WHERE auto_increment_column IS NULL. This is used by some ODBC programs like Access. | |||||||||
SQL_BIG_SELECTS = 0 | 1 | If set to 0, MySQL aborts SELECT statements that probably will take a very long time (that is, statements for which the optimizer estimates that the number of of examined rows probably will exceed the value of MAX_JOIN_SIZE). This is useful when an inadvisable WHERE statement has been issued. The default value for a new connection is 1, which allows all SELECT statements. If you set MAX_JOIN_SIZE to a value other than DEFAULT, SQL_BIG_SELECTS will be set to 0. | |||||||||
SQL_BUFFER_RESULT = 0 | 1 | SQL_BUFFER_RESULT forces the result from SELECT statements to be put into a temporary table. This will help MySQL free the table locks early and will help in cases where it takes a long time to send the result set to the client. | |||||||||
SQL_LOG_BIN = 0 | 1 | If set to 0, no logging is done to the binary log for the client, if the client has the SUPER privilege. | |||||||||
SQL_LOG_OFF = 0 | 1 | If set to 1, no logging is done to the standard log for this client, if the client has the SUPER privilege. | |||||||||
SQL_LOG_UPDATE = 0 | 1 | If set to 0, no logging is done to the update log for the client, if the client has the SUPER privilege. This variable is deprecated starting from version 5.0.0 and mapped to SQL_LOG_BIN (see News-5.0.0). | |||||||||
SQL_QUOTE_SHOW_CREATE = 0 | 1 | If set to 1, SHOW CREATE TABLE quotes table and column names. This is on by default, so that replication of tables with fancy column names will work. SHOW CREATE TABLE. | |||||||||
SQL_SAFE_UPDATES = 0 | 1 | If set to 1, MySQL aborts UPDATE or DELETE statements that do not use a key or LIMIT in the WHERE clause. This makes it possible to catch wrong updates when creating SQL statements by hand. | |||||||||
SQL_SELECT_LIMIT = value | DEFAULT | The maximum number of records to return from SELECT statements. If a SELECT has a LIMIT clause, the LIMIT takes precedence over the value of SQL_SELECT_LIMIT. The default value for a new connection is ``unlimited.'' If you have changed the limit, the default value can be restored by using a SQL_SELECT_LIMIT value of DEFAULT. | |||||||||
TIMESTAMP = timestamp_value | DEFAULT | Set the time for this client. This is used to get the original timestamp if you use the binary log to restore rows. timestamp_value should be a Unix epoch timestamp, not a MySQL timestamp. |
Table of Contents
As mentioned before, disks seeks are a big performance bottleneck. This problems gets more and more apparent when the data starts to grow so large that effective caching becomes impossible. For large databases, where you access data more or less randomly, you can be sure that you will need at least one disk seek to read and a couple of disk seeks to write things. To minimise this problem, use disks with low seek times.
Increase the number of available disk spindles (and thereby reduce the seek overhead) by either symlink files to different disks or striping the disks.
Using symbolic links | This means that, for MyISAM tables, you symlink the index file and/or datafile from their usual location in the data directory to another disk (that may also be striped). This makes both the seek and read times better, assuming the disk is not used for other purposes as well). See Symbolic links. |
Striping | Striping means that you have many disks and put the first block on the first disk, the second block on the second disk, and the Nth on the (N mod number_of_disks) disk, and so on. This means if your normal data size is less than the stripe size (or perfectly aligned) you will get much better performance. Striping is very dependent on the operating system and the stripe size, so benchmark your application with different stripe sizes. See Custom Benchmarks. Note that the speed difference for striping is very dependent on the parameters. Depending on how you set the striping parameters and number of disks you may get a difference in orders of magnitude. Note that you have to choose to optimize for random or sequential access. |
For reliability you may want to use RAID 0+1 (striping + mirroring), but in this case you will need 2*N drives to hold N drives of data. This is probably the best option if you have the money for it! However, you may also have to invest in some volume-management software to handle it efficiently.
A good option is to vary the RAID level according to how critical a type of data is. For example, have semi-important data that can be regenerated on a RAID 0 disk while storing really important data such as host information and logs on a RAID 0+1 or RAID N disk. RAID N can be a problem if you have many writes because of the time to update the parity bits.
On Linux, you can get much more performance (up to 100% under load is not uncommon) by using hdparm to configure your disk's interface! The following should be quite good hdparm options for MySQL (and probably many other applications):
hdparm -m 16 -d 1
Note that performance and reliability when using the above depends on your hardware, so we strongly suggest that you test your system thoroughly after using hdparm. Please consult the hdparm man page for more information. If hdparm is not used wisely, filesystem corruption may result, so back up everything before experimenting!
You may also set the parameters for the filesystem that the database uses:
If you don't need to know when files were last accessed (which is not really useful on a database server), you can mount your filesystems with the -o noatime option. That skips updates to the last access time in inodes on the filesystem, which avoids some disk seeks.
On many operating systems you can mount the disks with the -o async option to set the filesystem to be updated asynchronously. If your computer is reasonably stable, this should give you more performance without sacrificing too much reliability. (This flag is on by default on Linux.)
You can move tables and databases from the database directory to other locations and replace them with symbolic links to the new locations. You might want to do this, for example, to move a database to a file system with more free space or increase the speed of your system by spreading your tables to different disk.
The recommended way to do this is to just symlink databases to a different disk and only symlink tables as a last resort.
On Unix, the way to symlink a database is to first create a directory on some disk where you have free space and then create a symlink to it from the MySQL database directory.
shell> mkdir /dr1/databases/test shell> ln -s /dr1/databases/test mysqld-datadir
MySQL doesn't support that you link one directory to multiple databases. Replacing a database directory with a symbolic link will work fine as long as you don't make a symbolic link between databases. Suppose you have a database db1 under the MySQL data directory, and then make a symlink db2 that points to db1:
shell> cd /path/to/datadir shell> ln -s db1 db2
Now, for any table tbl_a in db1, there also appears to be a table tbl_a in db2. If one thread updates db1.tbl_a and another thread updates db2.tbl_a, there will be problems.
If you really need this, you must change the following code in mysys/mf_format.c:
if (flag & 32 || (!lstat(to,&stat_buff) && S_ISLNK(stat_buff.st_mode)))
to
if (1)
On Windows you can use internal symbolic links to directories by compiling MySQL with -DUSE_SYMDIR. This allows you to put different databases on different disks. See Windows symbolic links.
Before MySQL 4.0 you should not symlink tables unless you are very careful with them. The problem is that if you run ALTER TABLE, REPAIR TABLE, or OPTIMIZE TABLE on a symlinked table, the symlinks will be removed and replaced by the original files. This happens because these statements work by creating a temporary file in the database directory and replacing the original file with the temporary file when the statement operation is complete.
You should not symlink tables on systems that don't have a fully working realpath() call. (At least Linux and Solaris support realpath()). You can check if your system supports symbolic links by doing SHOW VARIABLES LIKE 'have_symlink'.
In MySQL 4.0, symlinks are fully supported only for MyISAM tables. For other table types, you will probably get strange problems if you try to use symbolic links on files in the operating system with any of the above commands.
The handling of symbolic links for MyISAM tables in MySQL 4.0 works the following way:
In the data directory you will always have the table definition file, the datafile, and the index files The datafile and index file can be moved elsewhere and replaced in the data directory by symlinks. The definition file cannot.
You can symlink the datafile and the index file to different directories independently of the other.
The symlinking can be done at the operating system level (if mysqld is not running) or with SQL by using the DATA DIRECTORY and INDEX DIRECTORY options to CREATE TABLE. See CREATE TABLE.
myisamchk will not replace a symlink with the datafile or index file. It works directly on the file a symlink points to. Any temporary files will be created in the same directory where the datafile or index file is located.
When you drop a table that is using symlinks, both the symlink and the file the symlink points to are dropped. This is a good reason to why you should not run mysqld as root or allow persons to have write access to the MySQL database directories.
If you rename a table with ALTER TABLE RENAME and you don't move the table to another database, the symlinks in the database directory are renamed to the new names and the datafile and index file are renamed accordingly.
If you use ALTER TABLE RENAME to move a table to another database, the table is moved to the other database directory and the old symlinks and the files to which they pointed are deleted. (In other words, the new table will not be symlinked.)
If you are not using symlinks, you should use the --skip-symlink option to mysqld to ensure that no one can use mysqld to drop or rename a file outside of the data directory.
SHOW CREATE TABLE doesn't report if the table has symbolic links prior to MySQL 4.0.15. This is also true for mysqldump, which uses SHOW CREATE TABLE to generate CREATE TABLE statements.
Things that are not yet supported:
ALTER TABLE ignores the DATA DIRECTORY and INDEX DIRECTORY table options.
BACKUP TABLE and RESTORE TABLE don't respect symbolic links.
The frm file must never be a symbolic link (as said previously, only the data and index files can be symbolic links). Doing this (for example to make synonyms), will produce incorrect results. Suppose you have a database db1 under the MySQL data directory, a table tbl1 in this database, and in the db1 directory you make a symlink tbl2 that points to tbl1:
shell> cd /path/to/datadir/db1 shell> ln -s tbl1.frm tbl2.frm shell> ln -s tbl1.MYD tbl2.MYD shell> ln -s tbl1.MYI tbl2.MYI
Now if one thread reads db1.tbl1 and another thread updates db1.tbl2, there will be problems: the query cache will be fooled (it will believe tbl1 has not been updated so will return out-of-date results), the ALTER commands on tbl2 will also fail.
Beginning with MySQL Version 3.23.16, the mysqld-max and mysql-max-nt servers in the MySQL distribution are compiled with the -DUSE_SYMDIR option. This allows you to put a database directory on a different disk by setting up a symbolic link to it. This is similar to the way that symbolic links work on Unix, though the procedure for setting up the link is different.
On Windows, you make a symbolic link to a MySQL database by creating a file that contains the path to the destination directory. Save the file in the data directory using the filename db_name.sym, where db_name is the database name.
For example, if the MySQL data directory is C:\mysql\data and you want to have database foo located at D:\data\foo, you should create the file C:\mysql\data\foo.sym that contains the pathname D:\data\foo\. After that, all tables created in the database foo will be created in D:\data\foo. The D:\data\foo directory must exist for this to work. Also, note that the symbolic link will not be used if a directory with the database name exists in the MySQL data directory. This means that if you already have a database directory named foo in the data directory, you must move it to D:\data before the symbolic link will be effective. (To avoid problems, the server should not be running when you move the database directory.)
Note that because of the speed penalty you get when opening every table, we have not enabled this by default even if you have compiled MySQL with support for this. To enable symlinks you should put in your my.cnf or my.ini file the following entry:
[mysqld] symbolic-links
In MySQL 4.0, symbolic links are enabled by default. If you don't need them, you can disable them with the skip-symbolic-links option.
Table of Contents
All MySQL clients that communicate with the server using the mysqlclient library use the following environment variables:
Name | Description |
MYSQL_UNIX_PORT | The default socket; used for connections to localhost |
MYSQL_TCP_PORT | The default TCP/IP port |
MYSQL_PWD | The default password |
MYSQL_DEBUG | Debug-trace options when debugging |
TMPDIR | The directory where temporary tables/files are created |
Use of MYSQL_PWD is insecure. See Connecting.
On Unix, the mysql client uses the file named in the MYSQL_HISTFILE environment variable to save the command-line history. The default value for the history file is $HOME/.mysql_history, where $HOME is the value of the HOME environment variable. See Environment variables.
If you do not want to maintain a file that contains a record of your queries, first remove .mysql_history if it exists, then use either of the following techniques:
Set the MYSQL_HISTFILE variable to /dev/null. To cause this setting to take effect each time you log in, put the setting in one of your shell's startup files.
Create .mysql_histfile as a symbolic link to /dev/null:
shell> ln -s /dev/null $HOME/.mysql_history
You need do this only once.
All MySQL programs take many different options. However, every MySQL program provides a --help option that you can use to get a full description of the program's different options. For example, try mysql --help.
You can override default options for all standard programs by specifying options on the command line or in an option file. Program Options.
The following list briefly describes the MySQL client programs and utilities:
msql2mysql | A shell script that converts mSQL programs to MySQL. It doesn't handle all cases, but it gives a good start when converting. |
mysql | The command-line tool for interactively entering queries or executing queries from a file in batch mode. See mysql. |
mysqlcc | This program provides a graphical interface for interacting with the server. See mysqlcc. |
mysqlaccess | A script that checks the access privileges for a host, user, and database combination. |
mysqladmin | Utility for performing administrative operations, such as creating or dropping databases, reloading the grant tables, flushing tables to disk, and reopening log files. mysqladmin can also be used to retrieve version, process, and status information from the server. See mysqladmin. |
mysqlbinlog | Utility for reading queries from a binary log. Can be used to recover from a crash with an old backup. See mysqlbinlog. |
mysqldump | Dumps a MySQL database into a file as SQL statements or as tab-separated text files. Enhanced freeware originally by Igor Romanenko. See mysqldump. |
mysqlimport | Imports text files into their respective tables using LOAD DATA INFILE. See mysqlimport. |
mysqlshow | Displays information about databases, tables, columns, and indexes. |
replace |
A utility program that is used by msql2mysql, but that has more
general applicability as well. replace changes strings in place in
files or on the standard input. Uses a finite state machine to match longer
strings first. Can be used to swap strings. For example, this command
swaps a and b in the given files:
shell> replace a b b a -- file1 file2 ... |
Table of Contents
mysql is a simple SQL shell (with GNU readline capabilities). It supports interactive and non-interactive use. When used interactively, query results are presented in an ASCII-table format. When used non-interactively (for example, as a filter), the result is presented in tab-separated format. (The output format can be changed using command-line options.) You can run scripts simply like this:
shell> mysql database < script.sql > output.tab
If you have problems due to insufficient memory in the client, use the --quick option! This forces mysql to use mysql_use_result() rather than mysql_store_result() to retrieve the result set.
Using mysql is very easy. Just start it as follows: mysql database or mysql --user=user_name --password=your_password database. Type an SQL statement, end it with ;, \g, or \G and press Enter.
mysql supports the following options:
You can also set the following variables with -O or --set-variable. Please note that --set-variable=name=value and -O name=value syntax is deprecated as of MySQL 4.0. Use --name=value instead.
Variable Name | Default | Description |
connect_timeout | 0 | Number of seconds before connection timeout. |
local-infile | 0 | Disable (0) or enable (1) LOCAL capability for LOAD DATA INFILE |
max_allowed_packet | 16777216 | Max packet length to send to/receive from server |
net_buffer_length | 16384 | Buffer for TCP/IP and socket communication |
select_limit | 1000 | Automatic limit for SELECT when using --safe-updates |
max_join_size | 1000000 | Automatic limit for rows in a join when using --safe-updates |
If the mysql client loses connection to the server while sending it a query, it will immediately and automatically try to reconnect once to the server and send the query again. Note that even if it succeeds in reconnecting, as your first connection has ended, all your previous session objects are lost: temporary tables, user and session variables. Therefore, the above behavior may be dangerous for you, as in this example where the server was shut down and restarted without you knowing it:
mysql> SET @a=1; Query OK, 0 rows affected (0.05 sec) mysql> INSERT INTO t VALUES(@a); ERROR 2006: MySQL server has gone away No connection. Trying to reconnect... Connection id: 1 Current database: test Query OK, 1 row affected (1.30 sec) mysql> SELECT * FROM t; +------+ | a | +------+ | NULL | +------+ 1 row in set (0.05 sec)
The @a user variable has been lost with the connection, and after the reconnection it is undefined. To protect from this risk, you can start the mysql client with the --disable-reconnect option.
If you type 'help' on the command-line, mysql will print out the commands that it supports:
mysql> help MySQL commands: help (\h) Display this text. ? (\h) Synonym for `help'. clear (\c) Clear command. connect (\r) Reconnect to the server. Optional arguments are db and host. delimiter (\d) Set query delimiter. edit (\e) Edit command with $EDITOR. ego (\G) Send command to mysql server, display result vertically. exit (\q) Exit mysql. Same as quit. go (\g) Send command to mysql server. nopager (\n) Disable pager, print to stdout. notee (\t) Don't write into outfile. pager (\P) Set PAGER [to_pager]. Print the query results via PAGER. print (\p) Print current command. prompt (\R) Change your mysql prompt. quit (\q) Quit mysql. rehash (\#) Rebuild completion hash. source (\.) Execute an SQL script file. Takes a file name as an argument. status (\s) Get status information from the server. system (\!) Execute a system shell command. tee (\T) Set outfile [to_outfile]. Append everything into given outfile. use (\u) Use another database. Takes database name as argument.
The edit, nopager, pager, and system commands work only in Unix.
The status command gives you some information about the connection and the server you are using. If you are running in the --safe-updates mode, status will also print the values for the mysql variables that affect your queries.
A useful startup option for beginners (introduced in MySQL Version 3.23.11) is --safe-updates (or --i-am-a-dummy for users that once may have done a DELETE FROM table_name but forgot the WHERE clause). When using this option, mysql sends the following command to the MySQL server when opening the connection:
SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=#select_limit#, SQL_MAX_JOIN_SIZE=#max_join_size#"
where #select_limit# and #max_join_size# are variables that can be set from the mysql command-line. See SET.
The effect of the above is:
You are not allowed to do an UPDATE or DELETE statement if you don't have a key constraint in the WHERE part. One can, however, force an UPDATE/DELETE by using LIMIT:
UPDATE table_name SET not_key_column=# WHERE not_key_column=# LIMIT 1;
All big results are automatically limited to #select_limit# rows.
SELECT statements that will probably need to examine more than #max_join_size row combinations will be aborted.
Some useful hints about the mysql client:
Some data is much more readable when displayed vertically, instead of the usual horizontal box type output. For example longer text, which includes new lines, is often much easier to be read with vertical output.
mysql> SELECT * FROM mails WHERE LENGTH(txt) < 300 lIMIT 300,1\G *************************** 1. row *************************** msg_nro: 3068 date: 2000-03-01 23:29:50 time_zone: +0200 mail_from: Monty reply: monty@no.spam.com mail_to: "Thimble Smith" <tim@no.spam.com> sbj: UTF-8 txt: >>>>> "Thimble" == Thimble Smith writes: Thimble> Hi. I think this is a good idea. Is anyone familiar with UTF-8 Thimble> or Unicode? Otherwise, I'll put this on my TODO list and see what Thimble> happens. Yes, please do that. Regards, Monty file: inbox-jani-1 hash: 190402944 1 row in set (0.09 sec)
For logging, you can use the tee option. The tee can be started with option --tee=..., or from the command-line interactively with command tee. All the data displayed on the screen will also be appended into a given file. This can be very useful for debugging purposes also. The tee can be disabled from the command-line with command notee. Executing tee again starts logging again. Without a parameter the previous file will be used. Note that tee will flush the results into the file after each command, just before the command-line appears again waiting for the next command.
Browsing, or searching the results in the interactive mode in Unix less, more, or any other similar program, is now possible with option --pager[=...]. Without argument, mysql client will look for the PAGER environment variable and set pager to that. pager can be started from the interactive command-line with command pager and disabled with command nopager. The command takes an argument optionally and the pager will be set to that. Command pager can be called without an argument, but this requires that the option --pager was used, or the pager will default to stdout. pager works only in Unix, since it uses the popen() function, which doesn't exist in Windows. In Windows, the tee option can be used instead, although it may not be as handy as pager can be in some situations.
A few tips about pager:
You can use it to write to a file:
mysql> pager cat > /tmp/log.txt
and the results will go only to a file. You can also pass any options for the programs that you want to use with the pager:
mysql> pager less -n -i -S
From the above do note the option -S. You may find it very useful when browsing the results; try the option with horizontal output (end commands with \g, or ;) and with vertical output (end commands with \G). Sometimes a very wide result set is hard to be read from the screen, with option -S to less you can browse the results within the interactive less from left to right, preventing lines longer than your screen from being continued to the next line. This can make the result set much more readable. You can switch the mode between on and off within the interactive less with -S. See the 'h' for more help about less.
You can combine very complex ways to handle the results, for example the following would send the results to two files in two different directories, on two different hard-disks mounted on /dr1 and /dr2, yet let the results still be seen on the screen via less:
mysql> pager cat | tee /dr1/tmp/res.txt | \ tee /dr2/tmp/res2.txt | less -n -i -S
You can also combine the two functions above; have the tee enabled, pager set to 'less' and you will be able to browse the results in Unix 'less' and still have everything appended into a file the same time. The difference between Unix tee used with the pager and the mysql client in-built tee, is that the in-built tee works even if you don't have the Unix tee available. The in-built tee also logs everything that is printed on the screen, where the Unix tee used with pager doesn't log quite that much. Last, but not least, the interactive tee is more handy to switch on and off, when you want to log something into a file, but want to be able to turn the feature off sometimes.
From MySQL version 4.0.2 it is possible to change the prompt in the mysql command-line client.
You can use the following prompt options:
Option | Description |
\v | mysqld version |
\d | database in use |
\h | host connected to |
\p | port connected on |
\u | username |
\U | full username@host |
\\ | \ |
\n | new line break |
\t | tab |
\ | space |
\_ | space |
\R | military hour time (0-23) |
\r | standard hour time (1-12) |
\m | minutes |
\y | two digit year |
\Y | four digit year |
\D | full date format |
\s | seconds |
\w | day of the week in three letter format (Mon, Tue, ...) |
\P | am/pm |
\o | month in number format |
\O | month in three letter format (Jan, Feb, ...) |
\c | counter that counts up for each command you do |
\ followed by any other letter just becomes that letter.
You may set the prompt in the following places:
Environment Variable |
You may set the MYSQL_PS1 environment variable to a prompt string. For
example:
shell> export MYSQL_PS1="(\u@\h) [\d]> " |
my.cnf , .my.cnf |
You may set the prompt option in any MySQL configuration file, in the
mysql group. For example:
[mysql] prompt=(\u@\h) [\d]>\_ |
Command Line |
You may set the --prompt option on the command line to mysql.
For example:
shell> mysql --prompt="(\u@\h) [\d]> " (user@host) [database]> |
Interactively |
You may also use the prompt (or \R) command to change your
prompt interactively. For example:
mysql> prompt (\u@\h) [\d]>\_ PROMPT set to '(\u@\h) [\d]>\_' (user@host) [database]> (user@host) [database]> prompt Returning to default PROMPT of mysql> mysql> |
The mysql client typically is used interactively, like this:
shell> mysql database
However, it's also possible to put your SQL commands in a file and tell mysql to read its input from that file. To do so, create a text file text_file that contains the commands you wish to execute. Then invoke mysql as shown here:
shell> mysql database < text_file
You can also start your text file with a USE db_name statement. In this case, it is unnecessary to specify the database name on the command line:
shell> mysql < text_file
If you are already running mysql, you can execute an SQL script file using the source command:
mysql> source filename;
For more information about batch mode, Batch mode.
mysqlcc, the MySQL Control Center, is a platform-independent client that provides a graphical user interface (GUI) to the MySQL database server. It supports interactive use, including syntax highlighting and tab-completion. It provides database and table management, and allows server administration.
Currently, mysqlcc runs on Windows and Linux platforms.
mysqlcc is not included with MySQL distributions, but can be downloaded separately at http://www.mysql.com/downloads/.
mysqlcc supports the following options:
You can also set the following variables with -O or --set-variable. please note that --set-variable Please note that --set-variable=name=value and -O name=value syntax is deprecated as of MySQL 4.0. Use --name=value instead.
Variable Name | Default | Description |
connect_timeout | 0 | Number of seconds before connection timeout. |
local-infile | 0 | Disable (0) or enable (1) LOCAL capability for LOAD DATA INFILE |
max_allowed_packet | 16777216 | Max packet length to send to/receive from server |
net_buffer_length | 16384 | Buffer for TCP/IP and socket communication |
select_limit | 1000 | Automatic limit for SELECT when using --safe-updates |
max_join_size | 1000000 | Automatic limit for rows in a join when using --safe-updates |
A utility for performing administrative operations. The syntax is:
shell> mysqladmin [OPTIONS] command [command-option] command ...
You can get a list of the options your version of mysqladmin supports by executing mysqladmin --help.
The current mysqladmin supports the following commands:
create databasename | Create a new database. |
drop databasename | Delete a database and all its tables. |
extended-status | Gives an extended status message from the server. |
flush-hosts | Flush all cached hosts. |
flush-logs | Flush all logs. |
flush-tables | Flush all tables. |
flush-privileges | Reload grant tables (same as reload). |
kill id,id,... | Kill mysql threads. |
password | Set a new password. Change old password to new-password. |
ping | Check if mysqld is alive. |
processlist | Show list of active threads in server, as with the SHOW PROCESSLIST statement. If the --verbose option is given, the output is like that of SHOW FULL PROCESSLIST. |
reload | Reload grant tables. |
refresh | Flush all tables and close and open log files. |
shutdown | Take down the server. |
slave-start | Start slave replication thread. |
slave-stop | Stop slave replication thread. |
status | Gives a short status message from the server. |
variables | Prints variables available. |
version | Get version information from server. |
All commands can be shortened to their unique prefix. For example:
shell> mysqladmin proc stat +----+-------+-----------+----+-------------+------+-------+------+ | Id | User | Host | db | Command | Time | State | Info | +----+-------+-----------+----+-------------+------+-------+------+ | 6 | monty | localhost | | Processlist | 0 | | | +----+-------+-----------+----+-------------+------+-------+------+ Uptime: 10077 Threads: 1 Questions: 9 Slow queries: 0 Opens: 6 Flush tables: 1 Open tables: 2 Memory in use: 1092K Max memory used: 1116K
The mysqladmin status command result has the following columns:
Column | Description |
Uptime | Number of seconds the MySQL server has been up. |
Threads | Number of active threads (clients). |
Questions | Number of questions from clients since mysqld was started. |
Slow queries | Queries that have taken more than long_query_time seconds. See Slow query log. |
Opens | How many tables mysqld has opened. |
Flush tables | Number of flush ..., refresh, and reload commands. |
Open tables | Number of tables that are open now. |
Memory in use | Memory allocated directly by the mysqld code (only available when MySQL is compiled with --with-debug=full). |
Max memory used | Maximum memory allocated directly by the mysqld code (only available when MySQL is compiled with --with-debug=full). |
If you do mysqladmin shutdown on a socket (in other words, on a the computer where mysqld is running), mysqladmin will wait until the MySQL pid-file is removed to ensure that the mysqld server has stopped properly.
You can examine the binary log file (see Binary log) with the mysqlbinlog utility.
shell> mysqlbinlog hostname-bin.001
will print all queries contained in binlog hostname-bin.001, together with information (time the query took, ID of the thread which issued it, timestamp when it was issued etc).
You can pipe the output of mysqlbinlog into a mysql client; this is used to recover from a crash when you have an old backup (see Backup):
shell> mysqlbinlog hostname-bin.001 | mysql
or:
shell> mysqlbinlog hostname-bin.[0-9]* | mysql
You can also redirect the output of mysqlbinlog to a text file instead, modify this text file (to cut queries you don't want to execute for some reason), then execute the queries from the text file into mysql.
mysqlbinlog has the position=# options which will print only queries whose offset in the binlog is greater or equal to #.
If you have more than one binary log to execute on the MySQL server, the safe method is to do it in one unique MySQL connection. Here is what may be UNsafe:
shell> mysqlbinlog hostname-bin.001 | mysql # DANGER!! shell> mysqlbinlog hostname-bin.002 | mysql # DANGER!!
It will cause problems if the first binlog contains a CREATE TEMPORARY TABLE and the second one contains a query which uses this temporary table: when the first mysql terminates, it will drop the temporary table, so the second mysql will report ``unknown table''. This is why you should run all binlogs you want in one unique connection, especially if you use temporary tables. Here are two possible ways:
shell> mysqlbinlog hostname-bin.001 hostname-bin.002 | mysql
shell> mysqlbinlog hostname-bin.001 > /tmp/queries.sql shell> mysqlbinlog hostname-bin.002 >> /tmp/queries.sql shell> mysql -e "source /tmp/queries.sql"
Starting from MySQL 4.0.14, mysqlbinlog can prepare suitable input for mysql to execute a LOAD DATA INFILE from a binlog. As the binlog contains the data to load (this is true for MySQL 4.0; MySQL 3.23 did not write the loaded data into the binlog, so the original file was needed when one wanted to execute the content of the binlog), mysqlbinlog will copy this data to a temporary file and print a LOAD DATA INFILE command for mysql to load this temporary file. The location where the temporary file is created is by default the temporary directory; it can be changed with the local-load option of mysqlbinlog.
Warning: When you run mysqlbinlog on a binary log file, it will create a temporary file for every found LOAD DATA INFILE command. These files will not be automatically deleted, because you will need them when executing the produced sql log. You should delete them yourself when you don't need the sql log anymore. The files are named temporary-dir/original_file_name-#-#.
In the future we will fix this problem by allowing mysqlbinlog to connect directly to a mysqld server. In this case we can safely remove the log files when the logs have been applied.
Before MySQL 4.1, mysqlbinlog could not prepare suitable output for mysql when the binary log contained queries from different threads using temporary tables of the same name, if these queries were interlaced. This is solved in MySQL 4.1.
You can also use mysqlbinlog --read-from-remote-server to read the binary log directly from a remote MySQL server. However, this is something that is deprecated as we instead want to make it easy to to apply binary logs to a running MySQL server.
mysqlbinlog --help will give you more information.
Since MySQL version 3.23.38 you will be able to use a new checking and repairing tool for MyISAM tables. The difference to myisamchk is that mysqlcheck should be used when the mysqld server is running, whereas myisamchk should be used when it is not. The benefit is that you no longer have to take down the server for checking or repairing your tables.
mysqlcheck uses MySQL server commands CHECK, REPAIR, ANALYZE and OPTIMIZE in a convenient way for the user.
There are three alternative ways to invoke mysqlcheck:
shell> mysqlcheck [OPTIONS] database [tables] shell> mysqlcheck [OPTIONS] --databases DB1 [DB2 DB3...] shell> mysqlcheck [OPTIONS] --all-databases
So it can be used in a similar way as mysqldump when it comes to what databases and tables you want to choose.
mysqlcheck does have a special feature compared to the other clients; the default behavior, checking tables (-c), can be changed by renaming the binary. So if you want to have a tool that repairs tables by default, you should just copy mysqlcheck to your harddrive with a new name, mysqlrepair, or alternatively make a symbolic link to mysqlcheck named mysqlrepair. If you invoke mysqlrepair now, it will repair tables by default.
The names that you can use to change mysqlcheck default behavior are here:
mysqlrepair: The default option will be -r mysqlanalyze: The default option will be -a mysqloptimize: The default option will be -o
The options available for mysqlcheck are listed here, please check what your version supports with mysqlcheck --help.
-A, --all-databases | Check all the databases. This will be same as --databases with all databases selected |
-1, --all-in-1 | Instead of making one query for each table, execute all queries in 1 query separately for each database. Table names will be in a comma separated list. |
-a, --analyze | Analyze given tables. |
--auto-repair | If a checked table is corrupted, automatically fix it. Repairing will be done after all tables have been checked, if corrupted ones were found. |
-#, --debug=... | Output debug log. Often this is 'd:t:o,filename' |
--character-sets-dir=... | Directory where character sets are |
-c, --check | Check table for errors |
-C, --check-only-changed | Check only tables that have changed since last check or haven't been closed properly. |
--compress | Use compression in server/client protocol. |
-?, --help | Display this help message and exit. |
-B, --databases | To check several databases. Note the difference in usage; in this case no tables are given. All name arguments are regarded as database names. |
--default-character-set=... | Set the default character set |
-F, --fast | Check only tables that hasn't been closed properly |
-f, --force | Continue even if we get an sql-error. |
-e, --extended | If you are using this option with CHECK TABLE, it will ensure that the table is 100 percent consistent, but will take a long time. If you are using this option with REPAIR TABLE, it will run an extended repair on the table, which may not only take a long time to execute, but may produce a lot of garbage rows also! |
-h, --host=... | Connect to host. |
-m, --medium-check | Faster than extended-check, but only finds 99.99 percent of all errors. Should be good enough for most cases. |
-o, --optimize | Optimize table |
-p, --password[=...] | Password to use when connecting to server. If password is not given it's solicited on the tty. |
-P, --port=... | Port number to use for TCP/IP connections. |
--protocol=(TCP | SOCKET | PIPE | MEMORY) | To specify the connect protocol to use. New in MySQL 4.1. |
-q, --quick | If you are using this option with CHECK TABLE, it prevents the check from scanning the rows to check for wrong links. This is the fastest check. If you are using this option with REPAIR TABLE, it will try to repair only the index tree. This is the fastest repair method for a table. |
-r, --repair | Can fix almost anything except unique keys that aren't unique. |
-s, --silent | Print only error messages. |
-S, --socket=... | Socket file to use for connection. |
--tables | Overrides option --databases (-B). All arguments following that option are regarded as table names. |
-u, --user=# | User for login if not current user. |
-v, --verbose | Print information about the various stages. |
-V, --version | Output version information and exit. |
The mysqldump client can be used to dump a database or a collection of database for backup or for transferring the data to another SQL server (not necessarily a MySQL server). The dump will contain SQL statements to create the table and/or populate the table.
If you are doing a backup on the server, you should consider using the mysqlhotcopy instead. See mysqlhotcopy.
shell> mysqldump [OPTIONS] database [tables] OR mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...] OR mysqldump [OPTIONS] --all-databases [OPTIONS]
If you don't give any tables or use the --databases or --all-databases option, entire databases will be dumped.
You can get a list of the options your version of mysqldump supports by executing mysqldump --help.
If you run mysqldump without --quick or --opt, mysqldump will load the whole result set into memory before dumping the result. This will probably be a problem if you are dumping a big database.
If you are using a recent copy of the mysqldump program and you are going to do a dump that will be read into a very old MySQL server, you should not use the --opt or -e options.
Out-of-range numeric values such as -inf and inf, as well as NaN (not-a-number) values are dumped by mysqldump as NULL. You can see this using the following example table:
mysql> CREATE TABLE t (f DOUBLE); mysql> INSERT INTO t VALUES(1e+111111111111111111111); mysql> INSERT INTO t VALUES(-1e111111111111111111111); mysql> SELECT f FROM t; +------+ | f | +------+ | inf | | -inf | +------+
For this table, mysqldump produces the following data output:
-- -- Dumping data for table `t` -- INSERT INTO t VALUES (NULL); INSERT INTO t VALUES (NULL);
The significance of this behavior is that if you dump and restore the table, the new table has contents that differ from the original contents.
mysqldump supports the following options:
--add-locks | Add LOCK TABLES before and UNLOCK TABLE after each table dump. (To get faster inserts into MySQL.) |
--add-drop-table | Add a drop table before each create statement. |
-A, --all-databases | Dump all the databases. This will be same as --databases with all databases selected. |
-a, --all | Include all MySQL-specific create options. |
--allow-keywords | Allow creation of column names that are keywords. This works by prefixing each column name with the table name. |
-c, --complete-insert | Use complete insert statements (with column names). |
--comments=... | If set to 0, suppresses additional information (like program version, server version, host) in dumps. The --skip-comments option does the same. Default is 1 to not suppress that information. New in MySQL 4.0.17. |
-C, --compress | Compress all information between the client and the server if both support compression. |
-B, --databases | To dump several databases. Note the difference in usage. In this case no tables are given. All name arguments are regarded as database names. USE db_name; will be included in the output before each new database. |
--default-character-set=... | Sets the character set for the dump. If not specified, mysqldump 10.3 (MySQL-4.1.2) or later will use utf8, earlier versions use latin1. |
--delayed | Insert rows with the INSERT DELAYED command. |
-e, --extended-insert | Use the new multiline INSERT syntax. (Gives more compact and faster inserts statements.) |
-#, --debug[=option_string] | Trace usage of the program (for debugging). |
--help | Display a help message and exit. |
--fields-terminated-by=... , --fields-enclosed-by=... , --fields-optionally-enclosed-by=... , --fields-escaped-by=... , --lines-terminated-by=... | These options are used with the -T option and have the same meaning as the corresponding clauses for LOAD DATA INFILE. See LOAD DATA. |
-F, --flush-logs | Flush log file in the MySQL server before starting the dump. Note that if you use this option in combination with the --all-databases (or -A) option, the logs will be flushed for each database dumped. |
-f, --force | Continue even if we get an SQL error during a table dump. |
-h, --host=... | Dump data from the MySQL server on the named host. The default host is localhost. |
-l, --lock-tables | Lock all tables before starting the dump. The tables are locked with READ LOCAL to allow concurrent inserts in the case of MyISAM tables. Please note that when dumping multiple databases, --lock-tables will lock tables for each database separately. So using this option will not guarantee your tables will be logically consistent between databases. Tables in different databases may be dumped in completely different states. |
-K, --disable-keys | /*!40000 ALTER TABLE tb_name DISABLE KEYS */; and /*!40000 ALTER TABLE tb_name ENABLE KEYS */; will be put in the output. This will make loading the data into a MySQL 4.0 server faster as the indexes are created after all data are inserted. |
-n, --no-create-db | CREATE DATABASE /*!32312 IF NOT EXISTS*/ db_name; will not be put in the output. The above line will be added otherwise, if a --databases or --all-databases option was given. |
-t, --no-create-info | Don't write table creation information (the CREATE TABLE statement). |
-d, --no-data | Don't write any row information for the table. This is very useful if you just want to get a dump of the structure for a table! |
--opt | Same as --quick --add-drop-table --add-locks --extended-insert --lock-tables. Should give you the fastest possible dump for reading into a MySQL server. |
-pyour_pass, --password[=your_pass] | The password to use when connecting to the server. If you specify no =your_pass part, mysqldump you will be prompted for a password. |
-P, --port=... | Port number to use for TCP/IP connections. |
--protocol=(TCP | SOCKET | PIPE | MEMORY) | To specify the connect protocol to use. New in MySQL 4.1. |
-q, --quick | Don't buffer query, dump directly to stdout. Uses mysql_use_result() to do this. Especially useful for big dumps. |
-Q, --quote-names | Quote table and column names within ` characters. |
-r, --result-file=... | Direct output to a given file. This option should be used in MSDOS, because it prevents new line \n from being converted to \n\r (new line + carriage return). |
--single-transaction | This option issues a BEGIN SQL command before dumping data from server. It is mostly useful with InnoDB tables and READ_COMMITTED transaction isolation level, as in this mode it will dump the consistent state of the database at the time then BEGIN was issued without blocking any applications. When using this option you should keep in mind that only transactional tables will be dumped in a consistent state, for example, any MyISAM or HEAP tables dumped while using this option may still change state. The --single-transaction option was added in version 4.0.2. This option is mutually exclusive with the --lock-tables option as LOCK TABLES already commits a previous transaction internally. |
-S /path/to/socket, --socket=/path/to/socket | The socket file to use when connecting to localhost (which is the default host). |
--skip-comments | Suppresses additional information (like program version, server version, host) in dumps. It does the same as setting --comments to 0. New in MySQL 4.0.17. |
--tables | Overrides option --databases (-B). |
-T, --tab=path-to-some-directory | Creates a table_name.sql file, that contains the SQL CREATE commands, and a table_name.txt file, that contains the data, for each give table. The format of the .txt file is made according to the --fields-xxx and --lines--xxx options. Note: This option works only if mysqldump is run on the same machine as the mysqld daemon. You must use a MySQL account that has the FILE privilege, and the login user/group that mysqld is running as (normally user mysql, group mysql) must have permission to create/write a file at the location you specify. |
-u user_name, --user=user_name | The MySQL username to use when connecting to the server. The default value is your Unix login name. |
-O name=value, --set-variable=name=value | Set the value of a variable. The possible variables are listed below. Please note that --set-variable=name=value and -O name=value syntax is deprecated as of MySQL 4.0. Use --name=value instead. |
-v, --verbose | Verbose mode. Print out more information on what the program does. |
-V, --version | Print version information and exit. |
-w, --where="where-condition" |
Dump only selected records. Note that quotes are mandatory:
"--where=user='jimf'" "-wuserid>1" "-wuserid<1" |
-X, --xml | Dumps a database as well formed XML |
-x, --first-slave | Locks all tables across all databases. |
--master-data | Like --first-slave, but also prints some CHANGE MASTER TO commands which will later make your slave start from the right position in the master's binlogs, if you have set up your slave using this SQL dump of the master. |
-O net_buffer_length=#, where # < 16M | When creating multi-row-insert statements (as with option --extended-insert or --opt), mysqldump will create rows up to net_buffer_length length. If you increase this variable, you should also ensure that the max_allowed_packet variable in the MySQL server is bigger than the net_buffer_length. |
The most normal use of mysqldump is probably for making a backup of whole databases. See Backup.
mysqldump --opt database > backup-file.sql
You can read this back into MySQL with:
mysql database < backup-file.sql
or:
mysql -e "source /path-to-backup/backup-file.sql" database
However, it's also very useful to populate another MySQL server with information from a database:
mysqldump --opt database | mysql ---host=remote-host -C database
It is possible to dump several databases with one command:
mysqldump --databases database1 [database2 ...] > my_databases.sql
If all the databases are wanted, one can use:
mysqldump --all-databases > all_databases.sql
mysqlhotcopy is a Perl script that uses LOCK TABLES, FLUSH TABLES and cp or scp to quickly make a backup of a database. It's the fastest way to make a backup of the database or single tables, but it can only be run on the same machine where the database directories are. mysqlhotcopy works only for backing up MyISAM and ISAM tables. It runs on Unix, and on NetWare as of MySQL 4.0.18.
mysqlhotcopy db_name [/path/to/new_directory] mysqlhotcopy db_name_1 ... db_name_n /path/to/new_directory mysqlhotcopy db_name./regex/
mysqlhotcopy supports the following options:
-?, --help | Display a help screen and exit |
-u, --user=# | User for database login |
-p, --password=# | Password to use when connecting to server |
-P, --port=# | Port to use when connecting to local server |
-S, --socket=# | Socket to use when connecting to local server |
--allowold | Don't abort if target already exists (rename it _old) |
--keepold | Don't delete previous (now renamed) target when done |
--noindices | Don't include full index files in copy to make the backup smaller and faster The indexes can later be reconstructed with myisamchk -rq.. |
--method=# | Method for copy (cp or scp). |
-q, --quiet | Be silent except for errors |
--debug | Enable debug |
-n, --dryrun | Report actions without doing them |
--regexp=# | Copy all databases with names matching regexp |
--suffix=# | Suffix for names of copied databases |
--checkpoint=# | Insert checkpoint entry into specified db.table |
--flushlog | Flush logs once all tables are locked. |
--tmpdir=# | Temporary directory (instead of /tmp). |
You can use perldoc mysqlhotcopy to get more complete documentation for mysqlhotcopy.
mysqlhotcopy reads the groups [client] and [mysqlhotcopy] from the option files.
To be able to execute mysqlhotcopy you need write access to the backup directory, the SELECT privilege for the tables you are about to copy and the MySQL RELOAD privilege (to be able to execute FLUSH TABLES).
mysqlimport provides a command-line interface to the LOAD DATA INFILE SQL statement. Most options to mysqlimport correspond directly to the same options to LOAD DATA INFILE. See LOAD DATA.
mysqlimport is invoked like this:
shell> mysqlimport [options] database textfile1 [textfile2 ...]
For each text file named on the command-line, mysqlimport strips any extension from the filename and uses the result to determine which table to import the file's contents into. For example, files named patient.txt, patient.text, and patient would all be imported into a table named patient.
mysqlimport supports the following options:
-c, --columns=... | This option takes a comma-separated list of field names as an argument. The field list is used to create a proper LOAD DATA INFILE command, which is then passed to MySQL. See LOAD DATA. |
-C, --compress | Compress all information between the client and the server if both support compression. |
-#, --debug[=option_string] | Trace usage of the program (for debugging). |
-d, --delete | Empty the table before importing the text file. |
--fields-terminated-by=... , --fields-enclosed-by=... , --fields-optionally-enclosed-by=... , --fields-escaped-by=... , --lines-terminated-by=... | These options have the same meaning as the corresponding clauses for LOAD DATA INFILE. See LOAD DATA. |
-f, --force | Ignore errors. For example, if a table for a text file doesn't exist, continue processing any remaining files. Without --force, mysqlimport exits if a table doesn't exist. |
--help | Display a help message and exit. |
-h host_name, --host=host_name | Import data to the MySQL server on the named host. The default host is localhost. |
-i, --ignore | See the description for the --replace option. |
--ignore-lines=n | Ignore first n lines of the datafile. |
-l, --lock-tables | Lock all tables for writing before processing any text files. This ensures that all tables are synchronized on the server. |
-L, --local | Read input files from the client. By default, text files are assumed to be on the server if you connect to localhost (which is the default host). |
-pyour_pass, --password[=your_pass] | The password to use when connecting to the server. If you specify no =your_pass part, mysqlimport you will be prompted for a password. |
-P port_num, --port=port_num | TCP/IP port number to use for connection. |
--protocol=(TCP | SOCKET | PIPE | MEMORY) | To specify the connect protocol to use. New in MySQL 4.1. |
-r, --replace | The --replace and --ignore options control handling of input records that duplicate existing records on unique key values. If you specify --replace, new rows replace existing rows that have the same unique key value. If you specify --ignore, input rows that duplicate an existing row on a unique key value are skipped. If you don't specify either option, an error occurs when a duplicate key value is found, and the rest of the text file is ignored. |
-s, --silent | Silent mode. Write output only when errors occur. |
-S /path/to/socket, --socket=/path/to/socket | The socket file to use when connecting to localhost (which is the default host). |
-u user_name, --user=user_name | The MySQL username to use when connecting to the server. The default value is your Unix login name. |
-v, --verbose | Verbose mode. Print out more information what the program does. |
-V, --version | Print version information and exit. |
Here is a sample run using mysqlimport:
$ mysql --version mysql Ver 9.33 Distrib 3.22.25, for pc-linux-gnu (i686) $ uname -a Linux xxx.com 2.2.5-15 #1 Mon Apr 19 22:21:09 EDT 1999 i586 unknown $ mysql -e 'CREATE TABLE imptest(id INT, n VARCHAR(30))' test $ ed a 100 Max Sydow 101 Count Dracula . w imptest.txt 32 q $ od -c imptest.txt 0000000 1 0 0 \t M a x S y d o w \n 1 0 0000020 1 \t C o u n t D r a c u l a \n 0000040 $ mysqlimport --local test imptest.txt test.imptest: Records: 2 Deleted: 0 Skipped: 0 Warnings: 0 $ mysql -e 'SELECT * FROM imptest' test +------+---------------+ | id | n | +------+---------------+ | 100 | Max Sydow | | 101 | Count Dracula | +------+---------------+
mysqlshow can be used to quickly look at which databases exist, their tables, and the table's columns.
With the mysql program you can get the same information with the SHOW commands. See SHOW.
mysqlshow is invoked like this:
shell> mysqlshow [OPTIONS] [database [table [column]]]
If no database is given, all matching databases are shown.
If no table is given, all matching tables in the database are shown.
If no column is given, all matching columns and column types in the table are shown.
Note that in newer MySQL versions, you only see those database/tables/columns for which you have some privileges.
If the last argument contains a shell or SQL wildcard (*, ?, % or _), only what's matched by the wildcard is shown. If a database name contains any underscores, those should be escaped with backslash (some Unix shells will require two), in order to get tables / columns properly. '*' are converted into SQL '%' wildcard and '?' into SQL '_' wildcard. This may cause some confusion when you try to display the columns for a table with a _ as in this case mysqlshow only shows you the table names that match the pattern. This is easily fixed by adding an extra % last on the command-line (as a separate argument).
myisampack is used to compress MyISAM tables, and pack_isam is used to compress ISAM tables. Because ISAM tables are deprecated, we will discuss only myisampack here, but everything said about myisampack should also be true for pack_isam.
myisampack works by compressing each column in the table separately. The information needed to decompress columns is read into memory when the table is opened. This results in much better performance when accessing individual records, because you only have to uncompress exactly one record, not a much larger disk block as when using Stacker on MS-DOS. Usually, myisampack packs the datafile 40%-70%.
MySQL uses memory mapping (mmap()) on compressed tables and falls back to normal read/write file usage if mmap() doesn't work.
Please note the following:
After packing, the table is read-only. This is generally intended (such as when accessing packed tables on a CD). Also allowing writes to a packed table is on our TODO list but with low priority.
myisampack can also pack BLOB or TEXT columns. The older pack_isam (for ISAM tables) cannot do this.
myisampack is invoked like this:
shell> myisampack [options] filename ...
Each filename should be the name of an index (.MYI) file. If you are not in the database directory, you should specify the pathname to the file. It is permissible to omit the .MYI extension.
myisampack supports the following options:
-b, --backup | Make a backup of the table as tbl_name.OLD. |
-#, --debug=debug_options | Output debug log. The debug_options string often is 'd:t:o,filename'. |
-f, --force | Force packing of the table even if it becomes bigger or if the temporary file exists. myisampack creates a temporary file named tbl_name.TMD while it compresses the table. If you kill myisampack, the .TMD file may not be deleted. Normally, myisampack exits with an error if it finds that tbl_name.TMD exists. With --force, myisampack packs the table anyway. |
-?, --help | Display a help message and exit. |
-j big_tbl_name, --join=big_tbl_name | Join all tables named on the command-line into a single table big_tbl_name. All tables that are to be combined must be identical (same column names and types, same indexes, etc.). |
-p #, --packlength=# | Specify the record length storage size, in bytes. The value should be 1, 2, or 3. (myisampack stores all rows with length pointers of 1, 2, or 3 bytes. In most normal cases, myisampack can determine the right length value before it begins packing the file, but it may notice during the packing process that it could have used a shorter length. In this case, myisampack will print a note that the next time you pack the same file, you could use a shorter record length.) |
-s, --silent | Silent mode. Write output only when errors occur. |
-t, --test | Don't actually pack table, just test packing it. |
-T dir_name, --tmp_dir=dir_name | Use the named directory as the location in which to write the temporary table. |
-v, --verbose | Verbose mode. Write information about progress and packing result. |
-V, --version | Display version information and exit. |
-w, --wait | Wait and retry if table is in use. If the mysqld server was invoked with the --skip-external-locking option, it is not a good idea to invoke myisampack if the table might be updated during the packing process. |
The sequence of commands shown here illustrates a typical table compression session:
shell> ls -l station.* -rw-rw-r-- 1 monty my 994128 Apr 17 19:00 station.MYD -rw-rw-r-- 1 monty my 53248 Apr 17 19:00 station.MYI -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm shell> myisamchk -dvv station MyISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-02-02 3:06:43 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafile pointer (bytes): 2 Keyfile pointer (bytes): 2 Max datafile length: 54657023 Max keyfile length: 33554431 Recordlength: 834 Record format: Fixed length table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 1024 1024 1 2 32 30 multip. text 10240 1024 1 Field Start Length Type 1 1 1 2 2 4 3 6 4 4 10 1 5 11 20 6 31 1 7 32 30 8 62 35 9 97 35 10 132 35 11 167 4 12 171 16 13 187 35 14 222 4 15 226 16 16 242 20 17 262 20 18 282 20 19 302 30 20 332 4 21 336 4 22 340 1 23 341 8 24 349 8 25 357 8 26 365 2 27 367 2 28 369 4 29 373 4 30 377 1 31 378 2 32 380 8 33 388 4 34 392 4 35 396 4 36 400 4 37 404 1 38 405 4 39 409 4 40 413 4 41 417 4 42 421 4 43 425 4 44 429 20 45 449 30 46 479 1 47 480 1 48 481 79 49 560 79 50 639 79 51 718 79 52 797 8 53 805 1 54 806 1 55 807 20 56 827 4 57 831 4 shell> myisampack station.MYI Compressing station.MYI: (1192 records) - Calculating statistics normal: 20 empty-space: 16 empty-zero: 12 empty-fill: 11 pre-space: 0 end-space: 12 table-lookups: 5 zero: 7 Original trees: 57 After join: 17 - Compressing file 87.14% shell> ls -l station.* -rw-rw-r-- 1 monty my 127874 Apr 17 19:00 station.MYD -rw-rw-r-- 1 monty my 55296 Apr 17 19:04 station.MYI -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm shell> myisamchk -dvv station MyISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-04-17 19:04:26 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafilepointer (bytes): 3 Keyfile pointer (bytes): 1 Max datafile length: 16777215 Max keyfile length: 131071 Recordlength: 834 Record format: Compressed table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 10240 1024 1 2 32 30 multip. text 54272 1024 1 Field Start Length Type Huff tree Bits 1 1 1 constant 1 0 2 2 4 zerofill(1) 2 9 3 6 4 no zeros, zerofill(1) 2 9 4 10 1 3 9 5 11 20 table-lookup 4 0 6 31 1 3 9 7 32 30 no endspace, not_always 5 9 8 62 35 no endspace, not_always, no empty 6 9 9 97 35 no empty 7 9 10 132 35 no endspace, not_always, no empty 6 9 11 167 4 zerofill(1) 2 9 12 171 16 no endspace, not_always, no empty 5 9 13 187 35 no endspace, not_always, no empty 6 9 14 222 4 zerofill(1) 2 9 15 226 16 no endspace, not_always, no empty 5 9 16 242 20 no endspace, not_always 8 9 17 262 20 no endspace, no empty 8 9 18 282 20 no endspace, no empty 5 9 19 302 30 no endspace, no empty 6 9 20 332 4 always zero 2 9 21 336 4 always zero 2 9 22 340 1 3 9 23 341 8 table-lookup 9 0 24 349 8 table-lookup 10 0 25 357 8 always zero 2 9 26 365 2 2 9 27 367 2 no zeros, zerofill(1) 2 9 28 369 4 no zeros, zerofill(1) 2 9 29 373 4 table-lookup 11 0 30 377 1 3 9 31 378 2 no zeros, zerofill(1) 2 9 32 380 8 no zeros 2 9 33 388 4 always zero 2 9 34 392 4 table-lookup 12 0 35 396 4 no zeros, zerofill(1) 13 9 36 400 4 no zeros, zerofill(1) 2 9 37 404 1 2 9 38 405 4 no zeros 2 9 39 409 4 always zero 2 9 40 413 4 no zeros 2 9 41 417 4 always zero 2 9 42 421 4 no zeros 2 9 43 425 4 always zero 2 9 44 429 20 no empty 3 9 45 449 30 no empty 3 9 46 479 1 14 4 47 480 1 14 4 48 481 79 no endspace, no empty 15 9 49 560 79 no empty 2 9 50 639 79 no empty 2 9 51 718 79 no endspace 16 9 52 797 8 no empty 2 9 53 805 1 17 1 54 806 1 3 9 55 807 20 no empty 3 9 56 827 4 no zeros, zerofill(2) 2 9 57 831 4 no zeros, zerofill(1) 2 9
The information printed by myisampack is described here:
normal | The number of columns for which no extra packing is used. |
empty-space | The number of columns containing values that are only spaces; these will occupy 1 bit. |
empty-zero | The number of columns containing values that are only binary 0's; these will occupy 1 bit. |
empty-fill | The number of integer columns that don't occupy the full byte range of their type; these are changed to a smaller type (for example, an INTEGER column may be changed to MEDIUMINT). |
pre-space | The number of decimal columns that are stored with leading spaces. In this case, each value will contain a count for the number of leading spaces. |
end-space | The number of columns that have a lot of trailing spaces. In this case, each value will contain a count for the number of trailing spaces. |
table-lookup | The column had only a small number of different values, which were converted to an ENUM before Huffman compression. |
zero | The number of columns for which all values are zero. |
Original trees | The initial number of Huffman trees. |
After join | The number of distinct Huffman trees left after joining trees to save some header space. |
After a table has been compressed, myisamchk -dvv prints additional information about each field:
Type | The field type may contain the following descriptors: |
| ||||||||||||||||
Huff tree | The Huffman tree associated with the field. | |||||||||||||||||
Bits | The number of bits used in the Huffman tree. |
After you have run pack_isam/myisampack you must run isamchk/myisamchk to re-create the index. At this time you can also sort the index blocks and create statistics needed for the MySQL optimizer to work more efficiently:
myisamchk -rq --analyze --sort-index table_name.MYI isamchk -rq --analyze --sort-index table_name.ISM
After you have installed the packed table into the MySQL database directory you should do mysqladmin flush-tables to force mysqld to start using the new table.
If you want to unpack a packed table, you can do this with the --unpack option to isamchk or myisamchk.
mysql_config provides you with useful information how to compile your MySQL client and connect it to MySQL.
mysql_config supports the following options:
--cflags | Compiler flags to find include files and critical ccompiler flags and defines used when compiling the libmysqlclient library. |
--include | Compiler options to find MySQL include files. (Normally one would use --cflags instead of this) |
--libs | Libraries and options required to link with the MySQL client library. |
--libs_r | Libraries and options required to link with the thread-safe MySQL client library. |
--socket | The default socket name, defined when configuring MySQL. |
--port | The default port number, defined when configuring MySQL. |
--version | Version number and version for the MySQL distribution. |
--libmysqld-libs or --embedded | Libraries and options required to link with the MySQL embedded server. |
If you execute mysql_config without any options it will print all options it supports plus the value of all options:
shell> mysql_config Usage: /usr/local/mysql/bin/mysql_config [OPTIONS] Options: --cflags [-I/usr/local/mysql/include/mysql -mcpu=pentiumpro] --include [-I/usr/local/mysql/include/mysql] --libs [-L/usr/local/mysql/lib/mysql -lmysqlclient -lz -lcrypt -lnsl -lm -L/usr/lib -lssl -lcrypto] --libs_r [-L/usr/local/mysql/lib/mysql -lmysqlclient_r -lpthread -lz -lcrypt -lnsl -lm -lpthread] --socket [/tmp/mysql.sock] --port [3306] --version [4.0.16] --libmysqld-libs [-L/usr/local/mysql/lib/mysql -lmysqld -lpthread -lz -lcrypt -lnsl -lm -lpthread -lrt]
You can use this to compile a MySQL client by as follows:
CFG=/usr/local/mysql/bin/mysql_config sh -c "gcc -o progname `$CFG --cflags` progname.c `$CFG --libs`"
For most system errors MySQL will, in addition to a internal text message, also print the system error code in one of the following styles: message ... (errno: #) or message ... (Errcode: #).
You can find out what the error code means by either examining the documentation for your system or use the perror utility.
perror prints a description for a system error code, or an MyISAM/ISAM storage engine (table handler) error code.
perror is invoked like this:
shell> perror [OPTIONS] [ERRORCODE [ERRORCODE...]] Example: shell> perror 13 64 Error code 13: Permission denied Error code 64: Machine is not on the network
Note that the error messages are mostly system dependent!
MySQL has a very complex, but intuitive and easy to learn SQL interface. The next several chapters of the manual comprise a language reference. They describe the various commands, types, and functions you will need to know in order to use MySQL efficiently and effectively. These chapters also serve as a reference to all functionality included in MySQL. The material they contain is grouped by topic:
See Language Structure for information about how to write data values, identifiers, and comments.
See Column types for information about the various column types that MySQL supports for storing data in tables.
See Functions for a list of the functions and operators that you can use when writing expressions.
See SQL Syntax for descriptions of the SQL statements that MySQL supports.
In order to use this material most effectively, you may find it useful to refer to the various indexes.
Table of Contents
This chapter discusses the rules for writing the following elements of SQL statements when using MySQL:
Literal values such as strings and numbers
Identifiers such as table and column names
User and system variables
Comments
Reserved words
Table of Contents
This section describes how to write literal values in MySQL. These include strings, numbers, hexadecimal values, boolean values, and NULL. The section also covers the various nuances and ``gotchas'' that you may run into when dealing with these basic types in MySQL.
A string is a sequence of characters, surrounded by either single quote (') or double quote. Examples:
'a string' "another string"
If the server SQL mode has ANSI_QUOTES enabled, string literals can be quoted only with single quotes. (A string quoted with double quotes will be interpreted as an identifier.)
Within a string, certain sequences have special meaning. Each of these sequences begins with a backslash (\), known as the escape character. MySQL recognizes the following escape sequences:
\0 | An ASCII 0 (NUL) character. |
\' | A single quote (') character. |
\" | A double quote (") character. |
\b | A backspace character. |
\n | A newline (linefeed) character. |
\r | A carriage return character. |
\t | A tab character. |
\z | ASCII 26 (Control-Z). This character can be encoded as \z to allow you to work around the problem that ASCII 26 stands for END-OF-FILE on Windows. (ASCII 26 will cause problems if you try to use mysql db_name < file_name.) |
\\ | A backslash (\) character. |
\% | A % character. This is used to search for literal instances of % in pattern-matching contexts where % would otherwise be interpreted as a wildcard character. See String comparison functions. |
\_ | A _ character. This is used to search for literal instances of _ in pattern-matching contexts where _ would otherwise be interpreted as a wildcard character. See String comparison functions. |
These sequences are case sensitive. For example, \b is interpreted as a backslash, but \B is interpreted as B.
Note that if you use \% or \_ in some string contexts, these will return the strings \% and \_ and not % and _.
There are several ways to include quotes within a string:
A ' inside a string quoted with ' may be written as ''.
A " inside a string quoted with " may be written as "".
You can precede the quote character with an escape character (\).
A ' inside a string quoted with " needs no special treatment and need not be doubled or escaped. In the same way, " inside a string quoted with ' needs no special treatment.
The SELECT statements shown here demonstrate how quoting and escaping work:
mysql> SELECT 'hello', '"hello"', '""hello""', 'hel''lo', '\'hello'; +-------+---------+-----------+--------+--------+ | hello | "hello" | ""hello"" | hel'lo | 'hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "hello", "'hello'", "''hello''", "hel""lo", "\"hello"; +-------+---------+-----------+--------+--------+ | hello | 'hello' | ''hello'' | hel"lo | "hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "This\nIs\nFour\nlines"; +--------------------+ | This Is Four lines | +--------------------+
If you want to insert binary data into a string column (such as a BLOB), the following characters must be represented by escape sequences:
NUL | NUL byte (ASCII 0). Represent this character by \0 (a backslash followed by an ASCII 0 character). |
\ | Backslash (ASCII 92). Represent this character by \\. |
' | Single quote (ASCII 39). Represent this character by \'. |
" | Double quote (ASCII 34). Represent this character by \". |
When writing application programs, any string that might contain any of these special characters must be properly escaped before the string is used as a data value in a SQL statement that is sent to the MySQL server. You can do this in two ways:
Process the string with a function that escapes the special characters. For example, if you write C code, you can use the C API function mysql_real_escape_string() to escape characters. See C API function overview. The Perl DBI interface provides a quote method to convert special characters to the proper escape sequences. See Perl.
As an alternative to explicitly escaping special characters, many MySQL APIs provide some sort of placeholder capability that allows you to insert special markers into a query string, and then bind data values to them when you issue the query. In this case, the API takes care of escaping special characters in the values for you.
Integers are represented as a sequence of digits. Floats use . as a decimal separator. Either type of number may be preceded by - to indicate a negative value.
Examples of valid integers:
1221 0 -32
Examples of valid floating-point numbers:
294.42 -32032.6809e+10 148.00
An integer may be used in a floating-point context; it is interpreted as the equivalent floating-point number.
MySQL supports hexadecimal values. In numeric contexts, these act like integers (64-bit precision). In string contexts, these act like binary strings, where each pair of hex digits is converted to a character:
mysql> SELECT x'4D7953514C'; -> 'MySQL' mysql> SELECT 0xa+0; -> 10 mysql> SELECT 0x5061756c; -> 'Paul'
In MySQL 4.1 (and in MySQL 4.0 when using the --new option) the default type of of a hexadecimal value is a string. If you want to ensure that the value is treated as a number, you can use CAST(... AS UNSIGNED):
mysql> SELECT 0x41, CAST(0x41 AS UNSIGNED); -> 'A', 65
The 0x syntax is based on ODBC. Hexadecimal strings are often used by ODBC to supply values for BLOB columns. The x'hexstring' syntax is new in 4.0 and is based on standard SQL.
Beginning with MySQL 4.0.1, you can convert a string or a number to a string in hexadecimal format with the HEX() function:
mysql> SELECT HEX('cat'); -> '636174' mysql> SELECT 0x636174; -> 'cat'
Beginning with MySQL 4.1.0, the constant TRUE evaluates to 1 and the constant FALSE evaluates to 0. The constant names can be written in any lettercase.
mysql> SELECT TRUE, true, FALSE, false; -> 1, 1, 0, 0
The NULL value means ``no data.'' NULL can be written in any lettercase.
Be aware that the NULL value is different than values such as 0 for numeric types or the empty string for string types. See Problems with NULL.
NULL may be represented by \N when using the text file import or export formats (LOAD DATA INFILE, SELECT ... INTO OUTFILE). See LOAD DATA.
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Database, table, index, column, and alias names are identifiers. This section describes the allowable syntax for identifiers in MySQL.
The following table describes the maximum length and allowable characters for each type of identifier.
Identifier | Maximum length (bytes) | Allowed characters |
Database | 64 | Any character that is allowed in a directory name except /, \, or . |
Table | 64 | Any character that is allowed in a filename, except /, \, or . |
Column | 64 | All characters |
Index | 64 | All characters |
Alias | 255 | All characters |
In addition to the restrictions noted in the table, no identifier can contain ASCII 0, ASCII 255, or the quoting character.
An identifier may be quoted or unquoted. If an identifier is a reserved word or contains special characters, you must quote it whenever you refer to it. For a list of reserved words, see Reserved words. Special characters are those outside the set of alphanumeric characters from the current character set, _, and $.
The quote character is the backtick (`):
mysql> SELECT * FROM `select` WHERE `select`.id > 100;
If the server SQL mode includes the ANSI_QUOTES mode option, it is also allowable to quote identifiers with double quotes:
mysql> CREATE TABLE "test" (col INT); ERROR 1064: You have an error in your SQL syntax. (...) mysql> SET sql_mode="ANSI_QUOTES"; mysql> CREATE TABLE "test" (col INT); Query OK, 0 rows affected (0.00 sec)
See SQL mode.
Identifier quoting was introduced in MySQL 3.23.6 to allow use of identifiers that are reserved words or that contain special characters. Before 3.23.6, cannot use identifiers that require quotes, so the rules for legal identifiers are more restrictive:
A name may consist of alphanumeric characters from the current character set, _, and $. The default character set is ISO-8859-1 (Latin1). This may be changed with the --default-character-set option to mysqld. See Character sets.
A name may start with any character that is legal in a name. In particular, a name may start with a digit; this differs from many other database systems! However, a name cannot consist only of digits.
You cannot use the . character in names because it is used to extend the format by which you can refer to columns (see immediately below).
It is recommended that you do not use names like 1e, because an expression like 1e+1 is ambiguous. It may be interpreted as the expression 1e + 1 or as the number 1e+1.
MySQL allows names that consist of a single identifier or multiple identifiers. The components of a multiple-part name should be separated by period (.) characters. The initial parts of a multiple-part name act as qualifiers that affect the context within which the final identifier is interpreted.
In MySQL you can refer to a column using any of the following forms:
Column reference | Meaning |
col_name | Column col_name from whichever table used in the query contains a column of that name. |
tbl_name.col_name | Column col_name from table tbl_name of the current database. |
db_name.tbl_name.col_name | Column col_name from table tbl_name of the database db_name. This syntax is unavailable before MySQL Version 3.22. |
If any components of a multiple-part name require quoting, quote them individually rather than quoting the name as a whole. For example, `my-table`.`my-column` is legal, but `my-table.my-column` is not.
You need not specify a tbl_name or db_name.tbl_name prefix for a column reference in a statement unless the reference would be ambiguous. Suppose tables t1 and t2 each contain a column c, and you retrieve c in a SELECT statement that uses both t1 and t2. In this case, c is ambiguous because it is not unique among the tables used in the statement. You must qualify it with a table name as t1.c or t2.c to indicate which table you mean. Similarly, to retrieve from a table t in database db1 and from a table t in database db2 in the same statement, you must refer to columns in those tables as db1.t.col_name and db2.t.col_name.
The syntax .tbl_name means the table tbl_name in the current database. This syntax is accepted for ODBC compatibility, because some ODBC programs prefix table names with a . character.
In MySQL, databases correspond to directories within the data directory. Tables within a database correspond to at least one file within the database directory (and possibly more, depending on the storage engine). Consequently, the case sensitivity of the underlying operating system determines the case sensitivity of database and table names. This means database and table names are not case sensitive in Windows, and case sensitive in most varieties of Unix. One notable exception is Mac OS X, for which the default filesystem type (HFS+) is not case sensitive. However Mac OS X also supports UFS volumes, which are case sensitive just as on any Unix. See Extensions to ANSI.
Note: Although database and table names are not case sensitive on some platforms, you should not refer to a given database or table using different cases within the same query. The following query would not work because it refers to a table both as my_table and as MY_TABLE:
mysql> SELECT * FROM my_table WHERE MY_TABLE.col=1;
Column names, index names, and column aliases are not case sensitive on any platform.
Table aliases are case sensitive before MySQL 4.1.1. The following query would not work because it refers to the alias both as a and as A:
mysql> SELECT col_name FROM tbl_name AS a -> WHERE a.col_name = 1 OR A.col_name = 2;
If you have trouble remembering the lettercase for database and table names, adopt a consistent convention, such as always creating databases and tables using lowercase names.
How table names are stored on disk and used in MySQL is defined by the lower_case_table_names variable, which you can set when starting mysqld. It can take one of the following values:
Value | Meaning |
0 | Table and database names are case sensitive and are stored on disk using the lettercase specified in the CREATE TABLE or CREATE DATABASE statement. This is the default on Unix systems. |
1 | Table and database names are not case sensitive and are stored on disk in lowercase. MySQL will convert all table names to lowercase on storage and lookup. This is the default on Windows and Mac OS X systems. (This option also applies to database names as of MySQL 4.0.2, and to table aliases as of 4.1.1.) |
2 | New in 4.0.18: Table and database names are not case sensitive, but are stored on disk using the lettercase specified in the CREATE TABLE or CREATE DATABASE statement. MySQL will convert all table names to lowercase on storage and lookup. Note: This works only on file systems that are not case sensitive! |
If you are using MySQL on only one platform, you don't normally have to change the lower_case_table_names variable. However, you may encounter difficulties if you want to transfer tables between platforms that differ in filesystem case sensitivity. For example, on Unix, you can have two different tables named my_table and MY_TABLE, but on Windows those names are considered the same. To avoid data transfer problems stemming from database or table name lettercase, you have two options:
Use lower_case_table_names=1 on all systems. The main disadvantage with this is that when you use SHOW TABLES or SHOW DATABASES, you don't see the names in their original case.
Use lower_case_table_names=0 on Unix and lower_case_table_names=2 on Windows. This will preserve the case of database and table names. The disadvantage of this is that you must ensure that you always refer to your database and table names with the correct case on Windows as things will not work on Unix if you use the wrong case (as Unix is case sensitive).
Note that if you set lower_case_table_names to 1 on Unix, you must first convert your old database and table names to lowercase before restarting mysqld.
MySQL supports user variables as of version 3.23.6. You can store a value in a user variable and refer to it later, which allows you to pass values from one statement to another. User variables are connection-specific. That is, a variable defined by one client cannot be seen or used by other clients. All variables for a client connection are automatically freed when the client exits.
User variables are written as @var_name, where the variable name var_name may consist of alphanumeric characters from the current character set, _, $, and . . The default character set is ISO-8859-1 (Latin1). This may be changed with the --default-character-set option to mysqld. See Character sets. User variable names are not case insensitive beginning with MySQL 5.0. Before that, they are case sensitive.
One way to set a user variable is by issuing a SET statement:
SET @var_name = expression [,@var_name = expression] ...
The expression assigned to the variable can evaluate to an integer, real, string, or NULL value.
You can also assign a value to a user variable in statements other than SET. However, in this case, the assignment operator is := rather than =, because = is treated as a comparison operator in non-SET statements:
mysql> SET @t1=0, @t2=0, @t3=0; mysql> SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3; +----------------------+------+------+------+ | @t1:=(@t2:=1)+@t3:=4 | @t1 | @t2 | @t3 | +----------------------+------+------+------+ | 5 | 5 | 1 | 4 | +----------------------+------+------+------+
User variables may be used where expressions are allowed. However, this does not currently include contexts that explicitly require a number, such as in the LIMIT clause of a SELECT statement, or the IGNORE number LINES clause of a LOAD DATA statement.
If you refer to a variable that has not been initialized, its value is NULL.
Note: In a SELECT statement, each expression is evaluated only when it's sent to the client. This means that in the HAVING, GROUP BY, or ORDER BY clause, you can't refer to an expression that involves variables that are set in the SELECT part. For example, the following statement will not work as expected:
mysql> SELECT (@aa:=id) AS a, (@aa+3) AS b FROM table_name HAVING b=5;
The reason is that @aa will not contain the value of the current row, but the value of id from the previous selected row.
The general rule is to never assign and use the same variable in the same statement.
Another issue with setting a variable and using it in the same statement is that the default result type of a variable is based on the type of the variable at the start of the statement. The following example illustrates this:
mysql> SET @a="test"; mysql> SELECT @a,(@a:=20) FROM table_name;
For the SELECT statement, MySQL will report to the client that column one is a string and convert all accesses of @a to strings, even if @a will be set to a number for the second row. After the SELECT statement is executed, @a will be regarded as a number for the next statement.
An unassigned variable has a value of NULL with a type of string.
To avoid problems with this behavior, either do not set and use the same variable within a single statement, or else set the variable to 0, 0.0, or '' to define its type before you use it.
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Starting from MySQL 4.0.3, we provide better access to a lot of system and connection variables. Many variables can be changed dynamically while the server is running. This allows you to modify server operation without having to stop and restart it.
The mysqld server maintains two kinds of variables while it runs. Global variables affect the overall operation of the server. Session variables affect its operation for individual client connections.
When the server starts, it initializes all global variables to their default values. These defaults may be changed by options specified in option files or on the command line. After the server starts, those global variables that are dynamic can be changed by connecting to the server and issuing a SET GLOBAL var_name statement. To change a global variable, you must have the SUPER privilege.
The server also maintains a set of session variables for each client that connects. The client's session variables are initialized at connect time using the current values of the corresponding global variables. For those session variables that are dynamic, the client can change them by issuing a SET SESSION var_name statement. Setting a session variable requires no special privilege, but a client can change only its own session variables, not those of any other client.
A change to a global variable affects only client connections that occur after the change. It does not affect session variables for any client that is already connected (not even those of the client that issues the SET GLOBAL statement).
Global or session variables may be set or retrieved using several syntax forms. The following examples use sort_buffer_size as a sample variable name.
To set the value of a GLOBAL variable, use one of the following syntaxes:
mysql> SET GLOBAL sort_buffer_size=value; mysql> SET @@global.sort_buffer_size=value;
To set the value of a SESSION variable, use one of the following syntaxes:
mysql> SET SESSION sort_buffer_size=value; mysql> SET @@session.sort_buffer_size=value; mysql> SET sort_buffer_size=value;
LOCAL is a synonym for SESSION.
If you don't specify GLOBAL, SESSION, or LOCAL when setting a variable, SESSION is the default. See SET OPTION.
To retrieve the value of a GLOBAL variable, use one of the following statements:
mysql> SELECT @@global.sort_buffer_size; mysql> SHOW GLOBAL VARIABLES like 'sort_buffer_size';
To retrieve the value of a SESSION variable, use one of the following statements:
mysql> SELECT @@session.sort_buffer_size; mysql> SHOW SESSION VARIABLES like 'sort_buffer_size';
Here, too, LOCAL is a synonym for SESSION.
If you don't specify @@global, @@session, or @@local when retrieving a variable with SELECT, MySQL returns the SESSION value if it exists and the GLOBAL value otherwise.
If you don't specify GLOBAL, SESSION, or LOCAL for SHOW VARIABLES, MySQL returns the SESSION value.
The reason for requiring the GLOBAL keyword when setting GLOBAL-only variables but not when retrieving them is to ensure that we don't later run into problems if we would introduce a SESSION variable with the same name or remove a SESSION variable. In that case, a client with the SUPER privilege might change the GLOBAL variable by accident, rather than just the SESSION variable for the client's own connection.
Further information about system variables can be found in the startup options section, and in the descriptions of the SHOW VARIABLES and SET statements. See Server options. See SHOW VARIABLES. See SET OPTION.
The following table shows the full list of all variables that you can change and retrieve using GLOBAL or SESSION. The last column indicates for each variable whether GLOBAL or SESSION (or both) apply.
Variable name | Value type | Type |
autocommit | bool | SESSION |
big_tables | bool | SESSION |
binlog_cache_size | num | GLOBAL |
bulk_insert_buffer_size | num | GLOBAL | SESSION |
concurrent_insert | bool | GLOBAL |
connect_timeout | num | GLOBAL |
convert_character_set | string | GLOBAL | SESSION |
delay_key_write | OFF | ON | ALL | GLOBAL |
delayed_insert_limit | num | GLOBAL |
delayed_insert_timeout | num | GLOBAL |
delayed_queue_size | num | GLOBAL |
error_count | num | SESSION |
flush | bool | GLOBAL |
flush_time | num | GLOBAL |
foreign_key_checks | bool | SESSION |
identity | num | SESSION |
insert_id | bool | SESSION |
interactive_timeout | num | GLOBAL | SESSION |
join_buffer_size | num | GLOBAL | SESSION |
key_buffer_size | num | GLOBAL |
last_insert_id | num | SESSION |
local_infile | bool | GLOBAL |
log_warnings | bool | GLOBAL |
long_query_time | num | GLOBAL | SESSION |
low_priority_updates | bool | GLOBAL | SESSION |
max_allowed_packet | num | GLOBAL | SESSION |
max_binlog_cache_size | num | GLOBAL |
max_binlog_size | num | GLOBAL |
max_connect_errors | num | GLOBAL |
max_connections | num | GLOBAL |
max_error_count | num | GLOBAL | SESSION |
max_delayed_threads | num | GLOBAL |
max_heap_table_size | num | GLOBAL | SESSION |
max_join_size | num | GLOBAL | SESSION |
max_relay_log_size | num | GLOBAL |
max_seeks_for_key | num | GLOBAL | SESSION |
max_sort_length | num | GLOBAL | SESSION |
max_tmp_tables | num | GLOBAL |
max_user_connections | num | GLOBAL |
max_write_lock_count | num | GLOBAL |
myisam_max_extra_sort_file_size | num | GLOBAL | SESSION |
myisam_repair_threads | num | GLOBAL | SESSION |
myisam_max_sort_file_size | num | GLOBAL | SESSION |
myisam_sort_buffer_size | num | GLOBAL | SESSION |
net_buffer_length | num | GLOBAL | SESSION |
net_read_timeout | num | GLOBAL | SESSION |
net_retry_count | num | GLOBAL | SESSION |
net_write_timeout | num | GLOBAL | SESSION |
query_alloc_block_size | num | GLOBAL | SESSION |
query_cache_limit | num | GLOBAL |
query_cache_size | num | GLOBAL |
query_cache_type | enum | GLOBAL |
query_prealloc_size | num | GLOBAL | SESSION |
range_alloc_block_size | num | GLOBAL | SESSION |
read_buffer_size | num | GLOBAL | SESSION |
read_rnd_buffer_size | num | GLOBAL | SESSION |
rpl_recovery_rank | num | GLOBAL |
safe_show_database | bool | GLOBAL |
server_id | num | GLOBAL |
slave_compressed_protocol | bool | GLOBAL |
slave_net_timeout | num | GLOBAL |
slow_launch_time | num | GLOBAL |
sort_buffer_size | num | GLOBAL | SESSION |
sql_auto_is_null | bool | SESSION |
sql_big_selects | bool | SESSION |
sql_big_tables | bool | SESSION |
sql_buffer_result | bool | SESSION |
sql_log_binlog | bool | SESSION |
sql_log_off | bool | SESSION |
sql_log_update | bool | SESSION |
sql_low_priority_updates | bool | GLOBAL | SESSION |
sql_max_join_size | num | GLOBAL | SESSION |
sql_quote_show_create | bool | SESSION |
sql_safe_updates | bool | SESSION |
sql_select_limit | bool | SESSION |
sql_slave_skip_counter | num | GLOBAL |
sql_warnings | bool | SESSION |
table_cache | num | GLOBAL |
table_type | enum | GLOBAL | SESSION |
thread_cache_size | num | GLOBAL |
timestamp | bool | SESSION |
tmp_table_size | enum | GLOBAL | SESSION |
transaction_alloc_block_size | num | GLOBAL | SESSION |
transaction_prealloc_size | num | GLOBAL | SESSION |
tx_isolation | enum | GLOBAL | SESSION |
wait_timeout | num | GLOBAL | SESSION |
warning_count | num | SESSION |
unique_checks | bool | SESSION |
Variables that are marked as num can be given a numeric value. Variables that are marked as bool can be set to 0, 1, ON or OFF. Variables that are marked as enum should normally be set to one of the available values for the variable, but can also be set to the number that correspond to the desired enumeration value. (The first enumeration value corresponds to 0; note that this differs from ENUM columns, for which the first enumeration value corresponds to 1.)
Here is a description of some of the variables:
Variable | Description |
identity | Alias for last_insert_id (Sybase compatibility) |
sql_low_priority_updates | Alias for low_priority_updates |
sql_max_join_size | Alias for max_join_size |
version | Alias for VERSION() (Sybase (?) compatibility) |
Structured system variables are supported beginning with MySQL 4.1.1. A structured variable differs from a regular system variable in two respects:
Its value is a structure with components that specify some parameters of the server that are considered to be closely related.
There might be several instances of a given type of structured variable. Each one will have a different name and refers to a different resource maintained by the server.
Currently, MySQL supports one structured variable type. It specifies parameters that govern the operation of key caches. A key cache structured variable has these components:
key_buffer_size
key_cache_block_size
key_cache_division_limit
key_cache_age_threshold
The purpose of this section is to describe the syntax for referring to structured variables. Key cache variables are used for syntax examples, but specific details about how key caches operate are found elsewhere, in MyISAM key cache.
To refer to a component of a structured variable instance, you can use a compound name in instance_name.component_name format. Examples:
hot_cache.key_buffer_size hot_cache.key_cache_block_size. cold_cache.key_cache_block_size.
An instance with the name of default is always predefined for each structured system variable. If you refer to a component of a structured variable without any instance name, the default instance is used. Thus, default.key_buffer_size and key_buffer_size both refer to the same system variable.
The naming rules for structured variable instances and components are as follows:
For a given type of structured variable, each instance must have a name that is unique within variables of that type. However, instance names need not be unique across structured variable types. For example, each structured variable will have an instance named default, so default is not unique across variable types.
The names of the components of each structured variable type must be unique across all system variable names. If this were not true (such that two different types of structured variables could share component member names), it would not be clear which default structured variable to use for references to member names that are not qualified by an instance name.
At the moment, these rules have no possibility of being violated, because the only structured variable type is the one for key caches. If some other type of structured variable is created in the future, these rules will assume greater significance.
With one exception, it is allowable to refer to structured variable components using compound names in any context where simple variable names can occur.
For example, you can assign a value to a structured variable using a command line option:
shell> mysqld --hot_cache.key_buffer_size=64K
In an option file, do this:
[mysqld] hot_cache.key_buffer_size=64K
If you start the server with such an option, it creates a key cache named hot_cache with a size of 64 KB in addition to the default key cache that has a default size of 8 MB.
Suppose you start the server as follows:
shell> mysqld --key_buffer_size=256K \ --extra_cache.key_buffer_size=128K \ --extra_cache.key_cache_block_size=2096
In this case, the server sets the size of the default key cache to 256 KB. (You could also have written --default.key_buffer_size=256.) In addition, the server creates a second key cache named extra_cache that has a size of 128 KB, with the size of block buffers for caching table index blocks set to 2096 bytes.
The following example starts the server with three different key caches having sizes in a 3:1:1 ratio:
shell> mysqld --key_buffer_size=6M \ --hot_cache.key_buffer_size=2M \ --cold_cache.key_buffer_size=2M
Structured variable values may be set and retrieved at runtime as well. For example, to set a key cache named hot_cache to a size of 10 MB, use either of these statements:
mysql> SET GLOBAL hot_cache.key_buffer_size = 10*1024*1024; mysql> SET @global.hot_cache.key_buffer_size = 10*1024*1024;
To retrieve the cache size, do this:
mysql> SELECT @global.hot_cache.key_buffer_size;
However, the following statement does not work, because the variable is not interpreted as a compound name, but as a simple string for a LIKE pattern-matching operation:
mysql> SHOW GLOBAL VARIABLES LIKE 'hot_cache.key_buffer_size';
This is the exception to being able to use structured variable names anywhere a simple variable name may occur.
The MySQL server supports three comment styles:
From a # character to the end of the line.
From a -- sequence to the end of the line. This style is supported as of MySQL 3.23.3. Note that the -- (double-dash) comment style requires the second dash to be followed by at least one space (or by a control character such as a newline). This syntax differs slightly from SQL-99 comment syntax, as discussed in ANSI diff comments.
From a /* sequence to the following */ sequence. The closing sequence need not be on the same line, so this syntax allows a comment to extend over multiple lines.
The following example demonstrates all three comment styles:
mysql> SELECT 1+1; # This comment continues to the end of line mysql> SELECT 1+1; -- This comment continues to the end of line mysql> SELECT 1 /* this is an in-line comment */ + 1; mysql> SELECT 1+ /* this is a multiple-line comment */ 1;
The comment syntax just described applies to how the mysqld server parses SQL statements. The mysql client program also performs some parsing of statements before sending them to the server. (For example, it does this to determine statement boundaries within a multiple-statement input line.) However, there are some limitations on the way that mysql parses /* ... */ comments:
A single-quote or double-quote character is taken to indicate the beginning of a quoted string, even within a comment. If the quote is not matched by a second quote within the comment, the parser doesn't realize the comment has ended. If you are running mysql interactively, you can tell that it has gotten confused like this because the prompt changes from mysql> to '> or ">. This problem was fixed in MySQL 4.1.1.
A semicolon within the comment is taken to indicate the end of the current SQL statement and anything following it to indicate the beginning of the next statement. This problem was fixed in MySQL 4.0.13.
For affected versions of MySQL, these limitations apply both when you run mysql interactively and when you put commands in a file and use mysql in batch mode to process the file with mysql < file_name.
A common problem stems from trying to use an identifier such as a table or column name that is the name of a built-in MySQL datatype or function, such as TIMESTAMP or GROUP. You're allowed to do this (for example, ABS is allowed as a column name). However, by default, no whitespace is allowed in function invocations between the function name and the following ( character. This requirement allows a function call to be distinguished from a reference to a column name.
A side-effect of this behavior is that omitting a space in some contexts causes an identifier to be interpreted as a function name. For example, this statement is legal:
mysql> CREATE TABLE abs (val INT);
But omitting the space after abs causes a syntax error, because the statement then appears to invoke the ABS() function:
mysql> CREATE TABLE abs(val INT);
If the server SQL mode includes the IGNORE_SPACE mode value, the server allows function invocations to have whitespace between a function name and the following ( character. This causes function names to be treated as reserved words. As a result, identifiers that are the same as function names must be quoted as described in Legal names. The server SQL mode is controlled as described in SQL mode.
The words in the following table are explicitly reserved in MySQL. Most of them are forbidden by SQL-92 as column and/or table names (for example, GROUP). A few are reserved because MySQL needs them and (currently) uses a yacc parser. A reserved word can be used as an identifier by quoting it.
Word | Word | Word |
ADD | ALL | ALTER |
ANALYZE | AND | AS |
ASC | ASENSITIVE | AUTO_INCREMENT |
BDB | BEFORE | BERKELEYDB |
BETWEEN | BIGINT | BINARY |
BLOB | BOTH | BY |
CALL | CASCADE | CASE |
CHANGE | CHAR | CHARACTER |
CHECK | COLLATE | COLUMN |
COLUMNS | CONDITION | CONNECTION |
CONSTRAINT | CONTINUE | CREATE |
CROSS | CURRENT_DATE | CURRENT_TIME |
CURRENT_TIMESTAMP | CURSOR | DATABASE |
DATABASES | DAY_HOUR | DAY_MICROSECOND |
DAY_MINUTE | DAY_SECOND | DEC |
DECIMAL | DECLARE | DEFAULT |
DELAYED | DELETE | DESC |
DESCRIBE | DETERMINISTIC | DISTINCT |
DISTINCTROW | DIV | DOUBLE |
DROP | ELSE | ELSEIF |
ENCLOSED | ESCAPED | EXISTS |
EXIT | EXPLAIN | FALSE |
FETCH | FIELDS | FLOAT |
FOR | FORCE | FOREIGN |
FOUND | FRAC_SECOND | FROM |
FULLTEXT | GRANT | GROUP |
HAVING | HIGH_PRIORITY | HOUR_MICROSECOND |
HOUR_MINUTE | HOUR_SECOND | IF |
IGNORE | IN | INDEX |
INFILE | INNER | INNODB |
INOUT | INSENSITIVE | INSERT |
INT | INTEGER | INTERVAL |
INTO | IO_THREAD | IS |
ITERATE | JOIN | KEY |
KEYS | KILL | LEADING |
LEAVE | LEFT | LIKE |
LIMIT | LINES | LOAD |
LOCALTIME | LOCALTIMESTAMP | LOCK |
LONG | LONGBLOB | LONGTEXT |
LOOP | LOW_PRIORITY | MASTER_SERVER_ID |
MATCH | MEDIUMBLOB | MEDIUMINT |
MEDIUMTEXT | MIDDLEINT | MINUTE_MICROSECOND |
MINUTE_SECOND | MOD | NATURAL |
NOT | NO_WRITE_TO_BINLOG | NULL |
NUMERIC | ON | OPTIMIZE |
OPTION | OPTIONALLY | OR |
ORDER | OUT | OUTER |
OUTFILE | PRECISION | PRIMARY |
PRIVILEGES | PROCEDURE | PURGE |
READ | REAL | REFERENCES |
REGEXP | RENAME | REPEAT |
REPLACE | REQUIRE | RESTRICT |
RETURN | REVOKE | RIGHT |
RLIKE | SECOND_MICROSECOND | SELECT |
SENSITIVE | SEPARATOR | SET |
SHOW | SMALLINT | SOME |
SONAME | SPATIAL | SPECIFIC |
SQL | SQLEXCEPTION | SQLSTATE |
SQLWARNING | SQL_BIG_RESULT | SQL_CALC_FOUND_ROWS |
SQL_SMALL_RESULT | SQL_TSI_DAY | SQL_TSI_FRAC_SECOND |
SQL_TSI_HOUR | SQL_TSI_MINUTE | SQL_TSI_MONTH |
SQL_TSI_QUARTER | SQL_TSI_SECOND | SQL_TSI_WEEK |
SQL_TSI_YEAR | SSL | STARTING |
STRAIGHT_JOIN | STRIPED | TABLE |
TABLES | TERMINATED | THEN |
TIMESTAMPADD | TIMESTAMPDIFF | TINYBLOB |
TINYINT | TINYTEXT | TO |
TRAILING | TRUE | UNDO |
UNION | UNIQUE | UNLOCK |
UNSIGNED | UPDATE | USAGE |
USE | USER_RESOURCES | USING |
UTC_DATE | UTC_TIME | UTC_TIMESTAMP |
VALUES | VARBINARY | VARCHAR |
VARCHARACTER | VARYING | WHEN |
WHERE | WHILE | WITH |
WRITE | XOR | YEAR_MONTH |
ZEROFILL |
The following symbols (from the table above) are disallowed by SQL-99 but allowed by MySQL as column/table names. This is because they are very natural names and a lot of people have already used them.
ACTION
BIT
DATE
ENUM
NO
TEXT
TIME
TIMESTAMP
Table of Contents
MySQL supports a number of column types, which may be grouped into three categories: numeric types, date and time types, and string (character) types. This section first gives an overview of the types available and summarizes the storage requirements for each column type, and then provides a more detailed description of the properties of the types in each category. The overview is intentionally brief. The more detailed descriptions should be consulted for additional information about particular column types, such as the allowable formats in which you can specify values.
The column types supported by MySQL follow. The following code letters are used in the descriptions:
M | Indicates the maximum display size. The maximum legal display size is 255. |
D | Applies to floating-point types and indicates the number of digits following the decimal point. The maximum possible value is 30, but should be no greater than M-2. |
Square brackets ([ and ]) indicate parts of type specifiers that are optional.
Note that if you specify ZEROFILL for a column, MySQL automatically adds the UNSIGNED attribute to the column.
Warning: You should be aware that when you use subtraction between integer values where one is of type UNSIGNED, the result will be unsigned! See Cast Functions.
TINYINT[(M)] [UNSIGNED] [ZEROFILL] | A very small integer. The signed range is -128 to 127. The unsigned range is 0 to 255. |
BIT , BOOL , BOOLEAN | These are synonyms for TINYINT(1). The BOOLEAN synonym was added in version 4.1.0 Full boolean type handling will be introduced in accordance with SQL-99. |
SMALLINT[(M)] [UNSIGNED] [ZEROFILL] | A small integer. The signed range is -32768 to 32767. The unsigned range is 0 to 65535. |
MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL] | A medium-size integer. The signed range is -8388608 to 8388607. The unsigned range is 0 to 16777215. |
INT[(M)] [UNSIGNED] [ZEROFILL] | A normal-size integer. The signed range is -2147483648 to 2147483647. The unsigned range is 0 to 4294967295. |
INTEGER[(M)] [UNSIGNED] [ZEROFILL] | This is a synonym for INT. |
BIGINT[(M)] [UNSIGNED] [ZEROFILL] |
A large integer. The signed range is -9223372036854775808 to
9223372036854775807. The unsigned range is 0 to
18446744073709551615.
Some things you should be aware of with respect to BIGINT columns:
|
FLOAT(precision) [UNSIGNED] [ZEROFILL] | A floating-point number. precision can be <=24 for a single-precision floating-point number and between 25 and 53 for a double-precision floating-point number. These types are like the FLOAT and DOUBLE types described immediately following. FLOAT(X) has the same range as the corresponding FLOAT and DOUBLE types, but the display size and number of decimals are undefined. In MySQL Version 3.23, this is a true floating-point value. In earlier MySQL versions, FLOAT(precision) always has 2 decimals. Note that using FLOAT might give you some unexpected problems because all calculations in MySQL are done with double precision. See No matching rows. This syntax is provided for ODBC compatibility. |
FLOAT[(M,D)] [UNSIGNED] [ZEROFILL] | A small (single-precision) floating-point number. Allowable values are -3.402823466E+38 to -1.175494351E-38, 0, and 1.175494351E-38 to 3.402823466E+38. If UNSIGNED is specified, negative values are disallowed. The M is the display width and D is the number of decimals. FLOAT without arguments or FLOAT(X) (where X is in the range from 0 to 24) stands for a single-precision floating-point number. |
DOUBLE[(M,D)] [UNSIGNED] [ZEROFILL] | A normal-size (double-precision) floating-point number. Allowable values are -1.7976931348623157E+308 to -2.2250738585072014E-308, 0, and 2.2250738585072014E-308 to 1.7976931348623157E+308. If UNSIGNED is specified, negative values are disallowed. The M is the display width and D is the number of decimals. DOUBLE without arguments or FLOAT(X) (where X is in the range from 25 to 53) stands for a double-precision floating-point number. |
DOUBLE PRECISION[(M,D)] [UNSIGNED] [ZEROFILL] , REAL[(M,D)] [UNSIGNED] [ZEROFILL] | These are synonyms for DOUBLE. |
DECIMAL[(M[,D])] [UNSIGNED] [ZEROFILL] | An unpacked floating-point number. Behaves like a CHAR column: ``unpacked'' means the number is stored as a string, using one character for each digit of the value. The decimal point and, for negative numbers, the - sign, are not counted in M (but space for these is reserved). If D is 0, values will have no decimal point or fractional part. The maximum range of DECIMAL values is the same as for DOUBLE, but the actual range for a given DECIMAL column may be constrained by the choice of M and D. If UNSIGNED is specified, negative values are disallowed. If D is omitted, the default is 0. If M is omitted, the default is 10. Prior to MySQL Version 3.23, the M argument must include the space needed for the sign and the decimal point. |
DEC[(M[,D])] [UNSIGNED] [ZEROFILL] , NUMERIC[(M[,D])] [UNSIGNED] [ZEROFILL] , FIXED[(M[,D])] [UNSIGNED] [ZEROFILL] | These are synonyms for DECIMAL. The FIXED alias was added in version 4.1.0 for compatibility with other servers. |
DATE | A date. The supported range is '1000-01-01' to '9999-12-31'. MySQL displays DATE values in 'YYYY-MM-DD' format, but allows you to assign values to DATE columns using either strings or numbers. See DATETIME. |
DATETIME | A date and time combination. The supported range is '1000-01-01 00:00:00' to '9999-12-31 23:59:59'. MySQL displays DATETIME values in 'YYYY-MM-DD HH:MM:SS' format, but allows you to assign values to DATETIME columns using either strings or numbers. See DATETIME. |
TIMESTAMP[(M)] | A timestamp. The range is '1970-01-01 00:00:00' to sometime in the year 2037. In MySQL 4.0 and earlier, TIMESTAMP values are displayed in YYYYMMDDHHMMSS, YYMMDDHHMMSS, YYYYMMDD, or YYMMDD format, depending on whether M is 14 (or missing), 12, 8, or 6, but allows you to assign values to TIMESTAMP columns using either strings or numbers. From MySQL 4.1, TIMESTAMP is returned as a string with the format 'YYYY-MM-DD HH:MM:SS'. If you want to have this as a number, you should add +0 to the timestamp column. Different timestamp lengths are not supported. From version 4.0.12, the --new option can be used to make the server behave as in version 4.1. A TIMESTAMP column is useful for recording the date and time of an INSERT or UPDATE operation because it is automatically set to the date and time of the most recent operation if you don't give it a value yourself. You can also set it to the current date and time by assigning it a NULL value. See Date and time types. The M argument affects only how a TIMESTAMP column is displayed; its values always are stored using 4 bytes each. Note that TIMESTAMP(M) columns where M is 8 or 14 are reported to be numbers, whereas other TIMESTAMP(M) columns are reported to be strings. This is just to ensure that you can reliably dump and restore the table with these types! See DATETIME. |
TIME | A time. The range is '-838:59:59' to '838:59:59'. MySQL displays TIME values in 'HH:MM:SS' format, but allows you to assign values to TIME columns using either strings or numbers. See TIME. |
YEAR[(2|4)] | A year in 2- or 4-digit format (default is 4-digit). The allowable values are 1901 to 2155, 0000 in the 4-digit year format, and 1970-2069 if you use the 2-digit format (70-69). MySQL displays YEAR values in YYYY format, but allows you to assign values to YEAR columns using either strings or numbers. (The YEAR type is unavailable prior to MySQL Version 3.22.) See YEAR. |
[NATIONAL] CHAR(M) [BINARY | ASCII | UNICODE] | A fixed-length string that is always right-padded with spaces to the specified length when stored. The range of M is 0 to 255 characters (1 to 255 prior to MySQL Version 3.23). Trailing spaces are removed when the value is retrieved. CHAR values are sorted and compared in case-insensitive fashion according to the default character set unless the BINARY keyword is given. From version 4.1.0, if the M value specified is greater than 255, the column type is converted to TEXT. This is a compatibility feature. NATIONAL CHAR (or its equivalent short form, NCHAR) is the SQL-99 way to define that a CHAR column should use the default CHARACTER set. This is the default in MySQL. CHAR is a shorthand for CHARACTER. From version 4.1.0, the ASCII attribute can be specified which assigns the latin1 character set to a CHAR column. From version 4.1.1, the UNICODE attribute can be specified which assigns the ucs2 character set to a CHAR column. MySQL allows you to create a column of type CHAR(0). This is mainly useful when you have to be compliant with some old applications that depend on the existence of a column but that do not actually use the value. This is also quite nice when you need a column that can take only two values: A CHAR(0), that is not defined as NOT NULL, will occupy only one bit and can take two values: NULL or "". See CHAR. |
CHAR | This is a synonym for CHAR(1). |
[NATIONAL] VARCHAR(M) [BINARY] | A variable-length string. Note: Trailing spaces are removed when the value is stored (this differs from the SQL-99 specification). The range of M is 0 to 255 characters (1 to 255 prior to MySQL Version 4.0.2). VARCHAR values are sorted and compared in case-insensitive fashion unless the BINARY keyword is given. See Silent column changes. From version 4.1.0, if the M value specified is greater than 255, the column type is converted to TEXT. This is a compatibility feature. VARCHAR is a shorthand for CHARACTER VARYING. See CHAR. |
TINYBLOB , TINYTEXT | A BLOB or TEXT column with a maximum length of 255 (2^8 - 1) characters. See Silent column changes. See BLOB. |
BLOB , TEXT | A BLOB or TEXT column with a maximum length of 65535 (2^16 - 1) characters. See Silent column changes. See BLOB. |
MEDIUMBLOB , MEDIUMTEXT | A BLOB or TEXT column with a maximum length of 16777215 (2^24 - 1) characters. See Silent column changes. See BLOB. |
LONGBLOB , LONGTEXT | A BLOB or TEXT column with a maximum length of 4294967295 or 4G (2^32 - 1) characters. See Silent column changes. Up to MySQL version 3.23 the server/client protocol and MyISAM tables had a limit of 16M per communication packet / table row, from version 4.x the maximum allowed length of LONGTEXT or LONGBLOB columns depends on the configured maximum packet size in the client/server protocol and available memory. See BLOB. |
ENUM('value1','value2',...) | An enumeration. A string object that can have only one value, chosen from the list of values 'value1', 'value2', ..., NULL or the special "" error value. An ENUM can have a maximum of 65535 distinct values. See ENUM. |
SET('value1','value2',...) | A set. A string object that can have zero or more values, each of which must be chosen from the list of values 'value1', 'value2', ... A SET can have a maximum of 64 members. See SET. |
MySQL supports all of the SQL-92 numeric datatypes. These types include the exact numeric datatypes (NUMERIC, DECIMAL, INTEGER, and SMALLINT), as well as the approximate numeric datatypes (FLOAT, REAL, and DOUBLE PRECISION). The keyword INT is a synonym for INTEGER, and the keyword DEC is a synonym for DECIMAL.
The NUMERIC and DECIMAL types are implemented as the same type by MySQL, as permitted by the SQL-92 standard. They are used for values for which it is important to preserve exact precision, for example with monetary data. When declaring a column of one of these types the precision and scale can be (and usually is) specified; for example:
salary DECIMAL(5,2)
In this example, 5 (precision) represents the number of significant decimal digits that will be stored for values, and 2 (scale) represents the number of digits that will be stored following the decimal point. In this case, therefore, the range of values that can be stored in the salary column is from -99.99 to 99.99. (MySQL can actually store numbers up to 999.99 in this column because it doesn't have to store the sign for positive numbers)
In SQL-92, the syntax DECIMAL(p) is equivalent to DECIMAL(p,0). Similarly, the syntax DECIMAL is equivalent to DECIMAL(p,0), where the implementation is allowed to decide the value of p. MySQL does not currently support either of these variant forms of the DECIMAL/NUMERIC datatypes. This is not generally a serious problem, as the principal benefits of these types derive from the ability to control both precision and scale explicitly.
DECIMAL and NUMERIC values are stored as strings, rather than as binary floating-point numbers, in order to preserve the decimal precision of those values. One character is used for each digit of the value, the decimal point (if scale > 0), and the - sign (for negative numbers). If scale is 0, DECIMAL and NUMERIC values contain no decimal point or fractional part.
The maximum range of DECIMAL and NUMERIC values is the same as for DOUBLE, but the actual range for a given DECIMAL or NUMERIC column can be constrained by the precision or scale for a given column. When such a column is assigned a value with more digits following the decimal point than are allowed by the specified scale, the value is converted to that scale. (The precise behavior is operating-system specific, but generally the effect is truncation to the allowable number of digits.) When a DECIMAL or NUMERIC column is assigned a value whose magnitude exceeds the range implied by the specified (or defaulted) precision and scale, MySQL stores the value representing the corresponding end point of that range.
As an extension to the SQL-92 standard, MySQL also supports the integer types TINYINT, MEDIUMINT, and BIGINT as listed in the tables above. Another extension is supported by MySQL for optionally specifying the display width of an integer value in parentheses following the base keyword for the type (for example, INT(4)). This optional width specification is used to left-pad the display of values whose width is less than the width specified for the column, but does not constrain the range of values that can be stored in the column, nor the number of digits that will be displayed for values whose width exceeds that specified for the column. When used in conjunction with the optional extension attribute ZEROFILL, the default padding of spaces is replaced with zeroes. For example, for a column declared as INT(5) ZEROFILL, a value of 4 is retrieved as 00004. Note that if you store larger values than the display width in an integer column, you may experience problems when MySQL generates temporary tables for some complicated joins, as in these cases MySQL trusts that the data did fit into the original column width.
All integer types can have an optional (non-standard) attribute UNSIGNED. Unsigned values can be used when you want to allow only positive numbers in a column and you need a little bigger numeric range for the column.
As of MySQL 4.0.2, floating-point types also can be UNSIGNED. As with integer types, this attribute prevents negative values from being stored in the column. Unlike the integer types, the upper range of column values remains the same.
The FLOAT type is used to represent approximate numeric datatypes. The SQL-92 standard allows an optional specification of the precision (but not the range of the exponent) in bits following the keyword FLOAT in parentheses. The MySQL implementation also supports this optional precision specification. When the keyword FLOAT is used for a column type without a precision specification, MySQL uses four bytes to store the values. A variant syntax is also supported, with two numbers given in parentheses following the FLOAT keyword. With this option, the first number continues to represent the storage requirements for the value in bytes, and the second number specifies the number of digits to be stored and displayed following the decimal point (as with DECIMAL and NUMERIC). When MySQL is asked to store a number for such a column with more decimal digits following the decimal point than specified for the column, the value is rounded to eliminate the extra digits when the value is stored.
The REAL and DOUBLE PRECISION types do not accept precision specifications. As an extension to the SQL-92 standard, MySQL recognizes DOUBLE as a synonym for the DOUBLE PRECISION type. In contrast with the standard's requirement that the precision for REAL be smaller than that used for DOUBLE PRECISION, MySQL implements both as 8-byte double-precision floating-point values (when not running in ``ANSI mode''). For maximum portability, code requiring storage of approximate numeric data values should use FLOAT or DOUBLE PRECISION with no specification of precision or number of decimal points.
When asked to store a value in a numeric column that is outside the column type's allowable range, MySQL clips the value to the appropriate endpoint of the range and stores the resulting value instead.
For example, the range of an INT column is -2147483648 to 2147483647. If you try to insert -9999999999 into an INT column, the value is clipped to the lower endpoint of the range, and -2147483648 is stored instead. Similarly, if you try to insert 9999999999, 2147483647 is stored instead.
If the INT column is UNSIGNED, the size of the column's range is the same but its endpoints shift up to 0 and 4294967295. If you try to store -9999999999 and 9999999999, the values stored in the column become 0 and 4294967296.
Conversions that occur due to clipping are reported as ``warnings'' for ALTER TABLE, LOAD DATA INFILE, UPDATE, and multi-row INSERT statements.
Type | Bytes | From | To |
TINYINT | 1 | -128 | 127 |
SMALLINT | 2 | -32768 | 32767 |
MEDIUMINT | 3 | -8388608 | 8388607 |
INT | 4 | -2147483648 | 2147483647 |
BIGINT | 8 | -9223372036854775808 | 9223372036854775807 |
Table of Contents
The date and time types are DATETIME, DATE, TIMESTAMP, TIME, and YEAR. Each of these has a range of legal values, as well as a ``zero'' value that is used when you specify a really illegal value. Note that MySQL allows you to store certain 'not strictly' legal date values, for example 1999-11-31. The reason for this is that we think it's the responsibility of the application to handle date checking, not the SQL servers. To make the date checking 'fast', MySQL only checks that the month is in the range of 0-12 and the day is in the range of 0-31. The above ranges are defined this way because MySQL allows you to store, in a DATE or DATETIME column, dates where the day or month-day is zero. This is extremely useful for applications that need to store a birth-date for which you don't know the exact date. In this case you simply store the date like 1999-00-00 or 1999-01-00. (You cannot expect to get a correct value from functions like DATE_SUB() or DATE_ADD for dates like these.)
Here are some general considerations to keep in mind when working with date and time types:
MySQL retrieves values for a given date or time type in a standard format, but it attempts to interpret a variety of formats for values that you supply (for example, when you specify a value to be assigned to or compared to a date or time type). Nevertheless, only the formats described in the following sections are supported. It is expected that you will supply legal values, and unpredictable results may occur if you use values in other formats.
Although MySQL tries to interpret values in several formats, it always expects the year part of date values to be leftmost. Dates must be given in year-month-day order (for example, '98-09-04'), rather than in the month-day-year or day-month-year orders commonly used elsewhere (for example, '09-04-98', '04-09-98').
MySQL automatically converts a date or time type value to a number if the value is used in a numeric context, and vice versa.
When MySQL encounters a value for a date or time type that is out of range or otherwise illegal for the type (see the start of this section), it converts the value to the ``zero'' value for that type. (The exception is that out-of-range TIME values are clipped to the appropriate endpoint of the TIME range.) The following table shows the format of the ``zero'' value for each type:
Column type | ``Zero'' value |
DATETIME | '0000-00-00 00:00:00' |
DATE | '0000-00-00' |
TIMESTAMP | 00000000000000 (length depends on display size) |
TIME | '00:00:00' |
YEAR | 0000 |
The ``zero'' values are special, but you can store or refer to them explicitly using the values shown in the table. You can also do this using the values '0' or 0, which are easier to write.
``Zero'' date or time values used through MyODBC are converted automatically to NULL in MyODBC Version 2.50.12 and above, because ODBC can't handle such values.
MySQL itself is Y2K-safe (see Year 2000 compliance), but input values presented to MySQL may not be. Any input containing 2-digit year values is ambiguous, because the century is unknown. Such values must be interpreted into 4-digit form because MySQL stores years internally using four digits.
For DATETIME, DATE, TIMESTAMP, and YEAR types, MySQL interprets dates with ambiguous year values using the following rules:
Year values in the range 00-69 are converted to 2000-2069.
Year values in the range 70-99 are converted to 1970-1999.
Remember that these rules provide only reasonable guesses as to what your data mean. If the heuristics used by MySQL don't produce the correct values, you should provide unambiguous input containing 4-digit year values.
ORDER BY will sort 2-digit YEAR/DATE/DATETIME types properly.
Note also that some functions like MIN() and MAX() will convert a TIMESTAMP/DATE to a number. This means that a timestamp with a 2-digit year will not work properly with these functions. The fix in this case is to convert the TIMESTAMP/DATE to 4-digit year format or use something like MIN(DATE_ADD(timestamp,INTERVAL 0 DAYS)).
The DATETIME, DATE, and TIMESTAMP types are related. This section describes their characteristics, how they are similar, and how they differ.
The DATETIME type is used when you need values that contain both date and time information. MySQL retrieves and displays DATETIME values in 'YYYY-MM-DD HH:MM:SS' format. The supported range is '1000-01-01 00:00:00' to '9999-12-31 23:59:59'. (``Supported'' means that although earlier values might work, there is no guarantee that they will.)
The DATE type is used when you need only a date value, without a time part. MySQL retrieves and displays DATE values in 'YYYY-MM-DD' format. The supported range is '1000-01-01' to '9999-12-31'.
The TIMESTAMP column type has varying properties and behavior, depending on the MySQL version and the SQL mode the server is running in.
When MySQL is running in MAXDB mode, TIMESTAMP behaves like DATETIME. No automatic updating of TIMESTAMP columns occurs, as described in the following paragraphs. MySQL can be run in MAXDB mode as of version 4.1.1. See Server options.
The TIMESTAMP column type provides a type that you can use to automatically mark INSERT or UPDATE operations with the current date and time. If you have multiple TIMESTAMP columns, only the first one is updated automatically.
Automatic updating of the first TIMESTAMP column occurs under any of the following conditions:
The column is not specified explicitly in an INSERT or LOAD DATA INFILE statement.
The column is not specified explicitly in an UPDATE statement and some other column changes value. (Note that an UPDATE that sets a column to the value it already has will not cause the TIMESTAMP column to be updated, because if you set a column to its current value, MySQL ignores the update for efficiency.)
You explicitly set the TIMESTAMP column to NULL.
TIMESTAMP columns other than the first may also be set to the current date and time. Just set the column to NULL or to NOW().
You can set any TIMESTAMP column to a value different from the current date and time by setting it explicitly to the desired value. This is true even for the first TIMESTAMP column. You can use this property if, for example, you want a TIMESTAMP to be set to the current date and time when you create a row, but not to be changed whenever the row is updated later:
Let MySQL set the column when the row is created. This will initialize it to the current date and time.
When you perform subsequent updates to other columns in the row, set the TIMESTAMP column explicitly to its current value.
On the other hand, you may find it just as easy to use a DATETIME column that you initialize to NOW() when the row is created and leave alone for subsequent updates.
When MySQL is running in MAXDB mode, TIMESTAMP is identical with DATETIME. It uses the same format to store and display values, and it has the same range. MySQL can be run in MAXDB mode as of version 4.1.1. See Server options.
In MySQL 4.1.0, TIMESTAMP columns are stored and displayed in the same format as DATETIME columns. This also means that they cannot be narrowed or widened in the ways described in the following paragraphs. In other words, you cannot use TIMESTAMP(2), TIMESTAMP(4), etc. Other than that, the properties are the same as in previous MySQL versions.
TIMESTAMP values may range from the beginning of 1970 to sometime in the year 2037, with a resolution of one second. Values are displayed as numbers.
The format in which MySQL retrieves and displays TIMESTAMP values depends on the display size, as illustrated by the following table. The `full' TIMESTAMP format is 14 digits, but TIMESTAMP columns may be created with shorter display sizes:
Column type | Display format |
TIMESTAMP(14) | YYYYMMDDHHMMSS |
TIMESTAMP(12) | YYMMDDHHMMSS |
TIMESTAMP(10) | YYMMDDHHMM |
TIMESTAMP(8) | YYYYMMDD |
TIMESTAMP(6) | YYMMDD |
TIMESTAMP(4) | YYMM |
TIMESTAMP(2) | YY |
All TIMESTAMP columns have the same storage size, regardless of display size. The most common display sizes are 6, 8, 12, and 14. You can specify an arbitrary display size at table creation time, but values of 0 or greater than 14 are coerced to 14. Odd-valued sizes in the range from 1 to 13 are coerced to the next higher even number.
Note: From version 4.1, TIMESTAMP is returned as a string with the format 'YYYY-MM-DD HH:MM:SS' and different timestamp lengths are no longer supported.
You can specify DATETIME, DATE, and TIMESTAMP values using any of a common set of formats:
As a string in either 'YYYY-MM-DD HH:MM:SS' or 'YY-MM-DD HH:MM:SS' format. A ``relaxed'' syntax is allowed---any punctuation character may be used as the delimiter between date parts or time parts. For example, '98-12-31 11:30:45', '98.12.31 11+30+45', '98/12/31 11*30*45', and '98@12@31 11^30^45' are equivalent.
As a string in either 'YYYY-MM-DD' or 'YY-MM-DD' format. A ``relaxed'' syntax is allowed here, too. For example, '98-12-31', '98.12.31', '98/12/31', and '98@12@31' are equivalent.
As a string with no delimiters in either 'YYYYMMDDHHMMSS' or 'YYMMDDHHMMSS' format, provided that the string makes sense as a date. For example, '19970523091528' and '970523091528' are interpreted as '1997-05-23 09:15:28', but '971122129015' is illegal (it has a nonsensical minute part) and becomes '0000-00-00 00:00:00'.
As a string with no delimiters in either 'YYYYMMDD' or 'YYMMDD' format, provided that the string makes sense as a date. For example, '19970523' and '970523' are interpreted as '1997-05-23', but '971332' is illegal (it has nonsensical month and day parts) and becomes '0000-00-00'.
As a number in either YYYYMMDDHHMMSS or YYMMDDHHMMSS format, provided that the number makes sense as a date. For example, 19830905132800 and 830905132800 are interpreted as '1983-09-05 13:28:00'.
As a number in either YYYYMMDD or YYMMDD format, provided that the number makes sense as a date. For example, 19830905 and 830905 are interpreted as '1983-09-05'.
As the result of a function that returns a value that is acceptable in a DATETIME, DATE, or TIMESTAMP context, such as NOW() or CURRENT_DATE.
Illegal DATETIME, DATE, or TIMESTAMP values are converted to the ``zero'' value of the appropriate type ('0000-00-00 00:00:00', '0000-00-00', or 00000000000000).
For values specified as strings that include date part delimiters, it is not necessary to specify two digits for month or day values that are less than 10. '1979-6-9' is the same as '1979-06-09'. Similarly, for values specified as strings that include time part delimiters, it is not necessary to specify two digits for hour, minute, or second values that are less than 10. '1979-10-30 1:2:3' is the same as '1979-10-30 01:02:03'.
Values specified as numbers should be 6, 8, 12, or 14 digits long. If the number is 8 or 14 digits long, it is assumed to be in YYYYMMDD or YYYYMMDDHHMMSS format and that the year is given by the first 4 digits. If the number is 6 or 12 digits long, it is assumed to be in YYMMDD or YYMMDDHHMMSS format and that the year is given by the first 2 digits. Numbers that are not one of these lengths are interpreted as though padded with leading zeros to the closest length.
Values specified as non-delimited strings are interpreted using their length as given. If the string is 8 or 14 characters long, the year is assumed to be given by the first 4 characters. Otherwise, the year is assumed to be given by the first 2 characters. The string is interpreted from left to right to find year, month, day, hour, minute, and second values, for as many parts as are present in the string. This means you should not use strings that have fewer than 6 characters. For example, if you specify '9903', thinking that will represent March, 1999, you will find that MySQL inserts a ``zero'' date into your table. This is because the year and month values are 99 and 03, but the day part is completely missing, so the value is not a legal date. However, as of MySQL 3.23, you can explicitly specify a value of zero to represent missing month or day parts. For example, you can use '990300' to insert the value '1999-03-00'.
TIMESTAMP columns store legal values using the full precision with which the value was specified, regardless of the display size. This has several implications:
Always specify year, month, and day, even if your column types are TIMESTAMP(4) or TIMESTAMP(2). Otherwise, the value will not be a legal date and 0 will be stored.
If you use ALTER TABLE to widen a narrow TIMESTAMP column, information will be displayed that previously was ``hidden''.
Similarly, narrowing a TIMESTAMP column does not cause information to be lost, except in the sense that less information is shown when the values are displayed.
Although TIMESTAMP values are stored to full precision, the only function that operates directly on the underlying stored value is UNIX_TIMESTAMP(). Other functions operate on the formatted retrieved value. This means you cannot use functions such as HOUR() or SECOND() unless the relevant part of the TIMESTAMP value is included in the formatted value. For example, the HH part of a TIMESTAMP column is not displayed unless the display size is at least 10, so trying to use HOUR() on shorter TIMESTAMP values produces a meaningless result.
You can to some extent assign values of one date type to an object of a different date type. However, there may be some alteration of the value or loss of information:
If you assign a DATE value to a DATETIME or TIMESTAMP object, the time part of the resulting value is set to '00:00:00', because the DATE value contains no time information.
If you assign a DATETIME or TIMESTAMP value to a DATE object, the time part of the resulting value is deleted, because the DATE type stores no time information.
Remember that although DATETIME, DATE, and TIMESTAMP values all can be specified using the same set of formats, the types do not all have the same range of values. For example, TIMESTAMP values cannot be earlier than 1970 or later than 2037. This means that a date such as '1968-01-01', while legal as a DATETIME or DATE value, is not a valid TIMESTAMP value and will be converted to 0 if assigned to such an object.
Be aware of certain pitfalls when specifying date values:
The relaxed format allowed for values specified as strings can be deceiving. For example, a value such as '10:11:12' might look like a time value because of the : delimiter, but if used in a date context will be interpreted as the year '2010-11-12'. The value '10:45:15' will be converted to '0000-00-00' because '45' is not a legal month.
The MySQL server only performs basic checking on the validity of a date: days 00-31, months 00-12, years 1000-9999. Any date not within this range will revert to 0000-00-00. Please note that this still allows you to store invalid dates such as 2002-04-31. It allows web applications to store data from a form without further checking. To ensure a date is valid, perform a check in your application.
Year values specified as two digits are ambiguous, because the century is unknown. MySQL interprets 2-digit year values using the following rules:
Year values in the range 00-69 are converted to 2000-2069.
Year values in the range 70-99 are converted to 1970-1999.
MySQL retrieves and displays TIME values in 'HH:MM:SS' format (or 'HHH:MM:SS' format for large hours values). TIME values may range from '-838:59:59' to '838:59:59'. The reason the hours part may be so large is that the TIME type may be used not only to represent a time of day (which must be less than 24 hours), but also elapsed time or a time interval between two events (which may be much greater than 24 hours, or even negative).
You can specify TIME values in a variety of formats:
As a string in 'D HH:MM:SS.fraction' format. (Note that MySQL doesn't yet store the fraction for the time column.) One can also use one of the following ``relaxed'' syntax:
HH:MM:SS.fraction, HH:MM:SS, HH:MM, D HH:MM:SS, D HH:MM, D HH or SS. Here D is days between 0-33.
As a string with no delimiters in 'HHMMSS' format, provided that it makes sense as a time. For example, '101112' is understood as '10:11:12', but '109712' is illegal (it has a nonsensical minute part) and becomes '00:00:00'.
As a number in HHMMSS format, provided that it makes sense as a time. For example, 101112 is understood as '10:11:12'. The following alternative formats are also understood: SS, MMSS,HHMMSS, HHMMSS.fraction. Note that MySQL doesn't yet store the fraction part.
As the result of a function that returns a value that is acceptable in a TIME context, such as CURRENT_TIME.
For TIME values specified as strings that include a time part delimiter, it is not necessary to specify two digits for hours, minutes, or seconds values that are less than 10. '8:3:2' is the same as '08:03:02'.
Be careful about assigning ``short'' TIME values to a TIME column. Without colons, MySQL interprets values using the assumption that the rightmost digits represent seconds. (MySQL interprets TIME values as elapsed time rather than as time of day.) For example, you might think of '1112' and 1112 as meaning '11:12:00' (12 minutes after 11 o'clock), but MySQL interprets them as '00:11:12' (11 minutes, 12 seconds). Similarly, '12' and 12 are interpreted as '00:00:12'. TIME values with colons, by contrast, are always treated as time of the day. That is '11:12' will mean '11:12:00', not '00:11:12'.
Values that lie outside the TIME range but are otherwise legal are clipped to the appropriate endpoint of the range. For example, '-850:00:00' and '850:00:00' are converted to '-838:59:59' and '838:59:59'.
Illegal TIME values are converted to '00:00:00'. Note that because '00:00:00' is itself a legal TIME value, there is no way to tell, from a value of '00:00:00' stored in a table, whether the original value was specified as '00:00:00' or whether it was illegal.
The YEAR type is a 1-byte type used for representing years.
MySQL retrieves and displays YEAR values in YYYY format. The range is 1901 to 2155.
You can specify YEAR values in a variety of formats:
As a four-digit string in the range '1901' to '2155'.
As a four-digit number in the range 1901 to 2155.
As a two-digit string in the range '00' to '99'. Values in the ranges '00' to '69' and '70' to '99' are converted to YEAR values in the ranges 2000 to 2069 and 1970 to 1999.
As a two-digit number in the range 1 to 99. Values in the ranges 1 to 69 and 70 to 99 are converted to YEAR values in the ranges 2001 to 2069 and 1970 to 1999. Note that the range for two-digit numbers is slightly different from the range for two-digit strings, because you cannot specify zero directly as a number and have it be interpreted as 2000. You must specify it as a string '0' or '00' or it will be interpreted as 0000.
As the result of a function that returns a value that is acceptable in a YEAR context, such as NOW().
Illegal YEAR values are converted to 0000.
The string types are CHAR, VARCHAR, BLOB, TEXT, ENUM, and SET. This section describes how these types work, their storage requirements, and how to use them in your queries.
Type | Max.size | Bytes |
TINYTEXT or TINYBLOB | 2^8-1 | 255 |
TEXT or BLOB | 2^16-1 (64K-1) | 65535 |
MEDIUMTEXT or MEDIUMBLOB | 2^24-1 (16M-1) | 16777215 |
LONGBLOB | 2^32-1 (4G-1) | 4294967295 |
The CHAR and VARCHAR types are similar, but differ in the way they are stored and retrieved.
The length of a CHAR column is fixed to the length that you declare when you create the table. The length can be any value between 1 and 255. (As of MySQL Version 3.23, the length of CHAR may be 0 to 255.) When CHAR values are stored, they are right-padded with spaces to the specified length. When CHAR values are retrieved, trailing spaces are removed.
Values in VARCHAR columns are variable-length strings. You can declare a VARCHAR column to be any length between 1 and 255, just as for CHAR columns. However, in contrast to CHAR, VARCHAR values are stored using only as many characters as are needed, plus one byte to record the length. Values are not padded; instead, trailing spaces are removed when values are stored. (This space removal differs from the SQL-99 specification.) No case conversion takes place during storage or retrieval.
If you assign a value to a CHAR or VARCHAR column that exceeds the column's maximum length, the value is truncated to fit.
The following table illustrates the differences between the two types of columns by showing the result of storing various string values into CHAR(4) and VARCHAR(4) columns:
Value | CHAR(4) | Storage required | VARCHAR(4) | Storage required |
'' | ' ' | 4 bytes | '' | 1 byte |
'ab' | 'ab ' | 4 bytes | 'ab' | 3 bytes |
'abcd' | 'abcd' | 4 bytes | 'abcd' | 5 bytes |
'abcdefgh' | 'abcd' | 4 bytes | 'abcd' | 5 bytes |
The values retrieved from the CHAR(4) and VARCHAR(4) columns will be the same in each case, because trailing spaces are removed from CHAR columns upon retrieval.
Values in CHAR and VARCHAR columns are sorted and compared in case-insensitive fashion, unless the BINARY attribute was specified when the table was created. The BINARY attribute means that column values are sorted and compared in case-sensitive fashion using the underlying character code values rather then a lexical ordering. BINARY doesn't affect how the column is stored or retrieved.
From version 4.1.0, column type CHAR BYTE is an alias for CHAR BINARY. This is a compatibility feature.
The BINARY attribute is sticky. This means that if a column marked BINARY is used in an expression, the whole expression is compared as a BINARY value.
MySQL may silently change the type of a CHAR or VARCHAR column at table creation time. See Silent column changes.
A BLOB is a binary large object that can hold a variable amount of data. The four BLOB types TINYBLOB, BLOB, MEDIUMBLOB, and LONGBLOB differ only in the maximum length of the values they can hold.
See Storage requirements.
The four TEXT types TINYTEXT, TEXT, MEDIUMTEXT, and LONGTEXT correspond to the four BLOB types and have the same maximum lengths and storage requirements. The only difference between BLOB and TEXT types is that sorting and comparison is performed in case-sensitive fashion for BLOB values and case-insensitive fashion for TEXT values. In other words, a TEXT is a case-insensitive BLOB. No case conversion takes place during storage or retrieval.
If you assign a value to a BLOB or TEXT column that exceeds the column type's maximum length, the value is truncated to fit.
In most respects, you can regard a TEXT column as a VARCHAR column that can be as big as you like. Similarly, you can regard a BLOB column as a VARCHAR BINARY column. The differences are:
From version 4.1.0, LONG and LONG VARCHAR map to the MEDIUMTEXT data type. This is a compatibility feature.
MyODBC defines BLOB values as LONGVARBINARY and TEXT values as LONGVARCHAR.
Because BLOB and TEXT values may be extremely long, you may run up against some constraints when using them:
If you want to use GROUP BY or ORDER BY on a BLOB or TEXT column, you must convert the column value into a fixed-length object. The standard way to do this is with the SUBSTRING function. For example:
mysql> SELECT comment FROM tbl_name,SUBSTRING(comment,20) AS substr -> ORDER BY substr;
If you don't do this, only the first max_sort_length bytes of the column are used when sorting. The default value of max_sort_length is 1024; this value can be changed using the -O option when starting the mysqld server. You can group on an expression involving BLOB or TEXT values by specifying the column position or by using an alias:
mysql> SELECT id,SUBSTRING(blob_col,1,100) FROM tbl_name GROUP BY 2; mysql> SELECT id,SUBSTRING(blob_col,1,100) AS b FROM tbl_name GROUP BY b;
The maximum size of a BLOB or TEXT object is determined by its type, but the largest value you can actually transmit between the client and server is determined by the amount of available memory and the size of the communications buffers. You can change the message buffer size (max_allowed_packet), but you must do so on both the server and client ends. See Server parameters.
Note that each BLOB or TEXT value is represented internally by a separately allocated object. This is in contrast to all other column types, for which storage is allocated once per column when the table is opened.
An ENUM is a string object whose value normally is chosen from a list of allowed values that are enumerated explicitly in the column specification at table creation time.
The value may also be the empty string ("") or NULL under certain circumstances:
If you insert an invalid value into an ENUM (that is, a string not present in the list of allowed values), the empty string is inserted instead as a special error value. This string can be distinguished from a 'normal' empty string by the fact that this string has the numerical value 0. More about this later.
If an ENUM is declared NULL, NULL is also a legal value for the column, and the default value is NULL. If an ENUM is declared NOT NULL, the default value is the first element of the list of allowed values.
Each enumeration value has an index:
Values from the list of allowable elements in the column specification are numbered beginning with 1.
The index value of the empty string error value is 0. This means that you can use the following SELECT statement to find rows into which invalid ENUM values were assigned:
mysql> SELECT * FROM tbl_name WHERE enum_col=0;
The index of the NULL value is NULL.
For example, a column specified as ENUM("one", "two", "three") can have any of the values shown here. The index of each value is also shown:
Value | Index |
NULL | NULL |
"" | 0 |
"one" | 1 |
"two" | 2 |
"three" | 3 |
An enumeration can have a maximum of 65535 elements.
Starting from 3.23.51 trailing spaces are automatically deleted from ENUM values when the table is created.
Lettercase is irrelevant when you assign values to an ENUM column. However, values retrieved from the column later have lettercase matching the values that were used to specify the allowable values at table creation time.
If you retrieve an ENUM in a numeric context, the column value's index is returned. For example, you can retrieve numeric values from an ENUM column like this:
mysql> SELECT enum_col+0 FROM tbl_name;
If you store a number into an ENUM, the number is treated as an index, and the value stored is the enumeration member with that index. (However, this will not work with LOAD DATA, which treats all input as strings.) It's not advisable to store numbers in an ENUM string because it will make things confusing.
ENUM values are sorted according to the order in which the enumeration members were listed in the column specification. (In other words, ENUM values are sorted according to their index numbers.) For example, "a" sorts before "b" for ENUM("a", "b"), but "b" sorts before "a" for ENUM("b", "a"). The empty string sorts before non-empty strings, and NULL values sort before all other enumeration values. To prevent unexpected results, specify the ENUM list in alphabetical order. You can also use GROUP BY CONCAT(col) to make sure the column is sorted alphabetically rather than by index number.
If you want to get all possible values for an ENUM column, you should use: SHOW COLUMNS FROM table_name LIKE enum_column_name and parse the ENUM definition in the second column.
A SET is a string object that can have zero or more values, each of which must be chosen from a list of allowed values specified when the table is created. SET column values that consist of multiple set members are specified with members separated by commas (,). A consequence of this is that SET member values cannot themselves contain commas.
For example, a column specified as SET("one", "two") NOT NULL can have any of these values:
"" "one" "two" "one,two"
A SET can have a maximum of 64 different members.
Starting from 3.23.51 trailing spaces are automatically deleted from SET values when the table is created.
MySQL stores SET values numerically, with the low-order bit of the stored value corresponding to the first set member. If you retrieve a SET value in a numeric context, the value retrieved has bits set corresponding to the set members that make up the column value. For example, you can retrieve numeric values from a SET column like this:
mysql> SELECT set_col+0 FROM tbl_name;
If a number is stored into a SET column, the bits that are set in the binary representation of the number determine the set members in the column value. Suppose a column is specified as SET("a","b","c","d"). Then the members have the following bit values:
SETmember | Decimal value | Binary value |
a | 1 | 0001 |
b | 2 | 0010 |
c | 4 | 0100 |
d | 8 | 1000 |
If you assign a value of 9 to this column, that is 1001 in binary, so the first and fourth SET value members "a" and "d" are selected and the resulting value is "a,d".
For a value containing more than one SET element, it does not matter what order the elements are listed in when you insert the value. It also does not matter how many times a given element is listed in the value. When the value is retrieved later, each element in the value will appear once, with elements listed according to the order in which they were specified at table creation time. For example, if a column is specified as SET("a","b","c","d"), then "a,d", "d,a", and "d,a,a,d,d" will all appear as "a,d" when retrieved.
If you set a SET column to an unsupported value, the value will be ignored.
SET values are sorted numerically. NULL values sort before non-NULL SET values.
Normally, you perform a SELECT on a SET column using the LIKE operator or the FIND_IN_SET() function:
mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%'; mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0;
But the following will also work:
mysql> SELECT * FROM tbl_name WHERE set_col = 'val1,val2'; mysql> SELECT * FROM tbl_name WHERE set_col & 1;
The first of these statements looks for an exact match. The second looks for values containing the first set member.
If you want to get all possible values for a SET column, you should use: SHOW COLUMNS FROM table_name LIKE set_column_name and parse the SET definition in the second column.
For the most efficient use of storage, try to use the most precise type in all cases. For example, if an integer column will be used for values in the range between 1 and 99999, MEDIUMINT UNSIGNED is the best type.
Accurate representation of monetary values is a common problem. In MySQL, you should use the DECIMAL type. This is stored as a string, so no loss of accuracy should occur. If accuracy is not too important, the DOUBLE type may also be good enough.
For high precision, you can always convert to a fixed-point type stored in a BIGINT. This allows you to do all calculations with integers and convert results back to floating-point values only when necessary.
To make it easier to use code written for SQL implementations from other vendors, MySQL maps column types as shown in the following table. These mappings make it easier to move table definitions from other database engines to MySQL:
Other vendor type | MySQL type |
BINARY(NUM) | CHAR(NUM) BINARY |
CHAR VARYING(NUM) | VARCHAR(NUM) |
FLOAT4 | FLOAT |
FLOAT8 | DOUBLE |
INT1 | TINYINT |
INT2 | SMALLINT |
INT3 | MEDIUMINT |
INT4 | INT |
INT8 | BIGINT |
LONG VARBINARY | MEDIUMBLOB |
LONG VARCHAR | MEDIUMTEXT |
MIDDLEINT | MEDIUMINT |
VARBINARY(NUM) | VARCHAR(NUM) BINARY |
Column type mapping occurs at table creation time. If you create a table with types used by other vendors and then issue a DESCRIBE tbl_name statement, MySQL reports the table structure using the equivalent MySQL types.
The storage requirements for each of the column types supported by MySQL are listed by category.
Column type | Storage required |
TINYINT | 1 byte |
SMALLINT | 2 bytes |
MEDIUMINT | 3 bytes |
INT | 4 bytes |
INTEGER | 4 bytes |
BIGINT | 8 bytes |
FLOAT(X) | 4 if X <= 24 or 8 if 25 <= X <= 53 |
FLOAT | 4 bytes |
DOUBLE | 8 bytes |
DOUBLE PRECISION | 8 bytes |
REAL | 8 bytes |
DECIMAL(M,D) | M+2 bytes if D > 0, M+1 bytes if D = 0 (D+2, if M < D) |
NUMERIC(M,D) | M+2 bytes if D > 0, M+1 bytes if D = 0 (D+2, if M < D) |
Column type | Storage required |
DATE | 3 bytes |
DATETIME | 8 bytes |
TIMESTAMP | 4 bytes |
TIME | 3 bytes |
YEAR | 1 byte |
Column type | Storage required |
CHAR(M) | M bytes, 1 <= M <= 255 |
VARCHAR(M) | L+1 bytes, where L <= M and 1 <= M <= 255 |
TINYBLOB, TINYTEXT | L+1 bytes, where L < 2^8 |
BLOB, TEXT | L+2 bytes, where L < 2^16 |
MEDIUMBLOB, MEDIUMTEXT | L+3 bytes, where L < 2^24 |
LONGBLOB, LONGTEXT | L+4 bytes, where L < 2^32 |
ENUM('value1','value2',...) | 1 or 2 bytes, depending on the number of enumeration values (65535 values maximum) |
SET('value1','value2',...) | 1, 2, 3, 4 or 8 bytes, depending on the number of set members (64 members maximum) |
VARCHAR and the BLOB and TEXT types are variable-length types, for which the storage requirements depend on the actual length of column values (represented by L in the preceding table), rather than on the type's maximum possible size. For example, a VARCHAR(10) column can hold a string with a maximum length of 10 characters. The actual storage required is the length of the string (L), plus 1 byte to record the length of the string. For the string 'abcd', L is 4 and the storage requirement is 5 bytes.
The BLOB and TEXT types require 1, 2, 3, or 4 bytes to record the length of the column value, depending on the maximum possible length of the type. See BLOB.
If a table includes any variable-length column types, the record format will also be variable-length. Note that when a table is created, MySQL may, under certain conditions, change a column from a variable-length type to a fixed-length type, or vice-versa. See Silent column changes.
The size of an ENUM object is determined by the number of different enumeration values. One byte is used for enumerations with up to 255 possible values. Two bytes are used for enumerations with up to 65535 values. See ENUM.
The size of a SET object is determined by the number of different set members. If the set size is N, the object occupies (N+7)/8 bytes, rounded up to 1, 2, 3, 4, or 8 bytes. A SET can have a maximum of 64 members. See SET.
The maximum size of a row in a MyISAM table is 65534 bytes. Each BLOB and TEXT column accounts for only 5-9 bytes toward this size.
Table of Contents
A select_expression or where_definition in an SQL statement can consist of any expression using the functions described below.
An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for the operators and functions involved in the expression.
Note: There must be no whitespace between a function name and the parentheses following it. This helps the MySQL parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. Spaces around arguments are permitted, though.
You can force MySQL to accept spaces after the function name by starting mysqld with --ansi or using the CLIENT_IGNORE_SPACE to mysql_connect(), but in this case all function names will become reserved words. See ANSI mode.
For the sake of brevity, examples display the output from the mysql program in abbreviated form. So this:
mysql> SELECT MOD(29,9); 1 rows in set (0.00 sec) +-----------+ | mod(29,9) | +-----------+ | 2 | +-----------+
is displayed like this:
mysql> SELECT MOD(29,9); -> 2
( ... )
Use parentheses to force the order of evaluation in an expression. For example:
mysql> SELECT 1+2*3; -> 7 mysql> SELECT (1+2)*3; -> 9
Comparison operations result in a value of 1 (TRUE), 0 (FALSE), or NULL. These functions work for both numbers and strings. Strings are automatically converted to numbers and numbers to strings as needed (as in Perl).
MySQL performs comparisons using the following rules:
If one or both arguments are NULL, the result of the comparison is NULL, except for the <=> operator.
If both arguments in a comparison operation are strings, they are compared as strings.
If both arguments are integers, they are compared as integers.
Hexadecimal values are treated as binary strings if not compared to a number.
If one of the arguments is a TIMESTAMP or DATETIME column and the other argument is a constant, the constant is converted to a timestamp before the comparison is performed. This is done to be more ODBC-friendly.
In all other cases, the arguments are compared as floating-point (real) numbers.
By default, string comparisons are done in case-independent fashion using the current character set (ISO-8859-1 Latin1 by default, which also works excellently for English).
If you are comparing case-insensitive strings with any of the standard operators (=, <>..., but not LIKE) trailing whitespace (spaces, tabs and newlines) will be ignored.
mysql> SELECT "a" ="A \n"; -> 1
The following examples illustrate conversion of strings to numbers for comparison operations:
mysql> SELECT 1 > '6x'; -> 0 mysql> SELECT 7 > '6x'; -> 1 mysql> SELECT 0 > 'x6'; -> 0 mysql> SELECT 0 = 'x6'; -> 1
Note that when you are comparing a string column with a number, MySQL can't use index to quickly look up the value:
SELECT * FROM table_name WHERE string_key=1
The reason for this is that there is many different strings that may return the value 1: "1", " 1", "1a" ...
= |
Equal:
mysql> SELECT 1 = 0; -> 0 mysql> SELECT '0' = 0; -> 1 mysql> SELECT '0.0' = 0; -> 1 mysql> SELECT '0.01' = 0; -> 0 mysql> SELECT '.01' = 0.01; -> 1 |
<> , != |
Not equal:
mysql> SELECT '.01' <> '0.01'; -> 1 mysql> SELECT .01 <> '0.01'; -> 0 mysql> SELECT 'zapp' <> 'zappp'; -> 1 |
<= |
Less than or equal:
mysql> SELECT 0.1 <= 2; -> 1 |
< |
Less than:
mysql> SELECT 2 < 2; -> 0 |
>= |
Greater than or equal:
mysql> SELECT 2 >= 2; -> 1 |
> |
Greater than:
mysql> SELECT 2 > 2; -> 0 |
<=> | NULL-safe equal:
mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL; -> 1 1 0 |
IS NULL , IS NOT NULL |
Test whether a value is or is not NULL:
mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL; -> 0 0 1 mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL; -> 1 1 0To be able to work well with other programs, MySQL supports the following extra features when using IS NULL:
|
expr BETWEEN min AND max |
If expr is greater than or equal to min and expr is
less than or equal to max, BETWEEN returns 1,
otherwise it returns 0. This is equivalent to the expression
(min <= expr AND expr <= max) if all the arguments are of the
same type. Otherwise type conversion takes place, according to the rules
above, but applied to all the three arguments. Note that before
4.0.5 arguments were converted to the type of expr instead.
mysql> SELECT 1 BETWEEN 2 AND 3; -> 0 mysql> SELECT 'b' BETWEEN 'a' AND 'c'; -> 1 mysql> SELECT 2 BETWEEN 2 AND '3'; -> 1 mysql> SELECT 2 BETWEEN 2 AND 'x-3'; -> 0 |
expr NOT BETWEEN min AND max | Same as NOT (expr BETWEEN min AND max). |
expr IN (value,...) |
Returns 1 if expr is any of the values in the IN list,
else returns 0. If all values are constants, then all values are
evaluated according to the type of expr and sorted. The search for the
item is then done using a binary search. This means IN is very quick
if the IN value list consists entirely of constants. If expr
is a case-sensitive string expression, the string comparison is performed in
case-sensitive fashion:
mysql> SELECT 2 IN (0,3,5,'wefwf'); -> 0 mysql> SELECT 'wefwf' IN (0,3,5,'wefwf'); -> 1The number of values in the IN list is only limited by the max_allowed_packet value. From 4.1 (to comply with the SQL-99 standard), IN returns NULL not only if the expression on the left hand side is NULL, but also if no match is found in the list and one of the expressions in the list is NULL. From MySQL version 4.1, an IN() clause may also contain a subquery. See ANY IN SOME subqueries. |
expr NOT IN (value,...) | Same as NOT (expr IN (value,...)). |
ISNULL(expr) |
If expr is NULL, ISNULL() returns 1, otherwise
it returns 0:
mysql> SELECT ISNULL(1+1); -> 0 mysql> SELECT ISNULL(1/0); -> 1Note that a comparison of NULL values using = will always be false! |
COALESCE(list) |
Returns first non-NULL element in list:
mysql> SELECT COALESCE(NULL,1); -> 1 mysql> SELECT COALESCE(NULL,NULL,NULL); -> NULL |
INTERVAL(N,N1,N2,N3,...) |
Returns 0 if N < N1, 1 if N < N2
and so on or -1 if N is NULL. All arguments are treated
as integers. It is required that N1 < N2 < N3 <
... < Nn for this function to work correctly. This is because
a binary search is used (very fast):
mysql> SELECT INTERVAL(23, 1, 15, 17, 30, 44, 200); -> 3 mysql> SELECT INTERVAL(10, 1, 10, 100, 1000); -> 2 mysql> SELECT INTERVAL(22, 23, 30, 44, 200); -> 0 |
In SQL, all logical operators evaluate to TRUE, FALSE or NULL (UNKNOWN). In MySQL, this is implemented as 1 (TRUE), 0 (FALSE), and NULL. Most of this is common between different SQL databases, however some may return any non-zero value for TRUE.
Table of Contents
String-valued functions return NULL if the length of the result would be greater than the max_allowed_packet server parameter. See Server parameters.
For functions that operate on string positions, the first position is numbered 1.
ASCII(str) |
Returns the ASCII code value of the leftmost character of the string
str. Returns 0 if str is the empty string. Returns
NULL if str is NULL:
mysql> SELECT ASCII('2'); -> 50 mysql> SELECT ASCII(2); -> 50 mysql> SELECT ASCII('dx'); -> 100See also the ORD() function. |
BIN(N) |
Returns a string representation of the binary value of N, where
N is a longlong (BIGINT) number. This is equivalent to
CONV(N,10,2). Returns NULL if N is NULL:
mysql> SELECT BIN(12); -> '1100' |
BIT_LENGTH(str) |
Returns the length of the string str in bits:
mysql> SELECT BIT_LENGTH('text'); -> 32 |
CHAR(N,...) | CHAR() interprets the arguments as integers and returns a string
consisting of the characters given by the ASCII code values of those
integers. NULL values are skipped:
mysql> SELECT CHAR(77,121,83,81,'76'); -> 'MySQL' mysql> SELECT CHAR(77,77.3,'77.3'); -> 'MMM' |
CHAR_LENGTH(str) | Returns the length of the string str, measured in characters. A multi-byte character counts as a single character. This means that for a string containing five two-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5. |
CHARACTER_LENGTH(str) | CHARACTER_LENGTH() is a synonym for CHAR_LENGTH(). |
COMPRESS(string_to_compress) |
Compresses a string.
mysql> SELECT LENGTH(COMPRESS(REPEAT("a",1000))); -> 21 mysql> SELECT LENGTH(COMPRESS("")); -> 0 mysql> SELECT LENGTH(COMPRESS("a")); -> 13 mysql> SELECT LENGTH(COMPRESS(REPEAT("a",16))); -> 15COMPRESS() was added in MySQL version 4.1.1. It requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL. The compressed string contents are stored the following way:
|
CONCAT(str1,str2,...) |
Returns the string that results from concatenating the arguments. Returns
NULL if any argument is NULL. May have more than two arguments.
A numeric argument is converted to its equivalent string form:
mysql> SELECT CONCAT('My', 'S', 'QL'); -> 'MySQL' mysql> SELECT CONCAT('My', NULL, 'QL'); -> NULL mysql> SELECT CONCAT(14.3); -> '14.3' |
CONCAT_WS(separator, str1, str2,...) | CONCAT_WS() stands for CONCAT With Separator and is a special form of
CONCAT(). The first argument is the separator for the rest of the
arguments.
The separator is added between the strings to be concatenated:
The separator can be a string as can the rest of the
arguments. If the separator is NULL, the result is NULL.
The function skips any NULL values after the
separator argument.
mysql> SELECT CONCAT_WS(",","First name","Second name","Last Name"); -> 'First name,Second name,Last Name' mysql> SELECT CONCAT_WS(",","First name",NULL,"Last Name"); -> 'First name,Last Name'Before MySQL 4.0.14, CONCAT_WS() skips empty strings as well as NULL values. |
CONV(N,from_base,to_base) |
Converts numbers between different number bases. Returns a string
representation of the number N, converted from base from_base
to base to_base. Returns NULL if any argument is NULL.
The argument N is interpreted as an integer, but may be specified as
an integer or a string. The minimum base is 2 and the maximum base is
36. If to_base is a negative number, N is regarded as a
signed number. Otherwise, N is treated as unsigned. CONV works
with 64-bit precision:
mysql> SELECT CONV("a",16,2); -> '1010' mysql> SELECT CONV("6E",18,8); -> '172' mysql> SELECT CONV(-17,10,-18); -> '-H' mysql> SELECT CONV(10+"10"+'10'+0xa,10,10); -> '40' |
ELT(N,str1,str2,str3,...) |
Returns str1 if N = 1, str2 if N =
2, and so on. Returns NULL if N is less than 1
or greater than the number of arguments. ELT() is the complement of
FIELD():
mysql> SELECT ELT(1, 'ej', 'Heja', 'hej', 'foo'); -> 'ej' mysql> SELECT ELT(4, 'ej', 'Heja', 'hej', 'foo'); -> 'foo' |
EXPORT_SET(bits,on,off,[separator,[number_of_bits]]) |
Returns a string in which for every bit set in bits, you get an on
string and for every reset bit you get an off string. Each string is
separated by separator (default ,), and only
number_of_bits (default 64) of bits is used:
mysql> SELECT EXPORT_SET(5,'Y','N',',',4) -> Y,N,Y,N |
FIELD(str,str1,str2,str3,...) |
Returns the index of str in the str1, str2,
str3, ... list.
Returns 0 if str is not found.
FIELD() is the complement of ELT():
mysql> SELECT FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo'); -> 2 mysql> SELECT FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo'); -> 0 |
FIND_IN_SET(str,strlist) |
Returns a value 1 to N if the string str is in the list
strlist consisting of N substrings. A string list is a string
composed of substrings separated by , characters. If the first
argument is a constant string and the second is a column of type SET,
the FIND_IN_SET() function is optimized to use bit arithmetic!
Returns 0 if str is not in strlist or if strlist
is the empty string. Returns NULL if either argument is NULL.
This function will not work properly if the first argument contains a comma
,:
mysql> SELECT FIND_IN_SET('b','a,b,c,d'); -> 2 |
HEX(N_or_S) |
If N_OR_S is a number, returns a string representation of the hexadecimal
value of N, where N is a longlong (BIGINT) number.
This is equivalent to CONV(N,10,16).
If N_OR_S is a string, returns a hexadecimal string of N_OR_S where each
character in N_OR_S is converted to two hexadecimal digits. This is the
inverse of the 0xff strings.
mysql> SELECT HEX(255); -> 'FF' mysql> SELECT HEX("abc"); -> 616263 mysql> SELECT 0x616263; -> "abc" |
INSERT(str,pos,len,newstr) |
Returns the string str, with the substring beginning at position
pos and len characters long replaced by the string
newstr:
mysql> SELECT INSERT('Quadratic', 3, 4, 'What'); -> 'QuWhattic'This function is multi-byte safe. |
INSTR(str,substr) |
Returns the position of the first occurrence of substring substr in
string str. This is the same as the two-argument form of
LOCATE(), except that the arguments are swapped:
mysql> SELECT INSTR('foobarbar', 'bar'); -> 4 mysql> SELECT INSTR('xbar', 'foobar'); -> 0This function is multi-byte safe. In MySQL 3.23 this function is case sensitive, while in 4.0 it's only case sensitive if either argument is a binary string. |
LCASE(str) | LCASE() is a synonym for LOWER(). |
LEFT(str,len) |
Returns the leftmost len characters from the string str:
mysql> SELECT LEFT('foobarbar', 5); -> 'fooba' |
LENGTH(str) |
Returns the length of the string str, measured in bytes.
A multi-byte character counts as multiple bytes.
This means that for a string containing five two-byte characters,
LENGTH() returns 10, whereas CHAR_LENGTH() returns
5.
mysql> SELECT LENGTH('text'); -> 4 |
LOAD_FILE(file_name) |
Reads the file and returns the file contents as a string. The file
must be on the server, you must specify the full pathname to the
file, and you must have the FILE privilege. The file must
be readable by all and be smaller than max_allowed_packet.
If the file doesn't exist or can't be read due to one of these reasons,
the function returns NULL:
mysql> UPDATE tbl_name SET blob_column=LOAD_FILE("/tmp/picture") WHERE id=1;If you are not using MySQL Version 3.23, you have to do the reading of the file inside your application and create an INSERT statement to update the database with the file information. One way to do this, if you are using the MySQL++ library, can be found at http://www.mysql.com/documentation/mysql++/mysql++-examples.html. |
LOCATE(substr,str) , LOCATE(substr,str,pos) |
The first syntax
returns the position of the first occurrence of substring substr
in string str.
The second syntax
returns the position of the first occurrence of substring substr in
string str, starting at position pos.
Returns 0 if substr is not in str.
mysql> SELECT LOCATE('bar', 'foobarbar'); -> 4 mysql> SELECT LOCATE('xbar', 'foobar'); -> 0 mysql> SELECT LOCATE('bar', 'foobarbar',5); -> 7This function is multi-byte safe. In MySQL 3.23 this function is case sensitive, while in 4.0 it's only case sensitive if either argument is a binary string. |
LOWER(str) |
Returns the string str with all characters changed to lowercase
according to the current character set mapping (the default is ISO-8859-1
Latin1):
mysql> SELECT LOWER('QUADRATICALLY'); -> 'quadratically'This function is multi-byte safe. |
LPAD(str,len,padstr) |
Returns the string str, left-padded with the string padstr
to a length of len characters. If str is longer
than len, the return value is shortened to len characters.
mysql> SELECT LPAD('hi',4,'??'); -> '??hi' |
LTRIM(str) |
Returns the string str with leading space characters removed:
mysql> SELECT LTRIM(' barbar'); -> 'barbar' |
MAKE_SET(bits,str1,str2,...) |
Returns a set (a string containing substrings separated by ,
characters) consisting of the strings that have the corresponding bit in
bits set. str1 corresponds to bit 0, str2 to bit 1,
etc. NULL strings in str1, str2, ...
are not appended to the result:
mysql> SELECT MAKE_SET(1,'a','b','c'); -> 'a' mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world'); -> 'hello,world' mysql> SELECT MAKE_SET(0,'a','b','c'); -> '' |
MID(str,pos,len) | MID(str,pos,len) is a synonym for SUBSTRING(str,pos,len). |
OCT(N) |
Returns a string representation of the octal value of N, where
N is a longlong number. This is equivalent to CONV(N,10,8).
Returns NULL if N is NULL:
mysql> SELECT OCT(12); -> '14' |
OCTET_LENGTH(str) | OCTET_LENGTH() is a synonym for LENGTH(). |
ORD(str) |
If the leftmost character of the string str is a multi-byte character,
returns the code for that character, calculated from the ASCII code values
of its constituent characters using this formula:
((first byte ASCII code)*256+(second byte ASCII code))[*256+third byte ASCII code...].
If the leftmost character is not a multi-byte character, returns the same
value that the ASCII() function does:
mysql> SELECT ORD('2'); -> 50 |
POSITION(substr IN str) | POSITION(substr IN str) is a synonym for LOCATE(substr,str). |
QUOTE(str) |
Quotes a string to produce a result that can be used as a properly escaped
data value in an SQL statement. The string is returned surrounded by single
quotes and with each instance of single quote ('), backslash (\),
ASCII NUL, and Control-Z preceded by a backslash. If the argument is
NULL, the return value is the word ``NULL'' without surrounding
single quotes.
The QUOTE() function was added in MySQL version 4.0.3.
mysql> SELECT QUOTE("Don't"); -> 'Don\'t!' mysql> SELECT QUOTE(NULL); -> NULL |
REPEAT(str,count) |
Returns a string consisting of the string str repeated count
times. If count <= 0, returns an empty string. Returns NULL if
str or count are NULL:
mysql> SELECT REPEAT('MySQL', 3); -> 'MySQLMySQLMySQL' |
REPLACE(str,from_str,to_str) |
Returns the string str with all occurrences of the string
from_str replaced by the string to_str:
mysql> SELECT REPLACE('www.mysql.com', 'w', 'Ww'); -> 'WwWwWw.mysql.com'This function is multi-byte safe. |
REVERSE(str) |
Returns the string str with the order of the characters reversed:
mysql> SELECT REVERSE('abc'); -> 'cba'This function is multi-byte safe. |
RIGHT(str,len) |
Returns the rightmost len characters from the string str:
mysql> SELECT RIGHT('foobarbar', 4); -> 'rbar'This function is multi-byte safe. |
RPAD(str,len,padstr) |
Returns the string str, right-padded with the string padstr
to a length of len characters. If str is longer
than len, the return value is shortened to len characters.
mysql> SELECT RPAD('hi',5,'?'); -> 'hi???'This function is multi-byte safe. |
RTRIM(str) |
Returns the string str with trailing space characters removed:
mysql> SELECT RTRIM('barbar '); -> 'barbar'This function is multi-byte safe. |
SOUNDEX(str) |
Returns a soundex string from str. Two strings that sound almost the
same should have identical soundex strings. A standard soundex string
is 4 characters long, but the SOUNDEX() function returns an
arbitrarily long string. You can use SUBSTRING() on the result to get
a standard soundex string. All non-alphanumeric characters are ignored
in the given string. All international alpha characters outside the A-Z range
are treated as vowels:
mysql> SELECT SOUNDEX('Hello'); -> 'H400' mysql> SELECT SOUNDEX('Quadratically'); -> 'Q36324' |
expr1 SOUNDS LIKE expr2 | Same as SOUNDEX(expr1)=SOUNDEX(expr2) (available only in version 4.1 or later). |
SPACE(N) |
Returns a string consisting of N space characters:
mysql> SELECT SPACE(6); -> ' ' |
SUBSTRING(str,pos) , SUBSTRING(str FROM pos) , SUBSTRING(str,pos,len) , SUBSTRING(str FROM pos FOR len) |
The forms without a len argument
return a substring from string str starting at position pos.
The forms with a len argument
return a substring len characters long from string str,
starting at position pos.
The forms that use FROM are SQL-92 syntax.
mysql> SELECT SUBSTRING('Quadratically',5); -> 'ratically' mysql> SELECT SUBSTRING('foobarbar' FROM 4); -> 'barbar' mysql> SELECT SUBSTRING('Quadratically',5,6); -> 'ratica'This function is multi-byte safe. |
SUBSTRING_INDEX(str,delim,count) |
Returns the substring from string str before count
occurrences of the delimiter delim.
If count is positive, everything to the left of the final delimiter
(counting from the left) is returned.
If count is negative, everything to the right of the final delimiter
(counting from the right) is returned:
mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', 2); -> 'www.mysql' mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', -2); -> 'mysql.com'This function is multi-byte safe. |
TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str) |
Returns the string str with all remstr prefixes and/or suffixes
removed. If none of the specifiers BOTH, LEADING or
TRAILING is given, BOTH is assumed. If remstr is not
specified, spaces are removed:
mysql> SELECT TRIM(' bar '); -> 'bar' mysql> SELECT TRIM(LEADING 'x' FROM 'xxxbarxxx'); -> 'barxxx' mysql> SELECT TRIM(BOTH 'x' FROM 'xxxbarxxx'); -> 'bar' mysql> SELECT TRIM(TRAILING 'xyz' FROM 'barxxyz'); -> 'barx'This function is multi-byte safe. |
UCASE(str) | UCASE() is a synonym for UPPER(). |
UNCOMPRESS(string_to_uncompress) |
Uncompresses a string compressed by the COMPRESS() function.
mysql> SELECT UNCOMPRESS(COMPRESS("any string")); -> 'any string'UNCOMPRESS() was added in MySQL version 4.1.1. It requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL. |
UNCOMPRESSED_LENGTH(compressed_string) |
Returns the length of a compressed string before compressing.
mysql> SELECT UNCOMPRESSED_LENGTH(COMPRESS(REPEAT("a",30))); -> 30UNCOMPRESSED_LENGTH() was added in MySQL version 4.1.1. |
UPPER(str) |
Returns the string str with all characters changed to uppercase
according to the current character set mapping (the default is ISO-8859-1
Latin1):
mysql> SELECT UPPER('Hej'); -> 'HEJ'This function is multi-byte safe. |
MySQL automatically converts numbers to strings as necessary, and vice-versa:
mysql> SELECT 1+"1"; -> 2 mysql> SELECT CONCAT(2,' test'); -> '2 test'
If you want to convert a number to a string explicitly, pass it as the argument to CONCAT().
If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This only affects comparisons.
Normally, if any expression in a string comparison is case sensitive, the comparison is performed in case-sensitive fashion.
expr LIKE pat [ESCAPE 'escape-char'] | Pattern matching using SQL simple regular expression comparison. Returns 1 (TRUE) or 0 (FALSE). With LIKE you can use the following two wildcard characters in the pattern: |
|
| ||||||||||||
MATCH (col1,col2,...) AGAINST (expr [IN BOOLEAN MODE | WITH QUERY EXPANSION] ) | MATCH ... AGAINST() is used for full-text search and returns relevance - similarity measure between the text in columns (col1,col2,...) and the query expr. Relevance is a positive floating-point number. Zero relevance means no similarity. MATCH ... AGAINST() is available in MySQL version 3.23.23 or later. IN BOOLEAN MODE extension was added in version 4.0.1, WITH QUERY EXPANSION was added in 4.1.1. For details and usage examples, see Fulltext Search. | ||||||||||||||
expr NOT LIKE pat [ESCAPE 'escape-char'] | Same as NOT (expr LIKE pat [ESCAPE 'escape-char']). | ||||||||||||||
expr NOT REGEXP pat , expr NOT RLIKE pat | Same as NOT (expr REGEXP pat). | ||||||||||||||
expr REGEXP pat , expr RLIKE pat |
Performs a pattern match of a string expression expr against a pattern
pat. The pattern can be an extended regular expression.
See Regexp. Returns 1 if expr matches pat, otherwise
returns 0. RLIKE is a synonym for REGEXP, provided for
mSQL compatibility. Note: Because MySQL uses the C escape
syntax in strings (for example, \n), you must double any \ that
you use in your REGEXP strings. As of MySQL Version 3.23.4,
REGEXP is not case sensitive for normal (not binary) strings:
mysql> SELECT 'Monty!' REGEXP 'm%y%%'; -> 0 mysql> SELECT 'Monty!' REGEXP '.*'; -> 1 mysql> SELECT 'new*\n*line' REGEXP 'new\\*.\\*line'; -> 1 mysql> SELECT "a" REGEXP "A", "a" REGEXP BINARY "A"; -> 1 0 mysql> SELECT "a" REGEXP "^[a-d]"; -> 1REGEXP and RLIKE use the current character set (ISO-8859-1 Latin1 by default) when deciding the type of a character. | ||||||||||||||
STRCMP(expr1,expr2) | STRCMP()
returns 0 if the strings are the same, -1 if the first
argument is smaller than the second according to the current sort order,
and 1 otherwise:
mysql> SELECT STRCMP('text', 'text2'); -> -1 mysql> SELECT STRCMP('text2', 'text'); -> 1 mysql> SELECT STRCMP('text', 'text'); -> 0As of MySQL 4.0, STRCMP() uses the current character set when performing comparisons. This makes the default comparison behavior case insensitive unless one or both of the operands are binary strings. Before MySQL 4.0, STRCMP() is case sensitive. |
BINARY |
The BINARY operator casts the string following it to a binary string.
This is an easy way to force a column comparison to be case sensitive even
if the column isn't defined as BINARY or BLOB:
mysql> SELECT "a" = "A"; -> 1 mysql> SELECT BINARY "a" = "A"; -> 0BINARY string is a shorthand for CAST(string AS BINARY). See Cast Functions. BINARY was introduced in MySQL Version 3.23.0. Note that in some contexts, if you cast an indexed column to BINARY, MySQL will not be able to use the index efficiently. |
If you want to compare a BLOB value in case-insensitive fashion, you can do so as follows:
Before MySQL 4.1.1, use the UPPER() function to convert the BLOB value to uppercase before performing the comparison:
SELECT 'A' LIKE UPPER(blob_col) FROM table_name;
If the comparison value is lowercase, convert the BLOB value using LOWER() instead.
For MySQL 4.1.1 and up, BLOB columns have a character set of binary, which has no concept of lettercase. To perform a case-insensitive comparison, use the CONVERT() function to convert the BLOB value to a character set that has lettercase but is not case sensitive. The result is a non-binary string, so the LIKE oepration is not case sensitive:
SELECT 'A' LIKE CONVERT(blob_col USING latin1) FROM table_name;
To use a different character set, substitute its name for latin1 in the preceding statement.
CONVERT() can be used more generally for comparing strings that are represented in different character sets.
Table of Contents
The usual arithmetic operators are available. Note that in the case of -, +, and *, the result is calculated with BIGINT (64-bit) precision if both arguments are integers! If one of the argument is an unsigned integer, and the other argument is also an integer, the result will be an unsigned integer. See Cast Functions.
+ |
Addition:
mysql> SELECT 3+5; -> 8 |
- |
Subtraction:
mysql> SELECT 3-5; -> -2 |
* |
Multiplication:
mysql> SELECT 3*5; -> 15 mysql> SELECT 18014398509481984*18014398509481984.0; -> 324518553658426726783156020576256.0 mysql> SELECT 18014398509481984*18014398509481984; -> 0The result of the last expression is incorrect because the result of the integer multiplication exceeds the 64-bit range of BIGINT calculations. |
/ |
Division:
mysql> SELECT 3/5; -> 0.60Division by zero produces a NULL result: mysql> SELECT 102/(1-1); -> NULLA division will be calculated with BIGINT arithmetic only if performed in a context where its result is converted to an integer! |
All mathematical functions return NULL in case of an error.
- |
Unary minus. Changes the sign of the argument:
mysql> SELECT - 2; -> -2Note that if this operator is used with a BIGINT, the return value is a BIGINT! This means that you should avoid using - on integers that may have the value of -2^63! |
ABS(X) |
Returns the absolute value of X:
mysql> SELECT ABS(2); -> 2 mysql> SELECT ABS(-32); -> 32This function is safe to use with BIGINT values. |
ACOS(X) |
Returns the arc cosine of X, that is, the value whose cosine is
X. Returns NULL if X is not in the range -1 to
1:
mysql> SELECT ACOS(1); -> 0.000000 mysql> SELECT ACOS(1.0001); -> NULL mysql> SELECT ACOS(0); -> 1.570796 |
ASIN(X) |
Returns the arc sine of X, that is, the value whose sine is
X. Returns NULL if X is not in the range -1 to
1:
mysql> SELECT ASIN(0.2); -> 0.201358 mysql> SELECT ASIN('foo'); -> 0.000000 |
ATAN(X) |
Returns the arc tangent of X, that is, the value whose tangent is
X:
mysql> SELECT ATAN(2); -> 1.107149 mysql> SELECT ATAN(-2); -> -1.107149 |
ATAN(Y,X) , ATAN2(Y,X) |
Returns the arc tangent of the two variables X and Y. It is
similar to calculating the arc tangent of Y / X, except that the
signs of both arguments are used to determine the quadrant of the
result:
mysql> SELECT ATAN(-2,2); -> -0.785398 mysql> SELECT ATAN2(PI(),0); -> 1.570796 |
CEILING(X) , CEIL(X) |
Returns the smallest integer value not less than X:
mysql> SELECT CEILING(1.23); -> 2 mysql> SELECT CEIL(-1.23); -> -1The CEIL() alias was added in version 4.0.6. Note that the return value is converted to a BIGINT! |
COS(X) |
Returns the cosine of X, where X is given in radians:
mysql> SELECT COS(PI()); -> -1.000000 |
COT(X) |
Returns the cotangent of X:
mysql> SELECT COT(12); -> -1.57267341 mysql> SELECT COT(0); -> NULL |
CRC32(expr) |
Computes a cyclic redundancy check value and returns a 32-bit unsigned value.
The result is NULL if the argument is NULL.
The argument is expected be a string and will be treated as one if it is not.
mysql> SELECT CRC32('MySQL'); -> 3259397556CRC32() is available as of MySQL 4.1.0. |
DEGREES(X) |
Returns the argument X, converted from radians to degrees:
mysql> SELECT DEGREES(PI()); -> 180.000000 |
DIV |
Integer division.
Similar to FLOOR() but safe with BIGINT values.
mysql> SELECT 5 DIV 2 -> 2DIV is new in MySQL 4.1.0. |
EXP(X) |
Returns the value of e (the base of natural logarithms) raised to
the power of X:
mysql> SELECT EXP(2); -> 7.389056 mysql> SELECT EXP(-2); -> 0.135335 |
FLOOR(X) |
Returns the largest integer value not greater than X:
mysql> SELECT FLOOR(1.23); -> 1 mysql> SELECT FLOOR(-1.23); -> -2Note that the return value is converted to a BIGINT! |
GREATEST(X,Y,...) |
Returns the largest (maximum-valued) argument.
The arguments are compared using the same rules as for LEAST:
mysql> SELECT GREATEST(2,0); -> 2 mysql> SELECT GREATEST(34.0,3.0,5.0,767.0); -> 767.0 mysql> SELECT GREATEST("B","A","C"); -> "C"In MySQL versions prior to Version 3.22.5, you can use MAX() instead of GREATEST. |
LEAST(X,Y,...) |
With two or more arguments, returns the smallest (minimum-valued) argument.
The arguments are compared using the following rules:
mysql> SELECT LEAST(2,0); -> 0 mysql> SELECT LEAST(34.0,3.0,5.0,767.0); -> 3.0 mysql> SELECT LEAST("B","A","C"); -> "A"In MySQL versions prior to Version 3.22.5, you can use MIN() instead of LEAST. Note that the above conversion rules can produce strange results in some borderline cases: SELECT CAST(least(3600, 9223372036854775808.0) as SIGNED); -> -9223372036854775808This happens because MySQL reads 9223372036854775808.0 in an integer context and the integer representation is not good enough to hold the value so it's wraps to a signed integer. |
LN(X) |
Returns the natural logarithm of X:
mysql> SELECT LN(2); -> 0.693147 mysql> SELECT LN(-2); -> NULLThis function was added in MySQL version 4.0.3. It is synonymous with LOG(X) in MySQL. |
LOG(X) , LOG(B,X) |
If called with one parameter, this function returns the natural logarithm
of X:
mysql> SELECT LOG(2); -> 0.693147 mysql> SELECT LOG(-2); -> NULLIf called with two parameters, this function returns the logarithm of X for an arbitary base B: mysql> SELECT LOG(2,65536); -> 16.000000 mysql> SELECT LOG(1,100); -> NULLThe arbitrary base option was added in MySQL version 4.0.3. LOG(B,X) is equivalent to LOG(X)/LOG(B). |
LOG2(X) |
Returns the base-2 logarithm of X:
mysql> SELECT LOG2(65536); -> 16.000000 mysql> SELECT LOG2(-100); -> NULLLOG2() is useful for finding out how many bits a number would require for storage. This function was added in MySQL version 4.0.3. In earlier versions, you can use LOG(X)/LOG(2) instead. |
LOG10(X) |
Returns the base-10 logarithm of X:
mysql> SELECT LOG10(2); -> 0.301030 mysql> SELECT LOG10(100); -> 2.000000 mysql> SELECT LOG10(-100); -> NULL |
MOD(N,M) , % |
Modulo (like the % operator in C).
Returns the remainder of N divided by M:
mysql> SELECT MOD(234, 10); -> 4 mysql> SELECT 253 % 7; -> 1 mysql> SELECT MOD(29,9); -> 2 mysql> SELECT 29 MOD 9; -> 2This function is safe to use with BIGINT values. The last example works only in MySQL 4.1 |
PI() |
Returns the value of PI. The default shown number of decimals is 5, but
MySQL internally uses the full double precession for PI.
mysql> SELECT PI(); -> 3.141593 mysql> SELECT PI()+0.000000000000000000; -> 3.141592653589793116 |
POW(X,Y) , POWER(X,Y) |
Returns the value of X raised to the power of Y:
mysql> SELECT POW(2,2); -> 4.000000 mysql> SELECT POW(2,-2); -> 0.250000 |
RADIANS(X) |
Returns the argument X, converted from degrees to radians:
mysql> SELECT RADIANS(90); -> 1.570796 |
RAND() , RAND(N) |
Returns a random floating-point value in the range 0 to 1.0.
If an integer argument N is specified, it is used as the seed value
(producing a repeatable sequence):
mysql> SELECT RAND(); -> 0.9233482386203 mysql> SELECT RAND(20); -> 0.15888261251047 mysql> SELECT RAND(20); -> 0.15888261251047 mysql> SELECT RAND(); -> 0.63553050033332 mysql> SELECT RAND(); -> 0.70100469486881You can't use a column with RAND() values in an ORDER BY clause, because ORDER BY would evaluate the column multiple times. From version 3.23 you can do: SELECT * FROM table_name ORDER BY RAND() This is useful to get a random sample of a set SELECT * FROM table1,table2 WHERE a=b AND c<d ORDER BY RAND() LIMIT 1000. Note that a RAND() in a WHERE clause will be re-evaluated every time the WHERE is executed. RAND() is not meant to be a perfect random generator, but instead a fast way to generate ad hoc random numbers that will be portable between platforms for the same MySQL version. |
ROUND(X) , ROUND(X,D) |
Returns the argument X, rounded to the nearest integer.
With two arguments, rounded to a number to D decimals.
mysql> SELECT ROUND(-1.23); -> -1 mysql> SELECT ROUND(-1.58); -> -2 mysql> SELECT ROUND(1.58); -> 2 mysql> SELECT ROUND(1.298, 1); -> 1.3 mysql> SELECT ROUND(1.298, 0); -> 1 mysql> SELECT ROUND(23.298, -1); -> 20Note that the behavior of ROUND() when the argument is halfway between two integers depends on the C library implementation. Some round to the nearest even number, always up, always down, or always toward zero. If you need one kind of rounding, you should use a well-defined function such as TRUNCATE() or FLOOR() instead. |
SIGN(X) |
Returns the sign of the argument as -1, 0, or 1, depending
on whether X is negative, zero, or positive:
mysql> SELECT SIGN(-32); -> -1 mysql> SELECT SIGN(0); -> 0 mysql> SELECT SIGN(234); -> 1 |
SIN(X) |
Returns the sine of X, where X is given in radians:
mysql> SELECT SIN(PI()); -> 0.000000 |
SQRT(X) |
Returns the non-negative square root of X:
mysql> SELECT SQRT(4); -> 2.000000 mysql> SELECT SQRT(20); -> 4.472136 |
TAN(X) |
Returns the tangent of X, where X is given in radians:
mysql> SELECT TAN(PI()+1); -> 1.557408 |
TRUNCATE(X,D) |
Returns the number X, truncated to D decimals. If D
is 0, the result will have no decimal point or fractional part:
mysql> SELECT TRUNCATE(1.223,1); -> 1.2 mysql> SELECT TRUNCATE(1.999,1); -> 1.9 mysql> SELECT TRUNCATE(1.999,0); -> 1 mysql> SELECT TRUNCATE(-1.999,1); -> -1.9Starting from MySQL 3.23.51, all numbers are rounded toward zero. If D is negative, the whole part of the number is zeroed out: mysql> SELECT TRUNCATE(122,-2); -> 100Note that decimal numbers are normally not stored as exact numbers in computers, but as double-precision values, so you may be fooled by the following result: mysql> SELECT TRUNCATE(10.28*100,0); -> 1027The above happens because 10.28 is actually stored as something like 10.2799999999999999. |
This section describes the functions that can be used to manipulate temporal values. See Date and time types for a description of the range of values each date and time type has and the valid formats in which values may be specified.
Here is an example that uses date functions. The following query selects all records with a date_col value from within the last 30 days:
mysql> SELECT something FROM tbl_name WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30;
(Note that the query will also select records with dates that lie in the future.)
Functions that expect date values usually will accept datetime values and ignore the time part. Functions that expect time values usually will accept datetime values and ignore the date part.
Functions that return the current date or time each are evaluated only once per query at the start of query execution. This means that multiple references to a function such as NOW() within a single query will always produce the same result. This principle also applies to CURDATE(), CURTIME(), UTC_DATE(), UTC_TIME(), UTC_TIMESTAMP(), and any of their synonyms.
The return value ranges in the following function descriptions apply for complete dates. If a date is a ``zero'' value or an incomplete date such as '2001-11-00', functions that extract a part of a date may return 0. For example, DAYOFMONTH('2001-11-00') returns 0.
ADDDATE(date,INTERVAL expr type) , ADDDATE(expr,days) |
When invoked with the INTERVAL form of the second argument,
ADDDATE() is a synonym for DATE_ADD(). The related
function SUBDATE() is a synonym for DATE_SUB().
mysql> SELECT DATE_ADD('1998-01-02', INTERVAL 31 DAY); -> '1998-02-02' mysql> SELECT ADDDATE('1998-01-02', INTERVAL 31 DAY); -> '1998-02-02'As of MySQL 4.1.1, the second syntax is allowed, where expr is a date or datetime expression and days is the number of days to be added to expr. mysql> SELECT ADDDATE('1998-01-02', 31); -> '1998-02-02' | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ADDTIME(expr,expr2) | ADDTIME() adds expr2 to expr and returns the result.
expr is a date or datetime expression, and expr2 is a time
expression.
mysql> SELECT ADDTIME("1997-12-31 23:59:59.999999", "1 1:1:1.000002"); -> '1998-01-02 01:01:01.000001' mysql> SELECT ADDTIME("01:00:00.999999", "02:00:00.999998"); -> '03:00:01.999997'ADDTIME() was added in MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CURDATE() |
Returns the current date as a value in 'YYYY-MM-DD' or YYYYMMDD
format, depending on whether the function is used in a string or numeric
context:
mysql> SELECT CURDATE(); -> '1997-12-15' mysql> SELECT CURDATE() + 0; -> 19971215 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CURRENT_DATE , CURRENT_DATE() | CURRENT_DATE and CURRENT_DATE() are synonyms for CURDATE(). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CURTIME() |
Returns the current time as a value in 'HH:MM:SS' or HHMMSS
format, depending on whether the function is used in a string or numeric
context:
mysql> SELECT CURTIME(); -> '23:50:26' mysql> SELECT CURTIME() + 0; -> 235026 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CURRENT_TIME , CURRENT_TIME() | CURRENT_TIME and CURRENT_TIME() are synonyms for CURTIME(). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CURRENT_TIMESTAMP , CURRENT_TIMESTAMP() | CURRENT_TIMESTAMP and CURRENT_TIMESTAMP() are synonyms for NOW(). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DATE(expr) |
Extracts the date part of the date or datetime expression expr.
mysql> SELECT DATE('2003-12-31 01:02:03'); -> '2003-12-31'DATE() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DATEDIFF(expr,expr2) | DATEDIFF() returns the number of days between the start date
expr and the end date expr2.
expr and expr2 are date or date-and-time expressions.
Only the date parts of the values are used in the calculation.
mysql> SELECT DATEDIFF('1997-12-31 23:59:59','1997-12-30'); -> 1 mysql> SELECT DATEDIFF('1997-11-31 23:59:59','1997-12-31'); -> -30DATEDIFF() was added in MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DATE_ADD(date,INTERVAL expr type) , DATE_SUB(date,INTERVAL expr type) | These functions perform date arithmetic. As of MySQL Version 3.23, INTERVAL expr type is allowed on either side of the + operator if the expression on the other side is a date or datetime value. For the - operator, INTERVAL expr type is allowed only on the right side, because it makes no sense to subtract a date or datetime value from an interval. (See examples below.) date is a DATETIME or DATE value specifying the starting date. expr is an expression specifying the interval value to be added or subtracted from the starting date. expr is a string; it may start with a - for negative intervals. type is a keyword indicating how the expression should be interpreted. The following table shows how the type and expr arguments are related: |
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DATE_FORMAT(date,format) | Formats the date value according to the format string. The following specifiers may be used in the format string: |
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DAY(date) | DAY() is a synonym for DAYOFMONTH(). It is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DAYNAME(date) |
Returns the name of the weekday for date:
mysql> SELECT DAYNAME('1998-02-05'); -> 'Thursday' | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DAYOFMONTH(date) |
Returns the day of the month for date, in the range 1 to
31:
mysql> SELECT DAYOFMONTH('1998-02-03'); -> 3 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DAYOFWEEK(date) |
Returns the weekday index
for date (1 = Sunday, 2 = Monday, ... 7 =
Saturday). These index values correspond to the ODBC standard.
mysql> SELECT DAYOFWEEK('1998-02-03'); -> 3 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
DAYOFYEAR(date) |
Returns the day of the year for date, in the range 1 to
366:
mysql> SELECT DAYOFYEAR('1998-02-03'); -> 34 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
EXTRACT(type FROM date) |
The EXTRACT() function uses the same kinds of interval type
specifiers as DATE_ADD() or DATE_SUB(), but extracts parts
from the date rather than performing date arithmetic.
mysql> SELECT EXTRACT(YEAR FROM "1999-07-02"); -> 1999 mysql> SELECT EXTRACT(YEAR_MONTH FROM "1999-07-02 01:02:03"); -> 199907 mysql> SELECT EXTRACT(DAY_MINUTE FROM "1999-07-02 01:02:03"); -> 20102 mysql> SELECT EXTRACT(MICROSECOND FROM "2003-01-02 10:30:00.00123"); -> 123 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
FROM_DAYS(N) |
Given a daynumber N, returns a DATE value:
mysql> SELECT FROM_DAYS(729669); -> '1997-10-07'FROM_DAYS() is not intended for use with values that precede the advent of the Gregorian calendar (1582), because it doesn't take into account the days that were lost when the calendar was changed. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
FROM_UNIXTIME(unix_timestamp) , FROM_UNIXTIME(unix_timestamp,format) |
Returns a representation of the unix_timestamp argument as a value in
'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on
whether the function is used in a string or numeric context:
mysql> SELECT FROM_UNIXTIME(875996580); -> '1997-10-04 22:23:00' mysql> SELECT FROM_UNIXTIME(875996580) + 0; -> 19971004222300If format is given, the result is formatted according to the format string. format may contain the same specifiers as those listed in the entry for the DATE_FORMAT() function: mysql> SELECT FROM_UNIXTIME(UNIX_TIMESTAMP(), -> '%Y %D %M %h:%i:%s %x'); -> '2003 6th August 06:22:58 2003' | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
GET_FORMAT(DATE | TIME | TIMESTAMP, 'EUR' | 'USA' | 'JIS' | 'ISO' | 'INTERNAL') | Returns a format string. This function is useful in combination with the DATE_FORMAT() and the STR_TO_DATE() functions. The three possible values for the first argument and the five possible values for the second argument result in 15 possible format strings (for the specifiers used, see the table in the DATE_FORMAT() function description): |
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HOUR(time) |
Returns the hour for time. The range of the return value will be
0 to 23 for time-of-day values:
mysql> SELECT HOUR('10:05:03'); -> 10However, the range of TIME values actually is much larger, so HOUR can return values greater than 23: mysql> SELECT HOUR('272:59:59'); -> 272 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
LAST_DAY(date) |
Takes a date or datetime value and returns the corresponding value for the
last day of the month. Returns NULL if the argument is invalid.
mysql> SELECT LAST_DAY('2003-02-05'), LAST_DAY('2004-02-05'); -> '2003-02-28', '2004-02-29' mysql> SELECT LAST_DAY('2004-01-01 01:01:01'); -> '2004-01-31' mysql> SELECT LAST_DAY('2003-03-32'); -> NULLLAST_DAY() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
LOCALTIME , LOCALTIME() | LOCALTIME and LOCALTIME() are synonyms for NOW(). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
LOCALTIMESTAMP , LOCALTIMESTAMP() | LOCALTIMESTAMP and LOCALTIMESTAMP() are synonyms for NOW(). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MAKEDATE(year,dayofyear) |
Returns a date, given year and day-of-year values.
dayofyear must be greater than 0 or the result will NULL.
mysql> SELECT MAKEDATE(2001,31), MAKEDATE(2001,32); -> '2001-01-31', '2001-02-01' mysql> SELECT MAKEDATE(2001,365), MAKEDATE(2004,365); -> '2001-12-31', '2004-12-30' mysql> SELECT MAKEDATE(2001,0); -> NULLMAKEDATE() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MAKETIME(hour,minute,second) |
Returns a time value calculated from the hour, minute, and
second arguments.
mysql> SELECT MAKETIME(12,15,30); -> '12:15:30'MAKETIME() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MICROSECOND(expr) |
Returns the microseconds from the time or datetime expression expr as a
number in the range from 0 to 999999.
mysql> SELECT MICROSECOND('12:00:00.123456'); -> 123456 mysql> SELECT MICROSECOND('1997-12-31 23:59:59.000010'); -> 10MICROSECOND() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MINUTE(time) |
Returns the minute for time, in the range 0 to 59:
mysql> SELECT MINUTE('98-02-03 10:05:03'); -> 5 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MONTH(date) |
Returns the month for date, in the range 1 to 12:
mysql> SELECT MONTH('1998-02-03'); -> 2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MONTHNAME(date) |
Returns the name of the month for date:
mysql> SELECT MONTHNAME('1998-02-05'); -> 'February' | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
NOW() |
Returns the current date and time as a value in 'YYYY-MM-DD HH:MM:SS'
or YYYYMMDDHHMMSS format, depending on whether the function is used in
a string or numeric context:
mysql> SELECT NOW(); -> '1997-12-15 23:50:26' mysql> SELECT NOW() + 0; -> 19971215235026 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
PERIOD_ADD(P,N) |
Adds N months to period P (in the format YYMM or
YYYYMM). Returns a value in the format YYYYMM.
Note that the period argument P is not a date value:
mysql> SELECT PERIOD_ADD(9801,2); -> 199803 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
PERIOD_DIFF(P1,P2) |
Returns the number of months between periods P1 and P2.
P1 and P2 should be in the format YYMM or YYYYMM.
Note that the period arguments P1 and P2 are not
date values:
mysql> SELECT PERIOD_DIFF(9802,199703); -> 11 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
QUARTER(date) |
Returns the quarter of the year for date, in the range 1
to 4:
mysql> SELECT QUARTER('98-04-01'); -> 2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SECOND(time) |
Returns the second for time, in the range 0 to 59:
mysql> SELECT SECOND('10:05:03'); -> 3 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SEC_TO_TIME(seconds) |
Returns the seconds argument, converted to hours, minutes, and seconds,
as a value in 'HH:MM:SS' or HHMMSS format, depending on whether
the function is used in a string or numeric context:
mysql> SELECT SEC_TO_TIME(2378); -> '00:39:38' mysql> SELECT SEC_TO_TIME(2378) + 0; -> 3938 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
STR_TO_DATE(str,format) |
This is the reverse function of the DATE_FORMAT() function. It takes a
string str, and a format string format, and returns a
DATETIME value.
The date, time, or datetime values contained in str should be given
in the format indicated by format. For the specifiers that can be
used in format, see the table in the DATE_FORMAT() function
description. All other characters are just taken verbatim, thus not being
interpreted.
If str contains an illegal date, time, or datetime value,
STR_TO_DATE() returns NULL.
mysql> SELECT STR_TO_DATE('03.10.2003 09.20', '%d.%m.%Y %H.%i') -> 2003-10-03 09:20:00 mysql> SELECT STR_TO_DATE('10rap', '%crap') -> 0000-10-00 00:00:00 mysql> SELECT STR_TO_DATE('2003-15-10 00:00:00', '%Y-%m-%d %H:%i:%s') -> NULLSTR_TO_DATE() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SUBDATE(date,INTERVAL expr type) , SUBDATE(expr,days) |
When invoked with the INTERVAL form of the second argument,
SUBDATE() is a synonym for DATE_SUB().
mysql> SELECT DATE_SUB('1998-01-02', INTERVAL 31 DAY); -> '1997-12-02' mysql> SELECT SUBDATE('1998-01-02', INTERVAL 31 DAY); -> '1997-12-02'As of MySQL 4.1.1, the second syntax is allowed, where expr is a date or datetime expression and days is the number of days to be subtracted from expr. mysql> SELECT SUBDATE('1998-01-02 12:00:00', 31); -> '1997-12-02 12:00:00' | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SUBTIME(expr,expr2) | SUBTIME() subtracts expr2 from expr and returns the result.
expr is a date or datetime expression, and expr2 is a time
expression.
mysql> SELECT SUBTIME("1997-12-31 23:59:59.999999", "1 1:1:1.000002"); -> '1997-12-30 22:58:58.999997' mysql> SELECT SUBTIME("01:00:00.999999", "02:00:00.999998"); -> '-00:59:59.999999'SUBTIME() was added in MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SYSDATE() | SYSDATE() is a synonym for NOW(). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TIME(expr) |
Extracts the time part of the time or datetime expression expr.
mysql> SELECT TIME('2003-12-31 01:02:03'); -> '01:02:03' mysql> SELECT TIME('2003-12-31 01:02:03.000123'); -> '01:02:03.000123'TIME() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TIMEDIFF(expr,expr2) | TIMEDIFF() returns the time between the start time
expr and the end time expr2.
expr and expr2 are time or date-and-time expressions, but both
must be of the same type.
mysql> SELECT TIMEDIFF('2000:01:01 00:00:00', '2000:01:01 00:00:00.000001'); -> '-00:00:00.000001' mysql> SELECT TIMEDIFF('1997-12-31 23:59:59.000001','1997-12-30 01:01:01.000002'); -> '46:58:57.999999'TIMEDIFF() was added in MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TIMESTAMP(expr) , TIMESTAMP(expr,expr2) |
With one argument, returns the date or datetime expression expr
as a datetime value.
With two arguments, adds the time expression expr2 to the
date or datetime expression expr and returns a datetime value.
mysql> SELECT TIMESTAMP('2003-12-31'); -> '2003-12-31 00:00:00' mysql> SELECT TIMESTAMP('2003-12-31 12:00:00','12:00:00'); -> '2004-01-01 00:00:00'TIMESTAMP() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TIMESTAMPADD(interval,int_expr,datetime_expr) |
Adds the integer expression int_expr to the date or datetime expression
datetime_expr. The unit for int_expr is given by the
interval argument, which should be one of the following values:
FRAC_SECOND,
SECOND,
MINUTE,
HOUR,
DAY,
WEEK,
MONTH,
QUARTER,
or
YEAR.
The interval value may be specified using one of keywords as shown,
or with a prefix of SQL_TSI_. For example, DAY or
SQL_TSI_DAY both are legal.
mysql> SELECT TIMESTAMPADD(MINUTE,1,'2003-01-02'); -> '2003-01-02 00:01:00' mysql> SELECT TIMESTAMPADD(WEEK,1,'2003-01-02'); -> '2003-01-09'TIMESTAMPADD() is available as of MySQL 5.0.0. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TIMESTAMPDIFF(interval,datetime_expr1,datetime_expr2) |
Returns the integer difference between the date or datetime expressions
datetime_expr1 and
datetime_expr2. The unit for the result is given by the
interval argument. The legal values for interval are the same as
those described in the desription of the TIMESTAMPADD() function.
mysql> SELECT TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01'); -> 3 mysql> SELECT TIMESTAMPDIFF(YEAR,'2002-05-01','2001-01-01'); -> -1TIMESTAMPDIFF() is available as of MySQL 5.0.0. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TIME_FORMAT(time,format) |
This is used like the DATE_FORMAT() function, but the
format string may contain only those format specifiers that handle
hours, minutes, and seconds. Other specifiers produce a NULL value or
0.
If the time value contains an hour part that is greater than
23, the %H and %k hour format specifiers produce a
value larger than the usual range of 0..23. The other hour format
specifiers produce the hour value modulo 12:
mysql> SELECT TIME_FORMAT('100:00:00', '%H %k %h %I %l'); -> '100 100 04 04 4' | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TIME_TO_SEC(time) |
Returns the time argument, converted to seconds:
mysql> SELECT TIME_TO_SEC('22:23:00'); -> 80580 mysql> SELECT TIME_TO_SEC('00:39:38'); -> 2378 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TO_DAYS(date) |
Given a date date, returns a daynumber (the number of days since year
0):
mysql> SELECT TO_DAYS(950501); -> 728779 mysql> SELECT TO_DAYS('1997-10-07'); -> 729669TO_DAYS() is not intended for use with values that precede the advent of the Gregorian calendar (1582), because it doesn't take into account the days that were lost when the calendar was changed. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
UNIX_TIMESTAMP() , UNIX_TIMESTAMP(date) |
If called with no argument, returns a Unix timestamp (seconds since
'1970-01-01 00:00:00' GMT) as an unsigned integer. If
UNIX_TIMESTAMP() is called with a date argument, it
returns the value of the argument as seconds since '1970-01-01 00:00:00' GMT. date may be a DATE string, a
DATETIME string, a TIMESTAMP, or a number in the format
YYMMDD or YYYYMMDD in local time:
mysql> SELECT UNIX_TIMESTAMP(); -> 882226357 mysql> SELECT UNIX_TIMESTAMP('1997-10-04 22:23:00'); -> 875996580When UNIX_TIMESTAMP is used on a TIMESTAMP column, the function returns the internal timestamp value directly, with no implicit ``string-to-Unix-timestamp'' conversion. If you pass an out-of-range date to UNIX_TIMESTAMP(), it returns 0, but please note that only basic checking is performed (year 1970-2037, month 01-12, day 01-31). If you want to subtract UNIX_TIMESTAMP() columns, you might want to cast the result to signed integers. See Cast Functions. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
UTC_DATE , UTC_DATE() |
Returns the current UTC date as a value in 'YYYY-MM-DD' or
YYYYMMDD format, depending on whether the function is used in a
string or numeric context:
mysql> SELECT UTC_DATE(), UTC_DATE() + 0; -> '2003-08-14', 20030814UTC_DATE() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
UTC_TIME , UTC_TIME() |
Returns the current UTC time as a value in 'HH:MM:SS' or HHMMSS
format, depending on whether the function is used in a string or numeric
context:
mysql> SELECT UTC_TIME(), UTC_TIME() + 0; -> '18:07:53', 180753UTC_TIME() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
UTC_TIMESTAMP , UTC_TIMESTAMP() |
Returns the current UTC date and time as a value in 'YYYY-MM-DD HH:MM:SS'
or YYYYMMDDHHMMSS format, depending on whether the function is used in
a string or numeric context:
mysql> SELECT UTC_TIMESTAMP(), UTC_TIMESTAMP() + 0; -> '2003-08-14 18:08:04', 20030814180804UTC_TIMESTAMP() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
WEEK(date [,mode]) | The function returns the week number for date. The two-argument form of WEEK() allows you to specify whether the week starts on Sunday or Monday and whether the return value should be in the range 0-53 or 1-52. When mode argument is omitted the value of a default_week_format server variable (or 0 in MySQL 4.0 or earlier) is assumed. See SET OPTION. The following table demonstrates how the mode argument works: |
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WEEKDAY(date) |
Returns the weekday index for
date (0 = Monday, 1 = Tuesday, ... 6 = Sunday):
mysql> SELECT WEEKDAY('1998-02-03 22:23:00'); -> 1 mysql> SELECT WEEKDAY('1997-11-05'); -> 2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
WEEKOFYEAR(date) |
Returns the calendar week of the date as a number in the
range from 1 to 53.
mysql> SELECT WEEKOFYEAR('1998-02-20'); -> 8WEEKOFYEAR() is available as of MySQL 4.1.1. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
YEAR(date) |
Returns the year for date, in the range 1000 to 9999:
mysql> SELECT YEAR('98-02-03'); -> 1998 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
YEARWEEK(date) , YEARWEEK(date,start) |
Returns year and week for a date. The start argument works exactly
like the start argument to WEEK(). Note that the year in the
result may be
different from the year in the date argument for the first and the last
week of the year:
mysql> SELECT YEARWEEK('1987-01-01'); -> 198653Note that the week number is different from what the WEEK() function would return (0) for optional arguments 0 or 1, as WEEK() then returns the week in the context of the given year. |
The CAST() and CONVERT() functions may be used to take a value of one type and produce a value of another type. Their syntax is:
CAST(expression AS type) CONVERT(expression,type) CONVERT(expr USING transcoding_name)
The type value can be one of the following:
BINARY
CHAR
DATE
DATETIME
SIGNED {INTEGER}
TIME
UNSIGNED {INTEGER}
CAST() and CONVERT() are available as of MySQL 4.0.2. The CHAR conversion type is available as of 4.0.6. The USING form of CONVERT() is available as of 4.1.0.
CAST() and CONVERT(... USING ...) are SQL-99 syntax. The non-USING form of CONVERT() is ODBC syntax.
The cast functions are useful when you want to create a column with a specific type in a CREATE ... SELECT statement:
CREATE TABLE new_table SELECT CAST('2000-01-01' AS DATE);
The functions also can be useful for sorting ENUM columns in lexical order. Normally sorting of ENUM columns occurs using the internal numeric values. Casting the values to CHAR results in a lexical sort:
SELECT enum_col FROM tbl_name ORDER BY CAST(enum_col AS CHAR);
CAST(string AS BINARY) is the same thing as BINARY string. CAST(expr AS CHAR) treats the expression as a string with the default character set.
NOTE: In MysQL 4.0 the CAST() to DATE, DATETIME, or TIME only marks the column to be a specific type but doesn't change the value of the column.
In MySQL 4.1.0 the value is converted to the correct column type when it's sent to the user (this is a feature of how the new protocol in 4.1 sends date information to the client):
mysql> SELECT CAST(NOW() AS DATE); -> 2003-05-26
In later MySQL versions (probably 4.1.2 or 5.0) we will fix that CAST also changes the result if you use it as part of a more complex expression, like CONCAT("Date: ",CAST(NOW() AS DATE)).
You should not use CAST() to extract data in different formats but instead use string functions like LEFT or EXTRACT(). See Date and time functions.
To cast a string to a numeric value, you don't normally have to do anything; just use the string value as it would be a number:
mysql> SELECT 1+'1'; -> 2
If you use a number in string context, the number automatically will be converted to a BINARY string.
mysql> SELECT CONCAT("hello you ",2); -> "hello you 2"
MySQL supports arithmetic with both signed and unsigned 64-bit values. If you are using numerical operations (like +) and one of the operands is unsigned integer, the result will be unsigned. You can override this by using the SIGNED and UNSIGNED cast operators to cast the operation to a signed or unsigned 64-bit integer, respectively.
mysql> SELECT CAST(1-2 AS UNSIGNED) -> 18446744073709551615 mysql> SELECT CAST(CAST(1-2 AS UNSIGNED) AS SIGNED); -> -1
Note that if either operand is a floating-point value, the result is a floating-point value and is not affected by the above rule. (In this context, DECIMAL values are regarded as floating-point values.)
mysql> SELECT CAST(1 AS UNSIGNED) - 2.0; -> -1.0
If you are using a string in an arithmetic operation, this is converted to a floating-point number.
The handing of unsigned values was changed in MySQL 4.0 to be able to support BIGINT values properly. If you have some code that you want to run in both MySQL 4.0 and 3.23 (in which case you probably can't use the CAST() function), you can use the following technique to get a signed result when subtracting two unsigned integer columns:
SELECT (unsigned_column_1+0.0)-(unsigned_column_2+0.0);
The idea is that the columns are converted to floating-point values before the subtraction occurs.
If you get a problem with UNSIGNED columns in your old MySQL application when porting to MySQL 4.0, you can use the --sql-mode=NO_UNSIGNED_SUBTRACTION option when starting mysqld. Note however that as long as you use this, you will not be able to make efficient use of the BIGINT UNSIGNED column type.
CONVERT() with USING is used to convert data between different character sets. In MySQL, transcoding names are the same as the corresponding character set names. For example, this statement converts the string 'abc' in the server's default character set to the corresponding string in the utf8 character set:
SELECT CONVERT('abc' USING utf8);
MySQL uses BIGINT (64-bit) arithmetic for bit operations, so these operators have a maximum range of 64 bits.
| |
Bitwise OR
mysql> SELECT 29 | 15; -> 31The result is an unsigned 64-bit integer. |
& |
Bitwise AND
mysql> SELECT 29 & 15; -> 13The result is an unsigned 64-bit integer. |
^ |
Bitwise XOR
mysql> SELECT 1 ^ 1; -> 0 mysql> SELECT 1 ^ 0; -> 1 mysql> SELECT 11 ^ 3; -> 8The result is an unsigned 64-bit integer. XOR was added in version 4.0.2. |
<< |
Shifts a longlong (BIGINT) number to the left:
mysql> SELECT 1 << 2; -> 4The result is an unsigned 64-bit integer. |
>> |
Shifts a longlong (BIGINT) number to the right:
mysql> SELECT 4 >> 2; -> 1The result is an unsigned 64-bit integer. |
~ |
Invert all bits:
mysql> SELECT 5 & ~1; -> 4The result is an unsigned 64-bit integer. |
BIT_COUNT(N) |
Returns the number of bits that are set in the argument N:
mysql> SELECT BIT_COUNT(29); -> 4 |
AES_ENCRYPT(string,key_string) , AES_DECRYPT(string,key_string) |
These functions allow encryption/decryption of data using the official
AES (Advanced Encryption Standard) algorithm, previously known as Rijndael.
Encoding with a 128-bit key length is used, but you can extend it up to
256 bits by modifying the source. We chose 128 bits because it is much
faster and it is usually secure enough.
The input arguments may be any length. If either argument is NULL,
the result of this function is also NULL.
Because AES is a block-level algorithm, padding is used to encode uneven length
strings and so the result string length may be calculated as
16*(trunc(string_length/16)+1).
If AES_DECRYPT() detects invalid data or incorrect padding, it
returns NULL. However, it is possible for AES_DECRYPT()
to return a non-NULL value (possibly garbage) if the input data or
the key is invalid.
You can use the AES functions to store data in an encrypted form by
modifying your queries:
INSERT INTO t VALUES (1,AES_ENCRYPT('text','password'));You can get even more security by not transferring the key over the connection for each query, which can be accomplished by storing it in a server-side variable at connection time. For example: SELECT @password:='my password'; INSERT INTO t VALUES (1,AES_ENCRYPT('text',@password));AES_ENCRYPT() and AES_DECRYPT() were added in version 4.0.2, and can be considered the most cryptographically secure encryption functions currently available in MySQL. | |||||||||
DECODE(crypt_str,pass_str) | Descrypts the encrypted string crypt_str using pass_str as the password. crypt_str should be a string returned from ENCODE(). | |||||||||
ENCODE(str,pass_str) | Encrypt str using pass_str as the password. To decrypt the result, use DECODE(). The result is a binary string of the same length as string. If you want to save it in a column, use a BLOB column type. | |||||||||
DES_DECRYPT(string_to_decrypt [, key_string]) | Decrypts a string encrypted with DES_ENCRYPT(). Note that this function works only if MySQL has been configured with SSL support. See Secure connections. If no key_string argument is given, DES_DECRYPT() examines the first byte of the encrypted string to determine the DES key number that was used to encrypt the original string, and then reads the key from the des-key-file to decrypt the message. For this to work, the user must have the SUPER privilege. If you pass this function a key_string argument, that string is used as the key for decrypting the message. If the string_to_decrypt doesn't look like an encrypted string, MySQL will return the given string_to_decrypt. On error, this function returns NULL. | |||||||||
DES_ENCRYPT(string_to_encrypt [, (key_number | key_string) ] ) | Encrypts the string with the given key using the Triple-DES algorithm. Note that this function works only if MySQL has been configured with SSL support. See Secure connections. The encryption key to use is chosen the following way: |
| ||||||||
ENCRYPT(str[,salt]) |
Encrypt str using the Unix crypt() system call. The
salt argument should be a string with two characters.
(As of MySQL Version 3.22.16, salt may be longer than two characters.)
mysql> SELECT ENCRYPT("hello"); -> 'VxuFAJXVARROc'ENCRYPT() ignores all but the first 8 characters of str, at least on some systems. This behavior is determined by the implementation of the underlying crypt() system call. If crypt() is not available on your system, ENCRYPT() always returns NULL. Because of this we recommend that you use MD5() or SHA1() instead; these two functions exist on all platforms. | |||||||||
MD5(string) |
Calculates an MD5 128-bit checksum for the string. The value is returned
as a 32-digit hex number that may, for example, be used as a hash key:
mysql> SELECT MD5("testing"); -> 'ae2b1fca515949e5d54fb22b8ed95575'This is the "RSA Data Security, Inc. MD5 Message-Digest Algorithm". | |||||||||
PASSWORD(str) , OLD_PASSWORD(str) |
Calculates a password string from the plaintext password str. This is
the function that is used for encrypting MySQL passwords for storage
in the Password column of the user grant table:
mysql> SELECT PASSWORD('badpwd'); -> '7f84554057dd964b'PASSWORD() encryption is irreversible. PASSWORD() does not perform password encryption in the same way that Unix passwords are encrypted. See ENCRYPT(). Note: The PASSWORD() function is used by the authentication system in MySQL Server, you should NOT use it in your own applications. For that purpose, use MD5() or SHA1() instead. Also see RFC-2195 for more information about handling passwords and authentication securely in your application. | |||||||||
SHA1(string) , SHA(string) |
Calculates an SHA1 160-bit checksum for the string, as described in
RFC 3174 (Secure Hash Algorithm). The value is returned as a 40-digit
hex number, or NULL in case the input argument was NULL.
One of the possible uses for this function is as a hash key. You can
also use it as cryptographically safe function for storing passwords.
mysql> SELECT SHA1("abc"); -> 'a9993e364706816aba3e25717850c26c9cd0d89d'SHA1() was added in version 4.0.2, and can be considered a cryptographically more secure equivalent of MD5(). SHA() is synonym for SHA1(). |
BENCHMARK(count,expr) |
The BENCHMARK() function executes the expression expr
repeatedly count times. It may be used to time how fast MySQL
processes the expression. The result value is always 0. The intended
use is in the mysql client, which reports query execution times:
mysql> SELECT BENCHMARK(1000000,ENCODE("hello","goodbye")); +----------------------------------------------+ | BENCHMARK(1000000,ENCODE("hello","goodbye")) | +----------------------------------------------+ | 0 | +----------------------------------------------+ 1 row in set (4.74 sec)The time reported is elapsed time on the client end, not CPU time on the server end. It may be advisable to execute BENCHMARK() several times, and interpret the result with regard to how heavily loaded the server machine is. | |||||||||
CHARSET(str) |
Returns the character set of the string argument.
mysql> SELECT CHARSET(_utf8'abc'); -> 'utf8'CHARSET() was added in version 4.1.0. | |||||||||
COERCIBILITY(str) |
Returns the collation coercibility value of the string argument.
mysql> SELECT COERCIBILITY('abc' COLLATE latin1_swedish_ci); -> 0 mysql> SELECT COERCIBILITY('abc'); -> 3 mysql> SELECT COERCIBILITY(USER()); -> 2The return values have the following meanings: |
| ||||||||
COLLATION(str) |
Returns the collation for the character set of the string argument.
mysql> SELECT COLLATION('abc'); -> 'latin1_swedish_ci' mysql> SELECT COLLATION(_utf8'abc'); -> 'utf8_general_ci'COLLATION() was added in version 4.1.0. | |||||||||
CONNECTION_ID() |
Returns the connection ID (thread ID) for the connection.
Every connection has its own unique ID:
mysql> SELECT CONNECTION_ID(); -> 23786 | |||||||||
CURRENT_USER() |
Returns the username and hostname that the current session was authenticated
as. This value corresponds to the account that is used for assessing your
access privileges. It may be different than the value of USER().
mysql> SELECT USER(); -> 'davida@localhost' mysql> SELECT * FROM mysql.user; -> ERROR 1044: Access denied for user: '@localhost' to database 'mysql' mysql> SELECT CURRENT_USER(); -> '@localhost'The example illustrates that although the client specified a username of davida (as indicated by the value of the USER() function), the server authenticated the client using an anonymous user account (as seen by the empty username part of the CURRENT_USER() value). One way this might occur is that there is no account listed in the grant tables for davida. | |||||||||
DATABASE() |
Returns the current database name:
mysql> SELECT DATABASE(); -> 'test'If there is no current database, DATABASE() returns NULL as of MySQL 4.1.1, and the empty string before that. | |||||||||
FOUND_ROWS() |
A SELECT statement may include a LIMIT clause to restrict the
number of rows the server returns to the client.
In some cases, it is desirable to know how many rows the statement would have
returned without the LIMIT, but without running the statement again.
To get this row count, include a SQL_CALC_FOUND_ROWS option in the
SELECT statement, then invoke FOUND_ROWS() afterward:
mysql> SELECT SQL_CALC_FOUND_ROWS * FROM tbl_name WHERE id > 100 LIMIT 10; mysql> SELECT FOUND_ROWS();The second SELECT will return a number indicating how many rows the first SELECT would have returned had it been written without the LIMIT clause. (If the preceding SELECT statement does not include the SQL_CALC_FOUND_ROWS option, then FOUND_ROWS() may return a different result when LIMIT is used than when it is not.) Note that if you are using SELECT SQL_CALC_FOUND_ROWS ... MySQL has to calculate how many rows are in the full result set. However, this is faster than running the query again without LIMIT, because the result set need not be sent to the client. SQL_CALC_FOUND_ROWS and FOUND_ROWS() can be useful in situations when you want to restrict the number of rows that a query returns, but also determine the number of rows in the full result set without running the query again. An example is a web script that presents a paged display containing links to the pages that show other sections of a search result. Using FOUND_ROWS() allows you to determine how many other pages are needed for the rest of the result. The use of SQL_CALC_FOUND_ROWS and FOUND_ROWS() is more complex for UNION queries than for simple SELECT statements, because LIMIT may occur at multiple places in a UNION. It may be applied to individual SELECT statements in the UNION, or global to the UNION result as a whole. The intent of SQL_CALC_FOUND_ROWS for UNION is that it should return the row count that would be returned without a global LIMIT. The conditions for use of SQL_CALC_FOUND_ROWS with UNION are:
| |||||||||
LAST_INSERT_ID([expr]) |
Returns the last automatically generated value that was inserted into
an AUTO_INCREMENT column.
mysql> SELECT LAST_INSERT_ID(); -> 195The last ID that was generated is maintained in the server on a per-connection basis. This means the value the function returns to a given client is the most recent AUTO_INCREMENT value generated by that client. The value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own. This behavior ensures that you can retrieve your own ID without concern for the activity of other clients, and without the need for locks or transactions. The value of LAST_INSERT_ID() is not changed if you update the AUTO_INCREMENT column of a row with a non-magic value (that is, a value that is not NULL and not 0). If you insert many rows at the same time with an insert statement, LAST_INSERT_ID() returns the value for the first inserted row. The reason for this is to make it possible to easily reproduce the same INSERT statement against some other server. If expr is given as an argument to LAST_INSERT_ID(), then the value of the argument is returned by the function, and is set as the next value to be returned by LAST_INSERT_ID(). This can be used to simulate sequences:
| |||||||||
SESSION_USER() | SESSION_USER() is a synonym for USER(). | |||||||||
SYSTEM_USER() | SYSTEM_USER() is a synonym for USER(). | |||||||||
USER() |
Returns the current MySQL username and hostname:
mysql> SELECT USER(); -> 'davida@localhost'The value indicates the username you specified when connecting to the server, and the client host from which you connected. (Prior to MySQL Version 3.22.11, the function value does not include the client hostname.) You can extract just the username part, regardless of whether the value includes a hostname part, like this: mysql> SELECT SUBSTRING_INDEX(USER(),'@',1); -> 'davida' | |||||||||
VERSION() |
Returns a string indicating the MySQL server version:
mysql> SELECT VERSION(); -> '3.23.13-log'Note that if your version ends with -log this means that logging is enabled. |
FORMAT(X,D) |
Formats the number X to a format like '#,###,###.##', rounded
to D decimals, and returns the result as a string.
If D is 0, the result will have no
decimal point or fractional part:
mysql> SELECT FORMAT(12332.123456, 4); -> '12,332.1235' mysql> SELECT FORMAT(12332.1,4); -> '12,332.1000' mysql> SELECT FORMAT(12332.2,0); -> '12,332' |
GET_LOCK(str,timeout) |
Tries to obtain a lock with a name given by the string str, with a
timeout of timeout seconds. Returns 1 if the lock was obtained
successfully, 0 if the attempt timed out (for example, because another
client has already locked the name), or NULL if an error
occurred (such as running out of memory or the thread was killed with
mysqladmin kill). A lock is released when you execute
RELEASE_LOCK(), execute a new GET_LOCK(), or the thread
terminates (either normally or abnormally).
This function can be used to implement application locks or to
simulate record locks. Names are locked on a server-wide basis.
If a name has been locked by one client, GET_LOCK() blocks
any request by another client for a lock with the same name. This
allows clients that agree on a given lock name to use the name to
perform cooperative advisory locking:
mysql> SELECT GET_LOCK('lock1',10); -> 1 mysql> SELECT IS_FREE_LOCK('lock2'); -> 1 mysql> SELECT GET_LOCK('lock2',10); -> 1 mysql> SELECT RELEASE_LOCK('lock2'); -> 1 mysql> SELECT RELEASE_LOCK('lock1'); -> NULLNote that the second RELEASE_LOCK() call returns NULL because the lock 'lock1' was automatically released by the second GET_LOCK() call. |
INET_ATON(expr) |
Given the dotted-quad representation of a network address as a string,
returns an integer that represents the numeric value of the address.
Addresses may be 4 or 8 byte addresses:
mysql> SELECT INET_ATON('209.207.224.40'); -> 3520061480The generated number is always in network byte order; for example the above number is calculated as 209*256^3 + 207*256^2 + 224*256 +40. As of MySQL 4.1.2, INET_ATON() also understands short-form IP addresses: mysql> SELECT INET_ATON('127.0.0.1'), INET_ATON('127.1'); -> 2130706433, 2130706433 |
INET_NTOA(expr) |
Given a numeric network address (4 or 8 byte), returns the dotted-quad
representation of the address as a string:
mysql> SELECT INET_NTOA(3520061480); -> "209.207.224.40" |
IS_FREE_LOCK(str) | Checks if the lock named str is free to use (that is, not locked). Returns 1 if the lock is free (no one is using the lock), 0 if the lock is in use, and NULL on errors (such as incorrect arguments). IS_FREE_LOCK() was added in MySQL version 4.0.2. |
IS_USED_LOCK(str) | Checks if the lock named str is in use (that is, locked). If so, it returns the connection identifier of the client that holds the lock. Otherwise, it returns NULL. IS_USED_LOCK() was added in MySQL version 4.1.0. |
MASTER_POS_WAIT(log_name, log_pos [, timeout]) | Blocks until the slave reaches (that is, has read and applied all updates up to) the specified position in the master log. If master information is not initialized, or if the arguments are incorrect, returns NULL. If the slave is not running, will block and wait until it is started and goes to or past the specified position. If the slave is already past the specified position, returns immediately. If timeout (new in 4.0.10) is specified, will give up waiting when timeout seconds have elapsed. timeout must be greater than 0; a zero or negative timeout means no timeout. The return value is the number of log events it had to wait to get to the specified position, or NULL in case of error, or -1 if the timeout has been exceeded. This command is useful for control of master/slave synchronization. |
RELEASE_LOCK(str) | Releases the lock named by the string str that was obtained with GET_LOCK(). Returns 1 if the lock was released, 0 if the lock wasn't locked by this thread (in which case the lock is not released), and NULL if the named lock didn't exist. (The lock will not exist if it was never obtained by a call to GET_LOCK() or if it already has been released.) The DO statement is convenient to use with RELEASE_LOCK(). See DO. |
Table of Contents
If you use a group function in a statement containing no GROUP BY clause, it is equivalent to grouping on all rows.
AVG(expr) |
Returns the average value of expr:
mysql> SELECT student_name, AVG(test_score) -> FROM student -> GROUP BY student_name; |
BIT_AND(expr) | Returns the bitwise AND of all bits in expr. The calculation is performed with 64-bit (BIGINT) precision. As of MySQL 4.0.17, this function returns 18446744073709551615 if there were no matching rows. (This is an unsigned BIGINT value with all bits set to 1.) Before 4.0.17, the function returns -1 if there were no matching rows. |
BIT_OR(expr) | Returns the bitwise OR of all bits in expr. The calculation is performed with 64-bit (BIGINT) precision. This function returns 0 if there were no matching rows. |
BIT_XOR(expr) | Returns the bitwise XOR of all bits in expr. The calculation is performed with 64-bit (BIGINT) precision. Function returns 0 if there were no matching rows. This function is available as of MySQL 4.1.1. |
COUNT(expr) |
Returns a count of the number of non-NULL values in the rows
retrieved by a SELECT statement:
mysql> SELECT student.student_name,COUNT(*) -> FROM student,course -> WHERE student.student_id=course.student_id -> GROUP BY student_name;COUNT(*) is somewhat different in that it returns a count of the number of rows retrieved, whether or not they contain NULL values. COUNT(*) is optimized to return very quickly if the SELECT retrieves from one table, no other columns are retrieved, and there is no WHERE clause. For example: mysql> SELECT COUNT(*) FROM student;This optimization applies only to MyISAM and ISAM tables only, because an exact record count is stored for these table types and can be accessed very quickly. For transactional storage engines (InnodB, BDB), storing an exact row count is more problematic because multiple transactions may be occurring, each of which may affect the count. |
COUNT(DISTINCT expr,[expr...]) |
Returns a count of the number of different non-NULL values:
mysql> SELECT COUNT(DISTINCT results) FROM student;In MySQL you can get the number of distinct expression combinations that don't contain NULL by giving a list of expressions. In SQL-99 you would have to do a concatenation of all expressions inside COUNT(DISTINCT ...). |
GROUP_CONCAT(expr) |
Full syntax:
GROUP_CONCAT([DISTINCT] expr [,expr ...] [ORDER BY {unsigned_integer | col_name | formula} [ASC | DESC] [,col ...]] [SEPARATOR str_val])This function was added in MySQL version 4.1. It returns a string result with the concatenated values from a group: mysql> SELECT student_name, -> GROUP_CONCAT(test_score) -> FROM student -> GROUP BY student_name;or: mysql> SELECT student_name, -> GROUP_CONCAT(DISTINCT test_score -> ORDER BY test_score DESC SEPARATOR " ") -> FROM student -> GROUP BY student_name;In MySQL you can get the concatenated values of expression combinations. You can eliminate duplicate values by using DISTINCT. If you want to sort values in the result you should use ORDER BY clause. To sort in reverse order, add the DESC (descending) keyword to the name of the column you are sorting by in the ORDER BY clause. The default is ascending order; this may be specified explicitly using the ASC keyword. SEPARATOR is the string value which should be inserted between values of result. The default is a comma (","). You can remove the separator altogether by specifying SEPARATOR "". You can set a maximum allowed length with the variable group_concat_max_len in your configuration. The syntax to do this at runtime is: SET [SESSION | GLOBAL] group_concat_max_len = unsigned_integer;If a maximum length has been set, the result is truncated to this maximum length. The GROUP_CONCAT() function is an enhanced implementation of the basic LIST() function supported by Sybase SQL Anywhere. GROUP_CONCAT() is backward compatible with the extremely limited functionality of LIST(), if only one column and no other options are specified. LIST() does have a default sorting order. |
MIN(expr) , MAX(expr) |
Returns the minimum or maximum value of expr. MIN() and
MAX() may take a string argument; in such cases they return the
minimum or maximum string value. See MySQL indexes.
mysql> SELECT student_name, MIN(test_score), MAX(test_score) -> FROM student -> GROUP BY student_name;In MIN(), MAX() and other aggregate functions, MySQL currently compares ENUM and SET columns by their string value rather than by the string's relative position in the set. This will be rectified. |
STD(expr) , STDDEV(expr) | Returns the standard deviation of expr (the square root of VARIANCE(). This is an extension to SQL-99. The STDDEV() form of this function is provided for Oracle compatibility. |
SUM(expr) | Returns the sum of expr. Note that if the return set has no rows, it returns NULL! |
VARIANCE(expr) | Returns the standard variance of expr (considering rows as the whole population, not as a sample; so it has the number of rows as denominator). This is an extension to SQL-99 (available only in version 4.1 or later). |
As of MySQL 4.1.1, the GROUP BY clause allows a WITH ROLLUP modifier that causes extra rows to be added to the summary output. These rows represent higher-level (or super-aggregate) summary operations. ROLLUP thus allows you to answer questions at multiple levels of analysis with a single query. It can be used, for example, to provide support for OLAP (Online Analytical Processing) operations.
As an illustration, suppose that a table named sales has year, country, product, and profit columns for recording sales profitability:
CREATE TABLE sales ( year INT NOT NULL, country VARCHAR(20) NOT NULL, product VARCHAR(32) NOT NULL, profit INT );
The table's contents can be summarized per year with a simple GROUP BY like this:
mysql> SELECT year, SUM(profit) FROM sales GROUP BY year; +------+-------------+ | year | SUM(profit) | +------+-------------+ | 2000 | 4525 | | 2001 | 3010 | +------+-------------+
This output shows the total profit for each year, but if you also want to determine the total profit summed over all years, you must add up the individual values yourself or run an additional query.
Or you can use ROLLUP, which provides both levels of analysis with a single query. Adding a WITH ROLLUP modifier to the GROUP BY clause causes the query to produce another row that shows the grand total over all year values:
mysql> SELECT year, SUM(profit) FROM sales GROUP BY year WITH ROLLUP; +------+-------------+ | year | SUM(profit) | +------+-------------+ | 2000 | 4525 | | 2001 | 3010 | | NULL | 7535 | +------+-------------+
The grand total super-aggregate line is identified by the value NULL in the year column.
ROLLUP has a more complex effect when there are multiple GROUP BY columns. In this case, each time there is a ``break'' (change in value) in any but the last grouping column, the query produces an extra super-aggregate summary row.
For example, without ROLLUP, a summary on the sales table based on year, country, and product might look like this:
mysql> SELECT year, country, product, SUM(profit) -> FROM sales -> GROUP BY year, country, product; +------+---------+------------+-------------+ | year | country | product | SUM(profit) | +------+---------+------------+-------------+ | 2000 | Finland | Computer | 1500 | | 2000 | Finland | Phone | 100 | | 2000 | India | Calculator | 150 | | 2000 | India | Computer | 1200 | | 2000 | USA | Calculator | 75 | | 2000 | USA | Computer | 1500 | | 2001 | Finland | Phone | 10 | | 2001 | USA | Calculator | 50 | | 2001 | USA | Computer | 2700 | | 2001 | USA | TV | 250 | +------+---------+------------+-------------+
The output indicates summary values only at the year/country/product level of analysis. When ROLLUP is added, the query produces several extra rows:
mysql> SELECT year, country, product, SUM(profit) -> FROM sales -> GROUP BY year, country, product WITH ROLLUP; +------+---------+------------+-------------+ | year | country | product | SUM(profit) | +------+---------+------------+-------------+ | 2000 | Finland | Computer | 1500 | | 2000 | Finland | Phone | 100 | | 2000 | Finland | NULL | 1600 | | 2000 | India | Calculator | 150 | | 2000 | India | Computer | 1200 | | 2000 | India | NULL | 1350 | | 2000 | USA | Calculator | 75 | | 2000 | USA | Computer | 1500 | | 2000 | USA | NULL | 1575 | | 2000 | NULL | NULL | 4525 | | 2001 | Finland | Phone | 10 | | 2001 | Finland | NULL | 10 | | 2001 | USA | Calculator | 50 | | 2001 | USA | Computer | 2700 | | 2001 | USA | TV | 250 | | 2001 | USA | NULL | 3000 | | 2001 | NULL | NULL | 3010 | | NULL | NULL | NULL | 7535 | +------+---------+------------+-------------+
For this query, adding ROLLUP causes the output to include summary information at four levels of analysis, not just one. Here's how to interpret the ROLLUP output:
Following each set of product rows for a given year and country, an extra summary row is produced showing the total for all products. These rows have the product column set to NULL.
Following each set of rows for a given year, an extra summary row is produced showing the total for all countries and products. These rows have the country and products columns set to NULL.
Finally, following all other rows, an extra summary row is produced showing the grand total for all years, countries, and products. This row has the year, country, and products columns set to NULL.
Other Considerations When using ROLLUP
The following items list some behaviors specific to the MySQL implementation of ROLLUP:
When you use ROLLUP, you cannot also use an ORDER BY clause to sort the results. (In other words, ROLLUP and ORDER BY are mutually exclusive.) However, you still have some control over sort order. GROUP BY in MySQL sorts results, and you can use explicit ASC and DESC keywords with columns named in the GROUP BY list to specify sort order for individual columns. (The higher-level summary rows added by ROLLUP still appear after the rows from which they are calculated, regardless of the sort order.)
LIMIT can be used to restrict the number of rows returned to the client. LIMIT is applied after ROLLUP, so the limit applies against the extra rows added by ROLLUP. For example:
mysql> SELECT year, country, product, SUM(profit) -> FROM sales -> GROUP BY year, country, product WITH ROLLUP -> LIMIT 5; +------+---------+------------+-------------+ | year | country | product | SUM(profit) | +------+---------+------------+-------------+ | 2000 | Finland | Computer | 1500 | | 2000 | Finland | Phone | 100 | | 2000 | Finland | NULL | 1600 | | 2000 | India | Calculator | 150 | | 2000 | India | Computer | 1200 | +------+---------+------------+-------------+
Note that using LIMIT with ROLLUP may produce results that are more difficult to interpret, because you have less context for understanding the super-aggregate rows.
The NULL indicators in each super-aggregate row are produced when the row is sent to the client. The server looks at the columns named in the GROUP BY clause following the leftmost one that has changed value. For any column in the result set with a name that is a lexical match to any of those names, its value is set to NULL. (If you specify grouping columns by column number, the server identifies which columns to set to NULL by number.)
Because the NULL values in the super-aggregate rows are placed into the result set at such a late stage in query processing, you cannot test them as NULL values within the query itself. For example, you cannot add HAVING product IS NULL to the query to eliminate from the output all but the super-aggregate rows.
On the other hand, the NULL values do appear as NULL on the client side and can be tested as such using any MySQL client programming interface.
MySQL has extended the use of GROUP BY. You can use columns or calculations in the SELECT expressions that don't appear in the GROUP BY part. This stands for any possible value for this group. You can use this to get better performance by avoiding sorting and grouping on unnecessary items. For example, you don't need to group on customer.name in the following query:
mysql> SELECT order.custid,customer.name,MAX(payments) -> FROM order,customer -> WHERE order.custid = customer.custid -> GROUP BY order.custid;
In standard SQL, you would have to add customer.name to the GROUP BY clause. In MySQL, the name is redundant if you don't run in ANSI mode.
Don't use this feature if the columns you omit from the GROUP BY part aren't unique in the group! You will get unpredictable results.
In some cases, you can use MIN() and MAX() to obtain a specific column value even if it isn't unique. The following gives the value of column from the row containing the smallest value in the sort column:
SUBSTR(MIN(CONCAT(RPAD(sort,6,' '),column)),7)
See example-Maximum-column-group-row.
Note that if you are using MySQL Version 3.22 (or earlier) or if you are trying to follow SQL-99, you can't use expressions in GROUP BY or ORDER BY clauses. You can work around this limitation by using an alias for the expression:
mysql> SELECT id,FLOOR(value/100) AS val FROM tbl_name -> GROUP BY id,val ORDER BY val;
In MySQL Version 3.23 you can do:
mysql> SELECT id,FLOOR(value/100) FROM tbl_name ORDER BY RAND();
Table of Contents
This chapter describes the syntax for the SQL statements supported in MySQL.
Table of Contents
DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM table_name [WHERE where_definition] [ORDER BY ...] [LIMIT row_count]
or:
DELETE [LOW_PRIORITY] [QUICK] [IGNORE] table_name[.*] [, table_name[.*] ...] FROM table-references [WHERE where_definition]
or:
DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM table_name[.*] [, table_name[.*] ...] USING table-references [WHERE where_definition]
DELETE deletes rows from table_name that satisfy the condition given by where_definition, and returns the number of records deleted.
If you issue a DELETE with no WHERE clause, all rows are deleted. If you do this in AUTOCOMMIT mode, this works as TRUNCATE. See TRUNCATE. In MySQL 3.23, DELETE without a WHERE clause will return zero as the number of affected records.
If you really want to know how many records are deleted when you are deleting all rows, and are willing to suffer a speed penalty, you can use a DELETE statement of this form:
mysql> DELETE FROM table_name WHERE 1>0;
Note that this is much slower than DELETE FROM table_name with no WHERE clause, because it deletes rows one at a time.
If you specify the keyword LOW_PRIORITY, execution of the DELETE is delayed until no other clients are reading from the table.
For MyISAM tables, if you specify the word QUICK then the storage engine will not merge index leaves during delete, which may speed up certain kind of deletes.
The speed of delete operations may also be affected by factors discussed in Delete speed.
Option IGNORE causes MySQL to ignore all errors during the process of deleting rows. Errors encountered during the parsing stage are processed in the usual manner. Errors that are ignored due to the use of this option are returned as warnings. This option first appeared in version 4.1.1.
In MyISAM tables, deleted records are maintained in a linked list and subsequent INSERT operations reuse old record positions. To reclaim unused space and reduce file-sizes, use the OPTIMIZE TABLE statement or the myisamchk utility to reorganize tables. OPTIMIZE TABLE is easier, but myisamchk is faster. See OPTIMIZE TABLE and Optimisation.
The first multiple-table delete format is supported starting from MySQL 4.0.0. The second multiple-table delete format is supported starting from MySQL 4.0.2.
The idea is that only matching rows from the tables listed before the FROM or before the USING clause are deleted. The effect is that you can delete rows from many tables at the same time and also have additional tables that are used for searching.
The .* after the table names is there just to be compatible with Access:
DELETE t1,t2 FROM t1,t2,t3 WHERE t1.id=t2.id AND t2.id=t3.id
or:
DELETE FROM t1,t2 USING t1,t2,t3 WHERE t1.id=t2.id AND t2.id=t3.id
In the above case we delete matching rows only from tables t1 and t2.
The examples show inner joins using the comma operator, but multiple-table DELETE statements can use any type of join allowed in SELECT statements, such as LEFT JOIN.
If an ORDER BY clause is used (available from MySQL 4.0.0), the rows will be deleted in that order. This is really useful only in conjunction with LIMIT. For example:
DELETE FROM somelog WHERE user = 'jcole' ORDER BY timestamp LIMIT 1
This will delete the oldest entry (by timestamp) where the row matches the WHERE clause.
The MySQL-specific LIMIT row_count option to DELETE tells the server the maximum number of rows to be deleted before control is returned to the client. This can be used to ensure that a specific DELETE command doesn't take too much time. You can simply repeat the DELETE command until the number of affected rows is less than the LIMIT value.
From MySQL 4.0, you can specify multiple tables in the DELETE statement to delete rows from one or more tables depending on a particular condition in multiple tables. However, you cannot use ORDER BY or LIMIT in a multiple-table DELETE.
DO expression, [expression, ...]
Execute the expression but don't return any results. This is a shorthand of SELECT expression, expression, but has the advantage that it's slightly faster when you don't care about the result.
This is mainly useful with functions that has side effects, like RELEASE_LOCK.
HANDLER tbl_name OPEN [ AS alias ] HANDLER tbl_name READ index_name { = | >= | <= | < } (value1,value2,...) [ WHERE ... ] [LIMIT ... ] HANDLER tbl_name READ index_name { FIRST | NEXT | PREV | LAST } [ WHERE ... ] [LIMIT ... ] HANDLER tbl_name READ { FIRST | NEXT } [ WHERE ... ] [LIMIT ... ] HANDLER tbl_name CLOSE
The HANDLER statement provides direct access to the MyISAM table storage engine interface.
The first form of HANDLER statement opens a table, making it accessible via subsequent HANDLER ... READ statements. This table object is not shared by other threads and will not be closed until the thread calls HANDLER tbl_name CLOSE or the thread dies.
The second form fetches one row (or more, specified by LIMIT clause) where the index specified satisfies the given values and the WHERE condition is met. If you have a multiple-column index, specify the index column values as a comma-separated list. Either specify values for all the columns in the index, or specify values for a leftmost prefix of the index columns. Suppose an index includes three columns named col_a, col_b, and col_c, in that order. The HANDLER statement can specify values for all three columns in the index, or for the columns in a leftmost prefix. For example:
HANDLER ... index_name = (col_a_val,col_b_val,col_c_val) ... HANDLER ... index_name = (col_a_val,col_b_val) ... HANDLER ... index_name = (col_a_val) ...
The third form fetches one row (or more, specified by LIMIT clause) from the table in index order, matching WHERE condition.
The fourth form (without index specification) fetches one row (or more, specified by LIMIT clause) from the table in natural row order (as stored in datafile) matching WHERE condition. It is faster than HANDLER tbl_name READ index_name when a full table scan is desired.
HANDLER ... CLOSE closes a table that was opened with HANDLER ... OPEN.
Note: If you're using HANDLER interface for PRIMARY KEY you should remember to quote the keyword PRIMARY with backticks: HANDLER tbl READ `PRIMARY` > (...)
HANDLER is a somewhat low-level statement. For example, it does not provide consistency. That is, HANDLER ... OPEN does NOT take a snapshot of the table, and does NOT lock the table. This means that after a HANDLER ... OPEN is issued, table data can be modified (by this or any other thread) and these modifications may appear only partially in HANDLER ... NEXT or HANDLER ... PREV scans.
The reasons to use this interface instead of normal SQL are:
It's faster than SELECT because:
A designated storage engine is allocated for the thread in HANDLER OPEN.
There is less parsing involved.
No optimizer and no query checking overhead.
The used table doesn't have to be locked between two handler requests.
The handler interface doesn't have to provide a consistent look of the data (for example, dirty-reads are allowed), so the storage engine can do optimizations that SQL doesn't normally allow.
It makes it much easier to port applications that uses an ISAM like interface to MySQL.
It allows one to traverse a database in a manner that is not easy (in some cases impossible) to do with SQL. The handler interface is more natural way to look at data when working with applications that provide an interactive user interfaces to the database.
INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name [(col_name,...)] VALUES ((expression | DEFAULT),...),(...),... [ ON DUPLICATE KEY UPDATE col_name=expression, ... ] or INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name [(col_name,...)] SELECT ... or INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name SET col_name=(expression | DEFAULT), ... [ ON DUPLICATE KEY UPDATE col_name=expression, ... ]
INSERT inserts new rows into an existing table. The INSERT ... VALUES form of the statement inserts rows based on explicitly specified values. The INSERT ... SELECT form inserts rows selected from another table or tables. The INSERT ... VALUES form with multiple value lists is supported in MySQL Version 3.22.5 or later. The col_name=expression syntax is supported in MySQL Version 3.22.10 or later.
tbl_name is the table into which rows should be inserted. The column name list or the SET clause indicates which columns the statement specifies values for:
If you specify no column list for INSERT ... VALUES or INSERT ... SELECT, values for all columns in the table must be provided in the VALUES() list or by the SELECT. If you don't know the order of the columns in the table, use DESCRIBE tbl_name to find out.
Any column not explicitly given a value is set to its default value. For example, if you specify a column list that doesn't name all the columns in the table, unnamed columns are set to their default values. Default value assignment is described in CREATE TABLE.
You can also use the keyword DEFAULT to set a column to its default value. (New in MySQL 4.0.3.) This makes it easier to write INSERT statements that assign values to all but a few columns, because it allows you to avoid writing an incomplete VALUES() list (a list that does not include a value for each column in the table). Otherwise, you would have to write out the list of column names corresponding to each value in the VALUES() list.
MySQL always has a default value for all fields. This is something that is imposed on MySQL to be able to work with both transactional and non-transactional tables.
Our view is that checking of fields content should be done in the application and not in the database server.
An expression may refer to any column that was set earlier in a value list. For example, you can say this:
mysql> INSERT INTO tbl_name (col1,col2) VALUES(15,col1*2);
But not this:
mysql> INSERT INTO tbl_name (col1,col2) VALUES(col2*2,15);
If you specify the keyword DELAYED, the server puts the row or rows to be inserted into a buffer, and the client issuing the INSERT DELAYED statement then may continue on. If the table is busy, the server holds the rows. When the table becomes free, it begins inserting rows, checking periodically to see whether there are new read requests for the table. If there are, the delayed row queue is suspended until the table becomes free again.
If you specify the keyword LOW_PRIORITY, execution of the INSERT is delayed until no other clients are reading from the table. This includes other clients that began reading while existing clients are reading, and while the INSERT LOW_PRIORITY statement is waiting. It is possible, therefore, for a client that issues an INSERT LOW_PRIORITY statement to wait for a very long time (or even forever) in a read-heavy environment. (This is in contrast to INSERT DELAYED, which lets the client continue at once.) See INSERT DELAYED. Note that LOW_PRIORITY should normally not be used with MyISAM tables as this disables concurrent inserts. See MyISAM.
If you specify the keyword IGNORE in an INSERT with many rows, any rows that duplicate an existing PRIMARY or UNIQUE key in the table are ignored and are not inserted. If you do not specify IGNORE, the insert is aborted if there is any row that duplicates an existing key value. You can determine with the C API function mysql_info() how many rows were inserted into the table.
If you specify ON DUPLICATE KEY UPDATE clause (new in MySQL 4.1.0), and a row is inserted that would cause a duplicate value in a PRIMARY or UNIQUE key, an UPDATE of the old row is performed. For example, the command:
mysql> INSERT INTO table (a,b,c) VALUES (1,2,3) -> ON DUPLICATE KEY UPDATE c=c+1;
in case of column a is declared as UNIQUE and already holds 1 once, would be identical to the
mysql> UPDATE table SET c=c+1 WHERE a=1;
Note: If column b is unique too, the UPDATE command would be written as
mysql> UPDATE table SET c=c+1 WHERE a=1 OR b=2 LIMIT 1;
and if a=1 OR b=2 matches several rows, only one row will be updated! In general, one should try to avoid using ON DUPLICATE KEY clause on tables with multiple UNIQUE keys.
Since MySQL 4.1.1 one can use function VALUES(col_name) to refer to the column value in the INSERT part of the INSERT ... UPDATE command - that is the value that would be inserted if there would be no duplicate key conflict. This function especially useful in multiple-row inserts. Naturally VALUES() function is only meaningful in INSERT ... UPDATE command and returns NULL otherwise.
Example:
mysql> INSERT INTO table (a,b,c) VALUES (1,2,3),(4,5,6) -> ON DUPLICATE KEY UPDATE c=VALUES(a)+VALUES(b);
The command above is identical to
mysql> INSERT INTO table (a,b,c) VALUES (1,2,3) -> ON DUPLICATE KEY UPDATE c=3; mysql> INSERT INTO table (a,b,c) VALUES (4,5,6) -> ON DUPLICATE KEY UPDATE c=9;
When one uses ON DUPLICATE KEY UPDATE, the DELAYED option is ignored.
If MySQL was configured using the DONT_USE_DEFAULT_FIELDS option, INSERT statements generate an error unless you explicitly specify values for all columns that require a non-NULL value. See configure options.
You can find the value used for an AUTO_INCREMENT column with the mysql_insert_id function. See mysql_insert_id().
If you use INSERT ... SELECT or an INSERT ... VALUES statement with multiple value lists, you can use the C API function mysql_info() to get information about the query. The format of the information string is shown here:
Records: 100 Duplicates: 0 Warnings: 0
Duplicates indicates the number of rows that couldn't be inserted because they would duplicate some existing unique index value. Warnings indicates the number of attempts to insert column values that were problematic in some way. Warnings can occur under any of the following conditions:
Inserting NULL into a column that has been declared NOT NULL. The column is set to the default value appropriate for the column type. This is 0 for numeric types, the empty string ('') for string types, and the ``zero'' value for date and time types.
Setting a numeric column to a value that lies outside the column's range. The value is clipped to the appropriate endpoint of the range.
Setting a numeric column to a value such as '10.34 a'. The trailing garbage is stripped and the remaining numeric part is inserted. If the value doesn't make sense as a number at all, the column is set to 0.
Inserting a string into a CHAR, VARCHAR, TEXT, or BLOB column that exceeds the column's maximum length. The value is truncated to the column's maximum length.
Inserting a value into a date or time column that is illegal for the column type. The column is set to the appropriate zero value for the type.
INSERT [LOW_PRIORITY] [IGNORE] [INTO] tbl_name [(column list)] SELECT ...
With INSERT ... SELECT, you can quickly insert many rows into a table from one or many tables.
INSERT INTO tblTemp2 (fldID) SELECT tblTemp1.fldOrder_ID FROM tblTemp1 WHERE tblTemp1.fldOrder_ID > 100;
The following conditions hold for an INSERT ... SELECT statement:
Prior to MySQL 4.0.1, INSERT ... SELECT implicitly operates in IGNORE mode. As of MySQL 4.0.1, you should specify IGNORE explicitly to ignore records that would cause duplicate-key violations.
Do not use DELAYED with INSERT ... SELECT.
Prior to MySQL 4.0.14, the target table of the INSERT statement cannot appear in the FROM clause of the SELECT part of the query. This limitation is lifted in 4.0.14.
AUTO_INCREMENT columns work as usual.
In C programs, you can use the C API function mysql_info() to get information about the query. See INSERT.
To ensure that the binary log can be used to re-create the original tables, MySQL will not allow concurrent inserts during INSERT ... SELECT.
You can use REPLACE instead of INSERT to overwrite old rows. REPLACE is the counterpart to INSERT IGNORE in the treatment of new rows that contain unique key values that duplicate old rows: The new rows are used to replace the old rows rather than being discarded.
INSERT DELAYED ...
The DELAYED option for the INSERT statement is a MySQL-specific option that is very useful if you have clients that can't wait for the INSERT to complete. This is a common problem when you use MySQL for logging and you also periodically run SELECT and UPDATE statements that take a long time to complete. DELAYED was introduced in MySQL Version 3.22.15. It is a MySQL extension to SQL-92.
INSERT DELAYED works only with ISAM and MyISAM tables. Note that as MyISAM tables support concurrent SELECT and INSERT, if there is no free blocks in the middle of the datafile, you very seldom need to use INSERT DELAYED with MyISAM. See MyISAM.
INSERT DELAYED should be used only for INSERT statements that specify value lists. This is enforced as of MySQL 4.0.18; the server ignores DELAYED for INSERT DELAYED ... SELECT statements.
When you use INSERT DELAYED, the client will get an OK at once and the row will be inserted when the table is not in use by any other thread.
Another major benefit of using INSERT DELAYED is that inserts from many clients are bundled together and written in one block. This is much faster than doing many separate inserts.
Note that currently the queued rows are only stored in memory until they are inserted into the table. This means that if you kill mysqld the hard way (kill -9) or if mysqld dies unexpectedly, any queued rows that weren't written to disk are lost!
The following describes in detail what happens when you use the DELAYED option to INSERT or REPLACE. In this description, the ``thread'' is the thread that received an INSERT DELAYED command and ``handler'' is the thread that handles all INSERT DELAYED statements for a particular table.
When a thread executes a DELAYED statement for a table, a handler thread is created to process all DELAYED statements for the table, if no such handler already exists.
The thread checks whether the handler has acquired a DELAYED lock already; if not, it tells the handler thread to do so. The DELAYED lock can be obtained even if other threads have a READ or WRITE lock on the table. However, the handler will wait for all ALTER TABLE locks or FLUSH TABLES to ensure that the table structure is up to date.
The thread executes the INSERT statement, but instead of writing the row to the table, it puts a copy of the final row into a queue that is managed by the handler thread. Any syntax errors are noticed by the thread and reported to the client program.
The client can't report the number of duplicates or the AUTO_INCREMENT value for the resulting row; it can't obtain them from the server, because the INSERT returns before the insert operation has been completed. If you use the C API, the mysql_info() function doesn't return anything meaningful, for the same reason.
The binary log is updated by the handler thread when the row is inserted into the table. In case of multiple-row inserts, the binary log is updated when the first row is inserted.
After every delayed_insert_limit rows are written, the handler checks whether any SELECT statements are still pending. If so, it allows these to execute before continuing.
When the handler has no more rows in its queue, the table is unlocked. If no new INSERT DELAYED commands are received within delayed_insert_timeout seconds, the handler terminates.
If more than delayed_queue_size rows are pending already in a specific handler queue, the thread requesting INSERT DELAYED waits until there is room in the queue. This is done to ensure that the mysqld server doesn't use all memory for the delayed memory queue.
The handler thread will show up in the MySQL process list with delayed_insert in the Command column. It will be killed if you execute a FLUSH TABLES command or kill it with KILL thread_id. However, it will first store all queued rows into the table before exiting. During this time it will not accept any new INSERT commands from another thread. If you execute an INSERT DELAYED command after this, a new handler thread will be created.
Note that the above means that INSERT DELAYED commands have higher priority than normal INSERT commands if there is an INSERT DELAYED handler already running! Other update commands will have to wait until the INSERT DELAYED queue is empty, someone kills the handler thread (with KILL thread_id), or someone executes FLUSH TABLES.
The following status variables provide information about INSERT DELAYED commands:
Variable | Meaning |
Delayed_insert_threads | Number of handler threads |
Delayed_writes | Number of rows written with INSERT DELAYED |
Not_flushed_delayed_rows | Number of rows waiting to be written |
You can view these variables by issuing a SHOW STATUS statement or by executing a mysqladmin extended-status command.
Note that INSERT DELAYED is slower than a normal INSERT if the table is not in use. There is also the additional overhead for the server to handle a separate thread for each table on which you use INSERT DELAYED. This means that you should use INSERT DELAYED only when you are really sure you need it!
LOAD DATA [LOW_PRIORITY | CONCURRENT] [LOCAL] INFILE 'file_name.txt' [REPLACE | IGNORE] INTO TABLE tbl_name [FIELDS [TERMINATED BY '\t'] [[OPTIONALLY] ENCLOSED BY ''] [ESCAPED BY '\\' ] ] [LINES [STARTING BY ''] [TERMINATED BY '\n'] ] [IGNORE number LINES] [(col_name,...)]
The LOAD DATA INFILE statement reads rows from a text file into a table at a very high speed. If the LOCAL keyword is specified, it is interpreted with respect to the client end of the connection. When LOCAL is specified, the file is read by the client program on the client host and sent to the server. If LOCAL is not specified, the file must be located on the server host and is read directly by the server. (LOCAL is available in MySQL Version 3.22.6 or later.)
For security reasons, when reading text files located on the server, the files must either reside in the database directory or be readable by all. Also, to use LOAD DATA INFILE on server files, you must have the FILE privilege on the server host.
See Privileges provided.
As of MySQL 3.23.49 and MySQL 4.0.2 (4.0.13 on Windows), LOCAL will work only if your server and your client both have been enabled to allow it. For example, if mysqld was started with --local-infile=0, LOCAL will not work. See LOAD DATA LOCAL.
If you specify the keyword LOW_PRIORITY, execution of the LOAD DATA statement is delayed until no other clients are reading from the table.
If you specify the keyword CONCURRENT with a MyISAM table, then other threads can retrieve data from the table while LOAD DATA is executing. Using this option will affect the performance of LOAD DATA a bit even if no other thread is using the table at the same time.
Using LOCAL will be a bit slower than letting the server access the files directly, because the contents of the file must be sent over the connection by the client to the server. On the other hand, you do not need the FILE privilege to load local files.
If you are using MySQL before Version 3.23.24 you can't read from a FIFO with LOAD DATA INFILE. If you need to read from a FIFO (for example the output from gunzip), use LOAD DATA LOCAL INFILE instead.
You can also load datafiles by using the mysqlimport utility; it operates by sending a LOAD DATA INFILE command to the server. The --local option causes mysqlimport to read datafiles from the client host. You can specify the --compress option to get better performance over slow networks if the client and server support the compressed protocol.
When locating files on the server host, the server uses the following rules:
If an absolute pathname is given, the server uses the pathname as is.
If a relative pathname with one or more leading components is given, the server searches for the file relative to the server's data directory.
If a filename with no leading components is given, the server looks for the file in the database directory of the current database.
Note that these rules mean a file named as ./myfile.txt is read from the server's data directory, whereas the same file named as myfile.txt is read from the database directory of the current database. For example, the following LOAD DATA statement reads the file data.txt from the database directory for db1 because db1 is the current database, even though the statement explicitly loads the file into a table in the db2 database:
mysql> USE db1; mysql> LOAD DATA INFILE "data.txt" INTO TABLE db2.my_table;
The REPLACE and IGNORE keywords control handling of input records that duplicate existing records on unique key values.
If you specify REPLACE, input rows replace existing rows (in other words rows that has the same value for a primary or unique index as an existing row). See REPLACE.
If you specify IGNORE, input rows that duplicate an existing row on a unique key value are skipped. If you don't specify either option, the behavior depends on whether or not the LOCAL keyword is specified. Without LOCAL, an error occurs when a duplicate key value is found, and the rest of the text file is ignored. With LOCAL, the default behavior is the same as if IGNORE is specified; this is because the server has no way to stop transmission of the file in the middle of the operation.
If you want to ignore foreign key constraints during load you can do SET FOREIGN_KEY_CHECKS=0 before executing LOAD DATA.
If you use LOAD DATA INFILE on an empty MyISAM table, all non-unique indexes are created in a separate batch (like in REPAIR). This normally makes LOAD DATA INFILE much faster when you have many indexes. Normally this is very fast, but in some extreme cases you can create the indexes even faster by turning them off with ALTER TABLE .. DISABLE KEYS and use ALTER TABLE .. ENABLE KEYS to re-create the indexes. See Table maintenance.
LOAD DATA INFILE is the complement of SELECT ... INTO OUTFILE. See SELECT. To write data from a table to a file, use SELECT ... INTO OUTFILE. To read the file back into a table, use LOAD DATA INFILE. The syntax of the FIELDS and LINES clauses is the same for both commands. Both clauses are optional, but FIELDS must precede LINES if both are specified.
If you specify a FIELDS clause, each of its subclauses (TERMINATED BY, [OPTIONALLY] ENCLOSED BY, and ESCAPED BY) is also optional, except that you must specify at least one of them.
If you don't specify a FIELDS clause, the defaults are the same as if you had written this:
FIELDS TERMINATED BY '\t' ENCLOSED BY '' ESCAPED BY '\\'
If you don't specify a LINES clause, the default is the same as if you had written this:
LINES TERMINATED BY '\n'
Note: If you have generated the text file on a Windows system you may have to change the above to: LINES TERMINATED BY '\r\n' as Windows uses two characters as a line terminator. Some programs, like wordpad, may use \r as a line terminator.
If all the lines you want to read in has a common prefix that you want to skip, you can use LINES STARTING BY prefix_string for this.
In other words, the defaults cause LOAD DATA INFILE to act as follows when reading input:
Look for line boundaries at newlines.
If LINES STARTING BY prefix is used, read until prefix is found and start reading at character after prefix. If line doesn't include prefix it will be skipped.
Break lines into fields at tabs.
Do not expect fields to be enclosed within any quoting characters.
Interpret occurrences of tab, newline, or \ preceded by \ as literal characters that are part of field values.
Conversely, the defaults cause SELECT ... INTO OUTFILE to act as follows when writing output:
Write tabs between fields.
Do not enclose fields within any quoting characters.
Use \ to escape instances of tab, newline or \ that occur within field values.
Write newlines at the ends of lines.
Note that to write FIELDS ESCAPED BY '\\', you must specify two backslashes for the value to be read as a single backslash.
The IGNORE number LINES option can be used to ignore lines at the start of the file. For example, you can use IGNORE 1 LINES to skip over an initial header line containing column names:
mysql> LOAD DATA INFILE "/tmp/file_name" INTO TABLE test IGNORE 1 LINES;
When you use SELECT ... INTO OUTFILE in tandem with LOAD DATA INFILE to write data from a database into a file and then read the file back into the database later, the field and line handling options for both commands must match. Otherwise, LOAD DATA INFILE will not interpret the contents of the file properly. Suppose you use SELECT ... INTO OUTFILE to write a file with fields delimited by commas:
mysql> SELECT * INTO OUTFILE 'data.txt' -> FIELDS TERMINATED BY ',' -> FROM ...;
To read the comma-delimited file back in, the correct statement would be:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2 -> FIELDS TERMINATED BY ',';
If instead you tried to read in the file with the statement shown here, it wouldn't work because it instructs LOAD DATA INFILE to look for tabs between fields:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2 -> FIELDS TERMINATED BY '\t';
The likely result is that each input line would be interpreted as a single field.
LOAD DATA INFILE can be used to read files obtained from external sources, too. For example, a file in dBASE format will have fields separated by commas and enclosed in double quotes. If lines in the file are terminated by newlines, the command shown here illustrates the field and line handling options you would use to load the file:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE tbl_name -> FIELDS TERMINATED BY ',' ENCLOSED BY '"' -> LINES TERMINATED BY '\n';
Any of the field or line handling options may specify an empty string (''). If not empty, the FIELDS [OPTIONALLY] ENCLOSED BY and FIELDS ESCAPED BY values must be a single character. The FIELDS TERMINATED BY and LINES TERMINATED BY values may be more than one character. For example, to write lines that are terminated by carriage return-linefeed pairs, or to read a file containing such lines, specify a LINES TERMINATED BY '\r\n' clause.
For example, to read a file of jokes, that are separated with a line of %%, into an SQL table you can do:
CREATE TABLE jokes (a INT NOT NULL AUTO_INCREMENT PRIMARY KEY, joke TEXT NOT NULL); LOAD DATA INFILE "/tmp/jokes.txt" INTO TABLE jokes FIELDS TERMINATED BY "" LINES TERMINATED BY "\n%%\n" (joke);
FIELDS [OPTIONALLY] ENCLOSED BY controls quoting of fields. For output (SELECT ... INTO OUTFILE), if you omit the word OPTIONALLY, all fields are enclosed by the ENCLOSED BY character. An example of such output (using a comma as the field delimiter) is shown here:
"1","a string","100.20" "2","a string containing a , comma","102.20" "3","a string containing a \" quote","102.20" "4","a string containing a \", quote and comma","102.20"
If you specify OPTIONALLY, the ENCLOSED BY character is used only to enclose CHAR and VARCHAR fields:
1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a \" quote",102.20 4,"a string containing a \", quote and comma",102.20
Note that occurrences of the ENCLOSED BY character within a field value are escaped by prefixing them with the ESCAPED BY character. Also note that if you specify an empty ESCAPED BY value, it is possible to generate output that cannot be read properly by LOAD DATA INFILE. For example, the preceding output just shown would appear as follows if the escape character is empty. Observe that the second field in the fourth line contains a comma following the quote, which (erroneously) appears to terminate the field:
1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a " quote",102.20 4,"a string containing a ", quote and comma",102.20
For input, the ENCLOSED BY character, if present, is stripped from the ends of field values. (This is true whether OPTIONALLY is specified; OPTIONALLY has no effect on input interpretation.) Occurrences of the ENCLOSED BY character preceded by the ESCAPED BY character are interpreted as part of the current field value.
If the field begins with the ENCLOSED BY character, instances of that character are recognized as terminating a field value only if followed by the field or line TERMINATED BY sequence. To avoid ambiguity, occurrences of the ENCLOSED BY character within a field value can be doubled and will be interpreted as a single instance of the character. For example, if ENCLOSED BY '"' is specified, quotes are handled as shown here:
"The ""BIG"" boss" -> The "BIG" boss The "BIG" boss -> The "BIG" boss The ""BIG"" boss -> The ""BIG"" boss
FIELDS ESCAPED BY controls how to write or read special characters. If the FIELDS ESCAPED BY character is not empty, it is used to prefix the following characters on output:
The FIELDS ESCAPED BY character
The FIELDS [OPTIONALLY] ENCLOSED BY character
The first character of the FIELDS TERMINATED BY and LINES TERMINATED BY values
ASCII 0 (what is actually written following the escape character is ASCII '0', not a zero-valued byte)
If the FIELDS ESCAPED BY character is empty, no characters are escaped. It is probably not a good idea to specify an empty escape character, particularly if field values in your data contain any of the characters in the list just given.
For input, if the FIELDS ESCAPED BY character is not empty, occurrences of that character are stripped and the following character is taken literally as part of a field value. The exceptions are an escaped 0 or N (for example, \0 or \N if the escape character is \). These sequences are interpreted as ASCII 0 (a zero-valued byte) and NULL. See below for the rules on NULL handling.
For more information about \-escape syntax, see Literals.
In certain cases, field and line handling options interact:
If LINES TERMINATED BY is an empty string and FIELDS TERMINATED BY is non-empty, lines are also terminated with FIELDS TERMINATED BY.
If the FIELDS TERMINATED BY and FIELDS ENCLOSED BY values are both empty (''), a fixed-row (non-delimited) format is used. With fixed-row format, no delimiters are used between fields (but you can still have a line terminator). Instead, column values are written and read using the ``display'' widths of the columns. For example, if a column is declared as INT(7), values for the column are written using 7-character fields. On input, values for the column are obtained by reading 7 characters.
LINES TERMINATED BY is still used to separate lines. If a line doesn't contain all fields, the rest of the fields will be set to their default values. If you don't have a line terminator, you should set this to ''. In this case the text file must contain all fields for each row.
Fixed-row format also affects handling of NULL values; see below. Note that fixed-size format will not work if you are using a multi-byte character set.
Handling of NULL values varies, depending on the FIELDS and LINES options you use:
For the default FIELDS and LINES values, NULL is written as \N for output and \N is read as NULL for input (assuming the ESCAPED BY character is \).
If FIELDS ENCLOSED BY is not empty, a field containing the literal word NULL as its value is read as a NULL value (this differs from the word NULL enclosed within FIELDS ENCLOSED BY characters, which is read as the string 'NULL').
If FIELDS ESCAPED BY is empty, NULL is written as the word NULL.
With fixed-row format (which happens when FIELDS TERMINATED BY and FIELDS ENCLOSED BY are both empty), NULL is written as an empty string. Note that this causes both NULL values and empty strings in the table to be indistinguishable when written to the file because they are both written as empty strings. If you need to be able to tell the two apart when reading the file back in, you should not use fixed-row format.
Some cases are not supported by LOAD DATA INFILE:
Fixed-size rows (FIELDS TERMINATED BY and FIELDS ENCLOSED BY both empty) and BLOB or TEXT columns.
If you specify one separator that is the same as or a prefix of another, LOAD DATA INFILE won't be able to interpret the input properly. For example, the following FIELDS clause would cause problems:
FIELDS TERMINATED BY '"' ENCLOSED BY '"'
If FIELDS ESCAPED BY is empty, a field value that contains an occurrence of FIELDS ENCLOSED BY or LINES TERMINATED BY followed by the FIELDS TERMINATED BY value will cause LOAD DATA INFILE to stop reading a field or line too early. This happens because LOAD DATA INFILE cannot properly determine where the field or line value ends.
The following example loads all columns of the persondata table:
mysql> LOAD DATA INFILE 'persondata.txt' INTO TABLE persondata;
No field list is specified, so LOAD DATA INFILE expects input rows to contain a field for each table column. The default FIELDS and LINES values are used.
If you want to load only some of a table's columns, specify a field list:
mysql> LOAD DATA INFILE 'persondata.txt' -> INTO TABLE persondata (col1,col2,...);
You must also specify a field list if the order of the fields in the input file differs from the order of the columns in the table. Otherwise, MySQL cannot tell how to match up input fields with table columns.
If a row has too few fields, the columns for which no input field is present are set to default values. Default value assignment is described in CREATE TABLE.
An empty field value is interpreted differently than if the field value is missing:
For string types, the column is set to the empty string.
For numeric types, the column is set to 0.
For date and time types, the column is set to the appropriate ``zero'' value for the type. See Date and time types.
Note that these are the same values that result if you assign an empty string explicitly to a string, numeric, or date or time type explicitly in an INSERT or UPDATE statement.
TIMESTAMP columns are set to the current date and time only if there is a NULL value for the column (that is, \N), or (for the first TIMESTAMP column only) if the TIMESTAMP column is omitted from the field list when a field list is specified.
If an input row has too many fields, the extra fields are ignored and the number of warnings is incremented. Note that before MySQL 4.1.1 the warnings is just a number to indicate that something went wrong. In MySQL 4.1.1 you can do SHOW WARNINGS to get more information for what went wrong.
LOAD DATA INFILE regards all input as strings, so you can't use numeric values for ENUM or SET columns the way you can with INSERT statements. All ENUM and SET values must be specified as strings!
If you are using the C API, you can get information about the query by calling the API function mysql_info() when the LOAD DATA INFILE query finishes. The format of the information string is shown here:
Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
Warnings occur under the same circumstances as when values are inserted via the INSERT statement (see INSERT), except that LOAD DATA INFILE also generates warnings when there are too few or too many fields in the input row. The warnings are not stored anywhere; the number of warnings can only be used as an indication if everything went well.
If you get warnings and want to know exactly why you got them, one way to do this is to use SELECT ... INTO OUTFILE into another file and compare this to your original input file.
If you need LOAD DATA to read from a pipe, you can use the following trick:
mkfifo /mysql/db/x/x chmod 666 /mysql/db/x/x cat < /dev/tcp/10.1.1.12/4711 > /nt/mysql/db/x/x mysql -e "LOAD DATA INFILE 'x' INTO TABLE x" x
If you are using a version of MySQL older than 3.23.25 you can only do the above with LOAD DATA LOCAL INFILE.
In MySQL 4.1.1 you can use SHOW WARNINGS to get a list of the first max_error_count warnings. See SHOW WARNINGS.
For more information about the efficiency of INSERT versus LOAD DATA INFILE and speeding up LOAD DATA INFILE, See Insert speed.
REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name [(col_name,...)] VALUES (expression,...),(...),... or REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name [(col_name,...)] SELECT ... or REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name SET col_name=expression, col_name=expression,...
REPLACE works exactly like INSERT, except that if an old record in the table has the same value as a new record on a UNIQUE index or PRIMARY KEY, the old record is deleted before the new record is inserted. See INSERT.
In other words, you can't access the values of the old row from a REPLACE statement. In some old MySQL versions it appeared that you could do this, but that was a bug that has been corrected.
To be able to use REPLACE, you must have INSERT and DELETE privileges for the table.
When you use a REPLACE command, mysql_affected_rows() will return 2 if the new row replaced an old row. This is because one row was inserted after the duplicate was deleted.
This fact makes it easy to determine whether REPLACE added or replaced a row: check whether the affected-rows value is 1 (added) or 2 (replaced).
Note that unless the table has a UNIQUE index or PRIMARY KEY, using a REPLACE command makes no sense. It becomes equivalent to INSERT, because there is no index to be used to determine whether a new row duplicates another.
Here follows the used algorithm in more detail: (This is also used with LOAD DATA ... REPLACE.)
- Insert the row into the table - While duplicate key error for primary or unique key - Revert changed keys - Read conflicting row from the table through the duplicate key value - Delete conflicting row - Try again to insert the original primary key and unique keys in the tree
SELECT [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT] [SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS] [HIGH_PRIORITY] [DISTINCT | DISTINCTROW | ALL] select_expression,... [INTO {OUTFILE | DUMPFILE} 'file_name' export_options] [FROM table_references [WHERE where_definition] [GROUP BY {unsigned_integer | col_name | formula} [ASC | DESC], ... [WITH ROLLUP]] [HAVING where_definition] [ORDER BY {unsigned_integer | col_name | formula} [ASC | DESC] ,...] [LIMIT [offset,] row_count | row_count OFFSET offset] [PROCEDURE procedure_name(argument_list)] [FOR UPDATE | LOCK IN SHARE MODE]]
SELECT is used to retrieve rows selected from one or more tables. Each select_expression indicates a column you want to retrieve. SELECT may also be used to retrieve rows computed without reference to any table.
For example:
mysql> SELECT 1 + 1; -> 2
All clauses used must be given in exactly the order shown in the syntax description. For example, a HAVING clause must come after any GROUP BY clause and before any ORDER BY clause.
A SELECT expression may be given an alias using AS alias_name. The alias is used as the expression's column name and can be used with ORDER BY or HAVING clauses. For example:
mysql> SELECT CONCAT(last_name,', ',first_name) AS full_name FROM mytable ORDER BY full_name;
The AS keyword is optional when aliasing a SELECT expression. The preceding example could have been written like this:
mysql> SELECT CONCAT(last_name,', ',first_name) full_name FROM mytable ORDER BY full_name;
Because the AS is optional, a subtle problem can occur if you forget the comma between two SELECT expressions: MySQL will interpret the second as an alias name. For example, in the following statement, columnb is treated as an alias name:
mysql> SELECT columna columnb FROM mytable;
It is not allowed to use a column alias in a WHERE clause, because the column value may not yet be determined when the WHERE clause is executed. See Problems with alias.
The FROM table_references clause indicates the tables from which to retrieve rows. If you name more than one table, you are performing a join. For information on join syntax, see JOIN. For each table specified, you may optionally specify an alias.
table_name [[AS] alias] [[USE INDEX (key_list)] | [IGNORE INDEX (key_list)] | [FORCE INDEX (key_list)]]
As of MySQL Version 3.23.12, you can give hints about which index MySQL should use when retrieving information from a table. This is useful if EXPLAIN shows that MySQL is using the wrong index from the list of possible indexes. By specifying USE INDEX (key_list), you can tell MySQL to use only one of the possible indexes to find rows in the table. The alternative syntax IGNORE INDEX (key_list) can be used to tell MySQL to not use some particular index.
In MySQL 4.0.9 you can also use FORCE INDEX. This acts likes USE INDEX (key_list) but with the addition that a table scan is assumed to be VERY expensive. In other words a table scan will only be used if there is no way to use one of the given index to find rows in the table.
USE/IGNORE/FORCE KEY are synonyms for USE/IGNORE/FORCE INDEX.
Note: USE/IGNORE/FORCE INDEX only affects which indexes are used when MySQL decides how to find rows in the table and how to do the join. It doesn't affect whether an index will be used when resolving an ORDER BY or GROUP BY.
In MySQL 4.0.14, you can use SET MAX_SEEKS_FOR_KEY=value as an alternative way to force MySQL to prefer key scans instead of table scans.
You can refer to a table as tbl_name (within the current database), or as dbname.tbl_name to explicitly specify a database. You can refer to a column as col_name, tbl_name.col_name, or db_name.tbl_name.col_name. You need not specify a tbl_name or db_name.tbl_name prefix for a column reference in a SELECT statement unless the reference would be ambiguous. See Legal names, for examples of ambiguity that require the more explicit column reference forms.
From version 4.1.0, you are allowed to specify DUAL as a dummy table name, in situations where no tables are referenced. This is purely compatibility feature, some other servers require this syntax.
mysql> SELECT 1 + 1 FROM DUAL; -> 2
A table reference may be aliased using tbl_name [AS] alias_name:
mysql> SELECT t1.name, t2.salary FROM employee AS t1, info AS t2 -> WHERE t1.name = t2.name; mysql> SELECT t1.name, t2.salary FROM employee t1, info t2 -> WHERE t1.name = t2.name;
Columns selected for output may be referred to in ORDER BY and GROUP BY clauses using column names, column aliases, or column positions. Column positions begin with 1:
mysql> SELECT college, region, seed FROM tournament -> ORDER BY region, seed; mysql> SELECT college, region AS r, seed AS s FROM tournament -> ORDER BY r, s; mysql> SELECT college, region, seed FROM tournament -> ORDER BY 2, 3;
To sort in reverse order, add the DESC (descending) keyword to the name of the column in the ORDER BY clause that you are sorting by. The default is ascending order; this may be specified explicitly using the ASC keyword.
In the WHERE clause, you can use any of the functions that MySQL supports, except for aggregate (summary) functions. See Functions.
The HAVING clause can refer to any column or alias named in the select_expression. It is applied nearly last, just before items are sent to the client, with no optimization. (LIMIT is applied after HAVING.) Don't use HAVING for items that should be in the WHERE clause. For example, do not write this:
mysql> SELECT col_name FROM tbl_name HAVING col_name > 0;
Write this instead:
mysql> SELECT col_name FROM tbl_name WHERE col_name > 0;
In MySQL Version 3.22.5 or later, you can also write queries like this:
mysql> SELECT user,MAX(salary) FROM users -> GROUP BY user HAVING MAX(salary)>10;
In older MySQL versions, you can write this instead:
mysql> SELECT user,MAX(salary) AS sum FROM users -> group by user HAVING sum>10;
The options DISTINCT, DISTINCTROW and ALL specify whether duplicate rows should be returned. The default is (ALL), all matching rows are returned. DISTINCT and DISTINCTROW are synonyms and specify that duplicate rows in the result set should be removed.
STRAIGHT_JOIN, HIGH_PRIORITY, and options beginning with SQL_ are MySQL extensions to SQL-99.
STRAIGHT_JOIN forces the optimizer to join the tables in the order in which they are listed in the FROM clause. You can use this to speed up a query if the optimizer joins the tables in non-optimal order. See EXPLAIN.
HIGH_PRIORITY will give the SELECT higher priority than a statement that updates a table. You should use this only for queries that are very fast and must be done at once. A SELECT HIGH_PRIORITY query will run if the table is locked for read even if there is an update statement that is waiting for the table to be free.
SQL_BIG_RESULT can be used with GROUP BY or DISTINCT to tell the optimizer that the result set will have many rows. In this case, MySQL will directly use disk-based temporary tables if needed. MySQL will also, in this case, prefer sorting to doing a temporary table with a key on the GROUP BY elements.
SQL_BUFFER_RESULT forces the result to be put into a temporary table. This helps MySQL free the table locks early and helps in cases where it takes a long time to send the result set to the client.
SQL_SMALL_RESULT, a MySQL-specific option, can be used with GROUP BY or DISTINCT to tell the optimizer that the result set will be small. In this case, MySQL uses fast temporary tables to store the resulting table instead of using sorting. In MySQL Version 3.23 this shouldn't normally be needed.
SQL_CALC_FOUND_ROWS (version 4.0.0 and up) tells MySQL to calculate how many rows there would be in the result set, disregarding any LIMIT clause. The number of rows can then be retrieved with SELECT FOUND_ROWS(). See Miscellaneous functions.
Please note that in versions prior to 4.1.0 this does not work with LIMIT 0, which is optimized to return instantly (resulting in a row count of 0). See LIMIT optimisation.
SQL_CACHE tells MySQL to store the query result in the query cache if you are using QUERY_CACHE_TYPE=2 (DEMAND). See Query Cache. For a query that uses UNION or subqueries, this option takes effect to be used in any SELECT of the query.
SQL_NO_CACHE tells MySQL not to store the query result in the query cache. See Query Cache. For a query that uses UNION or subqueries, this option takes effect to be used in any SELECT of the query.
If you use GROUP BY, the output rows will be sorted according to the GROUP BY as if you had an ORDER BY over all the fields in the GROUP BY. MySQL has extended the GROUP BY clause so that you can also specify ASC and DESC after columns named in the clause:
SELECT a,COUNT(b) FROM test_table GROUP BY a DESC
MySQL has extended the use of GROUP BY to allow you to select fields that are not mentioned in the GROUP BY clause. If you are not getting the results you expect from your query, please read the GROUP BY description. See Group by functions and modifiers.
As of MySQL 4.1.1, GROUP BY allows a WITH ROLLUP modifier. See GROUP BY Modifiers.
The LIMIT clause can be used to constrain the number of rows returned by the SELECT statement. LIMIT takes one or two numeric arguments, which must be integer constants.
With one argument, the value specifies the number of rows to return from the beginning of the result set. With two arguments, the first argument specifies the offset of the first row to return, and the second specifies the maximum number of rows to return. The offset of the initial row is 0 (not 1):
To be compatible with PostgreSQL MySQL also supports the syntax: LIMIT row_count OFFSET offset.
mysql> SELECT * FROM table LIMIT 5,10; # Retrieve rows 6-15
To retrieve all rows from a certain offset up to the end of the result set, you can use some large number for the second parameter:
mysql> SELECT * FROM table LIMIT 95,18446744073709551615; # Retrieve rows 96-last.
If one argument is given, it indicates the maximum number of rows to return:
mysql> SELECT * FROM table LIMIT 5; # Retrieve first 5 rows
In other words, LIMIT n is equivalent to LIMIT 0,n.
The SELECT ... INTO OUTFILE 'file_name' form of SELECT writes the selected rows to a file. The file is created on the server host and cannot already exist (among other things, this prevents database tables and files such as /etc/passwd from being destroyed). You must have the FILE privilege on the server host to use this form of SELECT.
The SELECT ... INTO OUTFILE statement is intended primarily to let you very quickly dump a table on the server machine. If you want to create the resulting file on some other host than the server host, you can't use SELECT ... INTO OUTFILE. In that case, you should instead use some client program like mysqldump --tab or mysql -e "SELECT ..." > outfile to generate the file.
SELECT ... INTO OUTFILE is the complement of LOAD DATA INFILE; the syntax for the export_options part of the statement consists of the same FIELDS and LINES clauses that are used with the LOAD DATA INFILE statement. See LOAD DATA.
In the resulting text file, only the following characters are escaped by the ESCAPED BY character:
The ESCAPED BY character
The first character in FIELDS TERMINATED BY
The first character in LINES TERMINATED BY
Additionally, ASCII 0 is converted to ESCAPED BY followed by 0 (ASCII 48).
The reason for the above is that you must escape any FIELDS TERMINATED BY, ESCAPED BY, or LINES TERMINATED BY characters to reliably be able to read the file back. ASCII 0 is escaped to make it easier to view with some pagers.
As the resulting file doesn't have to conform to the SQL syntax, nothing else need be escaped.
Here follows an example of getting a file in the format used by many old programs.
SELECT a,b,a+b INTO OUTFILE "/tmp/result.text" FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY "\n" FROM test_table;
If you use INTO DUMPFILE instead of INTO OUTFILE, MySQL will write only one row into the file, without any column or line terminations and without performing any escape processing. This is useful if you want to store a BLOB value in a file.
Note that any file created by INTO OUTFILE and INTO DUMPFILE will be writable by all users on the server host! The reason is that the MySQL server can't create a file that is owned by anyone else than the user it's running as (you should never run mysqld as root). The file thus must be world-writable so that you can manipulate its contents.
A PROCEDURE clause names a procedure that should process the data in the result set. For an example, see procedure analyse.
If you use FOR UPDATE on a storage engine with page or row locks, the examined rows are write-locked until the end of the current transaction.
MySQL supports the following JOIN syntaxes for use in SELECT statements:
table_reference, table_reference table_reference [INNER | CROSS] JOIN table_reference [join_condition] table_reference STRAIGHT_JOIN table_reference table_reference LEFT [OUTER] JOIN table_reference [join_condition] table_reference NATURAL [LEFT [OUTER]] JOIN table_reference { OJ table_reference LEFT OUTER JOIN table_reference ON conditional_expr } table_reference RIGHT [OUTER] JOIN table_reference [join_condition] table_reference NATURAL [RIGHT [OUTER]] JOIN table_reference
Where table_reference is defined as:
table_name [[AS] alias] [[USE INDEX (key_list)] | [IGNORE INDEX (key_list)] | [FORCE INDEX (key_list)]]
and join_condition is defined as:
ON conditional_expr | USING (column_list)
You should generally not have any conditions in the ON part that are used to restrict which rows you want in the result set, but rather specify these conditions in the WHERE clause. There are exceptions to this rule.
Note that INNER JOIN syntax allows a join_condition only from MySQL 3.23.17 on. The same is true for JOIN and CROSS JOIN only as of MySQL 4.0.11.
The last LEFT OUTER JOIN syntax shown in the preceding list exists only for compatibility with ODBC:
A table reference may be aliased using tbl_name AS alias_name or tbl_name alias_name:
mysql> SELECT t1.name, t2.salary FROM employee AS t1, info AS t2 -> WHERE t1.name = t2.name;
The ON conditional is any conditional of the form that may be used in a WHERE clause.
If there is no matching record for the right table in the ON or USING part in a LEFT JOIN, a row with all columns set to NULL is used for the right table. You can use this fact to find records in a table that have no counterpart in another table:
mysql> SELECT table1.* FROM table1 -> LEFT JOIN table2 ON table1.id=table2.id -> WHERE table2.id IS NULL;
This example finds all rows in table1 with an id value that is not present in table2 (that is, all rows in table1 with no corresponding row in table2). This assumes that table2.id is declared NOT NULL. See LEFT JOIN optimisation.
The USING (column_list) clause names a list of columns that must exist in both tables. The following two clauses are semantically identical:
a LEFT JOIN b USING (c1,c2,c3) a LEFT JOIN b ON a.c1=b.c1 AND a.c2=b.c2 AND a.c3=b.c3
The NATURAL [LEFT] JOIN of two tables is defined to be semantically equivalent to an INNER JOIN or a LEFT JOIN with a USING clause that names all columns that exist in both tables.
INNER JOIN and , (comma) are semantically equivalent in the absence of a join condition: both will produce a Cartesian product between the specified tables (that is, each and every row in the first table will be joined onto all rows in the second table).
RIGHT JOIN works analogously to LEFT JOIN. To keep code portable across databases, it's recommended to use LEFT JOIN instead of RIGHT JOIN.
STRAIGHT_JOIN is identical to JOIN, except that the left table is always read before the right table. This can be used for those (few) cases in which the join optimizer puts the tables in the wrong order.
As of MySQL Version 3.23.12, you can give hints about which index MySQL should use when retrieving information from a table. This is useful if EXPLAIN shows that MySQL is using the wrong index from the list of possible indexes. By specifying USE INDEX (key_list), you can tell MySQL to use only one of the possible indexes to find rows in the table. The alternative syntax IGNORE INDEX (key_list) can be used to tell MySQL to not use some particular index.
In MySQL 4.0.9 you can also use FORCE INDEX. This acts likes USE INDEX (key_list) but with the addition that a table scan is assumed to be VERY expensive. In other words a table scan will only be used if there is no way to use one of the given index to find rows in the table.
USE/IGNORE KEY are synonyms for USE/IGNORE INDEX.
Note: USE/IGNORE/FORCE INDEX only affects which indexes are used when MySQL decides how to find rows in the table and how to do the join. It doesn't affect whether an index will be used when resolving an ORDER BY or GROUP BY.
Some examples:
mysql> SELECT * FROM table1,table2 WHERE table1.id=table2.id; mysql> SELECT * FROM table1 LEFT JOIN table2 ON table1.id=table2.id; mysql> SELECT * FROM table1 LEFT JOIN table2 USING (id); mysql> SELECT * FROM table1 LEFT JOIN table2 ON table1.id=table2.id -> LEFT JOIN table3 ON table2.id=table3.id; mysql> SELECT * FROM table1 USE INDEX (key1,key2) -> WHERE key1=1 AND key2=2 AND key3=3; mysql> SELECT * FROM table1 IGNORE INDEX (key3) -> WHERE key1=1 AND key2=2 AND key3=3;
SELECT ... UNION [ALL | DISTINCT] SELECT ... [UNION [ALL | DISTINCT] SELECT ...]
UNION is implemented in MySQL 4.0.0.
UNION is used to combine the result from many SELECT statements into one result set.
The columns listed in the select_expression portion of the SELECT should have the same type. The column names used in the first SELECT query will be used as the column names for the results returned.
The SELECT commands are normal select commands, but with the following restrictions:
Only the last SELECT command can have INTO OUTFILE.
If you don't use the keyword ALL for the UNION, all returned rows will be unique, as if you had done a DISTINCT for the total result set. If you specify ALL, you will get all matching rows from all the used SELECT statements.
The DISTINCT keyword is an optional word (introduced in MySQL 4.0.17) that does nothing. But it is required by the SQL standard.
If you want to use an ORDER BY for the total UNION result, you should use parentheses:
(SELECT a FROM table_name WHERE a=10 AND B=1 ORDER BY a LIMIT 10) UNION (SELECT a FROM table_name WHERE a=11 AND B=2 ORDER BY a LIMIT 10) ORDER BY a;
Note: You cannot mix UNION ALL and UNION DISTINCT in the same query yet. If you use ALL for one UNION then it is used for all of them.
The types and lengths of the columns in the result set of a UNION take into acccount the values retrieved by all the SELECT statements. Before MySQL 4.1.1, a limitation of UNION is that only the values from the first SELECT were used to determine result types and lengths. This could result in value truncation if, for example, the second SELECT retrieved longer values than the first SELECT:
mysql> SELECT REPEAT('a',1) UNION SELECT REPEAT('b',10); +---------------+ | REPEAT('a',1) | +---------------+ | a | | b | +---------------+
That limitation has been removed as of MySQL 4.1.1:
mysql> SELECT REPEAT('a',1) UNION SELECT REPEAT('b',10); +---------------+ | REPEAT('a',1) | +---------------+ | a | | bbbbbbbbbb | +---------------+
A subquery is a SELECT statement inside another statement. For example:
SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2);
In the above example, SELECT * FROM t1 ... is the outer query (or outer statement), and (SELECT column1 FROM t2) is the subquery. We say that the subquery is nested in the outer query, and in fact it's possible to nest subqueries within other subqueries, to a great depth. A subquery must always be inside parentheses.
Starting with version 4.1, MySQL supports all subquery forms and operations which the SQL standard requires, as well as a few features which are MySQL-specific. The main advantages of subqueries are:
They allow queries which are structured so that it's possible to isolate each part of a statement.
They provide alternative ways to perform operations which would otherwise require complex joins and unions.
They are, in many people's opinion, readable. Indeed, it was the innovation of subqueries which gave people the original idea of calling the early SQL ``Structured Query Language''.
With earlier MySQL versions it was necessary to work around or avoid subqueries, but people starting to write code now will find that subqueries are a very useful part of the toolkit.
Here is an example statement which shows the major points about subquery syntax as specified by the SQL standard and supported in MySQL.
DELETE FROM t1 WHERE s11 > ANY (SELECT COUNT(*) /* no hint */ FROM t2 WHERE NOT EXISTS (SELECT * FROM t3 WHERE ROW(5*t2.s1,77)= (SELECT 50,11*s1 FROM t4 UNION SELECT 50,77 FROM (SELECT * FROM t5) AS t5)));
For MySQL versions prior to 4.1, most subqueries can be successfully rewritten using joins and and other methods. See Rewriting subqueries.
In its simplest form (the scalar subquery as opposed to the row or table subqueries which will be discussed later), a subquery is a simple operand. Thus you can use it wherever a column value or literal is legal, and you can expect it to have those characteristics that all operands have: a data type, a length, an indication whether it can be NULL, and so on. For example:
CREATE TABLE t1 (s1 INT, s2 CHAR(5) NOT NULL); SELECT (SELECT s2 FROM t1);
The subquery in the above SELECT has a data type of CHAR, a length of 5, a character set and collation equal to the defaults in effect at CREATE TABLE time, and an indication that the value in the column can be NULL. In fact almost all subqueries can be NULL, because if the table is empty -- as in the example -- then the value of the subquery will be NULL. There are few restrictions.
A subquery's outer statement can be any one of: SELECT, INSERT, UPDATE, DELETE, SET, or DO.
A subquery can contain any of the keywords or clauses that an ordinary SELECT can contain: DISTINCT, GROUP BY, ORDER BY, LIMIT, joins, hints, UNION constructs, comments, functions, and so on.
So, when you see examples in the following sections that contain the rather Spartan construct (SELECT column1 FROM t1), imagine that your own code will contain much more diverse and complex constructions.
For example, suppose we make two tables:
CREATE TABLE t1 (s1 INT); INSERT INTO t1 VALUES (1); CREATE TABLE t2 (s1 INT); INSERT INTO t2 VALUES (2);
Then perform a SELECT:
SELECT (SELECT s1 FROM t2) FROM t1;
The result will be 2 because there is a row in t2, with a column s1, with a value of 2.
The subquery may be part of an expression. If it is an operand for a function, don't forget the parentheses. For example:
SELECT UPPER((SELECT s1 FROM t1)) FROM t2;
The most common use of a subquery is in the form:
<non-subquery operand> <comparison operator> (<subquery>)
Where <comparison operator> is one of:
= > < >= <= <>
For example:
... 'a' = (SELECT column1 FROM t1)
At one time the only legal place for a subquery was on the right side of a comparison, and you might still find some old DBMSs which insist on that.
Here is an example of a common-form subquery comparison which you can't do with a join: find all the values in table t1 which are equal to a maximum value in table t2.
SELECT column1 FROM t1 WHERE column1 = (SELECT MAX(column2) FROM t2);
Here is another example, which again is impossible with a join because it involves aggregating for one of the tables: find all rows in table t1 which contain a value which occurs twice.
SELECT * FROM t1 WHERE 2 = (SELECT COUNT(column1) FROM t1);
Syntax:
<operand> <comparison operator> ANY (<subquery>) <operand> IN (<subquery>) <operand> <comparison operator> SOME (<subquery>)
The word ANY, which must follow a comparison operator, means ``return TRUE if the comparison is TRUE for ANY of the rows that the subquery returns.'' For example,
SELECT s1 FROM t1 WHERE s1 > ANY (SELECT s1 FROM t2);
Suppose that there is a row in table t1 containing {10}. The expression is TRUE if table t2 contains {21,14,7} because there is a value in t2 -- 7 -- which is less than 10. The expression is FALSE if table t2 contains {20,10}, or if table t2 is empty. The expression is UNKNOWN if table t2 contains {NULL,NULL,NULL}.
The word IN is an alias for = ANY. Thus these two statements are the same:
SELECT s1 FROM t1 WHERE s1 = ANY (SELECT s1 FROM t2); SELECT s1 FROM t1 WHERE s1 IN (SELECT s1 FROM t2);
The word SOME is an alias for ANY. Thus these two statements are the same:
SELECT s1 FROM t1 WHERE s1 <> ANY (SELECT s1 FROM t2); SELECT s1 FROM t1 WHERE s1 <> SOME (SELECT s1 FROM t2);
Use of the word SOME is rare, but the above example shows why it might be useful. The English phrase ``a is not equal to any b'' means, to most people's ears, ``there is no b which is equal to a'' -- which isn't what is meant by the SQL syntax. By using <> SOME instead, you ensure that everyone understands the true meaning of the query.
Syntax:
<operand> <comparison operator> ALL (<subquery>)
The word ALL, which must follow a comparison operator, means ``return TRUE if the comparison is TRUE for ALL of the rows that the subquery returns''. For example,
SELECT s1 FROM t1 WHERE s1 > ALL (SELECT s1 FROM t2);
Suppose that there is a row in table t1 containing {10}. The expression is TRUE if table t2 contains {-5,0,+5} because all three values in t2 are less than 10. The expression is FALSE if table t2 contains {12,6,NULL,-100} because there is a single value in table t2 -- 12 -- which is greater than 10. The expression is UNKNOWN if table t2 contains {0,NULL,1}.
Finally, if table t2 is empty, the result is TRUE. You might think the result should be UNKNOWN, but sorry, it's TRUE. So, rather oddly,
SELECT * FROM t1 WHERE 1 > ALL (SELECT s1 FROM t2);
is TRUE when table t2 is empty, but
SELECT * FROM t1 WHERE 1 > (SELECT s1 FROM t2);
is UNKNOWN when table t2 is empty. In addition,
SELECT * FROM t1 WHERE 1 > ALL (SELECT MAX(s1) FROM t2);
is UNKNOWN when table t2 is empty. In general, tables with NULLs and empty tables are edge cases -- when writing subquery code, always consider whether you have taken those two possibilities into account.
A correlated subquery is a subquery which contains a reference to a column which is also in the outer query. For example:
SELECT * FROM t1 WHERE column1 = ANY (SELECT column1 FROM t2 WHERE t2.column2 = t1.column2);
Notice, in the example, that the subquery contains a reference to a column of t1, even though the subquery's FROM clause doesn't mention a table t1. So MySQL looks outside the subquery, and finds t1 in the outer query.
Suppose that table t1 contains a row where column1 = 5 and column2 = 6; meanwhile table t2 contains a row where column1 = 5 and column2 = 7. The simple expression ... WHERE column1 = ANY (SELECT column1 FROM t2) would be TRUE, but in this example the WHERE clause within the subquery is FALSE (because 7 <> 5), so the subquery as a whole is FALSE.
Scoping rule: MySQL evaluates from inside to outside. For example:
SELECT column1 FROM t1 AS x WHERE x.column1 = (SELECT column1 FROM t2 AS x WHERE x.column1 = (SELECT column1 FROM t3 WHERE x.column2 = t3.column1));
In the above, x.column2 must be a column in table t2 because SELECT column1 FROM t2 AS x ... renames t2. It is not a column in table t1 because SELECT column1 FROM t1 ... is an outer query which is further out.
For subqueries in HAVING or ORDER BY clauses, MySQL also looks for column names in the outer select list.
MySQL's unofficial recommendation is: avoid correlation because it makes your queries look more complex, and run more slowly.
If a subquery returns any values at all, then EXISTS <subquery> is TRUE, and NOT EXISTS <subquery> is FALSE. For example:
SELECT column1 FROM t1 WHERE EXISTS (SELECT * FROM t2);
Traditionally an EXISTS subquery starts with SELECT * but it could begin with SELECT 5 or SELECT column1 or anything at all -- MySQL ignores the SELECT list in such a subquery, so it doesn't matter.
For the above example, if t2 contains any rows, even rows with nothing but NULL values, then the EXISTS condition is TRUE. This is actually an unlikely example, since almost always a [NOT] EXISTS subquery will contain correlations. Here are some more realistic examples.
Example: What kind of store is present in one or more cities?
SELECT DISTINCT store_type FROM Stores WHERE EXISTS (SELECT * FROM Cities_Stores WHERE Cities_Stores.store_type = Stores.store_type);
Example: What kind of store is present in no cities?
SELECT DISTINCT store_type FROM Stores WHERE NOT EXISTS (SELECT * FROM Cities_Stores WHERE Cities_Stores.store_type = Stores.store_type);
Example: What kind of store is present in all cities?
SELECT DISTINCT store_type FROM Stores S1 WHERE NOT EXISTS ( SELECT * FROM Cities WHERE NOT EXISTS ( SELECT * FROM Cities_Stores WHERE Cities_Stores.city = Cities.city AND Cities_Stores.store_type = Stores.store_type));
The last example is a double-nested NOT EXISTS query -- it has a NOT EXISTS clause within a NOT EXISTS clause. Formally, it answers the question ``does a city exist with a store which is not in Stores?''. But it's easier to say that a nested NOT EXISTS answers the question ``is x TRUE for all y?''.
The discussion to this point has been of column (or scalar) subqueries -- subqueries which return a single column value. A row subquery is a subquery variant that returns a single row value -- and may thus return more than one column value. Here are two examples:
SELECT * FROM t1 WHERE (1,2) = (SELECT column1, column2 FROM t2); SELECT * FROM t1 WHERE ROW(1,2) = (SELECT column1, column2 FROM t2);
The queries above are both TRUE if table t2 has a row where column1 = 1 and column2 = 2.
The expression (1,2) is sometimes called a row constructor and is legal in other contexts too. For example
SELECT * FROM t1 WHERE (column1,column2) = (1,1);
is equivalent to
SELECT * FROM t1 WHERE column1 = 1 AND column2 = 1;
The normal use of row constructors, though, is for comparisons with subqueries that return two or more columns. For example, this query answers the request: ``find all rows in table t1 which are duplicated in table t2'':
SELECT column1,column2,column3 FROM t1 WHERE (column1,column2,column3) IN (SELECT column1,column2,column3 FROM t2);
Subqueries are legal in a SELECT statement's FROM clause. The syntax that you'll actually see is:
SELECT ... FROM (<subquery>) AS <name> ...
The AS <name> clause is mandatory, because any table in a FROM clause must have a name. Any columns in the <subquery> select list must have unique names. You may find this syntax described elsewhere in this manual, where the term used is ``derived tables''.
For illustration, assume you have this table:
CREATE TABLE t1 (s1 INT, s2 CHAR(5), s3 FLOAT);
Here's how to use the Subqueries in the FROM clause feature, using the example table:
INSERT INTO t1 VALUES (1,'1',1.0); INSERT INTO t1 VALUES (2,'2',2.0); SELECT sb1,sb2,sb3 FROM (SELECT s1 AS sb1, s2 AS sb2, s3*2 AS sb3 FROM t1) AS sb WHERE sb1 > 1;
Result: 2, '2', 4.0.
Here's another example: Suppose you want to know the average of the sum for a grouped table. This won't work:
SELECT AVG(SUM(column1)) FROM t1 GROUP BY column1;
But this query will provide the desired information:
SELECT AVG(sum_column1) FROM (SELECT SUM(column1) AS sum_column1 FROM t1 GROUP BY column1) AS t1;
Notice that the column name used within the subquery (sum_column1) is recognized in the outer query.
At the moment, subqueries in the FROM clause cannot be correlated subqueries.
There are some new error returns which apply only to subqueries. This section groups them together because reviewing them will help remind you of some points.
ERROR 1235 (ER_NOT_SUPPORTED_YET) SQLSTATE = 42000 Message = "This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'"
This means that
SELECT * FROM t1 WHERE s1 IN (SELECT s2 FROM t2 ORDER BY s1 LIMIT 1)
will not work, but only in some early versions, such as MySQL 4.1.1.
ERROR 1240 (ER_CARDINALITY_COL) SQLSTATE = 21000 Message = "Operand should contain 1 column(s)"
This error will occur in cases like this:
SELECT (SELECT column1, column2 FROM t2) FROM t1;
It's okay to use a subquery that returns multiple columns, if the purpose is comparison. See Row subqueries. But in other contexts the subquery must be a scalar operand.
ERROR 1241 (ER_SUBSELECT_NO_1_ROW) SQLSTATE = 21000 Message = "Subquery returns more than 1 row"
This error will occur in cases like this:
SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2);
but only when there is more than one row in t2. That means this error might occur in code that has been working for years, because somebody happened to make a change which affected the number of rows that the subquery can return. Remember that if the object is to find any number of rows, not just one, then the correct statement would look like this:
SELECT * FROM t1 WHERE column1 = ANY (SELECT column1 FROM t2);
Error 1093 (ER_UPDATE_TABLE_USED) SQLSTATE = HY000 Message = "You can't specify target table 'x' for update in FROM clause"
This error will occur in cases like this:
UPDATE t1 SET column2 = (SELECT MAX(column1) FROM t1);
It's okay to use a subquery for assignment within an UPDATE statement, since subqueries are legal in UPDATE and in DELETE statements as well as in SELECT statements. However, you cannot use the same table, in this case table t1, for both the subquery's FROM clause and the update target.
Usually, failure of the subquery causes the entire statement to fail.
Development is ongoing, so no optimization tip is reliable for the long term. Some interesting tricks that you might want to play with are:
Using subquery clauses which affect the number or order of the rows in the subquery, for example
SELECT * FROM t1 WHERE t1.column1 IN (SELECT column1 FROM t2 ORDER BY column1); SELECT * FROM t1 WHERE t1.column1 IN (SELECT DISTINCT column1 FROM t2); SELECT * FROM t1 WHERE EXISTS (SELECT * FROM t2 LIMIT 1);
Replacing a join with a subquery, for example
SELECT DISTINCT column1 FROM t1 WHERE t1.column1 IN ( SELECT column1 FROM t2);
instead of
SELECT DISTINCT t1.column1 FROM t1, t2 WHERE t1.column1 = t2.column1;
Moving clauses from outside to inside the subquery, for example:
SELECT * FROM t1 WHERE s1 IN (SELECT s1 FROM t1 UNION ALL SELECT s1 FROM t2);
instead of
SELECT * FROM t1 WHERE s1 IN (SELECT s1 FROM t1) OR s1 IN (SELECT s1 FROM t2);
For another example:
SELECT (SELECT column1 + 5 FROM t1) FROM t2;
instead of
SELECT (SELECT column1 FROM t1) + 5 FROM t2;
Using a row subquery instead of a correlated subquery, for example:
SELECT * FROM t1 WHERE (column1,column2) IN (SELECT column1,column2 FROM t2);
instead of
SELECT * FROM t1 WHERE EXISTS (SELECT * FROM t2 WHERE t2.column1=t1.column1 AND t2.column2=t1.column2);
Using NOT (a = ANY (...)) rather than a <> ALL (...).
Using x = ANY (table containing {1,2}) rather than x=1 OR x=2.
Using = ANY rather than EXISTS
The above tricks may cause programs to go faster or slower. Using MySQL facilities like the BENCHMARK() function, you can get an idea about what helps in your own situation. Don't worry too much about transforming to joins except for compatibility with older versions.
Some optimizations that MySQL itself will make are:
MySQL will execute non-correlated subqueries only once, (use EXPLAIN to make sure that a given subquery really is non-correlated),
MySQL will rewrite IN/ALL/ANY/SOME subqueries in an attempt to take advantage of the possibility that the select-list columns in the subquery are indexed,
MySQL will replace subqueries of the form
... IN (SELECT indexed_column FROM single_table ...)
with an index-lookup function, which EXPLAIN will describe as a special join type,
MySQL will enhance expressions of the form
value {ALL|ANY|SOME} {> | < | >= | <=} (non-correlated subquery)
with an expression involving MIN or MAX (unless NULL values or empty sets are involved). For example,
WHERE 5 > ALL (SELECT x FROM t)
might be treated as
WHERE 5 > (SELECT MAX(x) FROM t)
There is a chapter titled ``How MySQL Transforms Subqueries'' in the MySQL Internals Manual, which you can find by downloading the MySQL source package and looking for a file named internals.texi.
Up to version 4.0, only nested queries of the form INSERT ... SELECT ... and REPLACE ... SELECT ... are supported. The IN() construct can be used in other contexts.
It is often possible to rewrite a query without a subquery:
SELECT * FROM t1 WHERE id IN (SELECT id FROM t2);
This can be rewritten as:
SELECT t1.* FROM t1,t2 WHERE t1.id=t2.id;
The queries:
SELECT * FROM t1 WHERE id NOT IN (SELECT id FROM t2); SELECT * FROM t1 WHERE NOT EXISTS (SELECT id FROM t2 WHERE t1.id=t2.id);
Can be rewritten as:
SELECT table1.* FROM table1 LEFT JOIN table2 ON table1.id=table2.id WHERE table2.id IS NULL;
A LEFT [OUTER] JOIN can be faster than an equivalent subquery because the server might be able to optimize it better -- a fact that is not specific to MySQL Server alone. Prior to SQL-92, outer joins did not exist, so subqueries were the only way to do certain things in those bygone days. Today, MySQL Server and many other modern database systems offer a whole range of outer joins types.
For more complicated subqueries you can often create temporary tables to hold the subquery. In some cases, however, this option will not work. The most frequently encountered of these cases arises with DELETE statements, for which standard SQL does not support joins (except in subqueries). For this situation there are three options available:
The first option is to upgrade to MySQL version 4.1.
The second option is to use a procedural programming language (such as Perl or PHP) to submit a SELECT query to obtain the primary keys for the records to be deleted, and then use these values to construct the DELETE statement (DELETE FROM ... WHERE ... IN (key1, key2, ...)).
The third option is to use interactive SQL to construct a set of DELETE statements automatically, using the MySQL extension CONCAT() (in lieu of the standard || operator). For example:
SELECT CONCAT('DELETE FROM tab1 WHERE pkid = ', "'", tab1.pkid, "'", ';') FROM tab1, tab2 WHERE tab1.col1 = tab2.col2;
You can place this query in a script file and redirect input from it to the mysql command-line interpreter, piping its output back to a second instance of the interpreter:
shell> mysql --skip-column-names mydb < myscript.sql | mysql mydb
MySQL Server 4.0 supports multiple-table DELETE statements that can be used to efficiently delete rows based on information from one table or even from many tables at the same time. Multiple-table UPDATE statements are also supported from version 4.0.
TRUNCATE TABLE table_name
In 3.23 TRUNCATE TABLE is mapped to COMMIT; DELETE FROM table_name. See DELETE.
TRUNCATE TABLE differs from DELETE FROM ... in the following ways:
Truncate operations drop and re-create the table, which is much faster than deleting rows one by one.
Truncate operations are not transaction-safe; you will get an error if you have an active transaction or an active table lock.
The number of deleted rows is not returned.
As long as the table definition file table_name.frm is valid, the table can be re-created this way, even if the data or index files have become corrupted.
The table handler may not remember the last used AUTO_INCREMENT value but may start counting from the beginning. This is true for MyISAM, ISAM, and BDB tables.
TRUNCATE TABLE is an Oracle SQL extension. This statement was added in MySQL 3.23.28, although from 3.23.28 to 3.23.32, the keyword TABLE must be omitted.
UPDATE [LOW_PRIORITY] [IGNORE] tbl_name SET col_name1=expr1 [, col_name2=expr2 ...] [WHERE where_definition] [ORDER BY ...] [LIMIT row_count]
or:
UPDATE [LOW_PRIORITY] [IGNORE] tbl_name [, tbl_name ...] SET col_name1=expr1 [, col_name2=expr2 ...] [WHERE where_definition]
UPDATE updates columns in existing table rows with new values. The SET clause indicates which columns to modify and the values they should be given. The WHERE clause, if given, specifies which rows should be updated. Otherwise, all rows are updated. If the ORDER BY clause is specified, the rows will be updated in the order that is specified.
If you specify the keyword LOW_PRIORITY, execution of the UPDATE is delayed until no other clients are reading from the table.
If you specify the keyword IGNORE, the update statement will not abort even if duplicate key errors occur during the update. Rows that would cause conflicts will not be updated.
If you access a column from tbl_name in an expression, UPDATE uses the current value of the column. For example, the following statement sets the age column to one more than its current value:
mysql> UPDATE persondata SET age=age+1;
UPDATE assignments are evaluated from left to right. For example, the following statement doubles the age column, then increments it:
mysql> UPDATE persondata SET age=age*2, age=age+1;
If you set a column to the value it currently has, MySQL notices this and doesn't update it.
UPDATE returns the number of rows that were actually changed. In MySQL Version 3.22 or later, the C API function mysql_info() returns the number of rows that were matched and updated and the number of warnings that occurred during the UPDATE. If you update a column that has been declared NOT NULL by setting to NULL, the column is set to the default value appropriate for the column type and the warning count is incremented. The default value is is 0 for numeric types, the empty string ('') for string types, and the ``zero'' value for date and time types.
Starting from MySQL version 3.23, you can use LIMIT row_count to restrict the scope of the UPDATE. A LIMIT clause works as follows:
Before MySQL 4.0.13, LIMIT is a rows-affected restriction. The statement stops as soon as it has changed row_count rows that satisfy the WHERE clause.
From 4.0.13 on, LIMIT is a rows-matched restriction. The statement stops as soon as it has found row_count rows that satisfy the WHERE clause, whether or not they actually were changed.
If an ORDER BY clause is used (available from MySQL 4.0.0), the rows will be updated in that order. This is really useful only in conjunction with LIMIT.
Starting with MySQL Version 4.0.4, you can also perform UPDATE operations that cover multiple tables:
UPDATE items,month SET items.price=month.price WHERE items.id=month.id;
The example shows an inner join using the comma operator, but multiple-table UPDATE statements can use any type of join allowed in SELECT statements, such as LEFT JOIN.
Note: You cannot use ORDER BY or LIMIT with multiple-table UPDATE.
Before MySQL 4.0.18 one needed the UPDATE privilege for all tables used in a multi table UPDATE (even if they where not updated). In MySQL 4.0.18 one need the SELECT privilege for any columns that are only read.
Table of Contents
ALTER DATABASE db_name alter_specification [, alter_specification] .... alter_specification: [DEFAULT] CHARACTER SET charset_name | [DEFAULT] COLLATE collation_name
ALTER DATABASE allows you to change the overall characteristics of a database.
The CHARACTER SET clause changes the database character set. The COLLATE clause changes the database collation.
Database characteristics are stored in the db.opt file in the database directory.
To use ALTER DATABASE, you need the ALTER privilege on the database.
ALTER DATABASE was added in MySQL 4.1.1.
ALTER [IGNORE] TABLE tbl_name alter_specification [, alter_specification] ... alter_specification: ADD [COLUMN] create_definition [FIRST | AFTER column_name ] | ADD [COLUMN] (create_definition, create_definition,...) | ADD INDEX [index_name] [index_type] (index_col_name,...) | ADD [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...) | ADD [CONSTRAINT [symbol]] UNIQUE [index_name] [index_type] (index_col_name,...) | ADD FULLTEXT [index_name] (index_col_name,...) | ADD [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (index_col_name,...) [reference_definition] | ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT} | CHANGE [COLUMN] old_col_name create_definition [FIRST | AFTER column_name] | MODIFY [COLUMN] create_definition [FIRST | AFTER column_name] | DROP [COLUMN] col_name | DROP PRIMARY KEY | DROP INDEX index_name | DISABLE KEYS | ENABLE KEYS | RENAME [TO] new_tbl_name | ORDER BY col | CHARACTER SET character_set_name [COLLATE collation_name] | table_options
ALTER TABLE allows you to change the structure of an existing table. For example, you can add or delete columns, create or destroy indexes, change the type of existing columns, or rename columns or the table itself. You can also change the comment for the table and type of the table.
See CREATE TABLE.
If you use ALTER TABLE to change a column specification but DESCRIBE tbl_name indicates that your column was not changed, it is possible that MySQL ignored your modification for one of the reasons described in Silent column changes. For example, if you try to change a VARCHAR column to CHAR, MySQL will still use VARCHAR if the table contains other variable-length columns.
ALTER TABLE works by making a temporary copy of the original table. The alteration is performed on the copy, then the original table is deleted and the new one is renamed. This is done in such a way that all updates are automatically redirected to the new table without any failed updates. While ALTER TABLE is executing, the original table is readable by other clients. Updates and writes to the table are stalled until the new table is ready.
Note that if you use any other option to ALTER TABLE than RENAME, MySQL will always create a temporary table, even if the data wouldn't strictly need to be copied (such as when you change the name of a column). We plan to fix this in the future, but as one doesn't normally do ALTER TABLE that often this isn't that high on our TODO. For MyISAM tables, you can speed up the index recreation part (which is the slowest part of the recreation process) by setting the myisam_sort_buffer_size variable to a high value.
To use ALTER TABLE, you need ALTER, INSERT, and CREATE privileges on the table.
IGNORE is a MySQL extension to SQL-92. It controls how ALTER TABLE works if there are duplicates on unique keys in the new table. If IGNORE isn't specified, the copy is aborted and rolled back. If IGNORE is specified, then for rows with duplicates on a unique key, only the first row is used; the others are deleted.
You can issue multiple ADD, ALTER, DROP, and CHANGE clauses in a single ALTER TABLE statement. This is a MySQL extension to SQL-92, which allows only one of each clause per ALTER TABLE statement.
CHANGE col_name, DROP col_name, and DROP INDEX are MySQL extensions to SQL-92.
MODIFY is an Oracle extension to ALTER TABLE.
The optional word COLUMN is a pure noise word and can be omitted.
If you use ALTER TABLE tbl_name RENAME TO new_name without any other options, MySQL simply renames the files that correspond to the table tbl_name. There is no need to create the temporary table. See RENAME TABLE.
create_definition clauses use the same syntax for ADD and CHANGE as for CREATE TABLE. Note that this syntax includes the column name, not just the column type. See CREATE TABLE.
You can rename a column using a CHANGE old_col_name create_definition clause. To do so, specify the old and new column names and the type that the column currently has. For example, to rename an INTEGER column from a to b, you can do this:
mysql> ALTER TABLE t1 CHANGE a b INTEGER;
If you want to change a column's type but not the name, CHANGE syntax still requires an old and new column name, even if they are the same. For example:
mysql> ALTER TABLE t1 CHANGE b b BIGINT NOT NULL;
However, as of MySQL Version 3.22.16a, you can also use MODIFY to change a column's type without renaming it:
mysql> ALTER TABLE t1 MODIFY b BIGINT NOT NULL;
If you use CHANGE or MODIFY to shorten a column for which an index exists on part of the column (for instance, if you have an index on the first 10 characters of a VARCHAR column), you cannot make the column shorter than the number of characters that are indexed.
When you change a column type using CHANGE or MODIFY, MySQL tries to convert data to the new type as well as possible.
In MySQL Version 3.22 or later, you can use FIRST or ADD ... AFTER col_name to add a column at a specific position within a table row. The default is to add the column last. From MySQL Version 4.0.1, you can also use the FIRST and AFTER keywords in CHANGE or MODIFY.
ALTER COLUMN specifies a new default value for a column or removes the old default value. If the old default is removed and the column can be NULL, the new default is NULL. If the column cannot be NULL, MySQL assigns a default value, as described in CREATE TABLE.
DROP INDEX removes an index. This is a MySQL extension to SQL-92. See DROP INDEX.
If columns are dropped from a table, the columns are also removed from any index of which they are a part. If all columns that make up an index are dropped, the index is dropped as well.
If a table contains only one column, the column cannot be dropped. If what you intend is to remove the table, use DROP TABLE instead.
DROP PRIMARY KEY drops the primary index. (Prior to MySQL 4.1.2, if no primary index exists, DROP PRIMARY KEY drops the first UNIQUE index in the table. MySQL marks the first UNIQUE key as the PRIMARY KEY if no PRIMARY KEY was specified explicitly.)
If you add a UNIQUE INDEX or PRIMARY KEY to a table, this is stored before any not UNIQUE index so that MySQL can detect duplicate keys as early as possible.
ORDER BY allows you to create the new table with the rows in a specific order. Note that the table will not remain in this order after inserts and deletes. In some cases, it might make sorting easier for MySQL if the table is in order by the column that you want to order it by later. This option is mainly useful when you know that you are mostly going to query the rows in a certain order; by using this option after big changes to the table, you might be able to get higher performance.
If you use ALTER TABLE on a MyISAM table, all non-unique indexes are created in a separate batch (like in REPAIR). This should make ALTER TABLE much faster when you have many indexes.
Since MySQL 4.0 the above feature can be activated explicitly. ALTER TABLE ... DISABLE KEYS makes MySQL to stop updating non-unique indexes for MyISAM table. ALTER TABLE ... ENABLE KEYS then should be used to re-create missing indexes. As MySQL does it with a special algorithm which is much faster then inserting keys one by one, disabling keys could give a considerable speedup on bulk inserts.
With the C API function mysql_info(), you can find out how many records were copied, and (when IGNORE is used) how many records were deleted due to duplication of unique key values.
The FOREIGN KEY, CHECK, and REFERENCES clauses don't actually do anything, except for InnoDB type tables which support ... ADD [CONSTRAINT [symbol]] FOREIGN KEY (...) REFERENCES ... (...) and ... DROP FOREIGN KEY .... See InnoDB foreign key constraints. The syntax for other table types is provided only for compatibility, to make it easier to port code from other SQL servers and to run applications that create tables with references. See Differences from ANSI.
ALTER TABLE ignores the DATA DIRECTORY and INDEX DIRECTORY table options.
If you want to change all CHAR/VARCHAR/TEXT columns to a new character set (for example after upgrading from MySQL 4.0.x to 4.1.1) you can do:
ALTER TABLE table_name CHARACTER SET character_set_name;
Note that the following command will change only the default character set for a table:
ALTER TABLE table_name DEFAULT CHARACTER SET character_set_name;
The default character set is the character set that is used if you don't specify the character set for a new column you add to a table (for example with ALTER TABLE ... ADD column).
Here is an example that shows some of the uses of ALTER TABLE. We begin with a table t1 that is created as shown here:
mysql> CREATE TABLE t1 (a INTEGER,b CHAR(10));
To rename the table from t1 to t2:
mysql> ALTER TABLE t1 RENAME t2;
To change column a from INTEGER to TINYINT NOT NULL (leaving the name the same), and to change column b from CHAR(10) to CHAR(20) as well as renaming it from b to c:
mysql> ALTER TABLE t2 MODIFY a TINYINT NOT NULL, CHANGE b c CHAR(20);
To add a new TIMESTAMP column named d:
mysql> ALTER TABLE t2 ADD d TIMESTAMP;
To add an index on column d, and make column a the primary key:
mysql> ALTER TABLE t2 ADD INDEX (d), ADD PRIMARY KEY (a);
To remove column c:
mysql> ALTER TABLE t2 DROP COLUMN c;
To add a new AUTO_INCREMENT integer column named c:
mysql> ALTER TABLE t2 ADD c INT UNSIGNED NOT NULL AUTO_INCREMENT, ADD INDEX (c);
Note that we indexed c, because AUTO_INCREMENT columns must be indexed, and also that we declare c as NOT NULL, because indexed columns cannot be NULL.
When you add an AUTO_INCREMENT column, column values are filled in with sequence numbers for you automatically. You can set the first sequence number by executing SET INSERT_ID=value before ALTER TABLE or using the AUTO_INCREMENT=value table option. See SET OPTION.
With MyISAM tables, if you don't change the AUTO_INCREMENT column, the sequence number will not be affected. If you drop an AUTO_INCREMENT column and then add another AUTO_INCREMENT column, the numbers will start from 1 again.
See ALTER TABLE problems.
CREATE DATABASE [IF NOT EXISTS] db_name [create_specification [, create_specification] ...] create_specification: [DEFAULT] CHARACTER SET charset_name | [DEFAULT] COLLATE collation_name
CREATE DATABASE creates a database with the given name.
Rules for allowable database names are given in Legal names. An error occurs if the database already exists and you didn't specify IF NOT EXISTS.
As of MySQL 4.1.1, create_specification options may be given. The CHARACTER SET clause specifies the database character set. The COLLATE clause specifies the database collation.
Database characteristics are stored in the db.opt file in the database directory.
Databases in MySQL are implemented as directories containing files that correspond to tables in the database. Because there are no tables in a database when it is initially created, the CREATE DATABASE statement only creates a directory under the MySQL data directory.
You can also create databases with mysqladmin. See Client-Side Scripts.
CREATE [UNIQUE|FULLTEXT] INDEX index_name [index_type] ON tbl_name (index_col_name,...) index_col_name: col_name [(length)] [ASC | DESC]
The CREATE INDEX statement doesn't do anything in MySQL prior to Version 3.22. In Version 3.22 or later, CREATE INDEX is mapped to an ALTER TABLE statement to create indexes.
See ALTER TABLE.
Normally, you create all indexes on a table at the time the table itself is created with CREATE TABLE. See CREATE TABLE. CREATE INDEX allows you to add indexes to existing tables.
A column list of the form (col1,col2,...) creates a multiple-column index. Index values are formed by concatenating the values of the given columns.
For CHAR and VARCHAR columns, indexes can be created that use only part of a column, using col_name(length) syntax to index the first length bytes of each column value. (For BLOB and TEXT columns, a prefix length is required; length may be a value up to 255.) The statement shown here creates an index using the first 10 characters of the name column:
mysql> CREATE INDEX part_of_name ON customer (name(10));
Because most names usually differ in the first 10 characters, this index should not be much slower than an index created from the entire name column. Also, using partial columns for indexes can make the index file much smaller, which could save a lot of disk space and might also speed up INSERT operations!
Note that you can add an index on a column that can have NULL values only if you are using MySQL Version 3.23.2 or newer and are using the MyISAM, InnoDB, or BDB table type. You can only add an index on a BLOB/TEXT column if you are using MySQL Version 3.23.2 or newer and are using the MyISAM or BDB table type, or MySQL Version 4.0.14 or newer and the InnoDB table type. For an index on a BLOB or TEXT column, a prefix length must always be specified.
An index_col_name specification may end with ASC or DESC. These keywords are allowed for future extensions for specifying ascending or descending index value storage. Currently they are parsed but ignored; index values are always stored in ascending order.
For more information about how MySQL uses indexes, see MySQL indexes.
FULLTEXT indexes can index only CHAR, VARCHAR, and TEXT columns, and only in MyISAM tables. FULLTEXT indexes are available in MySQL Version 3.23.23 and later. Fulltext Search.
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name [(create_definition,...)] [table_options] [select_statement]
or:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name [(] LIKE old_tbl_name [)]; create_definition: col_name type [NOT NULL | NULL] [DEFAULT default_value] [AUTO_INCREMENT] [[PRIMARY] KEY] [COMMENT 'string'] [reference_definition] | [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...) | KEY [index_name] [index_type] (index_col_name,...) | INDEX [index_name] [index_type] (index_col_name,...) | [CONSTRAINT [symbol]] UNIQUE [INDEX] [index_name] [index_type] (index_col_name,...) | FULLTEXT [INDEX] [index_name] (index_col_name,...) | [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (index_col_name,...) [reference_definition] | CHECK (expr) type: TINYINT[(length)] [UNSIGNED] [ZEROFILL] | SMALLINT[(length)] [UNSIGNED] [ZEROFILL] | MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL] | INT[(length)] [UNSIGNED] [ZEROFILL] | INTEGER[(length)] [UNSIGNED] [ZEROFILL] | BIGINT[(length)] [UNSIGNED] [ZEROFILL] | REAL[(length,decimals)] [UNSIGNED] [ZEROFILL] | DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL] | FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL] | DECIMAL(length,decimals) [UNSIGNED] [ZEROFILL] | NUMERIC(length,decimals) [UNSIGNED] [ZEROFILL] | CHAR(length) [BINARY | ASCII | UNICODE] | VARCHAR(length) [BINARY] | DATE | TIME | TIMESTAMP | DATETIME | TINYBLOB | BLOB | MEDIUMBLOB | LONGBLOB | TINYTEXT | TEXT | MEDIUMTEXT | LONGTEXT | ENUM(value1,value2,value3,...) | SET(value1,value2,value3,...) index_col_name: col_name [(length)] [ASC | DESC] reference_definition: REFERENCES tbl_name [(index_col_name,...)] [MATCH FULL | MATCH PARTIAL] [ON DELETE reference_option] [ON UPDATE reference_option] reference_option: RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT table_options: table_option [table_option] ... table_option: {ENGINE | TYPE} = {BDB | HEAP | ISAM | InnoDB | MERGE | MRG_MYISAM | MYISAM} | AUTO_INCREMENT = # | AVG_ROW_LENGTH = # | CHECKSUM = {0 | 1} | COMMENT = 'string' | MAX_ROWS = # | MIN_ROWS = # | PACK_KEYS = {0 | 1 | DEFAULT} | PASSWORD = 'string' | DELAY_KEY_WRITE = {0 | 1} | ROW_FORMAT = { DEFAULT | DYNAMIC | FIXED | COMPRESSED } | RAID_TYPE = { 1 | STRIPED | RAID0 } RAID_CHUNKS=# RAID_CHUNKSIZE=# | UNION = (table_name,[table_name...]) | INSERT_METHOD = { NO | FIRST | LAST } | DATA DIRECTORY = 'absolute path to directory' | INDEX DIRECTORY = 'absolute path to directory' | DEFAULT CHARACTER SET character_set_name [COLLATE collation_name] select_statement: [IGNORE | REPLACE] [AS] SELECT ... (Some legal select statement)
CREATE TABLE creates a table with the given name. Rules for allowable table names are given in Legal names. By default, the table is created in the current database. An error occurs if the table already exists, if there is no current database, or if the database does not exist.
In MySQL Version 3.22 or later, the table name can be specified as db_name.tbl_name to create the table in a specific database. This works regardless of whether there is a current database.
From MySQL Version 3.23, you can use the TEMPORARY keyword when you create a table. The temporary table is visible only to the current connection, and will be deleted automatically when the connection is closed. This means that two different connections can both use the same temporary table name without conflicting with each other or with an existing table of the same name. (The existing table is hidden until the temporary table is deleted.) From MySQL 4.0.2 on, you must have the CREATE TEMPORARY TABLES privilege to be able to create temporary tables.
In MySQL Version 3.23 or later, you can use the keywords IF NOT EXISTS so that an error does not occur if the table already exists. Note that there is no verification that the existing table has a structure identical to that indicated by the CREATE TABLE statement.
From version 4.1.0, the attribute SERIAL can be used as an alias for BIGINT NOT NULL AUTO_INCREMENT UNIQUE. This is compatibility feature.
As of MySQL 3.23, you can create one table from another by adding a SELECT statement at the end of the CREATE TABLE statement:
CREATE TABLE new_tbl SELECT * FROM orig_tbl;
Indexes are not carried over to the new table, and some conversion of column types may occur. For example, the AUTO_INCREMENT attribute is not preserved, and VARCHAR columns may become CHAR columns.
When creating a table with CREATE ... SELECT, make sure to alias any function calls or expressions in the query. If you do not, the CREATE statement may fail or result in undesirable column names.
CREATE TABLE artists_and_works SELECT artist.name, COUNT(work.artist_id) AS number_of_works FROM artist LEFT JOIN work ON artist.id = work.artist_id GROUP BY artist.id;
As of MySQL 4.1, you can explicitly specify the type for a generated column:
CREATE TABLE foo (a tinyint not null) SELECT b+1 AS 'a' FROM bar;
In MySQL 4.1, you can also use LIKE to create a table based on the definition of another table, including any column attributes and indexes the original table has:
CREATE TABLE new_tbl LIKE orig_tbl;
CREATE TABLE ... LIKE does not copy any DATA DIRECTORY or INDEX DIRECTORY table options that were specified for the original table.
Each table tbl_name is represented by some files in the database directory. In the case of MyISAM-type tables you will get:
File | Purpose |
tbl_name.frm | Table format (definition) file |
tbl_name.MYD | Datafile |
tbl_name.MYI | Index file |
For more information on the properties of the various column types, see Column types:
If neither NULL nor NOT NULL is specified, the column is treated as though NULL had been specified.
An integer column may have the additional attribute AUTO_INCREMENT. When you insert a value of NULL (recommended) or 0 into an indexed AUTO_INCREMENT column, the column is set to the next sequence value. Typically this is value+1, where value is the largest value for the column currently in the table. AUTO_INCREMENT sequences begin with 1. See mysql_insert_id().
As of MySQL 4.1.1, specifying the NO_AUTO_VALUE_ON_ZERO flag for the --sql-mode server option or the sql_mode server variable allows you to store 0 in AUTO_INCREMENT columns as 0, instead of generating a new sequence value. See Server options.
If you delete the row containing the maximum value for an AUTO_INCREMENT column, the value will be reused for an ISAM or BDB table, but not for a MyISAM or InnoDB table. If you delete all rows in the table with DELETE FROM table_name (without a WHERE) in AUTOCOMMIT mode, the sequence starts over for all table types except InnoDB. See InnoDB auto-increment column.
Note: There can be only one AUTO_INCREMENT column per table, it must be indexed and it can't have a DEFAULT value. In MySQL Version 3.23, an AUTO_INCREMENT column will work properly only if it contains only positive values. Inserting a negative number is regarded as inserting a very large positive number. This is done to avoid precision problems when numbers ``wrap'' over from positive to negative and also to ensure that one doesn't accidentally get an AUTO_INCREMENT column that contains 0.
In MyISAM and BDB tables you can specify AUTO_INCREMENT secondary column in a multiple-column key. See example-AUTO_INCREMENT.
To make MySQL compatible with some ODBC applications, you can find the AUTO_INCREMENT value for the last inserted row with the following query:
SELECT * FROM tbl_name WHERE auto_col IS NULL
NULL values are handled differently for TIMESTAMP columns than for other column types. You cannot store a literal NULL in a TIMESTAMP column; setting the column to NULL sets it to the current date and time. Because TIMESTAMP columns behave this way, the NULL and NOT NULL attributes do not apply in the normal way and are ignored if you specify them.
On the other hand, to make it easier for MySQL clients to use TIMESTAMP columns, the server reports that such columns may be assigned NULL values (which is true), even though TIMESTAMP never actually will contain a NULL value. You can see this when you use DESCRIBE tbl_name to get a description of your table.
Note that setting a TIMESTAMP column to 0 is not the same as setting it to NULL, because 0 is a valid TIMESTAMP value.
A DEFAULT value must be a constant; it cannot be a function or an expression.
If no DEFAULT value is specified for a column, MySQL automatically assigns one, as follows.
If the column may take NULL as a value, the default value is NULL.
If the column is declared as NOT NULL, the default value depends on the column type:
For numeric types other than those declared with the AUTO_INCREMENT attribute, the default is 0. For an AUTO_INCREMENT column, the default value is the next value in the sequence.
For date and time types other than TIMESTAMP, the default is the appropriate zero value for the type. For the first TIMESTAMP column in a table, the default value is the current date and time. See Date and time types.
For string types other than ENUM, the default value is the empty string. For ENUM, the default is the first enumeration value.
Default values must be constants. This means, for example, that you cannot set the default for a date column to be the value of a function such as NOW() or CURRENT_DATE.
A comment for a column may be specified with the COMMENT option. The comment is displayed by the SHOW CREATE TABLE statement, and by SHOW FULL COLUMNS. This option is available as of MySQL 4.1. (It is allowed but ignored in earlier versions.)
KEY is normally a synonym for INDEX. From version 4.1, the key attribute PRIMARY KEY may also be specified as just KEY. This was implemented for compatibility with other databases.
In MySQL, a UNIQUE key can have only distinct values. An error occurs if you try to add a new row with a key that matches an existing row.
A PRIMARY KEY is a unique KEY where all key columns must be defined as NOT NULL. If they are not explicitly declared as NOT NULL, it will be done implicitly (and quietly). In MySQL, the key is named PRIMARY. A table can have only one PRIMARY KEY. If you don't have a PRIMARY KEY and some applications ask for the PRIMARY KEY in your tables, MySQL will return the first UNIQUE key, which doesn't have any NULL columns, as the PRIMARY KEY.
A PRIMARY KEY can be a multiple-column index. However, you cannot create a multiple-column index using the PRIMARY KEY key attibute in a column specification. Doing so will mark only that single column as primary. You must use a separate PRIMARY KEY(index_col_name, ...) clause.
A UNIQUE index is one in which all values in the index must be distinct. The exception to this is that if a column in the index is allowed to contain NULL values, it may contain multiple NULL values. This exception does not apply to BDB tables, which allow only a single NULL.
If the PRIMARY or UNIQUE key consists of only one column and this is of type integer, you can also refer to it as _rowid (new in Version 3.23.11).
If you don't assign a name to an index that is not a PRIMARY KEY, the index will be assigned the same name as the first index_col_name, with an optional suffix (_2, _3, ...) to make it unique. You can see index names for a table using SHOW INDEX FROM tbl_name. See Show database info.
From MySQL 4.1.0 on, some storage engines allow you to specify an index type when creating an index. The syntax for the index_type specifier is USING type_name. The allowable type_name values supported by different storage engines are shown in the following table. Where multiple index types are listed, the first one is the default when no index_type specifier is given.
Storage engine | Allowable index types |
MyISAM | BTREE |
InnoDB | BTREE |
MEMORY/HEAP | HASH, BTREE |
Example:
CREATE TABLE lookup (id INT, INDEX USING BTREE (id)) ENGINE = MEMORY;
TYPE type_name may be used as a synonym for USING type_name to specify an index type. USING is the preferred form, however. (The preceding index name is not optional with TYPE, because unlike USING, TYPE is not a reserved word and thus is interpreted as an index name.)
Only the MyISAM, InnoDB, and BDB table types support indexes on columns that can have NULL values. In other cases you must declare such columns NOT NULL or an error results.
With col_name(length) syntax in an index specification, you can create an index that uses only the first length bytes of a CHAR or VARCHAR column. This can make the index file much smaller. See Indexes.
Only the MyISAM and (as of MySQL 4.0.14) InnoDB table types support indexing on BLOB and TEXT columns. When putting an index on a BLOB or TEXT column, you must always specify the length of the index, up to 255 bytes. For example:
CREATE TABLE test (blob_col BLOB, INDEX(blob_col(10)));
An index_col_name specification may end with ASC or DESC. These keywords are allowed for future extensions for specifying ascending or descending index value storage. Currently they are parsed but ignored; index values are always stored in ascending order.
When you use ORDER BY or GROUP BY with a TEXT or BLOB column, the server sorts values using only the initial number of bytes indicated by the max_sort_length server variable. See BLOB.
In MySQL Version 3.23.23 or later, you can also create special FULLTEXT indexes. They are used for full-text search. Only the MyISAM table type supports FULLTEXT indexes. They can be created only from CHAR, VARCHAR, and TEXT columns. Indexing always happens over the entire column; partial indexing is not supported. See Fulltext Search for details of operation.
In MySQL Version 3.23.44 or later, InnoDB tables support checking of foreign key constraints. See InnoDB. Note that the FOREIGN KEY syntax in InnoDB is more restrictive than the syntax presented above: The columns of the referenced table must always be explicitly named. InnoDB supports both ON DELETE and ON UPDATE actions on foreign keys as of MySQL 3.23.50 and 4.0.8, respectively. See the InnoDB manual section for the precise syntax. See InnoDB foreign key constraints. For other table types, MySQL Server does parse the FOREIGN KEY, CHECK, and REFERENCES syntax in CREATE TABLE commands, but without further action being taken. See ANSI diff Foreign Keys.
For MyISAM and ISAM tables, each NULL column takes one bit extra, rounded up to the nearest byte. The maximum record length in bytes can be calculated as follows:
row length = 1 + (sum of column lengths) + (number of NULL columns + delete_flag + 7)/8 + (number of variable-length columns)
delete_flag is 1 for tables with static record format. Static tables use a bit in the row record for a flag that indicates whether the row has been deleted. delete_flag is 0 for dynamic tables because the flag is stored in the dynamic row header.
These calculations do not apply for InnoDB tables, for which storage size is not different for NULL columns compared to NOT NULL columns.
The table_options and SELECT options are only implemented in MySQL Version 3.23 and above.
The ENGINE and TYPE options specify the storage engine for the table. ENGINE was added in MySQL 4.0.18 (for 4.0) and 4.1.2 (for 4.1). It is the preferred option name as of those versions, and TYPE has become deprecated. TYPE will be supported throughout the 4.x series, but likely will be removed in MySQL 5.1.
The ENGINE and TYPE options take the following values:
Storage engine | Description |
BDB or BerkeleyDB | Transaction-safe tables with page locking. See BDB. |
HEAP | The data for this table is only stored in memory. See HEAP. |
ISAM | The original storage engine. See ISAM. |
InnoDB | Transaction-safe tables with row locking. See InnoDB. |
MERGE | A collection of MyISAM tables used as one table. See MERGE. |
MRG_MyISAM | An alias for MERGE. |
MyISAM | The new binary portable storage engine that is the replacement for ISAM. See MyISAM. |
See Table types.
If a storage engine is specified and that particular engine is not available, MySQL will use MyISAM instead. For example, if a table definition includes the ENGINE=BDB option but the MySQL server does not support BDB tables, the table will be created as a MyISAM table. This makes it possible to have a replication setup where you have transactional tables on the master but tables created on the slave are non-transactional (to get more speed). In MySQL 4.1.1 you get a warning if the specified table type is not honored.
The other table options are used to optimize the behavior of the table. In most cases, you don't have to specify any of them. The options work for all table types unless otherwise indicated:
Option | Description |
AUTO_INCREMENT | The next AUTO_INCREMENT value you want to set for your table (MyISAM only; to set the first auto-increment value for an InnoDB table, insert a dummy row with a value one less, and delete the dummy row). |
AVG_ROW_LENGTH | An approximation of the average row length for your table. You need to set this only for large tables with variable size records. |
CHECKSUM | Set this to 1 if you want MySQL to maintain a checksum for all rows. It makes the table a little slower to update but it also makes it easier to find corrupted tables. (MyISAM only). |
COMMENT | A 60-character comment for your table. |
MAX_ROWS | Maximum number of rows you plan to store in the table. |
MIN_ROWS | Minimum number of rows you plan to store in the table. |
PACK_KEYS | Set this to 1 if you want to have a smaller index. This usually makes updates slower and reads faster (MyISAM and ISAM only). Setting this to 0 disables all packing of keys. Setting this to DEFAULT (MySQL 4.0) tells the storage engine to only pack long CHAR/VARCHAR columns. |
PASSWORD | Encrypt the .frm file with a password. This option doesn't do anything in the standard MySQL version. |
DELAY_KEY_WRITE | Set this to 1 if you want to delay key table updates until the table is closed (MyISAM only). |
ROW_FORMAT | Defines how the rows should be stored. Currently this option works only with MyISAM tables, which supports the DYNAMIC and FIXED row formats. See MyISAM table formats. |
When you use a MyISAM table, MySQL uses the product of MAX_ROWS * AVG_ROW_LENGTH to decide how big the resulting table will be. If you don't specify any of the above options, the maximum size for a table will be 4G (or 2G if your operating systems only supports 2G tables). The reason for this is just to keep down the pointer sizes to make the index smaller and faster if you don't really need big files.
If you don't use PACK_KEYS, the default is to only pack strings, not numbers. If you use PACK_KEYS=1, numbers will be packed as well.
When packing binary number keys, MySQL will use prefix compression. This means that you will get a big benefit from this only if you have many numbers that are the same. Prefix compression means that every key needs one extra byte to indicate how many bytes of the previous key are the same for the next key (note that the pointer to the row is stored in high-byte-first order directly after the key, to improve compression). This means that if you have many equal keys on two consecutive rows, all following ``same'' keys will usually only take 2 bytes (including the pointer to the row). Compare this to the ordinary case where the following keys will take storage_size_for_key + pointer_size (usually 4). On the other hand, if all keys are totally different, you will use 1 byte more per key, if the key isn't a key that can have NULL values. (In this case the packed key length will be stored in the same byte that is used to mark if a key is NULL.)
As of MySQL 3.23, if you specify a SELECT after the CREATE statement, MySQL will create new fields for all elements in the SELECT. For example:
mysql> CREATE TABLE test (a INT NOT NULL AUTO_INCREMENT, -> PRIMARY KEY (a), KEY(b)) -> TYPE=MyISAM SELECT b,c FROM test2;
This will create a MyISAM table with three columns, a, b, and c. Notice that the columns from the SELECT statement are appended to the right side of the table, not overlapped onto it. Take the following example:
mysql> SELECT * FROM foo; +---+ | n | +---+ | 1 | +---+ mysql> CREATE TABLE bar (m INT) SELECT n FROM foo; Query OK, 1 row affected (0.02 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> SELECT * FROM bar; +------+---+ | m | n | +------+---+ | NULL | 1 | +------+---+ 1 row in set (0.00 sec)
For each row in table foo, a row is inserted in bar with the values from foo and default values for the new columns.
CREATE TABLE ... SELECT will not automatically create any indexes for you. This is done intentionally to make the command as flexible as possible. If you want to have indexes in the created table, you should specify these before the SELECT statement:
mysql> CREATE TABLE bar (UNIQUE (n)) SELECT n FROM foo;
If any errors occur while copying the data to the table, it will automatically be deleted.
You can precede the SELECT by IGNORE or REPLACE to indicate how to handle records that duplicate unique key values. With IGNORE, new records that duplicate an existing record on a unique key value are discarded. With REPLACE, new records replace records that have the same unique key value. If neither IGNORE nor REPLACE are specified, duplicate unique key values result in an error.
To ensure that the update log/binary log can be used to re-create the original tables, MySQL will not allow concurrent inserts during CREATE TABLE ... SELECT.
The RAID_TYPE option will help you to exceed the 2G/4G limit for the MyISAM datafile (not the index file) on operating systems that don't support big files. Note that this option is not recommended for a filesystem that supports big files!
You can get more speed from the I/O bottleneck by putting RAID directories on different physical disks. RAID_TYPE will work on any operating system, as long as you have built MySQL with the --with-raid option to configure. For now, the only allowed RAID_TYPE is STRIPED (1 and RAID0 are aliases for this).
If you specify RAID_TYPE=STRIPED for a MyISAM table, MyISAM will create RAID_CHUNKS subdirectories named 00, 01, 02 in the database directory. In each of these directories, MyISAM will create a table_name.MYD. When writing data to the datafile, the RAID handler will map the first RAID_CHUNKSIZE *1024 bytes to the first file, the next RAID_CHUNKSIZE *1024 bytes to the next file and so on.
UNION is used when you want to use a collection of identical tables as one. This works only with MERGE tables. See MERGE.
For the moment, you need to have SELECT, UPDATE, and DELETE privileges on the tables you map to a MERGE table. All mapped tables must be in the same database as the MERGE table.
If you want to insert data in a MERGE table, you have to specify with INSERT_METHOD into which table the row should be inserted. INSERT_METHOD is an option useful for MERGE tables only. See MERGE. This option was introduced in MySQL 4.0.0.
In the created table the PRIMARY key will be placed first, followed by all UNIQUE keys, and then the normal keys. This helps the MySQL optimizer to prioritize which key to use and also more quickly to detect duplicated UNIQUE keys.
By using DATA DIRECTORY="directory" or INDEX DIRECTORY="directory" you can specify where the storage engine should put its datafile and index file. Note that the directory should be a full path to the directory (not a relative path).
This works only for MyISAM tables in MySQL 4.0, when you are not using the --skip-symlink option. Your operating system must also have a working, thread-safe realpath() call. See Symbolic links to tables.
In some cases, MySQL silently changes a column specification from that given in a CREATE TABLE statement. (This may also occur with ALTER TABLE.):
VARCHAR columns with a length less than four are changed to CHAR.
If any column in a table has a variable length, the entire row is variable-length as a result. Therefore, if a table contains any variable-length columns (VARCHAR, TEXT, or BLOB), all CHAR columns longer than three characters are changed to VARCHAR columns. This doesn't affect how you use the columns in any way; in MySQL, VARCHAR is just a different way to store characters. MySQL performs this conversion because it saves space and makes table operations faster. See Table types.
From version 4.1.0, if a CHAR or VARCHAR field with a length specification greater than 255 is converted to TEXT. This is a compatibility feature.
TIMESTAMP display sizes must be even and in the range from 2 to 14. If you specify a display size of 0 or greater than 14, the size is coerced to 14. Odd-valued sizes in the range from 1 to 13 are coerced to the next higher even number.
You cannot store a literal NULL in a TIMESTAMP column; setting it to NULL sets it to the current date and time. Because TIMESTAMP columns behave this way, the NULL and NOT NULL attributes do not apply in the normal way and are ignored if you specify them. DESCRIBE tbl_name always reports that a TIMESTAMP column may be assigned NULL values.
MySQL maps certain column types used by other SQL database vendors to MySQL types. See Other-vendor column types.
If you want to see whether MySQL used a column type other than the one you specified, issue a DESCRIBE tbl_name statement after creating or altering your table.
Certain other column type changes may occur if you compress a table using myisampack. See Compressed format.
DROP DATABASE [IF EXISTS] db_name
DROP DATABASE drops all tables in the database and deletes the database. If you do a DROP DATABASE on a symbolic linked database, both the link and the original database are deleted. Be very careful with this statement!
DROP DATABASE returns the number of files that were removed from the database directory. For MyISAM tables, this is three times the number of tables, because normally each table corresponds to a .MYD file, a .MYI file, and a .frm file.
The DROP DATABASE command removes from the given database directory all files with the following extensions:
Ext | Ext | Ext | Ext |
.BAK | .DAT | .HSH | .ISD |
.ISM | .ISM | .MRG | .MYD |
.MYI | .db | .frm |
All subdirectories that consists of 2 digits (RAID directories) are also removed.
In MySQL Version 3.22 or later, you can use the keywords IF EXISTS to prevent an error from occurring if the database doesn't exist.
You can also drop databases with mysqladmin. See Client-Side Scripts.
DROP INDEX index_name ON tbl_name
DROP INDEX drops the index named index_name from the table tbl_name. DROP INDEX doesn't do anything in MySQL prior to Version 3.22. In Version 3.22 or later, DROP INDEX is mapped to an ALTER TABLE statement to drop the index. See ALTER TABLE.
DROP [TEMPORARY] TABLE [IF EXISTS] tbl_name [, tbl_name,...] [RESTRICT | CASCADE]
DROP TABLE removes one or more tables. All table data and the table definition are removed, so be careful with this command!
In MySQL Version 3.22 or later, you can use the keywords IF EXISTS to prevent an error from occurring for tables that don't exist. In 4.1 one gets a NOTE for all not existing tables when using IF EXISTS. See SHOW WARNINGS.
RESTRICT and CASCADE are allowed to make porting easier. For the moment they don't do anything.
Note: DROP TABLE automatically commits the current active transaction (except if you are using 4.1 and the TEMPORARY key word.
Option TEMPORARY is ignored in 4.0. In 4.1 this option works as follows:
Only drops temporary tables.
It doesn't end a running transactions.
No access rights is checked.
Using TEMPORARY is a good way to ensure that you don't accidently drop a real table.
RENAME TABLE tbl_name TO new_tbl_name[, tbl_name2 TO new_tbl_name2,...]
The rename is done atomically, which means that no other thread can access any of the tables while the rename is running. This makes it possible to replace a table with an empty one
:
CREATE TABLE new_table (...); RENAME TABLE old_table TO backup_table, new_table TO old_table;
The rename is done from left to right, which means that if you want to swap two table names, you have to:
RENAME TABLE old_table TO backup_table, new_table TO old_table, backup_table TO new_table;
As long as two databases are on the same disk you can also rename from one database to another:
RENAME TABLE current_db.tbl_name TO other_db.tbl_name;
When you execute RENAME, you can't have any locked tables or active transactions. You must also have the ALTER and DROP privileges on the original table, and the CREATE and INSERT privileges on the new table.
If MySQL encounters any errors in a multiple-table rename, it will do a reverse rename for all renamed tables to get everything back to the original state.
RENAME TABLE was added in MySQL 3.23.23.
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{DESCRIBE | DESC} tbl_name [col_name | wild]
DESCRIBE is a shortcut for SHOW COLUMNS FROM.
See Show database info.
DESCRIBE provides information about a table's columns. col_name may be a column name or a string containing the SQL % and _ wildcard characters to obtain output only for the columns with names matching the string. There is no need to enclose the string in quotes.
If the column types are different from what you expect them to be based on a CREATE TABLE statement, note that MySQL sometimes changes column types. See Silent column changes.
This statement is provided for Oracle compatibility.
The SHOW statement provides similar information. See SHOW.
USE db_name
The USE db_name statement tells MySQL to use the db_name database as the default database for subsequent queries. The database remains current until the end of the session or until another USE statement is issued:
mysql> USE db1; mysql> SELECT COUNT(*) FROM mytable; # selects from db1.mytable mysql> USE db2; mysql> SELECT COUNT(*) FROM mytable; # selects from db2.mytable
Making a particular database current by means of the USE statement does not preclude you from accessing tables in other databases. The following example accesses the author table from the db1 database and the editor table from the db2 database:
mysql> USE db1; mysql> SELECT author_name,editor_name FROM author,db2.editor -> WHERE author.editor_id = db2.editor.editor_id;
The USE statement is provided for Sybase compatibility.
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By default, MySQL runs in autocommit mode. This means that as soon as you execute a statement that updates (modifies) a table, MySQL will store the update on disk.
If you are using transaction-safe tables (like InnoDB or BDB), you can put MySQL into non-autocommit mode with the following command:
SET AUTOCOMMIT=0
After disabling autocommit mode by setting the AUTOCOMMIT variable to zero, you must use COMMIT to store your changes to disk or ROLLBACK if you want to ignore the changes you have made since the beginning of your transaction.
If you want to disable autocommit mode for a single series of statements, you can use the START TRANSACTION statement:
:
START TRANSACTION; SELECT @A:=SUM(salary) FROM table1 WHERE type=1; UPDATE table2 SET summmary=@A WHERE type=1; COMMIT;
BEGIN and BEGIN WORK can be used instead of START TRANSACTION to initiate a transaction. START TRANSACTION was added in MySQL 4.0.11. This is SQL-99 syntax and is the recommended way to start an ad-hoc transaction. BEGIN and BEGIN WORK are available from MySQL 3.23.17 and 3.23.19, respectively.
Note that if you are not using transaction-safe tables, any changes will be stored at once, regardless of the status of autocommit mode.
If you issue a ROLLBACK statement after updating a non-transactional table, you will get an error (ER_WARNING_NOT_COMPLETE_ROLLBACK) as a warning. All transaction-safe tables will be restored, but any non-transaction-safe table will not change.
If you are using START TRANSACTION or SET AUTOCOMMIT=0, you should use the MySQL binary log for backups instead of the older update log. Transactions are stored in the binary log in one chunk, upon COMMIT, to ensure that transactions that are rolled back are not stored. See Binary log.
You can change the isolation level for transactions with SET TRANSACTION ISOLATION LEVEL. See SET TRANSACTION.
Some statements cannot be rolled back. In general, these include data definition language (DDL) statements, such as those that create or drop databases, or those that create, drop, or alter tables.
You may wish to design your transactions not to include such statements. If you issue a statement that cannot be rolled back early in a transaction, and then another statement later fails, the full effect of the transaction cannot be rolled back by issuing a ROLLBACK statement.
The following commands implicitly end a transaction (as if you had done a COMMIT before executing the command):
Command | Command | Command |
ALTER TABLE | BEGIN | CREATE INDEX |
DROP DATABASE | DROP INDEX | DROP TABLE |
LOAD MASTER DATA | LOCK TABLES | RENAME TABLE |
SET AUTOCOMMIT=1 | START TRANSACTION | TRUNCATE |
UNLOCK TABLES also ends a transaction if any tables currently are locked. Prior to MySQL 4.0.13, CREATE TABLE ends a transaction if the binary update log is enabled.
Transactions cannot be nested. This is a consequence of the implicit COMMIT performed for any current transaction when you issue a START TRANSACTION statement or one of its synonyms.
Starting from MySQL 4.0.14 and 4.1.1, InnoDB supports the SQL commands SAVEPOINT and ROLLBACK TO SAVEPOINT.
SAVEPOINT identifier
This statement sets a named transaction savepoint whose name is identifier. If the current transaction already has a savepoint with the same name, the old savepoint is deleted and a new one is set.
ROLLBACK TO SAVEPOINT identifier
This statement rolls back a transaction to the named savepoint. Modifications that this transaction made to rows after the savepoint was set are undone in the rollback, but InnoDB does not release the row locks that were stored in memory after the savepoint. (Note that for a new inserted row, the lock information is carried by the transaction ID stored in the row; the lock is not separately stored in memory. In this case, the row lock is released in the undo.) Savepoints that were set at a later time than the named savepoint are deleted.
If the command returns the following error, it means that no savepoint with the specified name exists:
ERROR 1181: Got error 153 during ROLLBACK
All savepoints of the current transaction are deleted if you execute a COMMIT, or a ROLLBACK that does not name a savepoint.
LOCK TABLES tbl_name [AS alias] {READ [LOCAL] | [LOW_PRIORITY] WRITE} [, tbl_name [AS alias] {READ [LOCAL] | [LOW_PRIORITY] WRITE} ...] ... UNLOCK TABLES
LOCK TABLES locks tables for the current thread. UNLOCK TABLES releases any locks held by the current thread. All tables that are locked by the current thread are implicitly unlocked when the thread issues another LOCK TABLES, or when the connection to the server is closed.
To use LOCK TABLES in MySQL 4.0.2, you need the global LOCK TABLES privilege and a SELECT privilege on the involved tables. In MySQL 3.23 you need to have SELECT, insert, DELETE and UPDATE privileges for the tables.
The main reasons to use LOCK TABLES are for emulating transactions or getting more speed when updating tables. This is explained in more detail later.
If a thread obtains a READ lock on a table, that thread (and all other threads) can only read from the table. If a thread obtains a WRITE lock on a table, only the thread holding the lock can read from or write to the table. Other threads are blocked.
The difference between READ LOCAL and READ is that READ LOCAL allows non-conflicting INSERT statements to execute while the lock is held. However, this can't be used if you are going to manipulate the database files outside MySQL while you hold the lock.
When you use LOCK TABLES, you must lock all tables that you are going to use and you must use the same alias that you are going to use in your queries! If you are using a table multiple times in a query (with aliases), you must get a lock for each alias!
WRITE locks normally have higher priority than READ locks, to ensure that updates are processed as soon as possible. This means that if one thread obtains a READ lock and then another thread requests a WRITE lock, subsequent READ lock requests will wait until the WRITE thread has gotten the lock and released it. You can use LOW_PRIORITY WRITE locks to allow other threads to obtain READ locks while the thread is waiting for the WRITE lock. You should use LOW_PRIORITY WRITE locks only if you are sure that there will eventually be a time when no threads will have a READ lock.
LOCK TABLES works as follows:
Sort all tables to be locked in a internally defined order (from the user standpoint, the order is undefined).
If a table is locked with a read and a write lock, put the write lock before the read lock.
Lock one table at a time until the thread gets all locks.
This policy ensures that table locking is deadlock free. There are, however, other things you need to be aware of with this schema:
If you are using a LOW_PRIORITY WRITE lock for a table, it means only that MySQL will wait for this particlar lock until there is no threads that want a READ lock. When the thread has gotten the WRITE lock and is waiting to get the lock for the next table in the lock table list, all other threads will wait for the WRITE lock to be released. If this becomes a serious problem with your application, you should consider converting some of your tables to transaction-safe tables.
You can safely kill a thread that is waiting for a table lock with KILL. See KILL.
Note that you should not lock any tables that you are using with INSERT DELAYED. This is because, in this case, the INSERT is done by a separate thread.
Normally, you don't have to lock tables, because all single UPDATE statements are atomic; no other thread can interfere with any other currently executing SQL statement. There are a few cases when you would like to lock tables anyway:
If you are going to run many operations on a bunch of tables, it's much faster to lock the tables you are going to use. The downside is that no thread can update a READ-locked table (including the one holding the lock) and no thread can read a WRITE-locked table other than the one holding the lock.
The reason some things are faster under LOCK TABLES is that MySQL will not flush the key cache for the locked tables until UNLOCK TABLES is called (normally the key cache is flushed after each SQL statement). This speeds up inserting, updating, or deleting on MyISAM tables.
If you are using a storage engine in MySQL that doesn't support transactions, you must use LOCK TABLES if you want to ensure that no other thread comes between a SELECT and an UPDATE. The example shown here requires LOCK TABLES to execute safely:
mysql> LOCK TABLES trans READ, customer WRITE; mysql> SELECT SUM(value) FROM trans WHERE customer_id=some_id; mysql> UPDATE customer SET total_value=sum_from_previous_statement -> WHERE customer_id=some_id; mysql> UNLOCK TABLES;
Without LOCK TABLES, there is a chance that another thread might insert a new row in the trans table between execution of the SELECT and UPDATE statements.
By using incremental updates (UPDATE customer SET value=value+new_value) or the LAST_INSERT_ID() function, you can avoid using LOCK TABLES in many cases.
You can also solve some cases by using the user-level lock functions GET_LOCK() and RELEASE_LOCK(). These locks are saved in a hash table in the server and implemented with pthread_mutex_lock() and pthread_mutex_unlock() for high speed. See Miscellaneous functions.
See Internal locking, for more information on locking policy.
You can lock all tables in all databases with read locks with the FLUSH TABLES WITH READ LOCK command. See FLUSH. This is very convenient way to get backups if you have a filesystem, such as Veritas, that can take snapshots in time.
NOTE: LOCK TABLES is not transaction-safe and will implicitly commit any active transactions before attempting to lock the tables.
SET [GLOBAL | SESSION] TRANSACTION ISOLATION LEVEL { READ UNCOMMITTED | READ COMMITTED | REPEATABLE READ | SERIALIZABLE }
Sets the transaction isolation level for the global, whole session, or the next transaction.
The default behavior is to set the isolation level for the next (not started) transaction. If you use the GLOBAL keyword, the statement sets the default transaction level globally for all new connections created from that point on (but not existing connections). You need the SUPER privilege to do this. Using the SESSION keyword sets the default transaction level for all future transactions performed on the current connection.
For description of each InnoDB transaction isolation level, see InnoDB transaction isolation. InnoDB supports each of these levels from MySQL 4.0.5 on. The default level is REPEATABLE READ.
You can set the default global isolation level for mysqld with --transaction-isolation=.... See Server options.
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GRANT priv_type [(column_list)] [, priv_type [(column_list)] ...] ON {tbl_name | * | *.* | db_name.*} TO user_name [IDENTIFIED BY [PASSWORD] 'password'] [, user_name [IDENTIFIED BY [PASSWORD] 'password'] ...] [REQUIRE NONE | [{SSL| X509}] [CIPHER cipher [AND]] [ISSUER issuer [AND]] [SUBJECT subject]] [WITH [GRANT OPTION | MAX_QUERIES_PER_HOUR # | MAX_UPDATES_PER_HOUR # | MAX_CONNECTIONS_PER_HOUR #]]
REVOKE priv_type [(column_list)] [, priv_type [(column_list)] ...] ON {tbl_name | * | *.* | db_name.*} FROM user_name [, user_name ...] REVOKE ALL PRIVILEGES,GRANT OPTION FROM user_name [, user_name ...]
GRANT and REVOKE are implemented in MySQL Version 3.22.11 or later. For earlier MySQL versions, these statements do nothing.
The GRANT and REVOKE statements allow system administrators to create users and grant and revoke rights to MySQL users at four privilege levels:
Global level | Global privileges apply to all databases on a given server. These privileges are stored in the mysql.user table. GRANT ALL ON *.* and REVOKE ALL ON *.* will grant and revoke only global privileges. |
Database level | Database privileges apply to all tables in a given database. These privileges are stored in the mysql.db and mysql.host tables. GRANT ALL ON db.* and REVOKE ALL ON db.* will grant and revoke only database privileges. |
Table level | Table privileges apply to all columns in a given table. These privileges are stored in the mysql.tables_priv table. GRANT ALL ON db.table and REVOKE ALL ON db.table will grant and revoke only table privileges. |
Column level | Column privileges apply to single columns in a given table. These privileges are stored in the mysql.columns_priv table. When using REVOKE you must specify the same columns that were granted. |
To make it easy to revoke all privileges for a user, MySQL 4.1.2 has added the syntax:
REVOKE ALL PRIVILEGES,GRANT OPTION FROM user_name [, user_name ...]
This will drop all database, table and column level privileges for the user.
For the GRANT and REVOKE statements, priv_type may be specified as any of the following:
ALL [PRIVILEGES] | Sets all simple privileges except WITH GRANT OPTION |
ALTER | Allows usage of ALTER TABLE |
CREATE | Allows usage of CREATE TABLE |
CREATE TEMPORARY TABLES | Allows usage of CREATE TEMPORARY TABLE |
DELETE | Allows usage of DELETE |
DROP | Allows usage of DROP TABLE. |
EXECUTE | Allows the user to run stored procedures (MySQL 5.0) |
FILE | Allows usage of SELECT ... INTO OUTFILE and LOAD DATA INFILE. |
INDEX | Allows usage of CREATE INDEX and DROP INDEX |
INSERT | Allows usage of INSERT |
LOCK TABLES | Allows usage of LOCK TABLES on tables for which one has the SELECT privilege. |
PROCESS | Allows usage of SHOW FULL PROCESSLIST |
REFERENCES | For the future |
RELOAD | Allows usage of FLUSH |
REPLICATION CLIENT | Gives the right to the user to ask where the slaves/masters are. |
REPLICATION SLAVE | Needed for the replication slaves (to read binlogs from master). |
SELECT | Allows usage of SELECT |
SHOW DATABASES | SHOW DATABASES shows all databases. |
SHUTDOWN | Allows usage of mysqladmin shutdown |
SUPER | Allows one connect (once) even if max_connections is reached and execute commands CHANGE MASTER, KILL thread, mysqladmin debug, PURGE MASTER LOGS and SET GLOBAL |
UPDATE | Allows usage of UPDATE |
USAGE | Synonym for ``no privileges.'' |
GRANT OPTION | Synonym for WITH GRANT OPTION |
USAGE can be used when you want to create a user that has no privileges.
The privileges CREATE TEMPORARY TABLES, EXECUTE, LOCK TABLES, REPLICATION ..., SHOW DATABASES and SUPER are new for in version 4.0.2. To use these new privileges after upgrading to 4.0.2, you have to run the mysql_fix_privilege_tables script. See Upgrading-grant-tables.
In older MySQL versions, the PROCESS privilege gives the same rights as the new SUPER privilege.
To revoke the GRANT privilege from a user, use a priv_type value of GRANT OPTION:
mysql> REVOKE GRANT OPTION ON ... FROM ...;
The only priv_type values you can specify for a table are SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, GRANT OPTION, INDEX, and ALTER.
The only priv_type values you can specify for a column (that is, when you use a column_list clause) are SELECT, INSERT, and UPDATE.
MySQL allows you to create database level privileges even if the database doesn't exist, to make it easy to prepare for database usage. Currently MySQL does however not allow one to create table level grants if the table doesn't exist. MySQL will not automatically revoke any privileges even if you drop a table or drop a database.
You can set global privileges by using ON *.* syntax. You can set database privileges by using ON db_name.* syntax. If you specify ON * and you have a current database, you will set the privileges for that database. (Warning: If you specify ON * and you don't have a current database, you will affect the global privileges!)
Please note: the _ and % wildcards are allowed when specifying database names in GRANT statements that grant privileges at the global or database levels. This means that if you wish to use for instance a _ character as part of a database name, you should specify it as \_ in the GRANT command, to prevent the user from being able to access additional databases matching the wildcard pattern, for example, GRANT ... ON `foo\_bar`.* TO ....
In order to accommodate granting rights to users from arbitrary hosts, MySQL supports specifying the user_name value in the form user@host. If you want to specify a user string containing special characters (such as -), or a host string containing special characters or wildcard characters (such as %), you can quote the username or hostname (for example, 'test-user'@'test-hostname').
You can specify wildcards in the hostname. For example, user@'%.loc.gov' applies to user for any host in the loc.gov domain, and user@'144.155.166.%' applies to user for any host in the 144.155.166 class C subnet.
The simple form user is a synonym for user@"%".
MySQL doesn't support wildcards in usernames. Anonymous users are defined by inserting entries with User="" into the mysql.user table or creating a user with an empty name with the GRANT command.
Note: If you allow anonymous users to connect to the MySQL server, you should also grant privileges to all local users as user@localhost because otherwise the anonymous user entry for the local host in the mysql.user table will be used when the user tries to log into the MySQL server from the local machine!
You can verify if this applies to you by executing this query:
mysql> SELECT Host,User FROM mysql.user WHERE User='';
For the moment, GRANT only supports host, table, database, and column names up to 60 characters long. A username can be up to 16 characters.
The privileges for a table or column are formed from the logical OR of the privileges at each of the four privilege levels. For example, if the mysql.user table specifies that a user has a global SELECT privilege, this can't be denied by an entry at the database, table, or column level.
The privileges for a column can be calculated as follows:
global privileges OR (database privileges AND host privileges) OR table privileges OR column privileges
In most cases, you grant rights to a user at only one of the privilege levels, so life isn't normally as complicated as above. The details of the privilege-checking procedure are presented in Privilege system.
If you grant privileges for a user/hostname combination that does not exist in the mysql.user table, an entry is added and remains there until deleted with a DELETE command. In other words, GRANT may create user table entries, but REVOKE will not remove them; you must do that explicitly using DELETE.
In MySQL Version 3.22.12 or later, if a new user is created or if you have global grant privileges, the user's password will be set to the password specified by the IDENTIFIED BY clause, if one is given. If the user already had a password, it is replaced by the new one.
If you don't want to send the password in clear text you can use the PASSWORD option followed by a scrambled password from SQL function PASSWORD() or the C API function make_scrambled_password(char *to, const char *password).
Warning: If you create a new user but do not specify an IDENTIFIED BY clause, the user has no password. This is insecure.
Passwords can also be set with the SET PASSWORD command. See SET.
If you grant privileges for a database, an entry in the mysql.db table is created if needed. When all privileges for the database have been removed with REVOKE, this entry is deleted.
If a user doesn't have any privileges on a table, the table is not displayed when the user requests a list of tables (for example, with a SHOW TABLES statement). The same is true for SHOW DATABASES.
The WITH GRANT OPTION clause gives the user the ability to give to other users any privileges the user has at the specified privilege level. You should be careful to whom you give the GRANT privilege, as two users with different privileges may be able to join privileges!
MAX_QUERIES_PER_HOUR #, MAX_UPDATES_PER_HOUR # and MAX_CONNECTIONS_PER_HOUR # are new in MySQL version 4.0.2. These options limit the number of queries/updates and logins the user can do during one hour. If # is 0 (default), then this means that there are no limitations for that user. See User resources. Note: To specify any of these options for an existing user without adding other additional privileges, use GRANT USAGE ON *.* ... WITH MAX_....
You cannot grant another user a privilege you don't have yourself; the GRANT privilege allows you to give away only those privileges you possess.
Be aware that when you grant a user the GRANT privilege at a particular privilege level, any privileges the user already possesses (or is given in the future!) at that level are also grantable by that user. Suppose you grant a user the INSERT privilege on a database. If you then grant the SELECT privilege on the database and specify WITH GRANT OPTION, the user can give away not only the SELECT privilege, but also INSERT. If you then grant the UPDATE privilege to the user on the database, the user can give away the INSERT, SELECT and UPDATE.
You should not grant ALTER privileges to a normal user. If you do that, the user can try to subvert the privilege system by renaming tables!
Note that if you are using table or column privileges for even one user, the server examines table and column privileges for all users and this will slow down MySQL a bit.
When mysqld starts, all privileges are read into memory. Database, table, and column privileges take effect at once, and user-level privileges take effect the next time the user connects. Modifications to the grant tables that you perform using GRANT or REVOKE are noticed by the server immediately. If you modify the grant tables manually (using INSERT, UPDATE, etc.), you should execute a FLUSH PRIVILEGES statement or run mysqladmin flush-privileges to tell the server to reload the grant tables. See Privilege changes.
The biggest differences between the SQL standard and MySQL versions of GRANT are:
In MySQL privileges are given for a username + hostname combination and not only for a username.
SQL-99 doesn't have global or database-level privileges, nor does it support all the privilege types that MySQL supports. MySQL doesn't support the SQL-99 TRIGGER or UNDER privileges.
SQL-99 privileges are structured in a hierarchal manner. If you remove an user, all privileges the user has granted are revoked. In MySQL the granted privileges are not automatically revoked, but you have to revoke these yourself if needed.
In MySQL, if you have the INSERT privilege on only some of the columns in a table, you can execute INSERT statements on the table; the columns for which you don't have the INSERT privilege will be set to their default values. SQL-99 requires you to have the INSERT privilege on all columns.
With SQL99, when you drop a table, all privileges for the table are revoked. With SQL-99, when you revoke a privilege, all privileges that were granted based on the privilege are also revoked. In MySQL, privileges can be dropped only with explicit REVOKE commands or by manipulating the MySQL grant tables.
For a description of using REQUIRE, see Secure connections.
ANALYZE [LOCAL | NO_WRITE_TO_BINLOG] TABLE tbl_name[,tbl_name...]
Analyze and store the key distribution for the table. During the analysis, the table is locked with a read lock. This works on MyISAM and BDB tables.
This is equivalent to running myisamchk -a on the table.
MySQL uses the stored key distribution to decide in which order tables should be joined when you perform a join on something other than a constant.
The command returns a table with the following columns:
Column | Value |
Table | Table name |
Op | Always analyze |
Msg_type | One of status, error, info, or warning |
Msg_text | The message |
You can check the stored key distribution with the SHOW INDEX command. See Show database info.
If the table hasn't changed since the last ANALYZE TABLE command, the table will not be analyzed again.
Before MySQL 4.1.1, ANALYZE commands are not written to the binary log. Since MySQL 4.1.1 they are written to the binary log unless the optional NO_WRITE_TO_BINLOG keyword (or its alias LOCAL) was used.
BACKUP TABLE tbl_name[,tbl_name...] TO '/path/to/backup/directory'
Note: This statement is deprecated. We are working on a better replacement for it that will provide online backup capabilities. In the meantime, the mysqlhotcopy script can be used instead.
Copies to the backup directory the minimum number of table files needed to restore the table, after flushing any buffered changes to disk. Currently works only for MyISAM tables. For MyISAM tables, copies .frm (definition) and .MYD (data) files. The index file can be rebuilt from those two files.
Before using this command, please see Backup.
During the backup, a read lock will be held for each table, one at time, as they are being backed up. If you want to back up several tables as a snapshot, you must first issue LOCK TABLES to obtain a read lock for each table in the group.
The command returns a table with the following columns:
Column | Value |
Table | Table name |
Op | Always backup |
Msg_type | One of status, error, info, or warning |
Msg_text | The message |
Note that BACKUP TABLE is only available in MySQL version 3.23.25 and later.
CHECK TABLE tbl_name[,tbl_name...] [option [option...]] option = QUICK | FAST | MEDIUM | EXTENDED | CHANGED
CHECK TABLE works only on MyISAM and InnoDB tables. On MyISAM tables, it's the same thing as running myisamchk --medium-check table_name on the table.
If you don't specify any option, MEDIUM is used.
Checks the table or tables for errors. For MyISAM tables, the key statistics are updated. The command returns a table with the following columns:
Column | Value |
Table | Table name |
Op | Always check |
Msg_type | One of status, error, info, or warning |
Msg_text | The message |
Note that the statement might produce many rows of information for each checked table. The last row will be of Msg_type status and should normally be OK. If you don't get OK, or Table is already up to date you should normally run a repair of the table. See Table maintenance. Table is already up to date means that the storage manager for the table indicated that there was no need to check the table.
The different check types are as follows:
Type | Meaning |
QUICK | Don't scan the rows to check for incorrect links. |
FAST | Only check tables that haven't been closed properly. |
CHANGED | Only check tables that have been changed since the last check or haven't been closed properly. |
MEDIUM | Scan rows to verify that deleted links are okay. This also calculates a key checksum for the rows and verifies this with a calculated checksum for the keys. |
EXTENDED | Do a full key lookup for all keys for each row. This ensures that the table is 100% consistent, but will take a long time! |
For dynamically sized MyISAM tables, a started check will always do a MEDIUM check. For statically sized rows, we skip the row scan for QUICK and FAST because the rows are very seldom corrupted.
You can combine check options, as in the following example, which does a quick check on the table to see whether it was closed properly:
CHECK TABLE test_table FAST QUICK;
Note: In some cases, CHECK TABLE will change the table! This happens if the table is marked as 'corrupted' or 'not closed properly' but CHECK TABLE didn't find any problems in the table. In this case, CHECK TABLE will mark the table as okay.
If a table is corrupted, it's most likely that the problem is in the indexes and not in the data part. All of the above check types checks the indexes thoroughly and should thus find most errors.
If you just want to check a table that you assume is okay, you should use no check options or the QUICK option. The latter should be used when you are in a hurry and can take the very small risk that QUICK didn't find an error in the datafile. (In most cases MySQL should find, under normal usage, any error in the datafile. If this happens then the table will be marked as 'corrupted', in which case the table can't be used until it's repaired.)
FAST and CHANGED are mostly intended to be used from a script (for example to be executed from cron) if you want to check your table from time to time. In most cases, FAST is to be preferred over CHANGED. (The only case when it isn't is when you suspect that you have found a bug in the MyISAM code.)
EXTENDED is to be used only after you have run a normal check but still get strange errors from a table when MySQL tries to update a row or find a row by key. (This is very unlikely if a normal check has succeeded!)
Some problems reported by CHECK TABLE can't be corrected automatically:
Found row where the auto_increment column has the value 0.
This means that you have a row in the table where the AUTO_INCREMENT index column contains the value 0. (It's possible to create a row where the AUTO_INCREMENT column is 0 by explicitly setting the column to 0 with an UPDATE statement.)
This isn't an error in itself, but could cause trouble if you decide to dump the table and restore it or do an ALTER TABLE on the table. In this case, the AUTO_INCREMENT column will change value according to the rules of AUTO_INCREMENT columns, which could cause problems such as a duplicate key error.
To get rid of the warning, just execute an UPDATE statement to set the column to some other value than 0.
CHECKSUM TABLE tbl_name[,tbl_name ...] [ QUICK | EXTENDED ]
Reports a table checksum. If QUICK is specified, live table checksum is reported, or NULL if the table does not support live checksum. This is very fast. In EXTENDED mode the whole table is read row by row and the checksum is calculated. This can be very slow for large tables. By default - with neither QUICK nor EXTENDED - MySQL returns live checksum if the table support it and scans the table otherwise.
This statement is implemented in MySQL 4.1.1.
OPTIMIZE [LOCAL | NO_WRITE_TO_BINLOG] TABLE tbl_name[,tbl_name]...
OPTIMIZE TABLE should be used if you have deleted a large part of a table or if you have made many changes to a table with variable-length rows (tables that have VARCHAR, BLOB, or TEXT columns). Deleted records are maintained in a linked list and subsequent INSERT operations reuse old record positions. You can use OPTIMIZE TABLE to reclaim the unused space and to defragment the datafile.
In most setups you don't have to run OPTIMIZE TABLE at all. Even if you do a lot of updates to variable length rows it's not likely that you need to do this more than once a month/week and only on certain tables.
For the moment, OPTIMIZE TABLE works only on MyISAM and BDB tables. For BDB tables, OPTIMIZE TABLE is currently mapped to ANALYZE TABLE. See ANALYZE TABLE.
You can get OPTIMIZE TABLE to work on other table types by starting mysqld with --skip-new or --safe-mode, but in this case OPTIMIZE TABLE is just mapped to ALTER TABLE.
OPTIMIZE TABLE works the following way:
If the table has deleted or split rows, repair the table.
If the index pages are not sorted, sort them.
If the statistics are not up to date (and the repair couldn't be done by sorting the index), update them.
Note that the table is locked during the time OPTIMIZE TABLE is running!
Before MySQL 4.1.1, OPTIMIZE commands are not written to the binary log. Since MySQL 4.1.1 they are written to the binary log unless the optional NO_WRITE_TO_BINLOG keyword (or its alias LOCAL) was used.
REPAIR [LOCAL | NO_WRITE_TO_BINLOG] TABLE tbl_name[,tbl_name...] [QUICK] [EXTENDED] [USE_FRM]
REPAIR TABLE works only on MyISAM tables and is the same as running myisamchk -r table_name on the table.
Normally you should never have to run this command, but if disaster strikes, you are very likely to get back all your data from a MyISAM table with REPAIR TABLE. If your tables get corrupted often, you should try to find the reason for it, to eliminate the need to use REPAIR TABLE. See Crashing. See MyISAM table problems.
REPAIR TABLE repairs a possibly corrupted table. The command returns a table with the following columns:
Column | Value |
Table | Table name |
Op | Always repair |
Msg_type | One of status, error, info, or warning |
Msg_text | The message |
Note that the statement might produce many rows of information for each repaired table. The last one row will be of Msg_type status and should normally be OK. If you don't get OK, you should try repairing the table with myisamchk --safe-recover, because REPAIR TABLE does not yet implement all the options of myisamchk. In the near future, we will make it more flexible.
If QUICK is given, REPAIR TABLE tries to repair only the index tree.
If you use EXTENDED, MySQL creates the index row by row instead of creating one index at a time with sorting; this might be better than sorting on fixed-length keys if you have long CHAR keys that compress very well. This type of repair is like that done by myisamchk --safe-recover.
As of MySQL 4.0.2, there is a USE_FRM mode for REPAIR. Use it if the .MYI file is missing or if its header is corrupted. In this mode MySQL will re-create the table, using information from the .frm file. This kind of repair cannot be done with myisamchk.
Warning: If mysqld dies during a REPAIR TABLE, it's essential that you do at once another REPAIR on the table before executing any other commands on it. (It's always good to start by making a backup). In the worst case you can have a new clean index file without information about the datafile and when the next command you do may overwrite the datafile. This is not a likely, but possible scenario.
Before MySQL 4.1.1, REPAIR commands are not written to the binary log. Since MySQL 4.1.1 they are written to the binary log unless the optional NO_WRITE_TO_BINLOG keyword (or its alias LOCAL) was used.
RESTORE TABLE tbl_name[,tbl_name...] FROM '/path/to/backup/directory'
Restores the table or tables from the backup that was made with BACKUP TABLE. Existing tables will not be overwritten; if you try to restore over an existing table, you will get an error. Restoring will take longer than backing up due to the need to rebuild the index. The more keys you have, the longer it will take. Just as BACKUP TABLE, RESTORE TABLE currently works only for MyISAM tables.
The command returns a table with the following columns:
Column | Value |
Table | Table name |
Op | Always restore |
Msg_type | One of status, error, info, or warning |
Msg_text | The message |
SHOW DATABASES [LIKE wild] or SHOW [OPEN] TABLES [FROM db_name] [LIKE wild] or SHOW [FULL] COLUMNS FROM tbl_name [FROM db_name] [LIKE wild] or SHOW INDEX FROM tbl_name [FROM db_name] or SHOW TABLE STATUS [FROM db_name] [LIKE wild] or SHOW STATUS [LIKE wild] or SHOW VARIABLES [LIKE wild] or SHOW [BDB] LOGS or SHOW [FULL] PROCESSLIST or SHOW GRANTS FOR user or SHOW CREATE TABLE table_name or SHOW MASTER STATUS or SHOW MASTER LOGS or SHOW SLAVE STATUS or SHOW WARNINGS [LIMIT row_count] or SHOW ERRORS [LIMIT row_count] or SHOW TABLE TYPES
SHOW provides information about databases, tables, columns, or status information about the server. If the LIKE wild part is used, the wild string can be a string that uses the SQL % and _ wildcard characters.
Note that there are other forms of the SHOW statement that provide information about replication master and slave servers. They are described in Replication SQL.
You can use db_name.tbl_name as an alternative to the tbl_name FROM db_name syntax. These two statements are equivalent:
mysql> SHOW INDEX FROM mytable FROM mydb; mysql> SHOW INDEX FROM mydb.mytable;
SHOW DATABASES lists the databases on the MySQL server host. You can also get this list using the mysqlshow command line tool. In version 4.0.2 you will see only those databases for which you have some kind of privilege, if you don't have the global SHOW DATABASES privilege.
SHOW TABLES lists the tables in a given database. You can also get this list using the mysqlshow db_name command.
Note: If a user doesn't have any privileges for a table, the table will not show up in the output from SHOW TABLES or mysqlshow db_name.
SHOW OPEN TABLES lists the tables that are currently open in the table cache. See Table cache. The Comment field tells how many times the table is cached and in_use.
SHOW COLUMNS lists the columns in a given table. If you specify the FULL option, you will also get the privileges you have for each column. If the column types are different from what you expect them to be based on a CREATE TABLE statement, note that MySQL sometimes changes column types. See Silent column changes. As of MySQL 4.1, the FULL keyword also causes any per-column comments to be displayed.
The DESCRIBE statement provides information similar to SHOW COLUMNS. See DESCRIBE.
SHOW FIELDS is a synonym for SHOW COLUMNS, and SHOW KEYS is a synonym for SHOW INDEX. You can also list a table's columns or indexes with mysqlshow db_name tbl_name or mysqlshow -k db_name tbl_name.
SHOW INDEX returns the index information in a format that closely resembles the SQLStatistics call in ODBC. The following columns are returned:
Column | Meaning |
Table | Name of the table. |
Non_unique | 0 if the index can't contain duplicates, 1 if it can. |
Key_name | Name of the index. |
Seq_in_index | Column sequence number in index, starting with 1. |
Column_name | Column name. |
Collation | How the column is sorted in the index. In MySQL, this can have values A (Ascending) or NULL (Not sorted). |
Cardinality | Number of unique values in the index. This is updated by running myisamchk -a. |
Sub_part | Number of indexed characters if the column is only partly indexed. NULL if the entire column is indexed. |
Packed | Indicates how the key is packed. NULL if it is not. |
Null | Contains YES if the column may contain NULL. |
Index_type | Index method used. |
Comment | Various remarks. For now, it tells in MySQL < 4.0.2 whether or not index is FULLTEXT. |
Note that as the Cardinality is counted based on statistics stored as integers, it's not necessarily accurate for small tables.
The Packed and Comments columns were added in MySQL 3.23.0. The Null and Index_type columns were added in MySQL 4.0.2.
SHOW TABLE STATUS [FROM db_name] [LIKE wild]
SHOW TABLE STATUS (new in Version 3.23) works likes SHOW TABLE, but provides a lot of information about each table. You can also get this list using the mysqlshow --status db_name command. The following columns are returned:
Column | Meaning |
Name | Name of the table. |
Type | Type of table. See Table types. |
Row_format | The row storage format (Fixed, Dynamic, or Compressed). |
Rows | Number of rows. |
Avg_row_length | Average row length. |
Data_length | Length of the datafile. |
Max_data_length | Max length of the datafile. For fixed row formats, this is the max number of rows in the table. For dynamic row formats, this is the total number of data bytes that can be stored in the table, given the data pointer size used. |
Index_length | Length of the index file. |
Data_free | Number of allocated but not used bytes. |
Auto_increment | Next autoincrement value. |
Create_time | When the table was created. |
Update_time | When the datafile was last updated. |
Check_time | When the table was last checked. |
Collation | Table's character set and collation. (new 4.1.1) |
Checksum | Live checksum value (if any). (new in 4.1.1) |
Create_options | Extra options used with CREATE TABLE. |
Comment | The comment used when creating the table (or some information why MySQL couldn't access the table information). |
InnoDB tables will report the free space in the tablespace in the table comment.
SHOW STATUS provides server status information (like mysqladmin extended-status). The output resembles that shown here, though the format and numbers probably differ:
+--------------------------+------------+ | Variable_name | Value | +--------------------------+------------+ | Aborted_clients | 0 | | Aborted_connects | 0 | | Bytes_received | 155372598 | | Bytes_sent | 1176560426 | | Connections | 30023 | | Created_tmp_disk_tables | 0 | | Created_tmp_tables | 8340 | | Created_tmp_files | 60 | | Delayed_insert_threads | 0 | | Delayed_writes | 0 | | Delayed_errors | 0 | | Flush_commands | 1 | | Handler_delete | 462604 | | Handler_read_first | 105881 | | Handler_read_key | 27820558 | | Handler_read_next | 390681754 | | Handler_read_prev | 6022500 | | Handler_read_rnd | 30546748 | | Handler_read_rnd_next | 246216530 | | Handler_update | 16945404 | | Handler_write | 60356676 | | Key_blocks_used | 14955 | | Key_read_requests | 96854827 | | Key_reads | 162040 | | Key_write_requests | 7589728 | | Key_writes | 3813196 | | Max_used_connections | 0 | | Not_flushed_key_blocks | 0 | | Not_flushed_delayed_rows | 0 | | Open_tables | 1 | | Open_files | 2 | | Open_streams | 0 | | Opened_tables | 44600 | | Questions | 2026873 | | Select_full_join | 0 | | Select_full_range_join | 0 | | Select_range | 99646 | | Select_range_check | 0 | | Select_scan | 30802 | | Slave_running | OFF | | Slave_open_temp_tables | 0 | | Slow_launch_threads | 0 | | Slow_queries | 0 | | Sort_merge_passes | 30 | | Sort_range | 500 | | Sort_rows | 30296250 | | Sort_scan | 4650 | | Table_locks_immediate | 1920382 | | Table_locks_waited | 0 | | Threads_cached | 0 | | Threads_created | 30022 | | Threads_connected | 1 | | Threads_running | 1 | | Uptime | 80380 | +--------------------------+------------+
The status variables listed above have the following meaning:
Variable | Meaning |
Aborted_clients | Number of connections aborted because the client died without closing the connection properly. See Communication errors. |
Aborted_connects | Number of tries to connect to the MySQL server that failed. See Communication errors. |
Bytes_received | Number of bytes received from all clients. |
Bytes_sent | Number of bytes sent to all clients. |
Com_xxx | Number of times each xxx command has been executed. |
Connections | Number of connection attempts to the MySQL server. |
Created_tmp_disk_tables | Number of implicit temporary tables on disk created while executing statements. |
Created_tmp_tables | Number of implicit temporary tables in memory created while executing statements. |
Created_tmp_files | How many temporary files mysqld has created. |
Delayed_insert_threads | Number of delayed insert handler threads in use. |
Delayed_writes | Number of rows written with INSERT DELAYED. |
Delayed_errors | Number of rows written with INSERT DELAYED for which some error occurred (probably duplicate key). |
Flush_commands | Number of executed FLUSH commands. |
Handler_commit | Number of internal COMMIT commands. |
Handler_delete | Number of times a row was deleted from a table. |
Handler_read_first | Number of times the first entry was read from an index. If this is high, it suggests that the server is doing a lot of full index scans, for example, SELECT col1 FROM foo, assuming that col1 is indexed. |
Handler_read_key | Number of requests to read a row based on a key. If this is high, it is a good indication that your queries and tables are properly indexed. |
Handler_read_next | Number of requests to read next row in key order. This will be incremented if you are querying an index column with a range constraint. This also will be incremented if you are doing an index scan. |
Handler_read_prev | Number of requests to read previous row in key order. This is mainly used to optimize ORDER BY ... DESC. |
Handler_read_rnd | Number of requests to read a row based on a fixed position. This will be high if you are doing a lot of queries that require sorting of the result. |
Handler_read_rnd_next | Number of requests to read the next row in the datafile. This will be high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have. |
Handler_rollback | Number of internal ROLLBACK commands. |
Handler_update | Number of requests to update a row in a table. |
Handler_write | Number of requests to insert a row in a table. |
Key_blocks_used | The number of used blocks in the key cache. You can use this value to determine how much of the key cache is in use. See the discussion of key_buffer_size in SHOW VARIABLES. |
Key_read_requests | The number of requests to read a key block from the cache. |
Key_reads | The number of physical reads of a key block from disk. |
Key_write_requests | The number of requests to write a key block to the cache. |
Key_writes | The number of physical writes of a key block to disk. |
Max_used_connections | The maximum number of connections in use simultaneously. |
Not_flushed_key_blocks | Keys blocks in the key cache that has changed but hasn't yet been flushed to disk. |
Not_flushed_delayed_rows | Number of rows waiting to be written in INSERT DELAY queues. |
Open_tables | Number of tables that are open. |
Open_files | Number of files that are open. |
Open_streams | Number of streams that are open (used mainly for logging). |
Opened_tables | Number of tables that have been opened. |
Rpl_status | Status of failsafe replication. (Not yet in use). |
Select_full_join | Number of joins without keys (If this is not 0, you should carefully check the indexes of your tables). |
Select_full_range_join | Number of joins where we used a range search on reference table. |
Select_range | Number of joins where we used ranges on the first table. (It's normally not critical even if this is big.) |
Select_scan | Number of joins where we did a full scan of the first table. |
Select_range_check | Number of joins without keys where we check for key usage after each row (If this is not 0, you should carefully check the indexes of your tables). |
Questions | Number of queries sent to the server. |
Slave_open_temp_tables | Number of temporary tables currently open by the slave thread |
Slave_running | Is ON if this is a slave that is connected to a master. |
Slow_launch_threads | Number of threads that have taken more than slow_launch_time to create. |
Slow_queries | Number of queries that have taken more than long_query_time seconds. See Slow query log. |
Sort_merge_passes | Number of merges passes the sort algoritm have had to do. If this value is large you should consider increasing sort_buffer. |
Sort_range | Number of sorts that were done with ranges. |
Sort_rows | Number of sorted rows. |
Sort_scan | Number of sorts that were done by scanning the table. |
ssl_xxx | Variables used by SSL; Not yet implemented. |
Table_locks_immediate | Number of times a table lock was acquired immediately. Available after 3.23.33. |
Table_locks_waited | Number of times a table lock could not be acquired immediately and a wait was needed. If this is high, and you have performance problems, you should first optimize your queries, and then either split your table or tables or use replication. Available after 3.23.33. |
Threads_cached | Number of threads in the thread cache. |
Threads_connected | Number of currently open connections. |
Threads_created | Number of threads created to handle connections. |
Threads_running | Number of threads that are not sleeping. |
Uptime | How many seconds the server has been up. |
Some comments about the above:
If Opened_tables is big, then your table_cache variable is probably too small.
If Key_reads is big, then your key_buffer_size variable is probably too small. The cache miss rate can be calculated with Key_reads/Key_read_requests.
If Handler_read_rnd is big, then you probably have a lot of queries that require MySQL to scan whole tables or you have joins that don't use keys properly.
If Threads_created is big, you may want to increase the thread_cache_size variable. The cache hit rate can be calculated with Threads_created/Connections.
If Created_tmp_disk_tables is big, you may want to increase the tmp_table_size variable to get the temporary tables memory-based instead of disk based.
SHOW [GLOBAL | SESSION] VARIABLES [LIKE wild]
SHOW VARIABLES shows the values of some MySQL system variables. The options GLOBAL and SESSION are new in MySQL 4.0.3. With GLOBAL, you will get the variables that will be used for new connections to MySQL. With SESSION, you will get the values that are in effect for the current connection. If you are not using either option, SESSION is used.
If the default values are unsuitable, you can set most of these variables using command-line options when mysqld starts. See Server options. It is also possible to change most variables with the SET statement. See SET.
The output from SHOW VARIABLES resembles that shown in the following list, though the format and numbers may differ somewhat. You can also get this information using the mysqladmin variables command.
+---------------------------------+------------------------------+ | Variable_name | Value | +---------------------------------+------------------------------| | back_log | 50 | | basedir | /usr/local/mysql | | bdb_cache_size | 8388572 | | bdb_log_buffer_size | 32768 | | bdb_home | /usr/local/mysql | | bdb_max_lock | 10000 | | bdb_logdir | | | bdb_shared_data | OFF | | bdb_tmpdir | /tmp/ | | bdb_version | Sleepycat Software: ... | | binlog_cache_size | 32768 | | bulk_insert_buffer_size | 8388608 | | character_set | latin1 | | character_sets | latin1 big5 czech euc_kr | | concurrent_insert | ON | | connect_timeout | 5 | | convert_character_set | | | datadir | /usr/local/mysql/data/ | | delay_key_write | ON | | delayed_insert_limit | 100 | | delayed_insert_timeout | 300 | | delayed_queue_size | 1000 | | flush | OFF | | flush_time | 0 | | ft_boolean_syntax | + -><()~*:""&| | | ft_min_word_len | 4 | | ft_max_word_len | 84 | | ft_query_expansion_limit | 20 | | ft_stopword_file | (built-in) | | have_bdb | YES | | have_innodb | YES | | have_isam | YES | | have_raid | NO | | have_symlink | DISABLED | | have_openssl | YES | | have_query_cache | YES | | init_file | | | innodb_additional_mem_pool_size | 1048576 | | innodb_buffer_pool_size | 8388608 | | innodb_data_file_path | ibdata1:10M:autoextend | | innodb_data_home_dir | | | innodb_file_io_threads | 4 | | innodb_force_recovery | 0 | | innodb_thread_concurrency | 8 | | innodb_flush_log_at_trx_commit | 1 | | innodb_fast_shutdown | ON | | innodb_flush_method | | | innodb_lock_wait_timeout | 50 | | innodb_log_arch_dir | | | innodb_log_archive | OFF | | innodb_log_buffer_size | 1048576 | | innodb_log_file_size | 5242880 | | innodb_log_files_in_group | 2 | | innodb_log_group_home_dir | ./ | | innodb_mirrored_log_groups | 1 | | interactive_timeout | 28800 | | join_buffer_size | 131072 | | key_buffer_size | 16773120 | | key_cache_block_size | 1024 | | key_cache_division_limit | 100 | | key_cache_age_threshold | 300 | | language | /usr/local/mysql/share/... | | large_files_support | ON | | local_infile | ON | | locked_in_memory | OFF | | log | OFF | | log_update | OFF | | log_bin | OFF | | log_slave_updates | OFF | | log_slow_queries | OFF | | log_warnings | OFF | | long_query_time | 10 | | low_priority_updates | OFF | | lower_case_table_names | 0 | | max_allowed_packet | 1047552 | | max_binlog_cache_size | 4294967295 | | max_binlog_size | 1073741824 | | max_connections | 100 | | max_connect_errors | 10 | | max_delayed_threads | 20 | | max_heap_table_size | 16777216 | | max_join_size | 4294967295 | | max_relay_log_size | 0 | | max_sort_length | 1024 | | max_user_connections | 0 | | max_tmp_tables | 32 | | max_write_lock_count | 4294967295 | | myisam_max_extra_sort_file_size | 268435456 | | myisam_repair_threads | 1 | | myisam_max_sort_file_size | 2147483647 | | myisam_recover_options | force | | myisam_sort_buffer_size | 8388608 | | net_buffer_length | 16384 | | net_read_timeout | 30 | | net_retry_count | 10 | | net_write_timeout | 60 | | open_files_limit | 1024 | | pid_file | /usr/local/mysql/name.pid | | port | 3306 | | protocol_version | 10 | | query_cache_limit | 1048576 | | query_cache_size | 0 | | query_cache_type | ON | | read_buffer_size | 131072 | | read_rnd_buffer_size | 262144 | | rpl_recovery_rank | 0 | | safe_show_database | OFF | | server_id | 0 | | slave_net_timeout | 3600 | | skip_external_locking | ON | | skip_networking | OFF | | skip_show_database | OFF | | slow_launch_time | 2 | | socket | /tmp/mysql.sock | | sort_buffer_size | 2097116 | | sql_mode | | | table_cache | 64 | | table_type | MYISAM | | thread_cache_size | 3 | | thread_stack | 131072 | | tx_isolation | READ-COMMITTED | | timezone | EEST | | tmp_table_size | 33554432 | | tmpdir | /tmp/:/mnt/hd2/tmp/ | | version | 4.0.4-beta | | wait_timeout | 28800 | +---------------------------------+------------------------------+
Each option is described here. Values for buffer sizes, lengths, and stack sizes are given in bytes. You can specify values with a suffix of K or M to indicate kilobytes or megabytes. For example, 16M indicates 16 megabytes. The case of suffix letters does not matter; 16M and 16m are equivalent:
ansi_mode. Is ON if mysqld was started with --ansi. See ANSI mode.
back_log The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.
In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix listen(2) system call should have more details. Check your OS documentation for the maximum value for this variable. Attempting to set back_log higher than your operating system limit will be ineffective.
basedir The value of the --basedir option.
bdb_cache_size The buffer that is allocated to cache index and rows for BDB tables. If you don't use BDB tables, you should start mysqld with --skip-bdb to not waste memory for this cache.
bdb_log_buffer_size The buffer that is allocated to cache index and rows for BDB tables. If you don't use BDB tables, you should set this to 0 or start mysqld with --skip-bdb to not waste memory for this cache.
bdb_home The base directory for BDB tables. This should be the same directory you use for --datadir.
bdb_max_lock The maximum number of locks (10,000 by default) you can have active on a BDB table. You should increase this if you get errors of type bdb: Lock table is out of available locks or Got error 12 from ... when you have do long transactions or when mysqld has to examine a lot of rows to calculate the query.
bdb_logdir The value of the --bdb-logdir option.
bdb_shared_data Is ON if you are using --bdb-shared-data.
bdb_tmpdir The value of the --bdb-tmpdir option.
binlog_cache_size. The size of the cache to hold the SQL statements for the binary log during a transaction. If you often use big, multiple-statement transactions you can increase this to get more performance. See COMMIT.
bulk_insert_buffer_size MyISAM uses special tree-like cache to make bulk inserts (that is, INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA INFILE) faster. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 will disable this optimization. Note: This cache is used only when adding data to a non-empty table. Default value is 8 MB. This option used to be named myisam_bulk_insert_tree_size.
character_set The default character set.
character_sets The supported character sets.
concurrent_inserts If ON (the default), MySQL will allow you to use INSERT on MyISAM tables at the same time as you run SELECT queries on them. You can turn this option off by starting mysqld with --safe or --skip-new.
connect_timeout The number of seconds the mysqld server is waiting for a connect packet before responding with Bad handshake.
datadir The value of the --datadir option.
delay_key_write Option for MyISAM tables. Can have one of the following values:
OFF | All CREATE TABLE ... DELAYED_KEY_WRITE are ignored. |
ON | (default) MySQL will honor the DELAY_KEY_WRITE option for CREATE TABLE. |
ALL | All new opened tables are treated as if they were created with the DELAY_KEY_WRITE option. |
If DELAY_KEY_WRITE is enabled this means that the key buffer for tables with this option will not get flushed on every index update, but only when a table is closed. This will speed up writes on keys a lot, but you should add automatic checking of all tables with myisamchk --fast --force if you use this.
delayed_insert_limit After inserting delayed_insert_limit rows, the INSERT DELAYED handler will check if there are any SELECT statements pending. If so, it allows these to execute before continuing.
delayed_insert_timeout How long a INSERT DELAYED thread should wait for INSERT statements before terminating.
delayed_queue_size What size queue (in rows) should be allocated for handling INSERT DELAYED. If the queue becomes full, any client that does INSERT DELAYED will wait until there is room in the queue again.
flush This is ON if you have started MySQL with the --flush option.
flush_time If this is set to a non-zero value, then every flush_time seconds all tables will be closed (to free up resources and sync unflushed data to disk). We only recommend this option on Windows 9x/Me, or on systems where you have very little resources.
ft_boolean_syntax List of operators supported by MATCH ... AGAINST(... IN BOOLEAN MODE). One needs a SUPER privilege to change it. See Fulltext Search.
ft_min_word_len The minimum length of the word to be included in a FULLTEXT index. Note: FULLTEXT indexes must be rebuilt after changing this variable. This variable is available as of MySQL 4.0.
ft_max_word_len The maximum length of the word to be included in a FULLTEXT index. Note: FULLTEXT indexes must be rebuilt after changing this variable. This variable is available as of MySQL 4.0.
ft_query_expansion_limit Number of top matches to use for query expansion (in MATCH ... AGAINST (... WITH QUERY EXPANSION). This variable is available as of MySQL 4.1.1.
ft_stopword_file The file from which to read the list of stopwords for full-text searches. All the words from the file will be used; comments are not honored. By default, built-in list of stopwords is used (as defined in myisam/ft_static.c). Setting this parameter to an empty string ("") will disable stopword filtering. Note: FULLTEXT indexes must be rebuilt after changing this variable. This variable is available as of MySQL 4.0.10.
have_innodb YES if mysqld supports InnoDB tables. DISABLED if --skip-innodb is used.
have_bdb YES if mysqld supports Berkeley DB tables. DISABLED if --skip-bdb is used.
have_raid YES if mysqld supports the RAID option.
have_openssl YES if mysqld supports SSL (encryption) on the client/server protocol.
init_connect A string to be executed by the server for each client that connects. The string consists of one or more SQL statements. To specify multiple statements, separate them by semicolon characters. This variable was added in MySQL 4.1.2.
For example, each client begins by default with auto-commit mode enabled. There is no global server variable to specify that auto-commit should be disabled by default, but init_connect can be used to achieve the same effect:
SET GLOBAL init_connect='SET AUTOCOMMIT=0';
This variable may also be set on the command line or in an option file. To set the variable as just shown using an option file, include these lines:
[mysqld] init_connect='SET AUTOCOMMIT=0'
init_file The name of the file specified with the --init-file option when you start the server. This is a file of SQL statements you want the server to execute when it starts.
init_slave This variable is similar to init_connect, but is a string to be executed by a slave server each time the SQL thread starts. The format of the string is the same as for the init_connect variable. This variable was added in MySQL 4.1.2.
interactive_timeout The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.
join_buffer_size The size of the buffer that is used for full joins (joins that do not use indexes). The buffer is allocated one time for each full join between two tables. Increase this value to get a faster full join when adding indexes is not possible. (Normally the best way to get fast joins is to add indexes.)
key_buffer_size Index blocks are buffered and are shared by all threads. key_buffer_size is the size of the buffer used for index blocks.
Increase this to get better index handling (for all reads and multiple writes) to as much as you can afford; 64M on a 256M machine that mainly runs MySQL is quite common. However, if you make this too large (for instance more than 50% of your total memory) your system might start to page and become extremely slow. Remember that because MySQL does not cache data reads, you will have to leave some room for the OS filesystem cache.
You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the variables Key_read_requests, Key_reads, Key_write_requests, and Key_writes. The Key_reads/Key_read_request ratio should normally be < 0.01. The Key_write/Key_write_requests is usually near 1 if you are using mostly updates/deletes but might be much smaller if you tend to do updates that affect many at the same time or if you are using DELAY_KEY_WRITE. See SHOW.
To get even more speed when writing many rows at the same time, use LOCK TABLES. See LOCK TABLES.
The fraction of the key buffer in use can be determined using key_buffer_size in conjunction with the Key_blocks_used status variable and the blocksize. Before MySQL 4.1.1, key cache blocks are 1024 bytes, so the fraction of the key buffer in use is:
(Key_blocks_used * 1024) / key_buffer_size
From 4.1.1 on, the buffer block size is available from the key_cache_block_size server variable. The fraction of the buffer in use is:
(Key_blocks_used * key_cache_block_size) / key_buffer_size
See MyISAM key cache.
key_cache_age_threshold This value controls the demotion of buffers from the hot sub-chain of a key cache to the warm sub-chain. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. This variable was added in MySQL 4.1.1. See MyISAM key cache.
key_cache_block_size The size in bytes of blocks in the key buffer. The default value is 1024. This variable was added in MySQL 4.1.1. See MyISAM key cache.
key_cache_division_limit The division point between the hot and warm sub-chains of the key cache buffer chain. The value is the percentage of the buffer chain to use for the warm sub-chain. Allowable values range from 1 to 100. The default value is 100. This variable was added in MySQL 4.1.1. See MyISAM key cache.
language The language used for error messages.
large_file_support If mysqld was compiled with options for big file support.
locked_in_memory If mysqld was locked in memory with --memlock
log If logging of all queries is enabled.
log_update If the update log is enabled.
log_bin If the binary log is enabled.
log_slave_updates If the updates from the slave should be logged.
long_query_time If a query takes longer than this (in seconds), the Slow_queries counter will be incremented. If you are using --log-slow-queries, the query will be logged to the slow query log file. This value is measured in real time, not CPU time, so a query that may be under the threshold on a lightly loaded system may be above the threshold on a heavily loaded one. See Slow query log.
lower_case_table_names If set to 1 table names are stored in lowercase on disk and table name comparisons will not be case sensitive. If set to 2 (new in 4.0.18) then table names will be stored as given but compared in lower case. From version 4.0.2, this option also applies to database names. From 4.1.1 this option also applies to table aliases. Note that you should NOT set this to 0 if you are running MYSQL on a system that does not have case sensitive filenames (such as Windows or Mac OS X). New in 4.0.18: If this value is 0 and the datadir is not case sensitive, MySQL automaticallys set lower_case_table_names to 1. See Name case sensitivity.
max_allowed_packet The maximum size of one packet. The message buffer is initialized to net_buffer_length bytes, but can grow up to max_allowed_packet bytes when needed. This value by default is small, to catch big (possibly wrong) packets. You must increase this value if you are using big BLOB columns. It should be as big as the biggest BLOB you want to use. The protocol limits for max_allowed_packet is 16M in MySQL 3.23 and 1G in MySQL 4.0.
max_binlog_cache_size If a multiple-statement transaction requires more than this amount of memory, one will get the error "Multi-statement transaction required more than 'max_binlog_cache_size' bytes of storage".
max_binlog_size Available after 3.23.33. If a write to the binary (replication) log exceeds the given value, rotate the logs. You cannot set it to less than 4096 bytes (1024 in MySQL versions older than 4.0.14), or more than 1 GB. Default is 1 GB. Note if you are using transactions: a transaction is written in one chunk to the binary log, hence it is never split between several binary logs. Therefore, if you have big transactions, you may see binlogs bigger than max_binlog_size. If max_relay_log_size (available starting from MySQL 4.0.14) is 0, then max_binlog_size will apply to relay logs as well.
max_connections The number of simultaneous clients allowed. Increasing this value increases the number of file descriptors that mysqld requires. See below for comments on file descriptor limits. See Too many connections.
max_connect_errors If there is more than this number of interrupted connections from a host this host will be blocked from further connections. You can unblock a host with the command FLUSH HOSTS.
max_delayed_threads Don't start more than this number of threads to handle INSERT DELAYED statements. If you try to insert data into a new table after all INSERT DELAYED threads are in use, the row will be inserted as if the DELAYED attribute wasn't specified. If you set this to 0, MySQL will never create a max_delayed thread.
max_heap_table_size This variable sets the maximum size to which subsequently created HEAP tables are allowed to grow. The value of the variable is used to calculate a HEAP table's MAX_ROWS value. Setting this variable has no effect on any existing HEAP table, unless the table is re-created with a statement such as CREATE TABLE or TRUNCATE TABLE, or altered with ALTER TABLE.
max_join_size Joins that are probably going to read more than max_join_size records return an error. Set this value if your users tend to perform joins that lack a WHERE clause, that take a long time, and that return millions of rows.
max_relay_log_size Available starting from 4.0.14. If a write to the relay log (a kind of log used by replication slaves, see Replication Implementation Details) exceeds the given value, rotate the relay log. This variable enables you to put different size constraints on relay logs and binary logs. However, setting the variable to 0 will make MySQL use max_binlog_size for both binary logs and relay logs. You have to set max_relay_log_size to 0 or more than 4096, and less than 1 GB. Default is 0.
max_seeks_for_key Limit assumed max number of seeks when looking up rows based on a key. The MySQL optimizer will assume that when searching after matching rows in a table through scanning a key, we will not cause more than this number of key seeks independent of the cardinality of the key. By setting this to a low value (100 ?) you can force MySQL to prefer keys instead of table scans.
max_sort_length The number of bytes to use when sorting BLOB or TEXT values. Only the first max_sort_length bytes of each value are used; the rest are ignored.
max_user_connections The maximum number of active connections for a single user (0 = no limit).
max_tmp_tables (This option doesn't yet do anything.) Maximum number of temporary tables a client can keep open at the same time.
max_write_lock_count After this many write locks, allow some read locks to run in between.
myisam_recover_options The value of the --myisam-recover option.
myisam_sort_buffer_size The buffer that is allocated when sorting the index when doing a REPAIR or when creating indexes with CREATE INDEX or ALTER TABLE.
myisam_max_extra_sort_file_size. If the temporary file used for fast index creation would be bigger than using the key cache by the amount specified here, then prefer the key cache method. This is mainly used to force long character keys in large tables to use the slower key cache method to create the index. Note that this parameter is given in megabytes before 4.0.3 and in bytes beginning with this version.
myisam_repair_threads. If this value is greater than one, MyISAM table indexes during Repair by sorting process will be created in parallel - each index in its own thread. Note: Multi-threaded repair is still alpha quality code.
myisam_max_sort_file_size The maximum size of the temporary file MySQL is allowed to use while recreating the index (during REPAIR, ALTER TABLE or LOAD DATA INFILE. If the file-size would be bigger than this, the index will be created through the key cache (which is slower). Note that this parameter is given in megabytes before 4.0.3 and in bytes beginning with this version.
net_buffer_length The communication buffer is reset to this size between queries. This should not normally be changed, but if you have very little memory, you can set it to the expected size of a query. (That is, the expected length of SQL statements sent by clients. If statements exceed this length, the buffer is automatically enlarged, up to max_allowed_packet bytes.)
net_read_timeout Number of seconds to wait for more data from a connection before aborting the read. Note that when we don't expect data from a connection, the timeout is defined by write_timeout. See also slave_net_timeout.
net_retry_count If a read on a communication port is interrupted, retry this many times before giving up. This value should be quite high on FreeBSD as internal interrupts are sent to all threads.
net_write_timeout Number of seconds to wait for a block to be written to a connection before aborting the write.
open_files_limit Number of files the system allows mysqld to open. This is the real value given for the system and may be different from the value you gave mysqld as a startup parameter. This is 0 on systems where MySQL can't change the number of open files.
pid_file The value of the --pid-file option.
port The value of the --port option.
protocol_version The protocol version used by the MySQL server.
query_alloc_block_size Size of memory allocation blocks that are allocated for objects created during query parsing and execution. If you have problem with memory fragmentation, it may help to increase this a bit. This variable was added in MySQL 4.0.16.
query_cache_limit Don't cache results that are bigger than this. (Default 1M).
query_cache_size The memory allocated to store results from old queries. If this is 0, the query cache is disabled (default).
query_cache_type This may be set (only numeric) to
Value | Alias | Comment |
0 | OFF | Don't cache or retrieve results. |
1 | ON | Cache all results except SELECT SQL_NO_CACHE ... queries. |
2 | DEMAND | Cache only SELECT SQL_CACHE ... queries. |
query_prealloc_size Size of the persistent buffer used for query parsing and execution. This buffer is not freed between queries. If you are running complex queries, a larger query_prealloc_size value may be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations.
This variable was added in MySQL 4.0.16.
range_alloc_block_size The size of blocks that are allocated when doing range optimization. This variable was added in MySQL 4.0.16.
read_buffer_size Each thread that does a sequential scan allocates a buffer of this size for each table it scans. If you do many sequential scans, you might want to increase this value. This option used to be named record_buffer.
read_rnd_buffer_size When reading rows in sorted order after a sort, the rows are read through this buffer to avoid disk seeks. Can improve ORDER BY by a lot if set to a high value. As this is a thread-specific variable, one should not set this big globally, but just change this when running some specific big queries. This option used to be named record_rnd_buffer.
safe_show_database Don't show databases for which the user doesn't have any database or table privileges. This can improve security if you're concerned about people being able to see what databases other users have. See also skip_show_database.
If the MySQL server has been started with the --secure-auth option, it will block all all connections from users with passwords stored in old (pre-4.1) format. In that case, the value of the variable is ON, otherwise it is OFF. Note, that the server start will fail with an error if this option has been enabled and the privilege tables are in pre-4.1 format. When used as a client-side option, the client will refuse connecting to a server if the server requires passwords in old format for this user/host combination. You should enable this option if you want to prevent all usage of passwords in old format (and hence insecure communication over the network). Available as of MySQL 4.1.1.
server_id The value of the --server-id option.
skip_locking Is OFF if mysqld uses external locking.
skip_networking Is ON if we only allow local (socket) connections.
skip_show_database This prevents people from doing SHOW DATABASES if they don't have the PROCESS privilege. This can improve security if you're concerned about people being able to see what databases other users have. See also safe_show_database.
slave_net_timeout Number of seconds to wait for more data from a master/slave connection before aborting the read.
slow_launch_time If creating the thread takes longer than this value (in seconds), the Slow_launch_threads counter will be incremented.
socket The Unix socket used by the server.
sort_buffer_size Each thread that needs to do a sort allocates a buffer of this size. Increase this value for faster ORDER BY or GROUP BY operations. See Temporary files.
sql_mode The current SQL mode. See SQL mode.
table_cache The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check if you need to increase the table cache by checking the Opened_tables variable. See Opened_tables. If this variable is big and you don't do FLUSH TABLES a lot (which just forces all tables to be closed and reopenend), then you should increase the value of this variable.
For more information about the table cache, see Table cache.
table_type The default table type.
thread_cache_size How many threads we should keep in a cache for reuse. When a client disconnects, the client's threads are put in the cache if there aren't more than thread_cache_size threads from before. All new threads are first taken from the cache, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. (Normally this doesn't give a notable performance improvement if you have a good thread implementation.) By examing the difference between the Connections and Threads_created status variables (see SHOW STATUS for details) you can see how efficient thread cache is.
thread_concurrency On Solaris, mysqld will call thr_setconcurrency() with this value. thr_setconcurrency() permits the application to give the threads system a hint for the desired number of threads that should be run at the same time.
thread_stack The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. The default is large enough for normal operation. See MySQL Benchmarks.
timezone The time zone for the server. This is set from the TZ environment variable when mysqld is started. This can also be given as a --timezone argument to mysqld_safe. See Timezone problems.
tmp_table_size If an in-memory temporary table exceeds this size, MySQL automaticallys convert it to an on-disk MyISAM table. Increase the value of tmp_table_size if you do many advanced GROUP BY queries and you have lots of memory.
tmpdir The directory used for temporary files and temporary tables. Starting from MySQL 4.1, it can be set to a list of paths separated by colon : (semicolon ; on Windows). They will be used in round-robin fashion. This feature can be used to spread load between several physical disks. It is possible to set tmpdir to point to a memory-based filesystem, except if the MySQL server is a slave. If it is a slave, it needs some of its temporary files (for replication of temporary tables or of LOAD DATA INFILE) to survive a machine's reboot, so a memory-based tmpdir which is cleared when the machine reboots is not suitable; a disk-based tmpdir is necessary.
transaction_alloc_block_size Size of memory allocation blocks that are allocated for storing queries that are part of a transaction that are to be stored in the binary log when doing a commit. This variable was added in MySQL 4.0.16.
transaction_prealloc_size Persistent buffer for transaction_alloc_blocks that is not freed between queries. By making this big enough to fit all queries in a common transaction you can avoid a lot of malloc() calls. This variable was added in MySQL 4.0.16.
version The version number for the server.
wait_timeout The number of seconds the server waits for activity on a not interactive connection before closing it.
On thread startup SESSION.WAIT_TIMEOUT is initialized from GLOBAL.WAIT_TIMEOUT or GLOBAL.INTERACTIVE_TIMEOUT depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option). See also interactive_timeout.
The manual section that describes tuning MySQL contains some information of how to tune the above variables. See Server parameters.
SHOW LOGS shows you status information about existing log files. It currently only displays information about Berkeley DB log files, so an alias for it (available as of MySQL 4.1.1) is SHOW BDB LOGS.
File shows the full path to the log file
Type shows the type of the log file (BDB for Berkeley DB log files)
Status shows the status of the log file (FREE if the file can be removed, or IN USE if the file is needed by the transaction subsystem)
SHOW [FULL] PROCESSLIST shows you which threads are running. You can also get this information using the mysqladmin processlist command. If you have the SUPER privilege, you can see all threads. Otherwise, you can see only your own threads. See KILL. If you don't use the FULL option, only the first 100 characters of each query are shown.
Starting from 4.0.12, MySQL reports the hostname for TCP/IP connections in hostname:client_port format to make it easier to find out which client is doing what.
This command is very useful if you get the 'too many connections' error message and want to find out what's going on. MySQL reserves one extra connection for a client with the SUPER privilege to ensure that you should always be able to log in and check the system (assuming you are not giving this privilege to all your users).
Some states commonly seen in mysqladmin processlist
Checking table The thread is performing [automatic] checking of the table.
Closing tables Means that the thread is flushing the changed table data to disk and closing the used tables. This should be a fast operation. If not, then you should check that you don't have a full disk or that the disk is not in very heavy use.
Connect Out Slave connecting to master.
Copying to tmp table on disk The temporary result set was larger than tmp_table_size and the thread is now changing the in memory-based temporary table to a disk based one to save memory.
Creating tmp table The thread is creating a temporary table to hold a part of the result for the query.
deleting from main table When executing the first part of a multiple-table delete and we are only deleting from the first table.
deleting from reference tables When executing the second part of a multiple-table delete and we are deleting the matched rows from the other tables.
Flushing tables The thread is executing FLUSH TABLES and is waiting for all threads to close their tables.
Killed Someone has sent a kill to the thread and it should abort next time it checks the kill flag. The flag is checked in each major loop in MySQL, but in some cases it may still take a short time for the thread to die. If the thread is locked by some other thread, the kill will take effect as soon as the other thread releases its lock.
Sending data The thread is processing rows for a SELECT statement and is also sending data to the client.
Sorting for group The thread is doing a sort to satisfy a GROUP BY.
Sorting for order The thread is doing a sort to satisfy a ORDER BY.
Opening tables This simply means that the thread is trying to open a table. This is should be very fast procedure, unless something prevents opening. For example an ALTER TABLE or a LOCK TABLE can prevent opening a table until the command is finished.
Removing duplicates The query was using SELECT DISTINCT in such a way that MySQL couldn't optimize that distinct away at an early stage. Because of this MySQL has to do an extra stage to remove all duplicated rows before sending the result to the client.
Reopen table The thread got a lock for the table, but noticed after getting the lock that the underlying table structure changed. It has freed the lock, closed the table and is now trying to reopen it.
Repair by sorting The repair code is using sorting to create indexes.
Repair with keycache The repair code is using creating keys one by one through the key cache. This is much slower than Repair by sorting.
Searching rows for update The thread is doing a first phase to find all matching rows before updating them. This has to be done if the UPDATE is changing the index that is used to find the involved rows.
Sleeping The thread is wating for the client to send a new command to it.
System lock The thread is waiting for getting to get a external system lock for the table. If you are not using multiple mysqld servers that are accessing the same tables, you can disable system locks with the --skip-external-locking option.
Upgrading lock The INSERT DELAYED handler is trying to get a lock for the table to insert rows.
Updating The thread is searching for rows to update and updating them.
User Lock The thread is waiting on a GET_LOCK().
Waiting for tables The thread got a notification that the underlying structure for a table has changed and it needs to reopen the table to get the new structure. To be able to reopen the table it must however wait until all other threads have closed the table in question.
This notification happens if another thread has used FLUSH TABLES or one of the following commands on the table in question: FLUSH TABLES table_name, ALTER TABLE, RENAME TABLE, REPAIR TABLE, ANALYZE TABLE or OPTIMIZE TABLE.
waiting for handler insert The INSERT DELAYED handler has processed all inserts and are waiting to get new ones.
Most states are very quick operations. If threads last in any of these states for many seconds, there may be a problem around that needs to be investigated.
There are some other states that are not mentioned previously, but most of these are useful only to find bugs in mysqld.
SHOW GRANTS FOR user lists the grant commands that must be issued to duplicate the grants for a user.
mysql> SHOW GRANTS FOR root@localhost; +---------------------------------------------------------------------+ | Grants for root@localhost | +---------------------------------------------------------------------+ | GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION | +---------------------------------------------------------------------+
To list grants for the current session, you can find out what user the session was authenticated as by selecting the value of the CURRENT_USER() function (new in version 4.0.6). Then use that value in the SHOW GRANTS statement. See CURRENT_USER().
Shows a CREATE TABLE statement that will create the given table:
mysql> SHOW CREATE TABLE t\G *************************** 1. row *************************** Table: t Create Table: CREATE TABLE t ( id INT(11) default NULL auto_increment, s char(60) default NULL, PRIMARY KEY (id) ) TYPE=MyISAM
SHOW CREATE TABLE quotes table and column names according to the value of the SQL_QUOTE_SHOW_CREATE option. SET SQL_QUOTE_SHOW_CREATE.
SHOW WARNINGS [LIMIT row_count] SHOW ERRORS [LIMIT row_count]
This command is implemented in MySQL 4.1.0.
It shows the errors, warnings and notes that one got for the last command. The errors/warnings are reset for each new command that uses a table.
The MySQL server sends back the total number of warnings and errors you got for the last commend; This can be retrieved by calling mysql_warning_count().
Up to max_error_count messages are stored (Global and thread specific variable).
You can retrieve the number of errors from @error_count and warnings from @warning_count.
SHOW WARNINGS shows all errors, warnings and notes you got for the last command while SHOW ERRORS only shows you the errors.
mysql> DROP TABLE IF EXISTS no_such_table; mysql> SHOW WARNINGS; +-------+------+-------------------------------+ | Level | Code | Message | +-------+------+-------------------------------+ | Note | 1051 | Unknown table 'no_such_table' | +-------+------+-------------------------------+
Note that in MySQL 4.1.0 we have just added the frame work for warnings and not many MySQL command do yet generate warnings. 4.1.1 supports all kind of warnings for LOAD DATA INFILE and DML statements such as INSERT, UPDATE and ALTER commands.
For example, here is a simple case which produces conversion warnings for a insert statement.
mysql> create table t1(a tinyint NOT NULL, b char(4)); Query OK, 0 rows affected (0.00 sec) mysql> insert into t1 values(10,'mysql'),(NULL,'test'),(300,'open source'); Query OK, 3 rows affected, 4 warnings (0.15 sec) Records: 3 Duplicates: 0 Warnings: 4 mysql> show warnings; +---------+------+---------------------------------------------------------------+ | Level | Code | Message | +---------+------+---------------------------------------------------------------+ | Warning | 1263 | Data truncated for column 'b' at row 1 | | Warning | 1261 | Data truncated, NULL supplied to NOT NULL column 'a' at row 2 | | Warning | 1262 | Data truncated, out of range for column 'a' at row 3 | | Warning | 1263 | Data truncated for column 'b' at row 3 | +---------+------+---------------------------------------------------------------+ 4 rows in set (0.00 sec)
Maximum number of warnings can be specified using the server variable 'max_error_count', SET max_error_count=[count]; By default it is 64. In case to disable warnings, simply reset this variable to '0'. In case if max_error_count is 0, then still the warning count represents how many warnings have occurred, but none of the messages are stored.
For example, consider the following ALTER table statement for the above example, which returns only one warning message even though total warnings occurred is 3 when you set max_error_count=1.
mysql> show variables like 'max_error_count'; +-----------------+-------+ | Variable_name | Value | +-----------------+-------+ | max_error_count | 64 | +-----------------+-------+ 1 row in set (0.00 sec) mysql> set max_error_count=1; Query OK, 0 rows affected (0.00 sec) mysql> alter table t1 modify b char; Query OK, 3 rows affected, 3 warnings (0.00 sec) Records: 3 Duplicates: 0 Warnings: 3 mysql> show warnings; +---------+------+----------------------------------------+ | Level | Code | Message | +---------+------+----------------------------------------+ | Warning | 1263 | Data truncated for column 'b' at row 1 | +---------+------+----------------------------------------+ 1 row in set (0.00 sec) mysql>
SHOW TABLE TYPES
This command is implemented in MySQL 4.1.0.
SHOW TABLE TYPES shows you status information about the table types. This is particulary useful for checking if a table type is supported; or to see what is the default table type is.
mysql> SHOW TABLE TYPES; +--------+---------+-----------------------------------------------------------+ | Type | Support | Comment | +--------+---------+-----------------------------------------------------------+ | MyISAM | DEFAULT | Default type from 3.23 with great performance | | HEAP | YES | Hash based, stored in memory, useful for temporary tables | | MERGE | YES | Collection of identical MyISAM tables | | ISAM | YES | Obsolete table type; Is replaced by MyISAM | | InnoDB | YES | Supports transactions, row-level locking and foreign keys | | BDB | NO | Supports transactions and page-level locking | +--------+---------+-----------------------------------------------------------+ 6 rows in set (0.00 sec)
The 'Support' option DEFAULT indicates whether the particular table type is supported, and which is the default type. If the server is started with --default-table-type=InnoDB, then the InnoDB 'Support' field will have the value DEFAULT.
SHOW PRIVILEGES
This command is implemented in MySQL 4.1.0.
SHOW PRIVILEGES shows the list of system privileges that the underlying MySQL server supports.
mysql> show privileges; +------------+------------------------- -+-------------------------------------------------------+ | Privilege | Context | Comment | +------------+--------------------------+-------------------------------------------------------+ | Select | Tables | To retrieve rows from table | | Insert | Tables | To insert data into tables | | Update | Tables | To update existing rows | | Delete | Tables | To delete existing rows | | Index | Tables | To create or drop indexes | | Alter | Tables | To alter the table | | Create | Databases,Tables,Indexes | To create new databases and tables | | Drop | Databases,Tables | To drop databases and tables | | Grant | Databases,Tables | To give to other users those privileges you possess | | References | Databases,Tables | To have references on tables | | Reload | Server Admin | To reload or refresh tables, logs and privileges | | Shutdown | Server Admin | To shutdown the server | | Process | Server Admin | To view the plain text of currently executing queries | | File | File access on server | To read and write files on the server | +------------+--------------------------+-------------------------------------------------------+ 14 rows in set (0.00 sec)
CACHE INDEX table_index_list [, table_index_list] ... IN key_cache_name table_index_list: table_name [[INDEX] (index_name[, index_name] ...)]
The CACHE INDEX statement assigns table indexes to a specific key cache. It is used only for MyISAM tables.
The following statement assigns indexes from the tables t1, t2, and t3 to the key cache named hot_cache:
mysql> CACHE INDEX t1, t2, t3 IN hot_cache; +---------+--------------------+----------+----------+ | Table | Op | Msg_type | Msg_text | +---------+--------------------+----------+----------+ | test.t1 | assign_to_keycache | status | OK | | test.t2 | assign_to_keycache | status | OK | | test.t3 | assign_to_keycache | status | OK | +---------+--------------------+----------+----------+
The syntax of CACHE INDEX allows you to specify that only particular indexes from a table should be assigned to the cache. However, the current implementation assigns all the table's indexes to the cache, so there is no reason to specify anything other than the table name.
The key cache referred to in a CACHE INDEX statement can be created by setting its size with a parameter setting statement or in the server parameter settings. For example:
mysql> SET GLOBAL keycache1.key_buffer_size=128*1024;
Key cache parameters can be accessed as members of a structured system variable. See Structured System Variables.
A key cache must exist before you can assign indexes to it:
mysql> CACHE INDEX t1 in non_existent_cache; ERROR 1283 (HY000): Unknown key cache 'non_existent_cache'
By default, table indexes are assigned to the main (default) key cache created at the server start-up. When a key cache is destroyed, all indexes assigned to it become assigned to the default key cache again.
Index assignment affects the server globally: If one client assigns an index to a given cache, this cache is used for all queries involving the index, no matter what client issues the queries.
CACHE INDEX was added in MySQL 4.1.1.
FLUSH [LOCAL | NO_WRITE_TO_BINLOG] flush_option [,flush_option] ...
You should use the FLUSH command if you want to clear some of the internal caches MySQL uses. To execute FLUSH, you must have the RELOAD privilege.
flush_option can be any of the following:
Option | Description |
HOSTS | Empties the host cache tables. You should flush the host tables if some of your hosts change IP number or if you get the error message Host ... is blocked. When more than max_connect_errors errors occur in a row for a given host while connection to the MySQL server, MySQL assumes something is wrong and blocks the host from further connection requests. Flushing the host tables allows the host to attempt to connect again. See Blocked host. You can start mysqld with -O max_connect_errors=999999999 to avoid this error message. |
DES_KEY_FILE | Reloads the DES keys from the file that was specified with the --des-key-file option at server startup time. |
LOGS | Closes and reopens all log files. If you have specified an update log file or a binary log file without an extension, the extension number of the log file will be incremented by one relative to the previous file. If you have used an extension in the file name, MySQL will close and reopen the update log file. See Update log. This is the same thing as sending the SIGHUP signal to the mysqld server. |
PRIVILEGES | Reloads the privileges from the grant tables in the mysql database. |
QUERY CACHE | Defragment the query cache to better utilize its memory. This command will not remove any queries from the cache, unlike RESET QUERY CACHE. |
TABLES | Closes all open tables and force all tables in use to be closed. This also flushes the query cache. |
[TABLE | TABLES] tbl_name [,tbl_name...] | Flushes only the given tables. |
TABLES WITH READ LOCK | Closes all open tables and locks all tables for all databases with a read lock until you execute UNLOCK TABLES. This is very convenient way to get backups if you have a filesystem, like Veritas, that can take snapshots in time. |
STATUS | Resets most status variables to zero. This is something you should use only when debugging a query. See Bug reports. |
USER_RESOURCES | Resets all user resources to zero. This will enable blocked users to log in again. See User resources. |
Before MySQL 4.1.1, FLUSH commands are not written to the binary log. Since MySQL 4.1.1 they are written to the binary log unless the optional NO_WRITE_TO_BINLOG keyword (or its alias LOCAL) was used, or unless the command contained one of these arguments: LOGS, MASTER, SLAVE, TABLES WITH READ LOCK, because any of these arguments may cause problems if replicated to a slave.
You can also access some of the commands shown above with the mysqladmin utility, using the flush-hosts, flush-logs, flush-privileges, flush-status or flush-tables commands.
Take also a look at the RESET command used with replication. See RESET.
KILL thread_id KILL CONNECTION thread_id KILL QUERY thread_id
Each connection to mysqld runs in a separate thread. You can see which threads are running with the SHOW PROCESSLIST command and kill a thread with the KILL thread_id command.
As of MySQL 5.0.0, KILL allows the optional CONNECTION or QUERY modifiers:
KILL CONNECTION is the same as KILL with no modifier: It terminates the connection associated with the given thread_id.
KILL QUERY terminates the statement that the connection is executing, but leaves the connection intact.
If you have the PROCESS privilege, you can see all threads. If you have the SUPER privilege, you can kill all threads and statements. Otherwise, you can only see and kill your own threads and statements.
You can also use the mysqladmin processlist and mysqladmin kill commands to examine and kill threads.
Note: You currently cannot use KILL with the Embedded MySQL Server library, because the embedded server merely runs inside the threads of the host application, it does not create connection threads of its own.
When you do a KILL, a thread-specific kill flag is set for the thread.
In most cases it may take some time for the thread to die, as the kill flag is only checked at specific intervals.
In SELECT, ORDER BY and GROUP BY loops, the flag is checked after reading a block of rows. If the kill flag is set, the statement is aborted.
When doing an ALTER TABLE the kill flag is checked before each block of rows are read from the original table. If the kill flag was set the command is aborted and the temporary table is deleted.
When doing an UPDATE or DELETE, the kill flag is checked after each block read and after each updated or deleted row. If the kill flag is set, the statement is aborted. Note that if you are not using transactions, the changes will not be rolled back!
GET_LOCK() will abort with NULL.
An INSERT DELAYED thread will quickly flush all rows it has in memory and die.
If the thread is in the table lock handler (state: Locked), the table lock will be quickly aborted.
If the thread is waiting for free disk space in a write call, the write is aborted with an disk full error message.
LOAD INDEX INTO CACHE table_index_list [, table_index_list] ... table_index_list: table_name [[INDEX] (index_name[, index_name] ...)] [IGNORE LEAVES]
The LOAD INDEX INTO CACHE statement preloads a table index into the key cache to which it has been assigned by an explicit CACHE INDEX statement, or into the default key cache otherwise. LOAD INDEX INTO CACHE is used only for MyISAM tables.
The IGNORE LEAVES modifier causes only blocks for the non-leaf nodes of the index to be preloaded.
The following statement preloads nodes (index blocks) of indexes of the tables t1 and t2:
mysql> LOAD INDEX INTO CACHE t1, t2 IGNORE LEAVES; +---------+--------------+----------+----------+ | Table | Op | Msg_type | Msg_text | +---------+--------------+----------+----------+ | test.t1 | preload_keys | status | OK | | test.t2 | preload_keys | status | OK | +---------+--------------+----------+----------+
This statement preloads all index blocks from t1. It preloads only blocks for the non-leaf nodes from t2.
The syntax of LOAD INDEX INTO CACHE allows you to specify that only particular indexes from a table should be preloaded. However, the current implementation preloads all the table's indexes into the cache, so there is no reason to specify anything other than the table name.
LOAD INDEX INTO CACHE was added in MySQL 4.1.1.
PURGE {MASTER|BINARY} LOGS TO binlog_name PURGE {MASTER|BINARY} LOGS BEFORE date
This statement is used to delete all binary logs strictly prior to the specified binlog or date. See Replication Master SQL.
PURGE BINARY LOGS is available as a synonym for PURGE MASTER LOGS as of MySQL 4.1.1.
RESET reset_option [,reset_option] ...
The RESET statement is used to clear things. It also acts as a stronger version of the FLUSH command. See FLUSH.
To execute RESET, you must have the RELOAD privilege.
Option | Description |
MASTER | Deletes all binary logs listed in the index file, resetting the binlog index file to be empty. Previously named FLUSH MASTER. See Replication Master SQL. |
SLAVE | Makes the slave forget its replication position in the master binlogs. Previously named FLUSH SLAVE. See Replication Slave SQL. |
QUERY CACHE | Removes all query results from the query cache. |
Table of Contents
This section describes replication-related SQL statements. One group of statements is used for controlling master servers. The other is used for controlling slave servers.
Replication can be controlled through the SQL interface. This section discusses statements for managing master replication servers. Replication Slave SQL discusses statements for managing slave servers.
PURGE {MASTER|BINARY} LOGS TO 'log_name' PURGE {MASTER|BINARY} LOGS BEFORE 'date'
Deletes all the binary logs listed in the log index that are strictly prior to the specified log or date. The logs also are removed from this list recorded in the log index file, so that the given log now becomes the first.
Example:
PURGE MASTER LOGS TO 'mysql-bin.010'; PURGE MASTER LOGS BEFORE '2003-04-02 22:46:26';
The BEFORE variant is available in MySQL 4.1; its date argument can be in 'YYYY-MM-DD hh:mm:ss' format. MASTER and BINARY are synonyms, though BINARY can be used only as of MySQL 4.1.1.
If you have an active slave that is currently reading one of the logs you are trying to delete, this command does nothing and fails with an error. However, if you have a dormant slave, and happen to purge one of the logs it wants to read, the slave will be unable to replicate once it comes up. The command is safe to run while slaves are replicating. You do not need to stop them.
You must first check all the slaves with SHOW SLAVE STATUS to see which log they are reading, then do a listing of the logs on the master with SHOW MASTER LOGS, find the earliest log among all the slaves (if all the slaves are up to date, this will be the last log on the list), backup all the logs you are about to delete (optional) and purge up to the target log.
RESET MASTER
Deletes all binary logs listed in the index file, resetting the binlog index file to be empty.
This statement was named FLUSH MASTER before MySQL 3.23.26.
SET SQL_LOG_BIN = {0|1}
Disables or enables binary logging for the current connection (SQL_LOG_BIN is a session variable) if the client connects using an account that has the SUPER privilege. The statement is ignored if the client does not have that privilege.
SHOW BINLOG EVENTS [ IN 'log_name' ] [ FROM pos ] [ LIMIT [offset,] row_count ]
Shows the events in the binary log. If you do not specify 'log_name', the first binary log will be displayed.
This statement is available as of MySQL 4.0
Replication can be controlled through the SQL interface. This section discusses statements for managing slave replication servers. Replication Master SQL discusses statements for managing master servers.
CHANGE MASTER TO master_def [, master_def] ... master_def = MASTER_HOST = 'host_name' | MASTER_USER = 'user_name' | MASTER_PASSWORD = 'password' | MASTER_PORT = port_num | MASTER_CONNECT_RETRY = count | MASTER_LOG_FILE = 'master_log_name' | MASTER_LOG_POS = master_log_pos | RELAY_LOG_FILE = 'relay_log_name' | RELAY_LOG_POS = relay_log_pos | MASTER_SSL = {0|1} | MASTER_SSL_CA = 'ca_file_name' | MASTER_SSL_CAPATH = 'ca_directory_name' | MASTER_SSL_CERT = 'cert_file_name' | MASTER_SSL_KEY = 'key_file_name' | MASTER_SSL_CIPHER = 'cipher_list'
Changes the parameters that the slave server uses for connecting to and communicating with the master server. The possible master_def values are shown above.
The relay log options (RELAY_LOG_FILE and RELAY_LOG_POS) are available beginning with MySQL 4.0.
The SSL options (MASTER_SSL, MASTER_SSL_CA, MASTER_SSL_CAPATH, MASTER_SSL_CERT, MASTER_SSL_KEY, and MASTER_SSL_CIPHER) are available beginning with MySQL 4.1.1. You can change these options even on slaves that are compiled without SSL support. They will be saved to the master.info file but ignored until you use a server that has SSL support enabled.
For example:
mysql> CHANGE MASTER TO -> MASTER_HOST='master2.mycompany.com', -> MASTER_USER='replication', -> MASTER_PASSWORD='bigs3cret', -> MASTER_PORT=3306, -> MASTER_LOG_FILE='master2-bin.001', -> MASTER_LOG_POS=4, -> MASTER_CONNECT_RETRY=10; mysql> CHANGE MASTER TO -> RELAY_LOG_FILE='slave-relay-bin.006', -> RELAY_LOG_POS=4025;
MASTER_USER, MASTER_PASSWORD, MASTER_SSL, MASTER_SSL_CA, MASTER_SSL_CAPATH, MASTER_SSL_CERT, MASTER_SSL_KEY, and MASTER_SSL_CIPHER are information for the slave to be able to connect to its master. If you don't specify some of these informations, the non-specified informations will keep their old value. For example, if the password to connect to your MySQL master has changed, you just need to issue
mysql> STOP SLAVE; -- if replication was running mysql> CHANGE MASTER TO MASTER_PASSWORD='new3cret'; mysql> START SLAVE; -- if you want to restart replication
to tell the slave about the new password; no need to specify the information which did not change (host, port, user etc).
MASTER_HOST, MASTER_PORT are the hostname or IP adress of the master host, and its TCP port. Note that if MASTER_HOST is equal to localhost, then, like in other parts of MySQL, the port may be ignored (if Unix socket files can be used for example).
If you specify MASTER_HOST or MASTER_PORT, the slave will assume that the master server is different than before (even if you specify a host or port value value that is the same as the current value.) In this case, the old values of master binlog name and position are considered no longer applicable, so if you do not specify MASTER_LOG_FILE and MASTER_LOG_POS in the command, MASTER_LOG_FILE="" and MASTER_LOG_POS=4 are silently appended to it.
MASTER_LOG_FILE and MASTER_LOG_POS are the coordinates at which the slave I/O thread should begin reading from the master the next time the thread starts. If you specify any of them, you can't specify RELAY_LOG_FILE or RELAY_LOG_POS. If none of MASTER_LOG_FILE and MASTER_LOG_POS was specified, then the last coordinates of the slave SQL thread before CHANGE MASTER was issued, are used. This ensures that replication has no discontinuity, even if the slave SQL thread was late compared to the slave I/O thread, when you just want to change, say, the password to use. This safe behavior was introduced starting from MySQL 4.0.17 and 4.1.1. (Before these versions, the used coordinates were the last coordinates of the slave I/O thread before CHANGE MASTER was issued, which caused the SQL thread to sometimes lose some events from the master, thus breaking replication.)
CHANGE MASTER deletes all relay logs (and starts a new one), unless you specified RELAY_LOG_FILE or RELAY_LOG_POS (in that case relay logs will be kept; since MySQL 4.1.1 the RELAY_LOG_PURGE global variable will silently be set to 0). CHANGE MASTER TO updates master.info and relay-log.info.
CHANGE MASTER is useful for setting up a slave when you have the snapshot of the master and have recorded the log and the offset on the master that the snapshot corresponds to. You can run CHANGE MASTER TO MASTER_LOG_FILE="log_name_on_master", MASTER_LOG_POS=log_offset_on_master on the slave after restoring the snapshot.
The first example above (CHANGE MASTER TO MASTER_HOST="master2.mycompany.com" etc) changes the master and master's binlog coordinates. This is when you want the slave to replicate the master. The second example, less frequently used, is when the slave has relay logs which, for some reason, you want the slave to execute again; to do this the master needn't be reachable, you just have to do CHANGE MASTER TO and start the SQL thread (START SLAVE SQL_THREAD). You can even use this out of a replication setup, on a standalone, slave-of-nobody server, to recover after a crash. Suppose your server has crashed and you have restored a backup. You want to replay the server's own binlogs (not relay logs, but regular binary logs), supposedly named myhost-bin.*. First make a backup copy of these binlogs in some safe place, in case you don't exactly follow the procedure below and accidentally have the server purge the binlogs. If using MySQL 4.1.1 or newer, do SET GLOBAL RELAY_LOG_PURGE=0 for additional safety. Then start the server without log-bin, with a new (different from before) server ID, with relay-log=myhost-bin (to make the server believe that these regular binlogs are relay logs) and skip-slave-start, then issue these statements:
mysql> CHANGE MASTER TO -> RELAY_LOG_FILE='myhost-bin.153', -> RELAY_LOG_POS=410, -> MASTER_HOST='some_dummy_string'; mysql> START SLAVE SQL_THREAD;
Then the server will read and execute its own binlogs, thus achieving crash recovery. Once the recovery is finished, run STOP SLAVE, shutdown the server, delete master.info and relay-log.info, and restart the server with its original options. For the moment, specifying MASTER_HOST (even with a dummy value) is compulsory to make the server think it is a slave, and giving the server a new, different from before, server ID is also compulsory otherwise the server will see events with its ID and think it is in a circular replication setup and skip the events, which is unwanted. In the future we plan to add options to get rid of these small constraints.
LOAD DATA FROM MASTER
Takes a snapshot of the master and copies it to the slave. Updates the values of MASTER_LOG_FILE and MASTER_LOG_POS so that the slave will start replicating from the correct position. Will honor table and database exclusion rules specified with replicate-* options.
Use of this statement is subject to the following conditions:
It works only with MyISAM tables.
It acquires a global read lock on the master while taking the snapshot, which prevents updates on the master during the load operation.
In the future, it is planned to make this statement work with InnoDB tables and to remove the need for global read lock by using the non-blocking online backup feature.
If you are loading big tables, you may have to increase the values of net_read_timeout and net_write_timeout on both your master and slave. See SHOW VARIABLES.
Note that LOAD DATA FROM MASTER does NOT copy any tables from the mysql database. This is to make it easy to have different users and privileges on the master and the slave.
This statement requires that the replication account that is used to connect to the master have RELOAD and SUPER privileges on the master, SELECT privileges on all master's tables you want to load. All master's tables on which the user has no SELECT privilege will be ignored by LOAD DATA FROM MASTER; this is because the master will hide them to the user: LOAD DATA FROM MASTER calls SHOW DATABASES to know the master databases to load, but SHOW DATABASES returns only databases on which the user has some privilege. See Show database info. On the slave's side, the user which issues LOAD DATA FROM MASTER should have grants to drop and create the involved databases and tables.
LOAD TABLE tbl_name FROM MASTER
Downloads a copy of the table from master to the slave. This statement is implemented mainly for debugging of LOAD DATA FROM MASTER. Requires that the account used for connecting to the master server have RELOAD and SUPER privileges on the master, and SELECT on the master table to load. On the slave's side, the user which issues LOAD TABLE FROM MASTER should have grants to drop and create the table. Please read the timeout notes in the description of LOAD DATA FROM MASTER above; they apply here, too. Please also read the limitations of LOAD DATA FROM MASTER above, they apply too (for example, LOAD TABLE FROM MASTER works only for MyISAM tables).
SELECT MASTER_POS_WAIT('master_log_file', master_log_pos)
This is a function, not a command. It is used to ensure that the slave has reached (read and executed up to) a given position in the master's binlog. See Miscellaneous functions for a full description.
RESET SLAVE
Makes the slave forget its replication position in the master's binlogs. This statement is meant to be used for a clean start: it deletes the master.info and relay-log.info files, all the relay logs, and starts a new relay log. Note: All relay logs are deleted, even if they had not been totally executed by the slave SQL thread. (This is a condition likely to exist on a replication slave that is highly loaded, or if you have issued a STOP SLAVE statement.) Connection information stored in the master.info file is immediately reset to the values specified in the corresponding startup options, if they were specified. This information includes values such as master host, master port, master user, and master password. If the slave SQL thread was in the middle of replicating temporary tables when it was stopped, and RESET SLAVE is issued, these replicated temporary tables are deleted on the slave.
This statement was named FLUSH SLAVE before MySQL 3.23.26.
SET GLOBAL SQL_SLAVE_SKIP_COUNTER = n
Skip the next n events from the master. This is useful for recovering from replication stops caused by a statement.
This statement is valid only when the slave thread is not running. Otherwise, it produces an error.
Before MySQL 4.0, omit the GLOBAL keyword from the statement.
SHOW SLAVE STATUS
Provides status information on essential parameters of the slave threads. If you issue this statement using the mysql client, you can use a \G statement terminator rather than semicolon to get a more readable vertical layout:
mysql> SHOW SLAVE STATUS\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: localhost Master_User: root Master_Port: 3306 Connect_Retry: 3 Master_Log_File: gbichot-bin.005 Read_Master_Log_Pos: 79 Relay_Log_File: gbichot-relay-bin.005 Relay_Log_Pos: 548 Relay_Master_Log_File: gbichot-bin.005 Slave_IO_Running: Yes Slave_SQL_Running: Yes Replicate_Do_DB: Replicate_Ignore_DB: Last_Errno: 0 Last_Error: Skip_Counter: 0 Exec_Master_Log_Pos: 79 Relay_Log_Space: 552 Until_Condition: None Until_Log_File: Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 8
Depending on your version of MySQL, you may not see all the fields just shown. In particular, several fields are present only as of MySQL 4.1.1.
The fields displayed by SHOW SLAVE STATUS have the following meanings:
Slave_IO_State | A copy of the State column of the output of SHOW PROCESSLIST for the slave I/O thread; will tell you if this thread is trying to connect to the master, waiting for events from the master, reconnecting to the master, etc. Possible states are listed in Replication Implementation Details. Looking at this column is necessary because, for example, the thread can be running but unsuccessfully trying to connect to the master: only this column will make you aware of the connection problem. On the opposite, the state of the SQL thread is not copied, because things are simpler for this thread: if it's running, there is no problem; if it's not, you will find the error in the Last_Error column (described below). This field is present beginning with MySQL 4.1.1. |
Master_Host | The current master host. |
Master_User | The current user used to connect to the master. |
Master_Port | The current master port. |
Connect_Retry | The current value of master-connect-retry. |
Master_Log_File | The name of the master's binlog file from which the I/O thread is currently reading. |
Read_Master_Log_Pos | The position which the I/O thread has read up to in this master's binlog. |
Relay_Log_File | The name of the relay log file from which the SQL thread is currently reading and executing. |
Relay_Log_Pos | The position which the SQL thread has read and executed up to in this relay log. |
Relay_Master_Log_File | The name of the master's binlog file that contains the last event executed by the SQL thread. |
Slave_IO_Running | Tells whether or not the I/O thread is started. |
Slave_SQL_Running | Tells whether or not the SQL thread is started. |
Replicate_Do_DB, Replicate_Ignore_DB | The lists of the databases that were specified with the --replicate-do-db and --replicate-ignore-db options, if any |
Replicate_Do_Table, Replicate_Ignore_Table, Replicate_Wild_Do_Table, Replicate_Wild_Ignore_Table | The lists of tables that were specified with the --replicate-do-table, --replicate-ignore-table, --replicate-wild-do-table, and --replicate-wild-ignore_table options, if any These fields are present beginning with MySQL 4.1.1. |
Last_Errno | The error number returned by the most recently executed query. A value of 0 means ``no error''. |
Last_Error |
The error message returned by the most recently executed query.
For example:
Last_Errno: 1051 Last_Error: error 'Unknown table 'z'' on query 'drop table z'The message indicates that the table z existed on the master and was dropped there, but it did not exist on the slave, so DROP TABLE failed on the slave. (This might occur if you forgot to copy the table to the slave when setting up replication.) The empty string means ``no error''. If the Last_Error value is not empty, it will also appear as a message in the slave's error log. |
Skip_Counter | The last used value for SQL_SLAVE_SKIP_COUNTER. |
Exec_Master_Log_Pos | The position in the master's binlog (Relay_Master_Log_File) of the last event executed by the SQL thread. ((Relay_Master_Log_File,Exec_Master_Log_Pos) in the master's binlog corresponds to (Relay_Log_File,Relay_Log_Pos) in the relay log). |
Relay_Log_Space | The total combined size of all existing relay logs. |
Until_Condition, Until_Log_File, Until_Log_Pos |
The values specified in the UNTIL clause of the START SLAVE
statement.
Until_Condition has these values:
|
Master_SSL_Allowed, Master_SSL_CA_File, Master_SSL_CA_Path, Master_SSL_Cert, Master_SSL_Cipher, Master_SSL_Key |
These fields show the
The SSL parameters used by the slave to connect to the master, if any.
Master_SSL_Allowed has these values:
|
Seconds_Behind_Master | The number of seconds that have elapsed since the timestamp of the last master's event executed by the slave SQL thread. Will be NULL when no event has been executed yet, or after CHANGE MASTER and RESET SLAVE. This column can be used to know how ``late'' your slave is. It will work even though your master and slave don't have identical clocks. This field is present beginning with MySQL 4.1.1. |
START SLAVE [thread_name [, thread_name] ... ] START SLAVE [SQL_THREAD] UNTIL MASTER_LOG_FILE = 'log_name', MASTER_LOG_POS = log_pos START SLAVE [SQL_THREAD] UNTIL RELAY_LOG_FILE = 'log_name', RELAY_LOG_POS = log_pos thread_name = IO_THREAD | SQL_THREAD
START SLAVE with no options starts both of the slave threads. The I/O thread reads queries from the master server and stores them in the relay log. The SQL thread reads the relay log and executes the queries. Note that if START SLAVE succeeds in starting the slave threads it will return without any error. But even in that case it might be that slave threads start and then later stop (because they don't manage to connect to the master or read his binlogs or any other problem). START SLAVE will not warn you about this. You must check your slave's error log for error messages generated by the slave threads, or check that these are running fine with SHOW SLAVE STATUS.
START SLAVE requires the SUPER privilege.
As of MySQL 4.0.2, you can add IO_THREAD or SQL_THREAD options to the statement to name which of the threads to start.
As of MySQL 4.1.1, an UNTIL clause may be added to specify that the slave should start until the SQL thread reaches a given point in the master binlogs or in the slave relay logs. When the SQL thread reaches that point, it stops. If the SQL_THREAD option is specified in the statement, it starts only the SQL thread. Otherwise, it starts both slave threads. If the SQL thread is already running, the UNTIL clause is ignored and a warning is issued.
With an UNTIL clause, you must specify both a log filename and position. Do not mix master and relay log options.
Any UNTIL condition is reset by a subsequent STOP SLAVE statement, or a START SLAVE statement that includes no UNTIL clause, or a server restart.
The UNTIL clause can be useful for debugging replication, or to cause replication to proceed until just before the point where you want to avoid having the slave replicated a statement. For example, if an unwise DROP TABLE statement was executed on the master, you can use UNTIL to tell the slave to execute up to that point but no farther. To find what the event is, use mysqlbinlog with the master logs or relay logs, or by using a SHOW BINLOG EVENTS statement.
If you are using UNTIL to have the slave process replicated queries in sections, it is recommended that you start the slave with the --skip-slave-start option to prevent the SQL thread from running when the slave starts. It's probably best to use this option in an option file rather than on the command line, so that an unexpected server restart does not cause it to be forgotten.
The SHOW SLAVE STATUS statement includes output fields that display the current values of the UNTIL condition.
This command is called SLAVE START before MySQL 4.0.5. For the moment, SLAVE START is still accepted for backward compatibility, but is deprecated.
STOP SLAVE [thread_name [, thread_name] ... ] thread_name = IO_THREAD | SQL_THREAD
Stops the slave threads. STOP SLAVE requires the SUPER privilege.
Like START SLAVE, this statement may be used with the IO_THREAD and SQL_THREAD options to name the thread or threads to stop.
This command is called SLAVE STOP before MySQL 4.0.5. For the moment, SLAVE STOP is still accepted for backward compatibility, but is deprecated.
MATCH (col1,col2,...) AGAINST (expr [IN BOOLEAN MODE | WITH QUERY EXPANSION] )
As of Version 3.23.23, MySQL has support for full-text indexing and searching. Full-text indexes in MySQL are an index of type FULLTEXT. FULLTEXT indexes are used with MyISAM tables only and can be created from CHAR, VARCHAR, or TEXT columns at CREATE TABLE time or added later with ALTER TABLE or CREATE INDEX. For large datasets, it will be much faster to load your data into a table that has no FULLTEXT index, then create the index with ALTER TABLE (or CREATE INDEX). Loading data into a table that already has a FULLTEXT index could be significantly slower.
Full-text searching is performed with the MATCH() function.
mysql> CREATE TABLE articles ( -> id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY, -> title VARCHAR(200), -> body TEXT, -> FULLTEXT (title,body) -> ); Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO articles VALUES -> (NULL,'MySQL Tutorial', 'DBMS stands for DataBase ...'), -> (NULL,'How To Use MySQL Efficiently', 'After you went through a ...'), -> (NULL,'Optimizing MySQL','In this tutorial we will show ...'), -> (NULL,'1001 MySQL Tricks','1. Never run mysqld as root. 2. ...'), -> (NULL,'MySQL vs. YourSQL', 'In the following database comparison ...'), -> (NULL,'MySQL Security', 'When configured properly, MySQL ...'); Query OK, 6 rows affected (0.00 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> SELECT * FROM articles -> WHERE MATCH (title,body) AGAINST ('database'); +----+-------------------+------------------------------------------+ | id | title | body | +----+-------------------+------------------------------------------+ | 5 | MySQL vs. YourSQL | In the following database comparison ... | | 1 | MySQL Tutorial | DBMS stands for DataBase ... | +----+-------------------+------------------------------------------+ 2 rows in set (0.00 sec)
The MATCH() function performs a natural language search for a string against a text collection (a set of one or more columns included in a FULLTEXT index). The search string is given as the argument to AGAINST(). The search is performed in case-insensitive fashion. For every row in the table, MATCH() returns a relevance value, that is, a similarity measure between the search string and the text in that row in the columns named in the MATCH() list.
When MATCH() is used in a WHERE clause (see example above) the rows returned are automatically sorted with highest relevance first. Relevance values are non-negative floating-point numbers. Zero relevance means no similarity. Relevance is computed based on the number of words in the row, the number of unique words in that row, the total number of words in the collection, and the number of documents (rows) that contain a particular word.
It is also possible to perform a boolean mode search. This is explained later in the section.
The preceding example is a basic illustration showing how to use the MATCH() function. Rows are returned in order of decreasing relevance.
The next example shows how to retrieve the relevance values explicitly. As neither WHERE nor ORDER BY clauses are present, returned rows are not ordered.
mysql> SELECT id,MATCH (title,body) AGAINST ('Tutorial') FROM articles; +----+-----------------------------------------+ | id | MATCH (title,body) AGAINST ('Tutorial') | +----+-----------------------------------------+ | 1 | 0.64840710366884 | | 2 | 0 | | 3 | 0.66266459031789 | | 4 | 0 | | 5 | 0 | | 6 | 0 | +----+-----------------------------------------+ 6 rows in set (0.00 sec)
The following example is more complex. The query returns the relevance and still sorts the rows in order of decreasing relevance. To achieve this result, you should specify MATCH() twice. This will cause no additional overhead, because the MySQL optimizer will notice that the two MATCH() calls are identical and invoke the full-text search code only once.
mysql> SELECT id, body, MATCH (title,body) AGAINST -> ('Security implications of running MySQL as root') AS score -> FROM articles WHERE MATCH (title,body) AGAINST -> ('Security implications of running MySQL as root'); +----+-------------------------------------+-----------------+ | id | body | score | +----+-------------------------------------+-----------------+ | 4 | 1. Never run mysqld as root. 2. ... | 1.5055546709332 | | 6 | When configured properly, MySQL ... | 1.31140957288 | +----+-------------------------------------+-----------------+ 2 rows in set (0.00 sec)
As of Version 4.1.1, full-text search supports query expansion (in particular, its variant ``blind query expansion''). It is generally useful when a search phrase is too short, which often means that the user is relying on implied knowledge that the full-text search engine usually lacks. For example, a user searching for ``database'' may really mean that ``MySQL'', ``Oracle'', ``DB2'', and ``RDBMS'' all are phrases that should match ``databases'' and should be returned, too. This is implied knowledge. Blind query expansion (also known as automatic relevance feedback) works by performing the search twice, where the search phrase for the second search is the original search phrase concatenated with the few top found documents from the first search. Thus, if one of these documents contained the word ``databases'' and the word ``MySQL'', then the second search will find the documents that contain the word ``MySQL'' but not ``database''. Another example could be searching for books by Georges Simenon about Maigret, when a user is not sure how to spell ``Maigret''. Then, searching for ``Megre and the reluctant witnesses'' will find only ``Maigret and the Reluctant Witnesses'' without query expansion, but all books with the word ``Maigret'' on the second pass of a search with query expansion. Note: Because blind query expansion tends to increase noise significantly, by returning non-relevant documents, it's only meaningful to use when a search phrase is rather short.
MySQL uses a very simple parser to split text into words. A ``word'' is any sequence of characters consisting of letters, digits, ', and _. Any ``word'' that is present in the stopword list or is just too short is ignored. The default minimum length of words that will be found by full-text searches is four characters. This can be changed as described in Fulltext Fine-tuning.
Every correct word in the collection and in the query is weighted according to its significance in the query or collection. This way, a word that is present in many documents will have lower weight (and may even have a zero weight), because it has lower semantic value in this particular collection. Otherwise, if the word is rare, it will receive a higher weight. The weights of the words are then combined to compute the relevance of the row.
Such a technique works best with large collections (in fact, it was carefully tuned this way). For very small tables, word distribution does not reflect adequately their semantic value, and this model may sometimes produce bizarre results.
mysql> SELECT * FROM articles WHERE MATCH (title,body) AGAINST ('MySQL'); Empty set (0.00 sec)
The search for the word MySQL produces no results in the above example, because that word is present in more than half the rows. As such, it is effectively treated as a stopword (that is, a word with zero semantic value). This is the most desirable behavior --- a natural language query should not return every second row from a 1 GB table.
A word that matches half of rows in a table is less likely to locate relevant documents. In fact, it will most likely find plenty of irrelevant documents. We all know this happens far too often when we are trying to find something on the Internet with a search engine. It is with this reasoning that such rows have been assigned a low semantic value in this particular dataset.
As of Version 4.0.1, MySQL can also perform boolean full-text searches using the IN BOOLEAN MODE modifier.
mysql> SELECT * FROM articles WHERE MATCH (title,body) -> AGAINST ('+MySQL -YourSQL' IN BOOLEAN MODE); +----+------------------------------+-------------------------------------+ | id | title | body | +----+------------------------------+-------------------------------------+ | 1 | MySQL Tutorial | DBMS stands for DataBase ... | | 2 | How To Use MySQL Efficiently | After you went through a ... | | 3 | Optimizing MySQL | In this tutorial we will show ... | | 4 | 1001 MySQL Tricks | 1. Never run mysqld as root. 2. ... | | 6 | MySQL Security | When configured properly, MySQL ... | +----+------------------------------+-------------------------------------+
This query retrieved all the rows that contain the word MySQL (note: the 50% threshold is not used), but that do not contain the word YourSQL. Note that a boolean mode search does not automatically sort rows in order of decreasing relevance. You can see this from result of the preceding query, where the row with the highest relevance (the one that contains MySQL twice) is listed last, not first. A boolean full-text search can also work even without a FULLTEXT index, although it would be slow.
The boolean full-text search capability supports the following operators:
+ | A leading plus sign indicates that this word must be present in every row returned. |
- | A leading minus sign indicates that this word must not be present in any row returned. |
By default (when neither plus nor minus is specified) the word is optional, but the rows that contain it will be rated higher. This mimicks the behavior of MATCH() ... AGAINST() without the IN BOOLEAN MODE modifier. | |
< > | These two operators are used to change a word's contribution to the relevance value that is assigned to a row. The < operator decreases the contribution and the > operator increases it. See the example below. |
( ) | Parentheses are used to group words into subexpressions. |
~ | A leading tilde acts as a negation operator, causing the word's contribution to the row relevance to be negative. It's useful for marking noise words. A row that contains such a word will be rated lower than others, but will not be excluded altogether, as it would be with the - operator. |
* | An asterisk is the truncation operator. Unlike the other operators, it should be appended to the word, not prepended. |
" | The phrase, that is enclosed in double quotes ", matches only rows that contain this phrase literally, as it was typed. |
And here are some examples:
apple banana | find rows that contain at least one of these words. |
+apple +juice | ... both words. |
+apple macintosh | ... word ``apple'', but rank it higher if it also contain ``macintosh''. |
+apple -macintosh | ... word ``apple'' but not ``macintosh''. |
+apple +(>turnover <strudel) | ... ``apple'' and ``turnover'', or ``apple'' and ``strudel'' (in any order), but rank ``apple pie'' higher than ``apple strudel''. |
apple* | ... ``apple'', ``apples'', ``applesauce'', and ``applet''. |
"some words" | ... ``some words of wisdom'', but not ``some noise words''. |
Full-text searches are supported for MyISAM tables only.
Full-text searches cannot be used with UCS-2 (but it works with UTF8 as of MySQL 4.1.1).
All parameters to the MATCH() function must be columns from the same table that is part of the same FULLTEXT index, unless the MATCH() is IN BOOLEAN MODE.
All columns in the FULLTEXT index must have the same character set.
The MATCH() column list must exactly match the column list in some FULLTEXT index definition for the table, unless this MATCH() is IN BOOLEAN MODE.
The argument to AGAINST() must be a constant string.
Unfortunately, full-text search has few user-tunable parameters yet, although adding some is very high on the TODO. If you have a MySQL source distribution (see Installing source), you can exert more control over full-text searching behavior.
Note that full-text search was carefully tuned for the best searching effectiveness. Modifying the default behavior will, in most cases, only make the search results worse. Do not alter the MySQL sources unless you know what you are doing!
The full-text variables described in the following list must be set at server startup time. You cannot modify them dynamically while the server is running.
The minimum length of words to be indexed is defined by the MySQL variable ft_min_word_len. See ft_min_word_len. (This variable is only available from MySQL version 4.0.) The default value is four characters. Change it to the value you prefer, and rebuild your FULLTEXT indexes. For example, if you want three-character words to be searchable, you can set this variable by putting the following lines in an option file:
[mysqld] ft_min_word_len=3
Then restart the server and rebuild your FULLTEXT indexes.
The stopword list can be loaded from the file specified by the ft_stopword_file variable. See ft_stopword_file. Rebuild your FULLTEXT indexes after modifying the stopword list. (This variable is only available from MySQL version 4.0.10 and onwards)
The 50% threshold is determined by the particular weighting scheme chosen. To disable it, change the following line in myisam/ftdefs.h:
#define GWS_IN_USE GWS_PROB
To:
#define GWS_IN_USE GWS_FREQ
Then recompile MySQL. There is no need to rebuild the indexes in this case. Note: By doing this you severely decrease MySQL's ability to provide adequate relevance values for the MATCH() function. If you really need to search for such common words, it would be better to search using IN BOOLEAN MODE instead, which does not observe the 50% threshold.
Sometimes the search engine maintainer would like to change the operators used for boolean full-text searches. These are defined by the ft_boolean_syntax variable. One needs a SUPER privilege to change it. See ft_boolean_syntax.
For full-text changes that require you to rebuild your FULLTEXT indexes, the easiest way to do so for a MyISAM table is to use the following statement, which rebuilds the index file:
mysql> REPAIR TABLE tbl_name QUICK;
Make all operations with FULLTEXT index faster.
Proximity operators
Support for "always-index words". They could be any strings the user wants to treat as words, examples are "C++", "AS/400", "TCP/IP", etc.
Support for full-text search in MERGE tables.
Support for UCS-2.
Make stopword list to depend of the language of the data.
Stemming (dependent of the language of the data).
Generic user-suppliable UDF preparser.
Make the model more flexible (by adding some adjustable parameters to FULLTEXT in CREATE/ALTER TABLE).
Table of Contents
From version 4.0.1, MySQL server features a Query Cache. When in use, the query cache stores the text of a SELECT query together with the corresponding result that was sent to the client. If an identical query is later received, the server will retrieve the results from the query cache rather than parsing and executing the same query again.
NOTE: The query cache does not return stale data. When data is modified, any relevant entries in the query cache are flushed.
The query cache is extremely useful in an environment where (some) tables don't change very often and you have a lot of identical queries. This is a typical situation for many web servers that use a lot of dynamic content.
Below is some performance data for the query cache. (These results were generated by running the MySQL benchmark suite on a Linux Alpha 2 x 500 MHz with 2 GB RAM and a 64 MB query cache):
If all of the queries you're performing are simple (such as selecting a row from a table with one row); but still differ so that the queries can not be cached, the overhead for having the query cache active is 13%. This could be regarded as the worst case scenario. However, in real life, queries are much more complicated than our simple example so the overhead is normally significantly lower.
Searches after one row in a one row table is 238% faster. This can be regarded as close to the minimum speedup to be expected for a query that is cached.
If you want to disable the query cache code set query_cache_size=0. By disabling the query cache code there is no noticeable overhead. (query cache can be excluded from code with help of configure option --without-query-cache)
Queries are compared before parsing, thus
SELECT * FROM tbl_name
and
Select * from tbl_name
are regarded as different queries for query cache, so queries need to be exactly the same (byte for byte) to be seen as identical. In addition, a query may be seen as different if for instance one client is using a new communication protocol format or another character set than another client.
Queries that uses different databases, uses different protocol versions or the uses different default character sets are considered different queries and cached separately.
The cache does work for SELECT SQL_CALC_FOUND_ROWS ... and SELECT FOUND_ROWS() ... type queries because the number of found rows is also stored in the cache.
If query result was returned from query cache then status variable Com_select will not be increased, but Qcache_hits will be. See Query Cache Status and Maintenance.
If a table changes (INSERT, UPDATE, DELETE, TRUNCATE, ALTER or DROP TABLE|DATABASE), then all cached queries that used this table (possibly through a MRG_MyISAM table!) become invalid and are removed from the cache.
Transactional InnoDB tables that have been changed will be invalidated when a COMMIT is performed.
In MySQL 4.0, the query cache is disabled inside of transactions (it does not return results). Beginning with MySQL 4.1.1, the query cache will also work inside of transactions when using InnoDB tables (it will use the table version number to detect if the data is still current or not).
Before MySQL 5.0, a query that begins with a leading comment might be cached, but could not be fetched from the cache. This problem is fixed in MySQL 5.0.
A query cannot be cached if it contains one of the functions:
Function | Function | Function |
User-Defined Functions | CONNECTION_ID | FOUND_ROWS |
GET_LOCK | RELEASE_LOCK | LOAD_FILE |
MASTER_POS_WAIT | NOW | SYSDATE |
CURRENT_TIMESTAMP | CURDATE | CURRENT_DATE |
CURTIME | CURRENT_TIME | DATABASE |
ENCRYPT (with one parameter) | LAST_INSERT_ID | RAND |
UNIX_TIMESTAMP (without parameters) | USER | BENCHMARK |
Nor can a query be cached if it contains user variables, references the mysql system database, is of the form SELECT ... IN SHARE MODE, SELECT ... INTO OUTFILE ..., SELECT ... INTO DUMPFILE ... or of the form SELECT * FROM AUTOINCREMENT_FIELD IS NULL (to retrieve last insert ID - ODBC work around).
However, FOUND_ROWS() will return the correct value, even if the preceding query was fetched from the cache.
In case a query does not use any tables, or uses temporary tables, or if the user has a column privilege for any of the involved tables, that query will not be cached.
Before a query is fetched from the query cache, MySQL will check that the user has SELECT privilege to all the involved databases and tables. If this is not the case, the cached result will not be used.
The query cache adds a few MySQL system variables for mysqld which may be set in a configuration file, on the command-line when starting mysqld.
query_cache_limit Don't cache results that are bigger than this. (Default 1M).
query_cache_min_res_unit
This variable is present from version 4.1.
The result of a query (the data that is also sent to the client) is stored in the query cache during result retrieval. Therefore the data is usually not handled in one big chunk. The query cache allocates blocks for storing this data on demand, so when one block is filled, a new block is allocated. Because memory allocation operation is costly (time wise), the query cache allocates blocks with a minimum size of query_cache_min_res_unit. When a query is executed, the last result block is trimmed to the actual data size, so that unused memory is freed.
The default value of query_cache_min_res_unit is 4 KB which should be adequate for most cases.
If you have a lot of queries with small results, the default block size may lead to memory fragmentation (indicated by a large number of free blocks (Qcache_free_blocks), which can cause the query cache to have to delete queries from the cache due to lack of memory (Qcache_lowmem_prunes)). In this case you should decrease query_cache_min_res_unit.
If you mostly have queres with big results (see Qcache_total_blocks and Qcache_queries_in_cache), you can increase performance by increasing query_cache_min_res_unit. However, be careful to not make it to large (see the previous point).
query_cache_size The amount of memory (specified in bytes) allocated to store results from old queries. If this is 0, the query cache is disabled (default).
query_cache_type This may be set (only numeric) to
Option | Description |
0 | (OFF, don't cache or retrieve results) |
1 | (ON, cache all results except SELECT SQL_NO_CACHE ... queries) |
2 | (DEMAND, cache only SELECT SQL_CACHE ... queries) |
Inside a thread (connection), the behavior of the query cache can be changed from the default. The syntax is as follows:
QUERY_CACHE_TYPE = OFF | ON | DEMAND QUERY_CACHE_TYPE = 0 | 1 | 2
Option | Description |
0 or OFF | Don't cache or retrieve results |
1 or ON | Cache all results except SELECT SQL_NO_CACHE ... queries |
2 or DEMAND | Cache only SELECT SQL_CACHE ... queries |
There are two possible query cache related parameters that may be specified in a SELECT query:
Option | Description |
SQL_CACHE | If QUERY_CACHE_TYPE is DEMAND, allow the query to be cached. If QUERY_CACHE_TYPE is ON, this is the default. If QUERY_CACHE_TYPE is OFF, do nothing. |
SQL_NO_CACHE | Make this query non-cachable, don't allow this query to be stored in the cache. |
With the FLUSH QUERY CACHE command you can defragment the query cache to better utilize its memory. This command will not remove any queries from the cache. FLUSH TABLES also flushes the query cache.
The RESET QUERY CACHE command removes all query results from the query cache.
You can check whether the query cache is present in your MySQL version:
mysql> SHOW VARIABLES LIKE 'have_query_cache'; +------------------+-------+ | Variable_name | Value | +------------------+-------+ | have_query_cache | YES | +------------------+-------+ 1 row in set (0.00 sec)
You can monitor query cache performance in SHOW STATUS:
Variable | Description |
Qcache_queries_in_cache | Number of queries registered in the cache. |
Qcache_inserts | Number of queries added to the cache. |
Qcache_hits | Number of cache hits. |
Qcache_lowmem_prunes | Number of queries that were deleted from cache because of low memory. |
Qcache_not_cached | Number of non-cached queries (not cachable, or due to QUERY_CACHE_TYPE). |
Qcache_free_memory | Amount of free memory for query cache. |
Qcache_free_blocks | Number of free memory blocks in query cache. |
Qcache_total_blocks | Total number of blocks in query cache. |
Total number of queries = Qcache_inserts + Qcache_hits + Qcache_not_cached.
The query cache uses variable length blocks, so Qcache_total_blocks and Qcache_free_blocks may indicate query cache memory fragmentation. After FLUSH QUERY CACHE only a single (big) free block remains.
Note: Every query needs a minimum of two blocks (one for the query text and one or more for the query results). Also, every table that is used by a query needs one block, but if two or more queries use same table only one block needs to be allocated.
You can use the Qcache_lowmem_prunes status variable to tune the query cache size. It counts the number of queries that have been removed from the cache to free up memory for caching new queries. The query cache uses a least recently used (LRU) strategy to decide which queries to remove from the cache.
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As of MySQL Version 3.23.6, you can choose between three basic table formats (ISAM, HEAP and MyISAM). Newer versions of MySQL support additional table types (InnoDB, or BDB), depending on how you compile it. A database may contain tables of different types.
When you create a new table, you can tell MySQL what type of table to create. The default table type is usually MyISAM.
MySQL will always create a .frm file to hold the table and column definitions. The table's index and data will be stored in one or more other files, depending on the table type.
If you try to use a table type that is not compiled-in or activated, MySQL will instead create a table of type MyISAM. This behavior is convenient when you want to copy tables between MySQL servers that support different table types. (Perhaps your master server supports transactional storage engines for increased safety, while the slave servers use only non-transactional storage engines for greater speed.)
This automatic change of table types can be confusing for new MySQL users. We plan to fix this by introducing warnings in the new client/server protocol in version 4.1 and generating a warning when a table type is automatically changed.
You can convert tables between different types with the ALTER TABLE statement. See ALTER TABLE.
Note that MySQL supports two different kinds of tables: transaction-safe tables (InnoDB and BDB) and not transaction-safe tables (HEAP, ISAM, MERGE, and MyISAM).
Advantages of transaction-safe tables (TST):
Safer. Even if MySQL crashes or you get hardware problems, you can get your data back, either by automatic recovery or from a backup + the transaction log.
You can combine many statements and accept these all in one go with the COMMIT command.
You can execute ROLLBACK to ignore your changes (if you are not running in auto-commit mode).
If an update fails, all your changes will be restored. (With NTST tables all changes that have taken place are permanent)
Can provide better concurrency if the table gets many updates concurrently with reads.
Note that to use InnoDB tables you have to use at least the innodb_data_file_path startup option. See InnoDB start.
Advantages of not transaction-safe tables (NTST):
Much faster as there is no transaction overhead.
Will use less disk space as there is no overhead of transactions.
Will use less memory to do updates.
You can combine TST and NTST tables in the same statements to get the best of both worlds.
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MyISAM is the default table type in MySQL Version 3.23. It's based on the ISAM code and has a lot of useful extensions.
The index is stored in a file with the .MYI (MYIndex) extension, and the data is stored in a file with the .MYD (MYData) extension. You can check/repair MyISAM tables with the myisamchk utility. See Crash recovery. You can compress MyISAM tables with myisampack to take up much less space. See myisampack.
The following is new in MyISAM:
There is a flag in the MyISAM file that indicates whether the table was closed correctly. If mysqld is started with --myisam-recover, MyISAM tables are automatically checked and/or repaired on open if the table wasn't closed properly.
You can INSERT new rows in a table that doesn't have free blocks in the middle of the datafile, at the same time other threads are reading from the table (concurrent insert). A free block can come from an update of a dynamic length row with much data to a row with less data or when deleting rows. When all free blocks are used up, all future inserts will be concurrent again.
Support for big files (63-bit) on filesystems/operating systems that support big files.
All data is stored with the low byte first. This makes the data machine and OS independent. The only requirement for binary portability is that the machine uses two's-complement signed integers (as every machine for the last 20 years has) and IEEE floating-point format (also totally dominant among mainstream machines). The only area of machines that may not support binary compatibility are embedded systems (because they sometimes have peculiar processors).
There is no big speed penalty in storing data low byte first; the bytes in a table row is normally unaligned and it doesn't take that much more power to read an unaligned byte in order than in reverse order. The actual fetch-column-value code is also not time critical compared to other code.
All number keys are stored with high byte first to give better index compression.
Internal handling of one AUTO_INCREMENT column. MyISAM will automatically update this on INSERT/UPDATE. The AUTO_INCREMENT value can be reset with myisamchk. This will make AUTO_INCREMENT columns faster (at least 10%) and old numbers will not be reused as with the old ISAM. Note that when an AUTO_INCREMENT is defined on the end of a multi-part-key the old behavior is still present.
When inserted in sorted order (as when you are using an AUTO_INCREMENT column) the key tree will be split so that the high node only contains one key. This will improve the space utilization in the key tree.
BLOB and TEXT columns can be indexed.
NULL values are allowed in indexed columns. This takes 0-1 bytes/key.
Maximum key length is 500 bytes by default (can be changed by recompiling). In cases of keys longer than 250 bytes, a bigger key block size than the default of 1024 bytes is used for this key.
Maximum number of keys/table is 32 as default. This can be enlarged to 64 without having to recompile myisamchk.
myisamchk will mark tables as checked if one runs it with --update-state. myisamchk --fast will check only those tables that don't have this mark.
myisamchk -a stores statistics for key parts (and not only for whole keys as in ISAM).
Dynamic size rows will now be much less fragmented when mixing deletes with updates and inserts. This is done by automatically combining adjacent deleted blocks and by extending blocks if the next block is deleted.
myisampack can pack BLOB and VARCHAR columns.
You can use put the datafile and index file on different directories to get more speed (with the DATA/INDEX DIRECTORY="path" option to CREATE TABLE). See CREATE TABLE.
MyISAM also supports the following things, which MySQL will be able to use in the near future:
Support for a true VARCHAR type; a VARCHAR column starts with a length stored in 2 bytes.
Tables with VARCHAR may have fixed or dynamic record length.
VARCHAR and CHAR may be up to 64K. All key segments have their own language definition. This will enable MySQL to have different language definitions per column.
A hashed computed index can be used for UNIQUE. This will allow you to have UNIQUE on any combination of columns in a table. (You can't search on a UNIQUE computed index, however.)
Note that index files are usually much smaller with MyISAM than with ISAM. This means that MyISAM will normally use less system resources than ISAM, but will need more CPU time when inserting data into a compressed index.
The following options to mysqld can be used to change the behavior of MyISAM tables. See SHOW VARIABLES.
Option | Description |
--myisam-recover=# | Automatic recovery of crashed tables. |
-O myisam_sort_buffer_size=# | Buffer used when recovering tables. |
--delay-key-write=ALL | Don't flush key buffers between writes for any MyISAM table |
-O myisam_max_extra_sort_file_size=# | Used to help MySQL to decide when to use the slow but safe key cache index create method. Note that this parameter is given in megabytes before 4.0.3 and in bytes beginning with this version. |
-O myisam_max_sort_file_size=# | Don't use the fast sort index method to created index if the temporary file would get bigger than this. Note that this parameter is given in megabytes before 4.0.3 and in bytes beginning with this version. |
-O bulk_insert_buffer_size=# | Size of tree cache used in bulk insert optimization. Note that this is a limit per thread! |
The automatic recovery is activated if you start mysqld with --myisam-recover=#. See Server options. On open, the table is checked if it's marked as crashed or if the open count variable for the table is not 0 and you are running with --skip-external-locking. If either of the above is true the following happens.
The table is checked for errors.
If we found an error, try to do a fast repair (with sorting and without re-creating the datafile) of the table.
If the repair fails because of an error in the datafile (for example a duplicate key error), we try again, but this time we re-create the datafile.
If the repair fails, retry once more with the old repair option method (write row by row without sorting) which should be able to repair any type of error with little disk requirements..
If the recover wouldn't be able to recover all rows from a previous completed statement and you didn't specify FORCE as an option to myisam-recover, then the automatic repair will abort with an error message in the error file:
Error: Couldn't repair table: test.g00pages
If you in this case had used the FORCE option you would instead have got a warning in the error file:
Warning: Found 344 of 354 rows when repairing ./test/g00pages
Note that if you run automatic recovery with the BACKUP option, you should have a cron script that automatically moves file with names like tablename-datetime.BAK from the database directories to a backup media.
See Server options.
MySQL can support different index types, but the normal type is ISAM or MyISAM. These use a B-tree index, and you can roughly calculate the size for the index file as (key_length+4)/0.67, summed over all keys. (This is for the worst case when all keys are inserted in sorted order and we don't have any compressed keys.)
String indexes are space compressed. If the first index part is a string, it will also be prefix compressed. Space compression makes the index file smaller than the above figures if the string column has a lot of trailing space or is a VARCHAR column that is not always used to the full length. Prefix compression is used on keys that start with a string. Prefix compression helps if there are many strings with an identical prefix.
In MyISAM tables, you can also prefix compress numbers by specifying PACK_KEYS=1 when you create the table. This helps when you have many integer keys that have an identical prefix when the numbers are stored high-byte first.
MyISAM supports 3 different table types. Two of them are chosen automatically depending on the type of columns you are using. The third, compressed tables, can only be created with the myisampack tool.
When you CREATE or ALTER a table that doesn't have BLOB values, you can force the table format to DYNAMIC or FIXED with the ROW_FORMAT=# table option. In the future you will be able to compress/decompress tables by specifying ROW_FORMAT=compressed | default to ALTER TABLE. See CREATE TABLE.
This is the default format. It's used when the table contains no VARCHAR, BLOB, or TEXT columns.
This format is the simplest and most secure format. It is also the fastest of the on-disk formats. The speed comes from the easy way data can be found on disk. When looking up something with an index and static format it is very simple. Just multiply the row number by the row length.
Also, when scanning a table it is very easy to read a constant number of records with each disk read.
The security is evidenced if your computer crashes when writing to a fixed-size MyISAM file, in which case myisamchk can easily figure out where each row starts and ends. So it can usually reclaim all records except the partially written one. Note that in MySQL all indexes can always be reconstructed:
All CHAR, NUMERIC, and DECIMAL columns are space-padded to the column width.
Very quick.
Easy to cache.
Easy to reconstruct after a crash, because records are located in fixed positions.
Doesn't have to be reorganized (with myisamchk) unless a huge number of records are deleted and you want to return free disk space to the operating system.
Usually requires more disk space than dynamic tables.
This format is used if the table contains any VARCHAR, BLOB, or TEXT columns or if the table was created with ROW_FORMAT=dynamic.
This format is a little more complex because each row has to have a header that says how long it is. One record can also end up at more than one location when it is made longer at an update.
You can use OPTIMIZE table or myisamchk to defragment a table. If you have static data that you access/change a lot in the same table as some VARCHAR or BLOB columns, it might be a good idea to move the dynamic columns to other tables just to avoid fragmentation:
All string columns are dynamic (except those with a length less than 4).
Each record is preceded by a bitmap indicating which columns are empty ('') for string columns, or zero for numeric columns. (This isn't the same as columns containing NULL values.) If a string column has a length of zero after removal of trailing spaces, or a numeric column has a value of zero, it is marked in the bit map and not saved to disk. Non-empty strings are saved as a length byte plus the string contents.
Usually takes much less disk space than fixed-length tables.
Each record uses only as much space as is required. If a record becomes larger, it is split into as many pieces as are required. This results in record fragmentation.
If you update a row with information that extends the row length, the row will be fragmented. In this case, you may have to run myisamchk -r from time to time to get better performance. Use myisamchk -ei tbl_name for some statistics.
Not as easy to reconstruct after a crash, because a record may be fragmented into many pieces and a link (fragment) may be missing.
The expected row length for dynamic sized records is:
3 + (number of columns + 7) / 8 + (number of char columns) + packed size of numeric columns + length of strings + (number of NULL columns + 7) / 8
There is a penalty of 6 bytes for each link. A dynamic record is linked whenever an update causes an enlargement of the record. Each new link will be at least 20 bytes, so the next enlargement will probably go in the same link. If not, there will be another link. You may check how many links there are with myisamchk -ed. All links may be removed with myisamchk -r.
This is a read-only type that is generated with the optional myisampack tool (pack_isam for ISAM tables):
All MySQL distributions, even those that existed before MySQL went GPL, can read tables that were compressed with myisampack.
Compressed tables take very little disk space. This minimises disk usage, which is very nice when using slow disks (such as CD-ROMs).
Each record is compressed separately (very little access overhead). The header for a record is fixed (1-3 bytes) depending on the biggest record in the table. Each column is compressed differently. Some of the compression types are:
There is usually a different Huffman table for each column.
Suffix space compression.
Prefix space compression.
Numbers with value 0 are stored using 1 bit.
If values in an integer column have a small range, the column is stored using the smallest possible type. For example, a BIGINT column (8 bytes) may be stored as a TINYINT column (1 byte) if all values are in the range 0 to 255.
If a column has only a small set of possible values, the column type is converted to ENUM.
A column may use a combination of the above compressions.
Can handle fixed- or dynamic-length records.
Can be uncompressed with myisamchk.
The file format that MySQL uses to store data has been extensively tested, but there are always circumstances that may cause database tables to become corrupted.
Even if the MyISAM table format is very reliable (all changes to a table is written before the SQL statements returns) , you can still get corrupted tables if some of the following things happens:
The mysqld process being killed in the middle of a write.
Unexpected shutdown of the computer (for example, if the computer is turned off).
A hardware error.
You are using an external program (such as myisamchk) on a live table.
A software bug in the MySQL or MyISAM code.
Typial typical symptoms for a corrupt table is:
You get the error Incorrect key file for table: '...'. Try to repair it while selecting data from the table.
Queries doesn't find rows in the table or returns incomplete data.
You can check if a table is ok with the command CHECK TABLE. See CHECK TABLE.
You can repair a corrupted table with REPAIR TABLE. See REPAIR TABLE. You can also repair a table, when mysqld is not running with the myisamchk command. myisamchk syntax.
If your tables get corrupted a lot you should try to find the reason for this! See Crashing.
In this case the most important thing to know is if the table got corrupted if the mysqld died (one can easily verify this by checking if there is a recent row restarted mysqld in the mysqld error file). If this isn't the case, then you should try to make a test case of this. See Reproduceable test case.
Each MyISAM .MYI file has in the header a counter that can be used to check if a table has been closed properly.
If you get the following warning from CHECK TABLE or myisamchk:
# clients is using or hasn't closed the table properly
this means that this counter has come out of sync. This doesn't mean that the table is corrupted, but means that you should at least do a check on the table to verify that it's okay.
The counter works as follows:
The first time a table is updated in MySQL, a counter in the header of the index files is incremented.
The counter is not changed during further updates.
When the last instance of a table is closed (because of a FLUSH or because there isn't room in the table cache) the counter is decremented if the table has been updated at any point.
When you repair the table or check the table and it was okay, the counter is reset to 0.
To avoid problems with interaction with other processes that may do a check on the table, the counter is not decremented on close if it was 0.
In other words, the only ways this can go out of sync are:
The MyISAM tables are copied without a LOCK and FLUSH TABLES.
MySQL has crashed between an update and the final close. (Note that the table may still be okay, as MySQL always issues writes for everything between each statement.)
Someone has done a myisamchk --recover or myisamchk --update-stateon a table that was in use by mysqld.
Many mysqld servers are using the table and one has done a REPAIR or CHECK of the table while it was in use by another server. In this setup the CHECK is safe to do (even if you will get the warning from other servers), but REPAIR should be avoided as it currently replaces the datafile with a new one, which is not signaled to the other servers.
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MERGE tables were introduced in MySQL Version 3.23.25. The code is now reasonably stable.
A MERGE table (also known as a MRG_MyISAM table) is a collection of identical MyISAM tables that can be used as one. You can only SELECT, DELETE, and UPDATE from the collection of tables. If you DROP the MERGE table, you are only dropping the MERGE specification.
Note that DELETE FROM merge_table used without a WHERE will clear only the mapping for the table, not delete everything in the mapped tables. (We plan to fix this in 4.1).
With identical tables we mean that all tables are created with identical column and key information. You can't merge tables in which the columns are packed differently, doesn't have exactly the same columns, or have the keys in different order. However, some of the tables can be compressed with myisampack. See myisampack.
When you create a MERGE table, you will get a .frm table definition file and a .MRG table list file. The .MRG just contains a list of the index files (.MYI files) that should be used as one. Before 4.1.1 all used tables had to be in the same database as the MERGE table itself.
For the moment, you need to have SELECT, UPDATE, and DELETE privileges on the tables you map to a MERGE table.
MERGE tables can help you solve the following problems:
Easily manage a set of log tables. For example, you can put data from different months into separate files, compress some of them with myisampack, and then create a MERGE to use these as one.
Give you more speed. You can split a big read-only table based on some criteria and then put the different table part on different disks. A MERGE table on this could be much faster than using the big table. (You can also use a RAID to get the same kind of benefits.)
Do more efficient searches. If you know exactly what you are looking after, you can search in just one of the split tables for some queries and use a MERGE table for others. You can even have many different MERGE tables active, with possible overlapping files.
More efficient repairs. It's easier to repair the individual files that are mapped to a MERGE file than trying to repair a really big file.
Instant mapping of many files as one. A MERGE table uses the index of the individual tables. It doesn't need to maintain an index of its one. This makes MERGE table collections VERY fast to make or remap. Note that you must specify the key definitions when you create a MERGE table!.
If you have a set of tables that you join to a big table on demand or batch, you should instead create a MERGE table on them on demand. This is much faster and will save a lot of disk space.
Go around the file-size limit for the operating system.
You can create an alias/synonym for a table by just using MERGE over one table. There shouldn't be any really notable performance impacts of doing this (only a couple of indirect calls and memcpy() calls for each read).
The disadvantages with MERGE tables are:
You can only use identical MyISAM tables for a MERGE table.
REPLACE doesn't work.
MERGE tables uses more file descriptors. If you are using a MERGE table that maps over 10 tables and 10 users are using this, you are using 10*10 + 10 file descriptors. (10 datafiles for 10 users and 10 shared index files.)
Key reads are slower. When you do a read on a key, the MERGE storage engine will need to issue a read on all underlying tables to check which one most closely matches the given key. If you then do a "read-next" then the MERGE storage engine will need to search the read buffers to find the next key. Only when one key buffer is used up, the storage engine will need to read the next key block. This makes MERGE keys much slower on eq_ref searches, but not much slower on ref searches. See EXPLAIN.
You can't do DROP TABLE, ALTER TABLE, DELETE FROM table_name without a WHERE clause, REPAIR TABLE, TRUNCATE TABLE, OPTIMIZE TABLE, or ANALYZE TABLE on any of the table that is mapped by a MERGE table that is "open". If you do this, the MERGE table may still refer to the original table and you will get unexpected results. The easiest way to get around this deficiency is to issue the FLUSH TABLES command, ensuring no MERGE tables remain "open".
When you create a MERGE table you have to specify with UNION=(list-of-tables) which tables you want to use as one. Optionally you can specify with INSERT_METHOD if you want insert for the MERGE table to happen in the first or last table in the UNION list. If you don't specify INSERT_METHOD or specify NO, then all INSERT commands on the MERGE table will return an error.
The following example shows you how to use MERGE tables:
CREATE TABLE t1 (a INT NOT NULL AUTO_INCREMENT PRIMARY KEY, message CHAR(20)); CREATE TABLE t2 (a INT NOT NULL AUTO_INCREMENT PRIMARY KEY, message CHAR(20)); INSERT INTO t1 (message) VALUES ("Testing"),("table"),("t1"); INSERT INTO t2 (message) VALUES ("Testing"),("table"),("t2"); CREATE TABLE total (a INT NOT NULL AUTO_INCREMENT, message CHAR(20), KEY(a)) TYPE=MERGE UNION=(t1,t2) INSERT_METHOD=LAST; SELECT * FROM total;
Note that we didn't create a UNIQUE or PRIMARY KEY in the total table as the key isn't going to be unique in the total table.
Note that you can also manipulate the .MRG file directly from the outside of the MySQL server:
shell> cd /mysql-data-directory/current-database shell> ls -1 t1.MYI t2.MYI > total.MRG shell> mysqladmin flush-tables
Now you can do things like:
mysql> SELECT * FROM total; +---+---------+ | a | message | +---+---------+ | 1 | Testing | | 2 | table | | 3 | t1 | | 1 | Testing | | 2 | table | | 3 | t2 | +---+---------+
Note that the a column, though declared as PRIMARY KEY, is not really unique, as MERGE table cannot enforce uniqueness over a set of underlying MyISAM tables.
To remap a MERGE table you can do one of the following:
DROP the table and re-create it
Use ALTER TABLE table_name UNION=(...)
Change the .MRG file and issue a FLUSH TABLE on the MERGE table and all underlying tables to force the storage engine to read the new definition file.
If you use ALTER TABLE to change a MERGE table to another table type, the mapping to the underlying tables is lost. Instead, the rows from the underlying MyISAM tables are copied into the altered table, which then is assigned the new type.
The following are the known problems with MERGE tables:
A MERGE table cannot maintain UNIQUE constraints over the whole table. When you do INSERT, the data goes into the first or last table (according to INSERT_METHOD=xxx) and this MyISAM table ensures that the data are unique, but it knows nothing about others MyISAM tables.
DELETE FROM merge_table used without a WHERE will clear only the mapping for the table, not delete everything in the mapped tables.
RENAME TABLE on a table used in an active MERGE table may corrupt the table. This will be fixed in MySQL 4.1.x.
Creation of a table of type MERGE doesn't check if the underlying tables are of compatible types or if they exists. MySQL will do a quick check if the record length is equal between mapped tables when the MERGE table is used, but this is not a fullproof check.
If you use MERGE tables in this fashion, you are very likely to run into strange problems.
If you use ALTER TABLE to first add an UNIQUE index to a table used in a MERGE table and then use ALTER TABLE to add a normal index on the MERGE table, the key order will be different for the tables if there was an old non-unique key in the table. This is because ALTER TABLE puts UNIQUE keys before normal keys to be able to detect duplicate keys as early as possible.
DROP TABLE on a table that is in use by a MERGE table will not work on Windows because the MERGE storage engine does the table mapping hidden from the upper layer of MySQL. Because Windows doesn't allow you to drop files that are open, you first must flush all MERGE tables (with FLUSH TABLES) or drop the MERGE table before dropping the table. We will fix this at the same time we introduce views.
HEAP tables use hashed indexes and are stored in memory. This makes them very fast, but if MySQL crashes you will lose all data stored in them. HEAP is very useful for temporary tables!
The MySQL internal HEAP tables use 100% dynamic hashing without overflow areas. There is no extra space needed for free lists. HEAP tables also don't have problems with delete + inserts, which normally is common with hashed tables:
mysql> CREATE TABLE test TYPE=HEAP SELECT ip,SUM(downloads) AS down -> FROM log_table GROUP BY ip; mysql> SELECT COUNT(ip),AVG(down) FROM test; mysql> DROP TABLE test;
Here are some things you should consider when you use HEAP tables:
You should always use specify MAX_ROWS in the CREATE statement to ensure that you accidentally do not use all memory.
Indexes will be used only with = and <=> (but are VERY fast).
HEAP tables can use only whole keys to search for a row; compare this to MyISAM tables where any prefix of the key can be used to find rows.
HEAP tables use a fixed record length format.
HEAP doesn't support BLOB/TEXT columns.
HEAP doesn't support AUTO_INCREMENT columns.
Prior to MySQL 4.0.2, HEAP doesn't support an index on a NULL column.
You can have non-unique keys in a HEAP table (this isn't common for hashed tables).
HEAP tables are shared between all clients (just like any other table).
You can't search for the next entry in order (that is, to use the index to do an ORDER BY).
Data for HEAP tables are allocated in small blocks. The tables are 100% dynamic (on inserting). No overflow areas and no extra key space are needed. Deleted rows are put in a linked list and are reused when you insert new data into the table.
You need enough extra memory for all HEAP tables that you want to use at the same time.
To free memory, you should execute DELETE FROM heap_table, TRUNCATE heap_table or DROP TABLE heap_table.
MySQL cannot find out approximately how many rows there are between two values (this is used by the range optimizer to decide which index to use). This may affect some queries if you change a MyISAM table to a HEAP table.
To ensure that you accidentally don't do anything foolish, you can't create HEAP tables bigger than max_heap_table_size.
If you have a hash index on a HEAP table with a high degree of key duplication (many index entries containing the same value), updates to the table that affect key values and all deletes will be significantly slower. The degree of slowdown is proportional to the degree of duplication (or, inversely proportional to the index cardinality). As of 4.1, MySQL supports BTREE indexes on HEAP tables, which you can use to avoid this problem.
If you want to populate the HEAP table when the MySQL server starts, you can use the init-file option for this (see Server options) (into the file you will for example put a LOAD DATA INFILE or INSERT...SELECT to load the table from some persistent storage location).
With replication: after the master is shutdown and restarted, the HEAP table is empty on master; the slave is not aware of this emptiness, so will still return out-of-date content if you issue a SELECT on the table. But (starting from MySQL 4.0.18) when the HEAP table is used on master for the first time since master's startup, a DELETE FROM statement will be automatically written to the master's binary log, thus syncing the slave. Note that even with this, between the master's restart and the first use of the table on master, the slave still has out-of-date data in the table. But if you use the init-file option to populate the HEAP table on the master at startup, it ensures that the failing time interval is zero.
The memory needed for one row in a HEAP table is:
SUM_OVER_ALL_KEYS(max_length_of_key + sizeof(char*) * 2) + ALIGN(length_of_row+1, sizeof(char*))
sizeof(char*) is 4 on 32-bit machines and 8 on 64-bit machines.
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InnoDB provides MySQL with a transaction-safe (ACID compliant) storage engine with commit, rollback, and crash recovery capabilities. InnoDB does locking on row level and also provides an Oracle-style consistent non-locking read in SELECT statements. These features increase multiuser concurrency and performance. There is no need for lock escalation in InnoDB, because row level locks in InnoDB fit in very small space. InnoDB is the first storage manager in MySQL to support FOREIGN KEY constraints.
InnoDB has been designed for maximum performance when processing large data volumes. Its CPU efficiency is probably not matched by any other disk-based relational database engine.
InnoDB is used in production at numerous large database sites requiring high performance. The famous Internet news site Slashdot.org runs on InnoDB. Mytrix, Inc. stores over 1 TB of data in InnoDB, and another site handles an average load of 800 inserts/updates per second in InnoDB.
Technically, InnoDB is a complete database backend placed under MySQL. InnoDB has its own buffer pool for caching data and indexes in main memory. InnoDB stores its tables and indexes in a tablespace, which may consist of several files (or raw disk partitions). This is different from, for example, MyISAM tables where each table is stored as a separate file. InnoDB tables can be of any size even on operating systems where file-size is limited to 2 GB.
You can find the latest information about InnoDB at http://www.innodb.com/. The most up-to-date version of the InnoDB manual is always placed there.
InnoDB is published under the same GNU GPL License Version 2 (of June 1991) as MySQL. If you distribute MySQL/InnoDB, and your application does not satisfy the restrictions of the GPL license, you have to buy a commercial MySQL Pro license from https://order.mysql.com/?sub=pg&pg_no=1.
From MySQL version 4.0, InnoDB is enabled by default. The following information only applies to the 3.23 series.
InnoDB tables are included in the MySQL source distribution starting from 3.23.34a and are activated in the MySQL -Max binary of the 3.23 series. For Windows, the MySQL-Max binaries are included in the standard distribution.
If you have downloaded a binary version of MySQL that includes support for InnoDB, simply follow the instructions of the MySQL manual for installing a binary version of MySQL. If you already have MySQL-3.23 installed, then the simplest way to install MySQL -Max is to replace the server executable mysqld with the corresponding executable in the -Max distribution. MySQL and MySQL -Max differ only in the server executable. See Installing binary. See mysqld-max.
To compile MySQL with InnoDB support, download MySQL-3.23.34a or newer version from http://www.mysql.com/ and configure MySQL with the --with-innodb option. See the MySQL manual about installing a MySQL source distribution. See Installing source.
cd /path/to/source/of/mysql-3.23.37 ./configure --with-innodb
To use InnoDB tables in MySQL-Max-3.23 you must specify configuration parameters in the [mysqld] section of the configuration file my.cnf, or on Windows optionally in my.ini.
At the minimum, in 3.23 you must specify innodb_data_file_path where you specify the names and the sizes of datafiles. If you do not mention innodb_data_home_dir in my.cnf the default is to create these files to the datadir of MySQL. If you specify innodb_data_home_dir as an empty string, then you can give absolute paths to your datafiles in innodb_data_file_path.
The minimal way to modify it is to add to the [mysqld] section the line
innodb_data_file_path=ibdata:30M
but to get good performance it is best that you specify options as recommended. See InnoDB start.
To enable InnoDB tables in MySQL version 3.23, see InnoDB in MySQL 3.23.
In MySQL-4.0 you are not required to do anything specific to enable InnoDB tables.
The default behavior in MySQL-4.0 and MySQL-4.1 is to create an auto-extending 10 MB file ibdata1 in the datadir of MySQL and two 5 MB ib_logfile log files to the datadir. (In MySQL-4.0.0 and 4.0.1 the datafile is 64 MB and not auto-extending.)
Note: To get good performance you should explicitly set the InnoDB parameters listed in the following examples.
If you don't want to use InnoDB tables, you can add the skip-innodb option to your MySQL option file.
Starting from versions 3.23.50 and 4.0.2, InnoDB allows the last datafile on the innodb_data_file_path line to be specified as auto-extending. The syntax for innodb_data_file_path is then the following:
pathtodatafile:sizespecification;pathtodatafile:sizespecification;... ... ;pathtodatafile:sizespecification[:autoextend[:max:sizespecification]]
If you specify the last datafile with the autoextend option, InnoDB will extend the last datafile if it runs out of free space in the tablespace. The increment is 8 MB at a time. An example:
innodb_data_home_dir = innodb_data_file_path = /ibdata/ibdata1:100M:autoextend
instructs InnoDB to create just a single datafile whose initial size is 100 MB and which is extended in 8 MB blocks when space runs out. If the disk becomes full you may want to add another datafile to another disk, for example. Then you have to look at the size of ibdata1, round the size downward to the closest multiple of 1024 * 1024 bytes (= 1 MB), and specify the rounded size of ibdata1 explicitly in innodb_data_file_path. After that you can add another datafile:
innodb_data_home_dir = innodb_data_file_path = /ibdata/ibdata1:988M;/disk2/ibdata2:50M:autoextend
Be cautious on filesystems where the maximum file-size is 2 GB. InnoDB is not aware of the OS maximum file-size. On those filesystems you might want to specify the max size for the datafile:
innodb_data_home_dir = innodb_data_file_path = /ibdata/ibdata1:100M:autoextend:max:2000M
A simple my.cnf example. Suppose you have a computer with 128 MB RAM and one hard disk. Below is an example of possible configuration parameters in my.cnf or my.ini for InnoDB. We assume you are running MySQL-Max-3.23.50 or later, or MySQL-4.0.2 or later. This example suits most users, both on Unix and Windows, who do not want to distribute InnoDB datafiles and log files on several disks. This creates an auto-extending datafile ibdata1 and two InnoDB log files ib_logfile0 and ib_logfile1 to the datadir of MySQL (typically /mysql/data). Also the small archived InnoDB log file ib_arch_log_0000000000 ends up in the datadir.
[mysqld] # You can write your other MySQL server options here # ... # Datafile(s) must be able to # hold your data and indexes. # Make sure you have enough # free disk space. innodb_data_file_path = ibdata1:10M:autoextend # Set buffer pool size to # 50 - 80 % of your computer's # memory set-variable = innodb_buffer_pool_size=70M set-variable = innodb_additional_mem_pool_size=10M # Set the log file size to about # 25 % of the buffer pool size set-variable = innodb_log_file_size=20M set-variable = innodb_log_buffer_size=8M # Set ..flush_log_at_trx_commit # to 0 if you can afford losing # some last transactions innodb_flush_log_at_trx_commit=1
Check that the MySQL server has the rights to create files in datadir.
Note that datafiles must be < 2 GB in some file systems! The combined size of the log files must be < 4 GB. The combined size of datafiles must be >= 10 MB.
When you for the first time create an InnoDB database, it is best that you start the MySQL server from the command prompt. Then InnoDB will print the information about the database creation to the screen, and you see what is happening. See below next section what the printout should look like. For example, in Windows you can start mysqld-max.exe with:
your-path-to-mysqld\mysqld-max --console
Where to put my.cnf or my.ini in Windows? The rules for Windows are the following:
Only one of my.cnf or my.ini should be created.
The my.cnf file should be placed in the root directory of the drive C:.
The my.ini file should be placed in the WINDIR directory, e.g, C:\WINDOWS or C:\WINNT. You can use the SET command of MS-DOS to print the value of WINDIR.
If your PC uses a boot loader where the C: drive is not the boot drive, then your only option is to use the my.ini file.
Where to specify options in Unix? On Unix, mysqld reads options from the following files, if they exist, in the following order:
/etc/my.cnf Global options.
COMPILATION_DATADIR/my.cnf Server-specific options.
defaults-extra-file The file specified with --defaults-extra-file=....
~/.my.cnf User-specific options.
COMPILATION_DATADIR is the MySQL data directory which was specified as a ./configure option when mysqld was compiled (typically /usr/local/mysql/data for a binary installation or /usr/local/var for a source installation).
If you are not sure from where mysqld reads its my.cnf or my.ini, you can give the path as the first command-line option to the server: mysqld --defaults-file=your_path_to_my_cnf.
InnoDB forms the directory path to a datafile by textually catenating innodb_data_home_dir to a datafile name or path in innodb_data_file_path, adding a possible slash or backslash in between if needed. If the keyword innodb_data_home_dir is not mentioned in my.cnf at all, the default for it is the 'dot' directory ./ which means the datadir of MySQL.
An advanced my.cnf example. Suppose you have a Linux computer with 2 GB RAM and three 60 GB hard disks (at directory paths /, /dr2 and /dr3). Below is an example of possible configuration parameters in my.cnf for InnoDB.
Note that InnoDB does not create directories: you have to create them yourself. Use the Unix or MS-DOS mkdir command to create the data and log group home directories.
[mysqld] # You can write your other MySQL server options here # ... innodb_data_home_dir = # Datafiles must be able to # hold your data and indexes innodb_data_file_path = /ibdata/ibdata1:2000M;/dr2/ibdata/ibdata2:2000M:autoextend # Set buffer pool size to # 50 - 80 % of your computer's # memory, but make sure on Linux # x86 total memory usage is # < 2 GB set-variable = innodb_buffer_pool_size=1G set-variable = innodb_additional_mem_pool_size=20M innodb_log_group_home_dir = /dr3/iblogs # .._log_arch_dir must be the same # as .._log_group_home_dir innodb_log_arch_dir = /dr3/iblogs set-variable = innodb_log_files_in_group=3 # Set the log file size to about # 15 % of the buffer pool size set-variable = innodb_log_file_size=150M set-variable = innodb_log_buffer_size=8M # Set ..flush_log_at_trx_commit to # 0 if you can afford losing # some last transactions innodb_flush_log_at_trx_commit=1 set-variable = innodb_lock_wait_timeout=50 #innodb_flush_method=fdatasync #set-variable = innodb_thread_concurrency=5
Note that we have placed the two datafiles on different disks. InnoDB will fill the tablespace formed by the datafiles from bottom up. In some cases it will improve the performance of the database if all data is not placed on the same physical disk. Putting log files on a different disk from data is very often beneficial for performance. You can also use raw disk partitions (raw devices) as datafiles. In some Unixes they speed up I/O. See the manual section on InnoDB file space management about how to specify them in my.cnf.
Warning: On Linux x86 you must be careful you do not set memory usage too high. glibc will allow the process heap to grow over thread stacks, which will crash your server. It is a risk if the value of
innodb_buffer_pool_size + key_buffer + max_connections * (sort_buffer + read_buffer_size) + max_connections * 2 MB
is close to 2 GB or exceeds 2 GB. Each thread will use a stack (often 2 MB, but in MySQL AB binaries only 256 KB) and in the worst case also sort_buffer + read_buffer_size additional memory.
How to tune other mysqld server parameters? Typical values which suit most users are:
skip-locking set-variable = max_connections=200 set-variable = read_buffer_size=1M set-variable = sort_buffer=1M # Set key_buffer to 5 - 50% # of your RAM depending on how # much you use MyISAM tables, but # keep key_buffer + InnoDB # buffer pool size < 80% of # your RAM set-variable = key_buffer=...
Note that some parameters are given using the numeric my.cnf parameter format: set-variable = innodb... = 123, others (string and boolean parameters) with another format: innodb_... = ... .
The meanings of the configuration parameters are the following:
Option | Description |
innodb_file_per_table | Available starting from 4.1.1. This option makes InnoDB to store each created table into its own .ibd file. See the section about multiple tablespaces. |
innodb_open_files | Available starting from 4.1.1. This is relevant only if you use multiple tablespaces in InnoDB. This specifies the maximum how many .ibd files InnoDB can keep open at one time. The minimum value for this is 10. The default is 300. Numeric my.cnf parameter format. |
innodb_data_home_dir | The common part of the directory path for all InnoDB datafiles. If you do not mentioned this option in my.cnf the default is the datadir of MySQL. You can specify this also as an empty string, in which case you can use absolute file paths in innodb_data_file_path. |
innodb_data_file_path | Paths to individual datafiles and their sizes. The full directory path to each datafile is acquired by concatenating innodb_data_home_dir to the paths specified here. The file sizes are specified in megabytes, hence the 'M' after the size specification above. InnoDB also understands the abbreviation 'G', 1 G meaning 1024 MB. Starting from 3.23.44 you can set the file-size bigger than 4 GB on those operating systems which support big files. On some operating systems files must be < 2 GB. If you do not specify innodb_data_file_path, the default behavior starting from 4.0 is to create a 10 MB auto-extending datafile ibdata1. The sum of the sizes of the files must be at least 10 MB. |
innodb_mirrored_log_groups | Number of identical copies of log groups we keep for the database. Currently this should be set to 1. |
innodb_log_group_home_dir | Directory path to InnoDB log files. If you do not mentioned this option in my.cnf the default is the datadir of MySQL. |
innodb_log_files_in_group | Number of log files in the log group. InnoDB writes to the files in a circular fashion. Value 2 is recommended here. The default is 2. |
innodb_log_file_size | Size of each log file in a log group in megabytes. Sensible values range from 1M to 1/n-th of the size of the buffer pool specified below, where n is the number of log files in the group. The larger the value, the less checkpoint flush activity is needed in the buffer pool, saving disk I/O. But larger log files also mean that recovery will be slower in case of a crash. The combined size of log files must be less than 4 GB on 32-bit computers. The default is 5M. |
innodb_log_buffer_size | The size of the buffer which InnoDB uses to write log to the log files on disk. Sensible values range from 1M to 8M. A big log buffer allows large transactions to run without a need to write the log to disk until the transaction commit. Thus, if you have big transactions, making the log buffer big will save disk I/O. |
innodb_flush_log_at_trx_commit | Normally you set this to 1, meaning that at a transaction commit, the log is flushed to disk, and the modifications made by the transaction become permanent, and survive a database crash. If you are willing to compromise this safety, and you are running small transactions, you may set this to 0 or 2 to reduce disk I/O to the logs. Value 0 means that the log is only written to the log file and the log file flushed to disk approximately once per second. Value 2 means the log is written to the log file at each commit, but the log file is only flushed to disk approximately once per second. The default value is 1 starting from MySQL-4.0.13; previously it was 0. |
innodb_log_arch_dir | The directory where fully written log files would be archived if we used log archiving. The value of this parameter should currently be set the same as innodb_log_group_home_dir. |
innodb_log_archive | This value should currently be set to 0. As recovery from a backup is done by MySQL using its own log files, there is currently no need to archive InnoDB log files. |
innodb_buffer_pool_size | The size of the memory buffer InnoDB uses to cache data and indexes of its tables. The larger you set this, the less disk I/O is needed to access data in tables. On a dedicated database server you may set this parameter up to 80% of the machine physical memory size. Do not set it too large, though, because competition of the physical memory might cause paging in the operating system. |
innodb_buffer_pool_awe_mem_mb | Size of the buffer pool in MB, if it is placed in the AWE memory of 32-bit Windows. Available starting from 4.1.0 and only relevant in 32-bit Windows. If your 32-bit Windows operating system supports > 4 GB memory, so-called Address Windowing Extensions, you can allocate the InnoDB buffer pool into the AWE physical memory using this parameter. The maximum possible value for this is 64000. If this parameter is specified, then innodb_buffer_pool_size is the window in the 32-bit address space of mysqld where InnoDB maps that AWE memory. A good value for innodb_buffer_pool_size is then 500M. |
innodb_additional_mem_pool_size | Size of a memory pool InnoDB uses to store data dictionary information and other internal data structures. A sensible value for this might be 2M, but the more tables you have in your application the more you will need to allocate here. If InnoDB runs out of memory in this pool, it will start to allocate memory from the operating system, and write warning messages to the MySQL error log. |
innodb_file_io_threads | Number of file I/O threads in InnoDB. Normally, this should be 4, but on Windows disk I/O may benefit from a larger number. |
innodb_lock_wait_timeout | Timeout in seconds an InnoDB transaction may wait for a lock before being rolled back. InnoDB automatically detects transaction deadlocks in its own lock table and rolls back the transaction. If you use the LOCK TABLES command, or other transaction-safe storage engines than InnoDB in the same transaction, then a deadlock may arise which InnoDB cannot notice. In cases like this the timeout is useful to resolve the situation. |
innodb_flush_method | (Available from 3.23.40 up.) The default value for this is fdatasync. Another option is O_DSYNC. |
innodb_force_recovery | Warning: This option should be defined only in an emergency situation when you want to dump your tables from a corrupt database! Possible values are 1 - 6. See below at section 'Forcing recovery' about the meanings of the values. As a safety measure InnoDB prevents a user from modifying data when this option is > 0. This option is available starting from version 3.23.44. |
Suppose you have installed MySQL and have edited my.cnf so that it contains the necessary InnoDB configuration parameters. Before starting MySQL you should check that the directories you have specified for InnoDB datafiles and log files exist and that you have access rights to those directories. InnoDB cannot create directories, only files. Check also you have enough disk space for the data and log files.
When you now start MySQL, InnoDB will start creating your datafiles and log files. InnoDB will print something like the following:
~/mysqlm/sql > mysqld InnoDB: The first specified datafile /home/heikki/data/ibdata1 did not exist: InnoDB: a new database to be created! InnoDB: Setting file /home/heikki/data/ibdata1 size to 134217728 InnoDB: Database physically writes the file full: wait... InnoDB: datafile /home/heikki/data/ibdata2 did not exist: new to be created InnoDB: Setting file /home/heikki/data/ibdata2 size to 262144000 InnoDB: Database physically writes the file full: wait... InnoDB: Log file /home/heikki/data/logs/ib_logfile0 did not exist: new to be created InnoDB: Setting log file /home/heikki/data/logs/ib_logfile0 size to 5242880 InnoDB: Log file /home/heikki/data/logs/ib_logfile1 did not exist: new to be created InnoDB: Setting log file /home/heikki/data/logs/ib_logfile1 size to 5242880 InnoDB: Log file /home/heikki/data/logs/ib_logfile2 did not exist: new to be created InnoDB: Setting log file /home/heikki/data/logs/ib_logfile2 size to 5242880 InnoDB: Started mysqld: ready for connections
A new InnoDB database has now been created. You can connect to the MySQL server with the usual MySQL client programs like mysql. When you shut down the MySQL server with mysqladmin shutdown, InnoDB output will be like the following:
010321 18:33:34 mysqld: Normal shutdown 010321 18:33:34 mysqld: Shutdown Complete InnoDB: Starting shutdown... InnoDB: Shutdown completed
You can now look at the datafiles and logs directories and you will see the files created. The log directory will also contain a small file named ib_arch_log_0000000000. That file resulted from the database creation, after which InnoDB switched off log archiving. When MySQL is again started, the output will be like the following:
~/mysqlm/sql > mysqld InnoDB: Started mysqld: ready for connections
If InnoDB prints an operating system error in a file operation, usually the problem is one of the following:
You did not create InnoDB data or log directories.
mysqld does not have the rights to create files in those directories.
mysqld does not read the right my.cnf or my.ini file, and consequently does not see the options you specified.
The disk is full or a disk quota is exceeded.
You have created a subdirectory whose name is equal to a datafile you specified.
There is a syntax error in innodb_data_home_dir or innodb_data_file_path.
If something goes wrong in an InnoDB database creation, you should delete all files created by InnoDB. This means all datafiles, all log files, the small archived log file, and in the case you already did create some InnoDB tables, delete also the corresponding .frm files for these tables from the MySQL database directories. Then you can try the InnoDB database creation again.
Suppose you have started the MySQL client with the command mysql test. To create a table in the InnoDB format you must specify TYPE = InnoDB in the table creation SQL command:
CREATE TABLE CUSTOMER (A INT, B CHAR (20), INDEX (A)) TYPE = InnoDB;
This SQL command will create a table and an index on column A into the InnoDB tablespace consisting of the datafiles you specified in my.cnf. In addition MySQL will create a file CUSTOMER.frm to the MySQL database directory test. Internally, InnoDB will add to its own data dictionary an entry for table 'test/CUSTOMER'. Thus you can create a table of the same name CUSTOMER in another database of MySQL, and the table names will not collide inside InnoDB.
You can query the amount of free space in the InnoDB tablespace by issuing the table status command of MySQL for any table you have created with TYPE = InnoDB. Then the amount of free space in the tablespace appears in the table comment section in the output of SHOW. An example:
SHOW TABLE STATUS FROM test LIKE 'CUSTOMER'
Note that the statistics SHOW gives about InnoDB tables are only approximate: they are used in SQL optimization. Table and index reserved sizes in bytes are accurate, though.
InnoDB does not have a special optimization for separate index creation. Therefore it does not pay to export and import the table and create indexes afterwards. The fastest way to alter a table to InnoDB is to do the inserts directly to an InnoDB table, that is, use ALTER TABLE ... TYPE=INNODB, or create an empty InnoDB table with identical definitions and insert the rows with INSERT INTO ... SELECT * FROM ....
To get better control over the insertion process, it may be good to insert big tables in pieces:
INSERT INTO newtable SELECT * FROM oldtable WHERE yourkey > something AND yourkey <= somethingelse;
After all data has been inserted you can rename the tables.
During the conversion of big tables you should set the InnoDB buffer pool size big to reduce disk I/O. Not bigger than 80% of the physical memory, though. You should set InnoDB log files big, and also the log buffer large.
Make sure you do not run out of tablespace: InnoDB tables take a lot more space than MyISAM tables. If an ALTER TABLE runs out of space, it will start a rollback, and that can take hours if it is disk-bound. In inserts InnoDB uses the insert buffer to merge secondary index records to indexes in batches. That saves a lot of disk I/O. In rollback no such mechanism is used, and the rollback can take 30 times longer than the insertion.
In the case of a runaway rollback, if you do not have valuable data in your database, it is better that you kill the database process and delete all InnoDB datafiles and log files and all InnoDB table .frm files, and start your job again, rather than wait for millions of disk I/Os to complete.
Starting from version 3.23.43b InnoDB features foreign key constraints. InnoDB is the first MySQL table type which allows you to define foreign key constraints to guard the integrity of your data.
The syntax of a foreign key constraint definition in InnoDB:
[CONSTRAINT [symbol]] FOREIGN KEY (index_col_name, ...) REFERENCES table_name (index_col_name, ...) [ON DELETE {CASCADE | SET NULL | NO ACTION | RESTRICT}] [ON UPDATE {CASCADE | SET NULL | NO ACTION | RESTRICT}]
Both tables have to be InnoDB type, in the table there must be an INDEX where the foreign key columns are listed as the FIRST columns in the same order, and in the referenced table there must be an INDEX where the referenced columns are listed as the FIRST columns in the same order. InnoDB does not auto-create indexes on foreign keys or referenced keys: you have to create them explicitly. The indexes are needed for foreign key checks to be fast and not require a table scan.
Corresponding columns in the foreign key and the referenced key must have similar internal datatypes inside InnoDB so that they can be compared without a type conversion. The size and the signedness of integer types has to be the same. The length of string types need not be the same. If you specify a SET NULL action, make sure you have not declared the columns in the child table NOT NULL.
If MySQL gives the error number 1005 from a CREATE TABLE statement, and the error message string refers to errno 150, then the table creation failed because a foreign key constraint was not correctly formed. Similarly, if an ALTER TABLE fails and it refers to errno 150, that means a foreign key definition would be incorrectly formed for the altered table. Starting from version 4.0.13, you can use SHOW INNODB STATUS to look at a detailed explanation of the latest InnoDB foreign key error in the server.
Starting from version 3.23.50, InnoDB does not check foreign key constraints on those foreign key or referenced key values which contain a NULL column.
A deviation from SQL standards: if in the parent table there are several rows which have the same referenced key value, then InnoDB acts in foreign key checks like the other parent rows with the same key value would not exist. For example, if you have defined a RESTRICT type constraint, and there is a child row with several parent rows, InnoDB does not allow the deletion of any of those parent rows.
Starting from version 3.23.50, you can also associate the ON DELETE CASCADE or ON DELETE SET NULL clause with the foreign key constraint. Corresponding ON UPDATE options are available starting from 4.0.8. If ON DELETE CASCADE is specified, and a row in the parent table is deleted, then InnoDB automatically deletes also all those rows in the child table whose foreign key values are equal to the referenced key value in the parent row. If ON DELETE SET NULL is specified, the child rows are automatically updated so that the columns in the foreign key are set to the SQL NULL value.
A deviation from SQL standards: if ON UPDATE CASCADE or ON UPDATE SET NULL recurses to update the SAME TABLE it has already updated during the cascade, it acts like RESTRICT. This is to prevent infinite loops resulting from cascaded updates. A self-referential ON DELETE SET NULL, on the other hand, works starting from 4.0.13. A self-referential ON DELETE CASCADE has always worked.
An example:
CREATE TABLE parent(id INT NOT NULL, PRIMARY KEY (id)) TYPE=INNODB; CREATE TABLE child(id INT, parent_id INT, INDEX par_ind (parent_id), FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE SET NULL ) TYPE=INNODB;
A complex example:
CREATE TABLE product (category INT NOT NULL, id INT NOT NULL, price DECIMAL, PRIMARY KEY(category, id)) TYPE=INNODB; CREATE TABLE customer (id INT NOT NULL, PRIMARY KEY (id)) TYPE=INNODB; CREATE TABLE product_order (no INT NOT NULL AUTO_INCREMENT, product_category INT NOT NULL, product_id INT NOT NULL, customer_id INT NOT NULL, PRIMARY KEY(no), INDEX (product_category, product_id), FOREIGN KEY (product_category, product_id) REFERENCES product(category, id) ON UPDATE CASCADE ON DELETE RESTRICT, INDEX (customer_id), FOREIGN KEY (customer_id) REFERENCES customer(id)) TYPE=INNODB;
Starting from version 3.23.50, InnoDB allows you to add a new foreign key constraint to a table through
ALTER TABLE yourtablename ADD [CONSTRAINT [symbol]] FOREIGN KEY (...) REFERENCES anothertablename(...) [on_delete_and_on_update_actions]
Remember to create the required indexes first, though.
Starting from version 4.0.13, InnoDB supports
ALTER TABLE yourtablename DROP FOREIGN KEY internally_generated_foreign_key_id
You have to use SHOW CREATE TABLE to determine the internally generated foreign key ID when you want to drop a foreign key.
In InnoDB versions < 3.23.50 ALTER TABLE or CREATE INDEX should not be used in connection with tables which have foreign key constraints or which are referenced in foreign key constraints: Any ALTER TABLE removes all foreign key constraints defined for the table. You should not use ALTER TABLE to the referenced table either, but use DROP TABLE and CREATE TABLE to modify the schema. When MySQL does an ALTER TABLE it may internally use RENAME TABLE, and that will confuse the foreign key costraints which refer to the table. A CREATE INDEX statement is in MySQL processed as an ALTER TABLE, and these restrictions apply also to it.
When doing foreign key checks, InnoDB sets shared row level locks on child or parent records it has to look at. InnoDB checks foreign key constraints immediately: the check is not deferred to transaction commit.
If you want to ignore foreign key constraints during, for example for a LOAD DATA operation, you can do SET FOREIGN_KEY_CHECKS=0.
To make it easier to reload dump files for tables that have foreign key relationships, mysqldump includes a statement in the dump output to set FOREIGN_KEY_CHECKS to 0. This avoids problems with tables having to be reloaded in a particular order when the dump is reloaded. mysqldump includes this statement as of MySQL 4.1.1. For earlier versions, you can disable the variable manually within mysql when loading the dump file like this:
mysql> SET FOREIGN_KEY_CHECKS = 0; mysql> SOURCE dump_file_name; mysql> SET FOREIGN_KEY_CHECKS = 1;
InnoDB allows you to drop any table even though that would break the foreign key constraints which reference the table. When you drop a table the constraints which were defined in its create statement are also dropped.
If you re-create a table which was dropped, it has to have a definition which conforms to the foreign key constraints referencing it. It must have the right column names and types, and it must have indexes on the referenced keys, as stated above. If these are not satisfied, MySQL returns error number 1005 and refers to errno 150 in the error message string.
Starting from version 3.23.50 InnoDB returns the foreign key definitions of a table when you call
SHOW CREATE TABLE yourtablename
Then also mysqldump produces correct definitions of tables to the dump file, and does not forget about the foreign keys.
You can also list the foreign key constraints for a table T with
SHOW TABLE STATUS FROM yourdatabasename LIKE 'T'
The foreign key constraints are listed in the table comment of the output.
IMPORTANT NOTE: if you upgrade to InnoDB-4.1.1 or higher, it is difficult to downgrade back to 4.0 or 4.1.0! That is because earlier versions of InnoDB are not aware of multiple tablespaces. If you need to downgrade to 4.0, you have to take table dumps and re-create the whole InnoDB tablespace. If you have not created new InnoDB tables under >= 4.1.1, and need to downgrade quickly, you can also do a direct downgrade to the MySQL version 4.0.18, or later in the 4.0 series. Before doing the direct downgrade to 4.0.xx, you have to end all connections to >= 4.1.1, and let mysqld to run purge and the insert buffer merge to completion, so that SHOW INNODB STATUS shows the Main thread in the state waiting for server activity. Then you can shut down mysqld and start 4.0.18 or later in the 4.0 series. A direct downgrade is not recommended, however, because it is not extensively tested.
Starting from MySQL-4.1.1, you can now store each InnoDB table and its indexes into its own file. This feature is called multiple tablespaces, because then each table is stored into its own tablespace.
You can enable this feature by putting the line
innodb_file_per_table
in the [mysqld] section of my.cnf. Then InnoDB stores each table into its own file tablename.ibd in the database directory where the table belongs. This is like MyISAM does, but MyISAM divides the table into a data file tablename.MYD and the index file tablename.MYI. For InnoDB, both the data and the indexes are in the .ibd file.
If you remove the line innodb_file_per_table from my.cnf, then InnoDB creates tables inside the ibdata files again. The old tables you had in the ibdata files before an upgrade to >= 4.1.1 remain there, they are not converted into .ibd files.
InnoDB always needs the system tablespace, .ibd files are not enough. The system tablespace consists of the familiar ibdata files. InnoDB puts there its internal data dictionary and undo logs.
You CANNOT FREELY MOVE .ibd files around, like you can MyISAM tables. This is because the table definition is stored in the InnoDB system tablespace, and also because InnoDB must preserve the consistency of transaction id's and log sequence numbers.
You can move an .ibd file and the associated table from a database to another (within the same MySQL/InnoDB installation) with the familiar RENAME command:
RENAME TABLE olddatabasename.tablename TO newdatabasename.tablename;
If you have a clean backup of an .ibd file taken from the SAME MySQL/InnoDB installation, you can restore it to an InnoDB database with the commands:
ALTER TABLE tablename DISCARD TABLESPACE; /* CAUTION: deletes the current .ibd file! */ <put the backup .ibd file to the proper place> ALTER TABLE tablename IMPORT TABLESPACE;
Clean in this context means:
There are no uncommitted modifications by transactions in the .ibd file.
There are no unmerged insert buffer entries to the .ibd file.
Purge has removed all delete-marked index records from the .ibd file.
mysqld has flushed all modified pages of the .ibd file from the buffer pool to the file.
You can make such a clean backup .ibd file with the following method.
Stop all activity from the mysqld server and commit all transactions.
Wait that SHOW INNODB STATUS\G shows that there are no active transactions in the database, and the main thread of InnoDB is Waiting for server activity. Then you can take a copy of the .ibd file.
Another (non-free) method to make such a clean .ibd file is to
Use InnoDB Hot Backup to backup the InnoDB installation.
Start a second mysqld server on the backup and let it clean up the .ibd files in the backup.
It is in the TODO to allow moving clean .ibd files also to another MySQL/InnoDB installation. That requires resetting of trx id's and log sequence numbers in the .ibd file.
From version 3.23.50 and 4.0.2 you can specify the last InnoDB datafile to autoextend. Alternatively, you can increase to your tablespace by specifying an additional datafile. To do this you have to shut down the MySQL server, edit the my.cnf file adding a new datafile to the end of innodb_data_file_path, and then start the MySQL server again.
Currently you cannot remove a datafile from InnoDB. To decrease the size of your database you have to use mysqldump to dump all your tables, create a new database, and import your tables to the new database.
If you want to change the number or the size of your InnoDB log files, you have to shut down MySQL and make sure that it shuts down without errors. Then copy the old log files into a safe place just in case something went wrong in the shutdown and you will need them to recover the database. Delete then the old log files from the log file directory, edit my.cnf, and start MySQL again. InnoDB will tell you at the startup that it is creating new log files.
The key to safe database management is taking regular backups.
InnoDB Hot Backup is an online backup tool you can use to backup your InnoDB database while it is running. InnoDB Hot Backup does not require you to shut down your database and it does not set any locks or disturb your normal database processing. InnoDB Hot Backup is a non-free additional tool which is not included in the standard MySQL distribution. See the InnoDB Hot Backup homepage http://www.innodb.com/manual.php for detailed information and screenshots.
If you are able to shut down your MySQL server, then to take a 'binary' backup of your database you have to do the following:
Shut down your MySQL database and make sure it shuts down without errors.
Copy all your datafiles into a safe place.
Copy all your InnoDB log files to a safe place.
Copy your my.cnf configuration file or files to a safe place.
Copy all the .frm files for your InnoDB tables into a safe place.
In addition to taking the binary backups described above, you should also regularly take dumps of your tables with mysqldump. The reason to this is that a binary file may be corrupted without you noticing it. Dumped tables are stored into text files which are human-readable and much simpler than database binary files. Seeing table corruption from dumped files is easier, and since their format is simpler, the chance for serious data corruption in them is smaller.
A good idea is to take the dumps at the same time you take a binary backup of your database. You have to shut out all clients from your database to get a consistent snapshot of all your tables into your dumps. Then you can take the binary backup, and you will then have a consistent snapshot of your database in two formats.
To be able to recover your InnoDB database to the present from the binary backup described above, you have to run your MySQL database with the general logging and log archiving of MySQL switched on. Here by the general logging we mean the logging mechanism of the MySQL server which is independent of InnoDB logs.
To recover from a crash of your MySQL server process, the only thing you have to do is to restart it. InnoDB will automatically check the logs and perform a roll-forward of the database to the present. InnoDB will automatically roll back uncommitted transactions which were present at the time of the crash. During recovery, InnoDB will print out something like the following:
~/mysqlm/sql > mysqld InnoDB: Database was not shut down normally. InnoDB: Starting recovery from log files... InnoDB: Starting log scan based on checkpoint at InnoDB: log sequence number 0 13674004 InnoDB: Doing recovery: scanned up to log sequence number 0 13739520 InnoDB: Doing recovery: scanned up to log sequence number 0 13805056 InnoDB: Doing recovery: scanned up to log sequence number 0 13870592 InnoDB: Doing recovery: scanned up to log sequence number 0 13936128 ... InnoDB: Doing recovery: scanned up to log sequence number 0 20555264 InnoDB: Doing recovery: scanned up to log sequence number 0 20620800 InnoDB: Doing recovery: scanned up to log sequence number 0 20664692 InnoDB: 1 uncommitted transaction(s) which must be rolled back InnoDB: Starting rollback of uncommitted transactions InnoDB: Rolling back trx no 16745 InnoDB: Rolling back of trx no 16745 completed InnoDB: Rollback of uncommitted transactions completed InnoDB: Starting an apply batch of log records to the database... InnoDB: Apply batch completed InnoDB: Started mysqld: ready for connections
If your database gets corrupted or your disk fails, you have to do the recovery from a backup. In the case of corruption, you should first find a backup which is not corrupted. From a backup do the recovery from the general log files of MySQL according to instructions in the MySQL manual.
If there is database page corruption, you may want to dump your tables from the database with SELECT INTO OUTFILE, and usually most of the data is intact and correct. But the corruption may cause SELECT * FROM table, or InnoDB background operations to crash or assert, or even the InnoDB roll-forward recovery to crash. Starting from the InnoDB version 3.23.44, there is a my.cnf option with which you can force InnoDB to start up, and you can also prevent background operations from running, so that you will be able to dump your tables. For example, you can set
set-variable = innodb_force_recovery = 4
in my.cnf.
The alternatives for innodb_force_recovery follow. The database must not otherwise be used with these options! As a safety measure InnoDB prevents a user from doing INSERT, UPDATE, or DELETE when this option is > 0.
Starting from version 3.23.53 and 4.0.4, you are allowed to DROP or CREATE a table even if forced recovery is used. If you know that a certain table is causing a crash in rollback, you can drop it. You can use this also to stop a runaway rollback caused by a failing mass import or ALTER TABLE. You can kill the mysqld process and use the my.cnf option innodb_force_recovery=3 to bring your database up without the rollback. Then DROP the table which is causing the runaway rollback.
A bigger number below means that all precautions of lower numbers are included. If you are able to dump your tables with an option at most 4, then you are relatively safe that only some data on corrupt individual pages is lost. Option 6 is more dramatic, because database pages are left in an obsolete state, which in turn may introduce more corruption into B-trees and other database structures.
1 (SRV_FORCE_IGNORE_CORRUPT) let the server run even if it detects a corrupt page; try to make SELECT * FROM table jump over corrupt index records and pages, which helps in dumping tables;
2 (SRV_FORCE_NO_BACKGROUND) prevent the main thread from running: if a crash would occur in purge, this prevents it;
3 (SRV_FORCE_NO_TRX_UNDO) do not run transaction rollbacks after recovery;
4 (SRV_FORCE_NO_IBUF_MERGE) prevent also insert buffer merge operations: if they would cause a crash, better not do them; do not calculate table statistics;
5 (SRV_FORCE_NO_UNDO_LOG_SCAN) do not look at undo logs when starting the database: InnoDB will treat even incomplete transactions as committed;
6 (SRV_FORCE_NO_LOG_REDO) do not do the log roll-forward in connection with recovery.
InnoDB implements a checkpoint mechanism called a fuzzy checkpoint. InnoDB will flush modified database pages from the buffer pool in small batches, there is no need to flush the buffer pool in one single batch, which would in practice stop processing of user SQL statements for a while.
In crash recovery InnoDB looks for a checkpoint label written to the log files. It knows that all modifications to the database before the label are already present on the disk image of the database. Then InnoDB scans the log files forward from the place of the checkpoint applying the logged modifications to the database.
InnoDB writes to the log files in a circular fashion. All committed modifications which make the database pages in the buffer pool different from the images on disk must be available in the log files in case InnoDB has to do a recovery. This means that when InnoDB starts to reuse a log file in the circular fashion, it has to make sure that the database page images on disk already contain the modifications logged in the log file InnoDB is going to reuse. In other words, InnoDB has to make a checkpoint and often this involves flushing of modified database pages to disk.
The above explains why making your log files very big may save disk I/O in checkpointing. It can make sense to set the total size of the log files as big as the buffer pool or even bigger. The drawback in big log files is that crash recovery can last longer because there will be more log to apply to the database.
On Windows InnoDB stores the database names and table names internally always in lowercase. To move databases in a binary format from Unix to Windows or from Windows to Unix you should have all table and database names in lowercase. A convenient way to accomplish this is to add on Unix the line
set-variable=lower_case_table_names=1
to the [mysqld] section of your my.cnf before you start creating your tables. On Windows the setting 1 is the default.
InnoDB data and log files are binary-compatible on all platforms if the floating-point number format on the machines is the same. You can move an InnoDB database simply by copying all the relevant files, which we already listed in the previous section on backing up a database. If the floating-point formats on the machines are different but you have not used FLOAT or DOUBLE datatypes in your tables then the procedure is the same: just copy the relevant files. If the formats are different and your tables contain floating-point data, you have to use mysqldump and mysqlimport to move those tables.
A performance tip is to switch off auto-commit mode when you import data into your database, assuming your tablespace has enough space for the big rollback segment the big import transaction will generate. Do the commit only after importing a whole table or a segment of a table.
In the InnoDB transaction model the goal has been to combine the best properties of a multi-versioning database to traditional two-phase locking. InnoDB does locking on row level and runs queries by default as non-locking consistent reads, in the style of Oracle. The lock table in InnoDB is stored so space-efficiently that lock escalation is not needed: typically several users are allowed to lock every row in the database, or any random subset of the rows, without InnoDB running out of memory.
In InnoDB all user activity happens inside transactions. If the autocommit mode is used in MySQL, then each SQL statement forms a single transaction. MySQL always starts a new connection with the autocommit mode switched on.
If the autocommit mode is switched off with SET AUTOCOMMIT = 0, then we can think that a user always has a transaction open. If he issues the SQL COMMIT or ROLLBACK statement, it ends the current transaction, and a new one starts. Both statements will release all InnoDB locks that were set during the current transaction. A COMMIT means that the changes made in the current transaction are made permanent and become visible to other users. A ROLLBACK statement, on the other hand, cancels all modifications made by the current transaction.
If the connection has AUTOCOMMIT = 1, then the user can still perform a multiple-statement transaction by starting it with START TRANSACTION or BEGIN and ending it with COMMIT or ROLLBACK.
In terms of the SQL-92 transaction isolation levels, the InnoDB default is REPEATABLE READ. Starting from version 4.0.5, InnoDB offers all 4 different transaction isolation levels described by the SQL-92 standard. You can set the default isolation level for all connections in the [mysqld] section of my.cnf:
transaction-isolation = {READ-UNCOMMITTED | READ-COMMITTED | REPEATABLE-READ | SERIALIZABLE}
A user can change the isolation level of a single session or all new incoming connections with the SET TRANSACTION statement. Its syntax is as follows:
SET [SESSION | GLOBAL] TRANSACTION ISOLATION LEVEL {READ UNCOMMITTED | READ COMMITTED | REPEATABLE READ | SERIALIZABLE}
Note that there are no hyphens in level names in the SQL syntax.
The default behavior is to set the isolation level for the next (not started) transaction. If you use the GLOBAL keyword, the statement sets the default transaction level globally for all new connections created from that point on (but not existing connections). You need the SUPER privilege to do this. Using the SESSION keyword sets the default transaction level for all future transactions performed on the current connection. Any client is free to change the session isolation level (even in the middle of a transaction), or the isolation level for the next transaction. In versions earlier than 3.23.50, SET TRANSACTION had no effect on InnoDB tables. In versions < 4.0.5 only REPEATABLE READ and SERIALIZABLE were available.
You can query the global and session transaction isolation levels with:
SELECT @@global.tx_isolation; SELECT @@tx_isolation;
In row level locking InnoDB uses so-called next-key locking. That means that besides index records, InnoDB can also lock the ``gap'' before an index record to block insertions by other users immediately before the index record. A next-key lock means a lock which locks an index record and the gap before it. A gap lock means a lock which only locks a gap before some index record.
A detailed description of each isolation level in InnoDB:
READ UNCOMMITTED This is also called ``dirty read'': non-locking SELECT statements are performed so that we do not look at a possible earlier version of a record; thus they are not 'consistent' reads under this isolation level; otherwise this level works like READ COMMITTED.
READ COMMITTED Somewhat Oracle-like isolation level. All SELECT ... FOR UPDATE and SELECT ... LOCK IN SHARE MODE statements only lock the index records, not the gaps before them, and thus allow free inserting of new records next to locked records. UPDATE and DELETE which use a unique index with a unique search condition, only lock the index record found, not the gap before it. But still in range type UPDATE and DELETE, InnoDB must set next-key or gap locks and block insertions by other users to the gaps covered by the range. This is necessary since ``phantom rows'' have to be blocked for MySQL replication and recovery to work. Consistent reads behave as in Oracle: each consistent read, even within the same transaction, sets and reads its own fresh snapshot.
REPEATABLE READ This is the default isolation level of InnoDB. SELECT ... FOR UPDATE, SELECT ... LOCK IN SHARE MODE, UPDATE, and DELETE which use a unique index with a unique search condition, only lock the index record found, not the gap before it. Otherwise these operations employ next-key locking, locking the index range scanned with next-key or gap locks, and block new insertions by other users. In consistent reads there is an important difference from the previous isolation level: in this level all consistent reads within the same transaction read the same snapshot established by the first read. This convention means that if you issue several plain SELECT statements within the same transaction, these SELECT statements are consistent also with respect to each other.
SERIALIZABLE This level is like the previous one, but all plain SELECT statements are implicitly converted to SELECT ... LOCK IN SHARE MODE.
A consistent read means that InnoDB uses its multi-versioning to present to a query a snapshot of the database at a point in time. The query will see the changes made by exactly those transactions that committed before that point of time, and no changes made by later or uncommitted transactions. The exception to this rule is that the query will see the changes made by the transaction itself which issues the query.
If you are running with the default REPEATABLE READ isolation level, then all consistent reads within the same transaction read the snapshot established by the first such read in that transaction. You can get a fresher snapshot for your queries by committing the current transaction and after that issuing new queries.
Consistent read is the default mode in which InnoDB processes SELECT statements in READ COMMITTED and REPEATABLE READ isolation levels. A consistent read does not set any locks on the tables it accesses, and therefore other users are free to modify those tables at the same time a consistent read is being performed on the table.
A consistent read is not convenient in some circumstances. Suppose you want to add a new row into your table CHILD, and make sure that the child already has a parent in table PARENT.
Suppose you use a consistent read to read the table PARENT and indeed see the parent of the child in the table. Can you now safely add the child row to table CHILD? No, because it may happen that meanwhile some other user has deleted the parent row from the table PARENT, and you are not aware of that.
The solution is to perform the SELECT in a locking mode, LOCK IN SHARE MODE.
SELECT * FROM PARENT WHERE NAME = 'Jones' LOCK IN SHARE MODE;
Performing a read in share mode means that we read the latest available data, and set a shared mode lock on the rows we read. If the latest data belongs to a yet uncommitted transaction of another user, we will wait until that transaction commits. A shared mode lock prevents others from updating or deleting the row we have read. After we see that the above query returns the parent 'Jones', we can safely add his child to table CHILD, and commit our transaction. This example shows how to implement referential integrity in your application code.
Let us look at another example: we have an integer counter field in a table CHILD_CODES which we use to assign a unique identifier to each child we add to table CHILD. Obviously, using a consistent read or a shared mode read to read the present value of the counter is not a good idea, since then two users of the database may see the same value for the counter, and we will get a duplicate key error when we add the two children with the same identifier to the table.
In this case there are two good ways to implement the reading and incrementing of the counter: (1) update the counter first by incrementing it by 1 and only after that read it, or (2) read the counter first with a lock mode FOR UPDATE, and increment after that:
SELECT COUNTER_FIELD FROM CHILD_CODES FOR UPDATE; UPDATE CHILD_CODES SET COUNTER_FIELD = COUNTER_FIELD + 1;
A SELECT ... FOR UPDATE will read the latest available data setting exclusive locks on each row it reads. Thus it sets the same locks a searched SQL UPDATE would set on the rows.
In row level locking InnoDB uses an algorithm called next-key locking. InnoDB does the row level locking so that when it searches or scans an index of a table, it sets shared or exclusive locks on the index records it encounters. Thus the row level locks are more precisely called index record locks.
The locks InnoDB sets on index records also affect the 'gap' before that index record. If a user has a shared or exclusive lock on record R in an index, then another user cannot insert a new index record immediately before R in the index order. This locking of gaps is done to prevent the so-called phantom problem. Suppose I want to read and lock all children with identifier bigger than 100 from table CHILD, and update some field in the selected rows.
SELECT * FROM CHILD WHERE ID > 100 FOR UPDATE;
Suppose there is an index on table CHILD on column ID. Our query will scan that index starting from the first record where ID is bigger than 100. Now, if the locks set on the index records would not lock out inserts made in the gaps, a new child might meanwhile be inserted to the table. If now I in my transaction execute
SELECT * FROM CHILD WHERE ID > 100 FOR UPDATE;
again, I will see a new child in the result set the query returns. This is against the isolation principle of transactions: a transaction should be able to run so that the data it has read does not change during the transaction. If we regard a set of rows as a data item, then the new 'phantom' child would break this isolation principle.
When InnoDB scans an index it can also lock the gap after the last record in the index. Just that happens in the previous example: the locks set by InnoDB will prevent any insert to the table where ID would be bigger than 100.
You can use next-key locking to implement a uniqueness check in your application: if you read your data in share mode and do not see a duplicate for a row you are going to insert, then you can safely insert your row and know that the next-key lock set on the successor of your row during the read will prevent anyone meanwhile inserting a duplicate for your row. Thus the next-key locking allows you to 'lock' the non-existence of something in your table.
A locking read, an UPDATE or a DELETE generally sets record locks on every index record which is scanned in the processing of the SQL query. It does not matter if there are WHERE conditions in the query which would exclude the row from the result set of the query. InnoDB does not remember the exact WHERE condition, but only knows which index ranges were scanned. The record locks are normally next-key locks which also block inserts to the 'gap' immediately before the record.
If the locks to be set are exclusive, then InnoDB always retrieves also the clustered index record and sets a lock on it.
If you do not have good indexes for your query and MySQL has to scan the whole table to process the query, then every row of the table will become locked, which in turn blocks all inserts by other users to the table. It is important to create good indexes so that your queries do not unnecessarily need to scan many rows.
SELECT ... FROM ...: this is a consistent read, reading a snapshot of the database and setting no locks.
SELECT ... FROM ... LOCK IN SHARE MODE: sets shared next-key locks on all index records the read encounters.
SELECT ... FROM ... FOR UPDATE: sets exclusive next-key locks on all index records the read encounters.
INSERT INTO ... VALUES (...): sets an exclusive lock on the inserted row; note that this lock is not a next-key lock and does not prevent other users from inserting to the gap before the inserted row. If a duplicate key error occurs, sets a shared lock on the duplicate index record.
INSERT INTO T SELECT ... FROM S WHERE ... sets an exclusive (non-next-key) lock on each row inserted into T. Does the search on S as a consistent read, but sets shared next-key locks on S if the MySQL logging is on. InnoDB has to set locks in the latter case because in roll-forward recovery from a backup every SQL statement has to be executed in exactly the same way as it was done originally.
CREATE TABLE ... SELECT ... performs the SELECT as a consistent read or with shared locks, like in the previous item.
REPLACE is done like an insert if there is no collision on a unique key. Otherwise, an exclusive next-key lock is placed on the row which has to be updated.
UPDATE ... SET ... WHERE ...: sets an exclusive next-key lock on every record the search encounters.
DELETE FROM ... WHERE ...: sets an exclusive next-key lock on every record the search encounters.
If a FOREIGN KEY constraint is defined on a table, any insert, update, or delete which requires checking of the constraint condition sets shared record level locks on the records it looks at to check the constraint. Also in the case where the constraint fails, InnoDB sets these locks.
LOCK TABLES ... : sets table locks. In the implementation the MySQL layer of code sets these locks. The automatic deadlock detection of InnoDB cannot detect deadlocks where such table locks are involved: see the following section. Also, since MySQL does know about row level locks, it is possible that you get a table lock on a table where another user currently has row level locks. But that does not put transaction integrity into danger. See InnoDB restrictions.
InnoDB automatically detects a deadlock of transactions and rolls back a transaction or transactions to prevent the deadlock. Starting from version 4.0.5, InnoDB will try to pick small transactions to roll back. The size of a transaction is determined by the number of rows it has inserted, updated, or deleted. Previous to 4.0.5, InnoDB always rolled back the transaction whose lock request was the last one to build a deadlock, that is, a cycle in the waits-for graph of transactions.
InnoDB cannot detect deadlocks where a lock set by a MySQL LOCK TABLES statement is involved, or if a lock set in another storage engine than InnoDB is involved. You have to resolve these situations using innodb_lock_wait_timeout set in my.cnf.
When InnoDB performs a complete rollback of a transaction, all the locks of the transaction are released. However, if just a single SQL statement is rolled back as a result of an error, some of the locks set by the SQL statement may be preserved. This is because InnoDB stores row locks in a format where it cannot afterwards know which was set by which SQL statement.
Suppose you are running on the default REPEATABLE READ isolation level. When you issue a consistent read, that is, an ordinary SELECT statement, InnoDB will give your transaction a timepoint according to which your query sees the database. Thus, if transaction B deletes a row and commits after your timepoint was assigned, then you will not see the row deleted. Similarly with inserts and updates.
You can advance your timepoint by committing your transaction and then doing another SELECT.
This is called multi-versioned concurrency control.
User A User B SET AUTOCOMMIT=0; SET AUTOCOMMIT=0; time | SELECT * FROM t; | empty set | INSERT INTO t VALUES (1, 2); | v SELECT * FROM t; empty set COMMIT; SELECT * FROM t; empty set; COMMIT; SELECT * FROM t; --------------------- | 1 | 2 | ---------------------
Thus user A sees the row inserted by B only when B has committed the insert, and A has committed his own transaction so that the timepoint is advanced past the commit of B.
If you want to see the ``freshest'' state of the database, you should use a locking read:
SELECT * FROM t LOCK IN SHARE MODE;
Deadlocks are a classic problem in transactional databases, but they are not dangerous, unless they are so frequent that you cannot run certain transactions at all. Normally you have to write your applications so that they are always prepared to re-issue a transaction if it gets rolled back because of a deadlock.
InnoDB uses automatic row level locking. You can get deadlocks even in the case of transactions which just insert or delete a single row. That is because these operations are not really 'atomic': they automatically set locks on the (possibly several) index records of the row inserted/deleted.
You can cope with deadlocks and reduce the number of them with the following tricks:
Use SHOW INNODB STATUS in MySQL versions >= 3.23.52 and >= 4.0.3 to determine the cause of the latest deadlock. That can help you to tune your application to avoid deadlocks.
Always be prepared to re-issue a transaction if it fails in a deadlock. Deadlocks are not dangerous. Just try again.
Commit your transactions often. Small transactions are less prone to collide.
If you are using locking reads SELECT ... FOR UPDATE or ... LOCK IN SHARE MODE, try using a lower isolation level READ COMMITTED.
Access your tables and rows in a fixed order. Then transactions will form nice queues, and do not deadlock.
Add well-chosen indexes to your tables. Then your queries need to scan fewer index records and consequently set fewer locks. Use EXPLAIN SELECT to determine that MySQL picks appropriate indexes for your queries.
Use less locking: if you can afford a SELECT to return data from an old snapshot, do not add the clause FOR UPDATE or LOCK IN SHARE MODE to it. Using READ COMMITTED isolation level is good here, because each consistent read within the same transaction reads from its own fresh snapshot.
If nothing helps, serialize your transactions with table level locks: LOCK TABLES t1 WRITE, t2 READ, ... ; [do something with tables t1 and t2 here]; UNLOCK TABLES. Table level locks make you transactions to queue nicely, and deadlocks are avoided. Note that LOCK TABLES implicitly starts a transaction, just like the command BEGIN, and UNLOCK TABLES implicitly ends the transaction in a COMMIT.
Another solution to serialize transactions is to create an auxiliary 'semaphore' table where there is just a single row. Each transaction updates that row before accessing other tables. In that way all transactions happen in a serial fashion. Note that then also the InnoDB instant deadlock detection algorithm works, because the serializing lock is a row level lock. In MySQL table level locks we have to resort to the timeout method to resolve a deadlock.
If the Unix top or the Windows Task Manager shows that the CPU usage percentage with your workload is less than 70%, your workload is probably disk-bound. Maybe you are making too many transaction commits, or the buffer pool is too small. Making the buffer pool bigger can help, but do not set it bigger than 80% of physical memory.
Wrap several modifications into one transaction. InnoDB must flush the log to disk at each transaction commit, if that transaction made modifications to the database. Since the rotation speed of a disk is typically at most 167 revolutions/second, that constrains the number of commits to the same 167/second if the disk does not fool the operating system.
If you can afford the loss of some latest committed transactions, you can set the my.cnf parameter innodb_flush_log_at_trx_commit to 0. InnoDB tries to flush the log once per second anyway, though the flush is not guaranteed.
Make your log files big, even as big as the buffer pool. When InnoDB has written the log files full, it has to write the modified contents of the buffer pool to disk in a checkpoint. Small log files will cause many unnecessary disk writes. The drawback in big log files is that recovery time will be longer.
Also the log buffer should be quite big, say 8 MB.
(Relevant from 3.23.39 up.) In some versions of Linux and Unix, flushing files to disk with the Unix fdatasync and other similar methods is surprisingly slow. The default method InnoDB uses is the fdatasync function. If you are not satisfied with the database write performance, you may try setting innodb_flush_method in my.cnf to O_DSYNC, though O_DSYNC seems to be slower on most systems.
In importing data to InnoDB, make sure that MySQL does not have autocommit=1 on. Then every insert requires a log flush to disk. Put before your plain SQL import file line
SET AUTOCOMMIT=0;
and after it
COMMIT;
If you use the mysqldump option --opt, you will get dump files which are fast to import also to an InnoDB table, even without wrapping them to the above SET AUTOCOMMIT=0; ... COMMIT; wrappers.
Beware of big rollbacks of mass inserts: InnoDB uses the insert buffer to save disk I/O in inserts, but in a corresponding rollback no such mechanism is used. A disk-bound rollback can take 30 times the time of the corresponding insert. Killing the database process will not help because the rollback will start again at the database startup. The only way to get rid of a runaway rollback is to increase the buffer pool so that the rollback becomes CPU-bound and runs fast, or delete the whole InnoDB database.
Beware also of other big disk-bound operations. Use DROP TABLE or TRUNCATE (from MySQL-4.0 up) to empty a table, not DELETE FROM yourtable.
Use the multi-line INSERT to reduce communication overhead between the client and the server if you need to insert many rows:
INSERT INTO yourtable VALUES (1, 2), (5, 5);
This tip is valid for inserts into any table type, not just InnoDB.
Starting from version 3.23.42, InnoDB includes InnoDB Monitors that print information about the InnoDB internal state. Starting from versions 3.23.52 and 4.0.3 you can use the SQL command SHOW INNODB STATUS to fetch the output of the standard InnoDB Monitor to the SQL client. The information is useful in performance tuning. If you are using the mysql interactive SQL client, the output is more readable if you replace the usual semicolon statement terminator by \G:
SHOW INNODB STATUS\G
Another way to use InnoDB Monitors is to let them continuosly write data to the standard output of the server mysqld (note: the MySQL client will not print anything). When switched on, InnoDB Monitors print data about once every 15 seconds. If you run mysqld as a daemon then this output is usually directed to the .err log in the MySQL datadir. This data is useful in performance tuning. On Windows you must start mysqld-max from an MS-DOS prompt with the --console option if you want to direct the output to the MS-DOS prompt window.
There is a separate innodb_lock_monitor which prints the same information as innodb_monitor plus information on locks set by each transaction.
The printed information includes data on:
lock waits of a transactions,
semaphore waits of threads,
pending file I/O requests,
buffer pool statistics, and
purge and insert buffer merge activity of the main thread of InnoDB.
You can start InnoDB Monitor through the following SQL command:
CREATE TABLE innodb_monitor(a INT) type = innodb;
and stop it by
DROP TABLE innodb_monitor;
The CREATE TABLE syntax is just a way to pass a command to the InnoDB engine through the MySQL SQL parser: the created table is not relevant at all for InnoDB Monitor. If you shut down the database when the monitor is running, and you want to start the monitor again, you have to drop the table before you can issue a new CREATE TABLE to start the monitor. This syntax may change in a future release.
A sample output of the InnoDB Monitor:
================================ 010809 18:45:06 INNODB MONITOR OUTPUT ================================ -------------------------- LOCKS HELD BY TRANSACTIONS -------------------------- LOCK INFO: Number of locks in the record hash table 1294 LOCKS FOR TRANSACTION ID 0 579342744 TABLE LOCK table test/mytable trx id 0 582333343 lock_mode IX RECORD LOCKS space id 0 page no 12758 n bits 104 table test/mytable index PRIMARY trx id 0 582333343 lock_mode X Record lock, heap no 2 PHYSICAL RECORD: n_fields 74; 1-byte offs FALSE; info bits 0 0: len 4; hex 0001a801; asc ;; 1: len 6; hex 000022b5b39f; asc ";; 2: len 7; hex 000002001e03ec; asc ;; 3: len 4; hex 00000001; ... ----------------------------------------------- CURRENT SEMAPHORES RESERVED AND SEMAPHORE WAITS ----------------------------------------------- SYNC INFO: Sorry, cannot give mutex list info in non-debug version! Sorry, cannot give rw-lock list info in non-debug version! ----------------------------------------------------- SYNC ARRAY INFO: reservation count 6041054, signal count 2913432 4a239430 waited for by thread 49627477 op. S-LOCK file NOT KNOWN line 0 Mut ex 0 sp 5530989 r 62038708 sys 2155035; rws 0 8257574 8025336; rwx 0 1121090 1848344 ----------------------------------------------------- CURRENT PENDING FILE I/O'S -------------------------- Pending normal aio reads: Reserved slot, messages 40157658 4a4a40b8 Reserved slot, messages 40157658 4a477e28 ... Reserved slot, messages 40157658 4a4424a8 Reserved slot, messages 40157658 4a39ea38 Total of 36 reserved aio slots Pending aio writes: Total of 0 reserved aio slots Pending insert buffer aio reads: Total of 0 reserved aio slots Pending log writes or reads: Reserved slot, messages 40158c98 40157f98 Total of 1 reserved aio slots Pending synchronous reads or writes: Total of 0 reserved aio slots ----------- BUFFER POOL ----------- LRU list length 8034 Free list length 0 Flush list length 999 Buffer pool size in pages 8192 Pending reads 39 Pending writes: LRU 0, flush list 0, single page 0 Pages read 31383918, created 51310, written 2985115 ---------------------------- END OF INNODB MONITOR OUTPUT ============================ 010809 18:45:22 InnoDB starts purge 010809 18:45:22 InnoDB purged 0 pages
Some notes on the output:
If the section LOCKS HELD BY TRANSACTIONS reports lock waits, then your application may have lock contention. The output can also help to trace reasons for transaction deadlocks.
Section SYNC INFO will report reserved semaphores if you compile InnoDB with UNIV_SYNC_DEBUG defined in univ.i.
Section SYNC ARRAY INFO reports threads waiting for a semaphore and statistics on how many times threads have needed a spin or a wait on a mutex or a rw-lock semaphore. A large number of threads waiting for semaphores may be a result of disk I/O, or contention problems inside InnoDB. Contention can be due to heavy parallelism of queries, or problems in operating system thread scheduling.
Section CURRENT PENDING FILE I/O'S lists pending file I/O requests. A large number of these indicates that the workload is disk I/O-bound.
Section BUFFER POOL gives you statistics on pages read and written. You can calculate from these numbers how many datafile I/Os your queries are currently doing.
Since InnoDB is a multi-versioned database, it must keep information of old versions of rows in the tablespace. This information is stored in a data structure we call a rollback segment after an analogous data structure in Oracle.
InnoDB internally adds two fields to each row stored in the database. A 6-byte field tells the transaction identifier for the last transaction which inserted or updated the row. Also a deletion is internally treated as an update where a special bit in the row is set to mark it as deleted. Each row also contains a 7-byte field called the roll pointer. The roll pointer points to an undo log record written to the rollback segment. If the row was updated, then the undo log record contains the information necessary to rebuild the content of the row before it was updated.
InnoDB uses the information in the rollback segment to perform the undo operations needed in a transaction rollback. It also uses the information to build earlier versions of a row for a consistent read.
Undo logs in the rollback segment are divided into insert and update undo logs. Insert undo logs are only needed in transaction rollback and can be discarded as soon as the transaction commits. Update undo logs are used also in consistent reads, and they can be discarded only after there is no transaction present for which InnoDB has assigned a snapshot that in a consistent read could need the information in the update undo log to build an earlier version of a database row.
You must remember to commit your transactions regularly, also those transactions which only issue consistent reads. Otherwise InnoDB cannot discard data from the update undo logs, and the rollback segment may grow too big, filling up your tablespace.
The physical size of an undo log record in the rollback segment is typically smaller than the corresponding inserted or updated row. You can use this information to calculate the space need for your rollback segment.
In our multi-versioning scheme a row is not physically removed from the database immediately when you delete it with an SQL statement. Only when InnoDB can discard the update undo log record written for the deletion, it can also physically remove the corresponding row and its index records from the database. This removal operation is called a purge, and it is quite fast, usually taking the same order of time as the SQL statement which did the deletion.
MySQL stores its data dictionary information of tables in .frm files in database directories. But every InnoDB type table also has its own entry in InnoDB internal data dictionaries inside the tablespace. When MySQL drops a table or a database, it has to delete both a .frm file or files, and the corresponding entries inside the InnoDB data dictionary. This is the reason why you cannot move InnoDB tables between databases simply by moving the .frm files, and why DROP DATABASE did not work for InnoDB type tables in MySQL versions <= 3.23.43.
Every InnoDB table has a special index called the clustered index where the data of the rows is stored. If you define a PRIMARY KEY on your table, then the index of the primary key will be the clustered index.
If you do not define a primary key for your table, InnoDB will internally generate a clustered index where the rows are ordered by the row ID that InnoDB assigns to the rows in such a table. The row ID is a 6-byte field which monotonically increases as new rows are inserted. Thus the rows ordered by the row ID will be physically in the insertion order.
Accessing a row through the clustered index is fast, because the row data will be on the same page where the index search leads us. In many databases the data is traditionally stored on a different page from the index record. If a table is large, the clustered index architecture often saves a disk I/O when compared to the traditional solution.
The records in non-clustered indexes (we also call them secondary indexes), in InnoDB contain the primary key value for the row. InnoDB uses this primary key value to search for the row from the clustered index. Note that if the primary key is long, the secondary indexes will use more space.
All indexes in InnoDB are B-trees where the index records are stored in the leaf pages of the tree. The default size of an index page is 16 KB. When new records are inserted, InnoDB tries to leave 1 / 16 of the page free for future insertions and updates of the index records.
If index records are inserted in a sequential (ascending or descending) order, the resulting index pages will be about 15/16 full. If records are inserted in a random order, then the pages will be 1/2 - 15/16 full. If the fillfactor of an index page drops below 1/2, InnoDB will try to contract the index tree to free the page.
It is a common situation in a database application that the primary key is a unique identifier and new rows are inserted in the ascending order of the primary key. Thus the insertions to the clustered index do not require random reads from a disk.
On the other hand, secondary indexes are usually non-unique and insertions happen in a relatively random order into secondary indexes. This would cause a lot of random disk I/Os without a special mechanism used in InnoDB.
If an index record should be inserted to a non-unique secondary index, InnoDB checks if the secondary index page is already in the buffer pool. If that is the case, InnoDB will do the insertion directly to the index page. But, if the index page is not found from the buffer pool, InnoDB inserts the record to a special insert buffer structure. The insert buffer is kept so small that it entirely fits in the buffer pool, and insertions can be made to it very fast.
The insert buffer is periodically merged to the secondary index trees in the database. Often we can merge several insertions on the same page in of the index tree, and hence save disk I/Os. It has been measured that the insert buffer can speed up insertions to a table up to 15 times.
If a database fits almost entirely in main memory, then the fastest way to perform queries on it is to use hash indexes. InnoDB has an automatic mechanism which monitors index searches made to the indexes defined for a table, and if InnoDB notices that queries could benefit from building of a hash index, such an index is automatically built.
But note that the hash index is always built based on an existing B-tree index on the table. InnoDB can build a hash index on a prefix of any length of the key defined for the B-tree, depending on what search pattern InnoDB observes on the B-tree index. A hash index can be partial: it is not required that the whole B-tree index is cached in the buffer pool. InnoDB will build hash indexes on demand to those pages of the index which are often accessed.
In a sense, through the adaptive hash index mechanism InnoDB adapts itself to ample main memory, coming closer to the architecture of main memory databases.
Each index record in InnoDB contains a header of 6 bytes. The header is used to link consecutive records together, and also in the row level locking.
Records in the clustered index contain fields for all user-defined columns. In addition, there is a 6-byte field for the transaction id and a 7-byte field for the roll pointer.
If the user has not defined a primary key for a table, then each clustered index record contains also a 6-byte row ID field.
Each secondary index record contains also all the fields defined for the clustered index key.
A record contains also a pointer to each field of the record. If the total length of the fields in a record is < 128 bytes, then the pointer is 1 byte, else 2 bytes.
After a database startup, when a user first does an insert to a table T where an auto-increment column has been defined, and the user does not provide an explicit value for the column, then InnoDB executes SELECT MAX(auto-inc-column) FROM T, and assigns that value incremented by one to the column and the auto-increment counter of the table. We say that the auto-increment counter for table T has been initialized.
InnoDB follows the same procedure in initializing the auto-increment counter for a freshly created table.
Note that if the user specifies in an insert the value 0 to the auto-increment column, then InnoDB treats the row like the value would not have been specified.
After the auto-increment counter has been initialized, if a user inserts a row where he explicitly specifies the column value, and the value is bigger than the current counter value, then the counter is set to the specified column value. If the user does not explicitly specify a value, then InnoDB increments the counter by one and assigns its new value to the column.
The auto-increment mechanism, when assigning values from the counter, bypasses locking and transaction handling. Therefore you may also get gaps in the number sequence if you roll back transactions which have got numbers from the counter.
The behavior of auto-increment is not defined if a user gives a negative value to the column or if the value becomes bigger than the maximum integer that can be stored in the specified integer type.
In disk I/O InnoDB uses asynchronous I/O. On Windows NT it uses the native asynchronous I/O provided by the operating system. On Unix, InnoDB uses simulated asynchronous I/O built into InnoDB: InnoDB creates a number of I/O threads to take care of I/O operations, such as read-ahead. In a future version we will add support for simulated aio on Windows NT and native aio on those versions of Unix which have one.
On Windows NT InnoDB uses non-buffered I/O. That means that the disk pages InnoDB reads or writes are not buffered in the operating system file cache. This saves some memory bandwidth.
Starting from 3.23.41 InnoDB uses a novel file flush technique called doublewrite. It adds safety to crash recovery after an operating system crash or a power outage, and improves performance on most Unix flavors by reducing the need for fsync operations.
Doublewrite means that InnoDB before writing pages to a datafile first writes them to a contiguous tablespace area called the doublewrite buffer. Only after the write and the flush to the doublewrite buffer has completed, InnoDB writes the pages to their proper positions in the datafile. If the operating system crashes in the middle of a page write, InnoDB will in recovery find a good copy of the page from the doublewrite buffer.
Starting from 3.23.41 you can also use a raw disk partition as a datafile, though this has not been tested yet. When you create a new datafile you have to put the keyword newraw immediately after the datafile size in innodb_data_file_path. The partition must be at least as large as the size that you specify. Note that 1M in InnoDB is 1024 x 1024 bytes, while in disk specifications 1 MB usually means 1000 000 bytes.
innodb_data_file_path=/dev/hdd1:5Gnewraw;/dev/hdd2:2Gnewraw
When you start the database again you must change the keyword to raw. Otherwise, InnoDB will write over your partition!
innodb_data_file_path=/dev/hdd1:5Graw;/dev/hdd2:2Graw
By using a raw disk you can on some versions of Unix perform unbuffered I/O.
When you use raw disk partitions, make sure they have permissions that allow read and write access to the account used for running the MySQL server.
There are two read-ahead heuristics in InnoDB: sequential read-ahead and random read-ahead. In sequential read-ahead InnoDB notices that the access pattern to a segment in the tablespace is sequential. Then InnoDB will post in advance a batch of reads of database pages to the I/O system. In random read-ahead InnoDB notices that some area in a tablespace seems to be in the process of being fully read into the buffer pool. Then InnoDB posts the remaining reads to the I/O system.
The datafiles you define in the configuration file form the tablespace of InnoDB. The files are simply catenated to form the tablespace, there is no striping in use. Currently you cannot define where in the tablespace your tables will be allocated. However, in a newly created tablespace, InnoDB will allocate space starting from the low end.
The tablespace consists of database pages whose default size is 16 KB. The pages are grouped into extents of 64 consecutive pages. The 'files' inside a tablespace are called segments in InnoDB. The name of the rollback segment is somewhat misleading because it actually contains many segments in the tablespace.
For each index in InnoDB we allocate two segments: one is for non-leaf nodes of the B-tree, the other is for the leaf nodes. The idea here is to achieve better sequentiality for the leaf nodes, which contain the data.
When a segment grows inside the tablespace, InnoDB allocates the first 32 pages to it individually. After that InnoDB starts to allocate whole extents to the segment. InnoDB can add to a large segment up to 4 extents at a time to ensure good sequentiality of data.
Some pages in the tablespace contain bitmaps of other pages, and therefore a few extents in an InnoDB tablespace cannot be allocated to segments as a whole, but only as individual pages.
When you issue a query SHOW TABLE STATUS FROM ... LIKE ... to ask for available free space in the tablespace, InnoDB will report the extents which are definitely free in the tablespace. InnoDB always reserves some extents for clean-up and other internal purposes; these reserved extents are not included in the free space.
When you delete data from a table, InnoDB will contract the corresponding B-tree indexes. It depends on the pattern of deletes if that frees individual pages or extents to the tablespace, so that the freed space is available for other users. Dropping a table or deleting all rows from it is guaranteed to release the space to other users, but remember that deleted rows can be physically removed only in a purge operation after they are no longer needed in transaction rollback or consistent read.
If there are random insertions or deletions in the indexes of a table, the indexes may become fragmented. By fragmentation we mean that the physical ordering of the index pages on the disk is not close to the alphabetical ordering of the records on the pages, or that there are many unused pages in the 64-page blocks which were allocated to the index.
It can speed up index scans if you periodically use mysqldump to dump the table to a text file, drop the table, and reload it from the dump. Another way to do the defragmenting is to perform a 'null' alter table operation ALTER TABLE tablename TYPE=InnoDB. That makes MySQL to rebuild the table.
If the insertions to an index are always ascending and records are deleted only from the end, then the file space management algorithm of InnoDB guarantees that fragmentation in the index will not occur.
The error handling in InnoDB is not always the same as specified in the SQL standard. According to SQL-99, any error during an SQL statement should cause the rollback of that statement. InnoDB sometimes rolls back only part of the statement, or the whole transaction. The following list specifies the error handling of InnoDB.
If you run out of file space in the tablespace, you will get the MySQL 'Table is full' error and InnoDB rolls back the SQL statement.
A transaction deadlock or a timeout in a lock wait make InnoDB to roll back the whole transaction.
A duplicate key error only rolls back the insert of that particular row, even in a statement like INSERT INTO ... SELECT .... This will probably change so that the SQL statement will be rolled back if you have not specified the IGNORE option in your statement.
A 'row too long' error rolls back the SQL statement.
Other errors are mostly detected by the MySQL layer of code, and they roll back the corresponding SQL statement.
InnoDB tables do not support full-text indexes.
In Windows, InnoDB stores the database names and table names internally always in lowercase. To move databases in a binary format from Unix to Windows or from Windows to Unix you should have all table and database names in lowercase.
TRUNCATE table_name doesn't reset any AUTO_INCREMENT counters.
Warning: Do NOT convert MySQL system tables from MyISAM TO InnoDB tables! This is not supported; if you do this MySQL will not restart until you restore the old system tables from a backup or re-generate them with the mysql_install_db script.
SHOW TABLE STATUS does not give accurate statistics on InnoDB tables, except for the physical size reserved by the table. The row count is only a rough estimate used in SQL optimization.
If you try to create a unique index on a prefix of a column you will get an error:
CREATE TABLE T (A CHAR(20), B INT, UNIQUE (A(5))) TYPE = InnoDB;
If you create a non-unique index on a prefix of a column, InnoDB will create an index over the whole column.
INSERT DELAYED is not supported for InnoDB tables.
The MySQL LOCK TABLES operation does not know of InnoDB row level locks set in already completed SQL statements: this means that you can get a table lock on a table even if there still exist transactions of other users which have row level locks on the same table. Thus your operations on the table may have to wait if they collide with these locks of other users. Also a deadlock is possible. However, this does not endanger transaction integrity, because the row level locks set by InnoDB will always take care of the integrity. Also, a table lock prevents other transactions from acquiring more row level locks (in a conflicting lock mode) on the table.
A table cannot contain more than 1000 columns.
DELETE FROM TABLE does not regenerate the table but instead deletes all rows, one by one, which is not that fast. In future versions of MySQL you can use TRUNCATE which is fast.
The default database page size in InnoDB is 16 KB. By recompiling the code one can set it from 8 KB to 64 KB. The maximun row length is slightly less than half of a database page in versions <= 3.23.40 of InnoDB. Starting from source release 3.23.41 BLOB and TEXT columns are allowed to be < 4 GB, the total row length must also be < 4 GB. InnoDB does not store fields whose size is <= 128 bytes on separate pages. After InnoDB has modified the row by storing long fields on separate pages, the remaining length of the row must be less than half a database page. The maximun key length is 7000 bytes.
On some operating systems datafiles must be < 2 GB. The combined size of log files must be < 4 GB.
The maximum tablespace size is 4 billion database pages. This is also the maximum size for a table. The minimum tablespace size is 10 MB.
When you restart the MySQL server, InnoDB may reuse an old value for an AUTO_INCREMENT column.
You cannot set the first AUTO_INCREMENT column value in InnoDB with CREATE TABLE ... AUTO_INCREMENT=... (or ALTER TABLE ...). To set the value insert a dummy row with a value one less, and delete that dummy row.
IMPORTANT NOTE: if you upgrade to InnoDB-4.1.1 or higher, you cannot downgrade to a version lower than 4.1.1 any more! That is because earlier versions of InnoDB are not aware of multiple tablespaces.
InnoDB in 5.0.0 is essentially the same as InnoDB-4.1.1 with the bug fixes of InnoDB-4.0.17 included.
Fixed a bug: if you created a column prefix secondary index and updated it so that the last characters in the column prefix were spaces, InnoDB would assert in row0upd.c, line 713. The same assertion failed if you updated a column in an ordinary secondary index so that the new value was alphabetically equivalent, but had a different length. This could happen, for example, in the UTF8 character set if you updated a letter to its accented or umlaut form.
Fixed a bug: InnoDB could think that a secondary index record was not locked though it had been updated to an alphabetically equivalent value, e.g., 'abc' -> 'aBc'.
Fixed a bug: if you updated a secondary index column to an alphabetically equivalent value, and rolled back your update, InnoDB failed to restore the field in the secondary index to its original value.
There are still several outstanding non-critical bugs reported in the MySQL bugs database. Their fixing has been delayed, because resources were allocated to the 4.1.1 release.
IMPORTANT NOTE: if you upgrade to InnoDB-4.1.1 or higher, you cannot downgrade to a version lower than 4.1.1 any more! That is because earlier versions of InnoDB are not aware of multiple tablespaces.
Multiple tablespaces now available for InnoDB. You can store each InnoDB type table and its indexes into a separate .ibd file into a MySQL database directory, into the same directory where the .frm file is stored.
The MySQL query cache now works for InnoDB tables also if AUTOCOMMIT=0, or the statements are enclosed inside BEGIN ... COMMIT.
Reduced InnoDB memory consumption by a few megabytes if one sets the buffer pool size < 8 MB.
You can use raw disk partitions also in Windows.
Fixed a bug: in contrary to what was said in the manual, in a locking read InnoDB set two record locks if a unique exact match search condition was used on a multi-column unique key. For a single column unique key it worked right.
Fixed a bug: if one used the rename trick #sql... -> rsql... to recover a temporary table, InnoDB asserted in row_mysql_lock_data_dictionary().
There are several outstanding non-critical bugs reported in the MySQL bugs database. Their fixing has been delayed, because resources are allocated to the upcoming 4.1.1 release.
Fixed a bug: InnoDB could make the index page directory corrupt in the first B-tree page splits after mysqld startup. A symptom would be an assertion failure in page0page.c, in function page_dir_find_slot().
Fixed a bug: InnoDB could in rare cases return an extraneous row if a rollback, purge, and a SELECT coincided.
Fixed a possible hang over the btr0sea.c latch if SELECT was used inside LOCK TABLES.
Fixed a bug: if a single DELETE statement first managed to delete some rows and then failed in a FOREIGN KEY error or a Table is full error, MySQL did not roll back the whole SQL statement as it should.
Fixed a bug: if you updated a row so that the 8000 byte maximum length (without BLOB and TEXT) was exceeded, InnoDB simply removed the record from the clustered index. In a similar insert, InnoDB would leak reserved file space extents, which would only be freed at the next mysqld startup.
Fixed a bug: if you used big BLOB values, and your log files were relatively small, InnoDB could in a big BLOB operation temporarily write over the log produced after the latest checkpoint. If InnoDB would crash at that moment, then the crash recovery would fail, because InnoDB would not be able to scan the log even up to the latest checkpoint. Starting from this version, InnoDB tries to ensure the latest checkpoint is young enough. If that is not possible, InnoDB prints a warning to the .err log of MySQL and advises you to make the log files bigger.
Fixed a bug: setting innodb_fast_shutdown=0 had no effect.
Fixed a bug introduced in 4.0.13: if a CREATE TABLE ended in a comment, that could cause a memory overrun.
Fixed a bug: If InnoDB printed Operating system error number .. in a file operation to the .err log in Windows, the error number explanation was wrong. Workaround: look at section 13.2 of http://www.innodb.com/ibman.php about Windows error numbers.
Fixed a bug: If you created a column prefix PRIMARY KEY like in t(a CHAR(200), PRIMARY KEY (a(10))) on a fixed-length CHAR column, InnoDB would crash even in a simple SELECT. CCHECK TABLE would report the table as corrupt, also in the case where the created key was not PRIMARY.
InnoDB now supports the SAVEPOINT and ROLLBACK TO SAVEPOINT SQL statements. See http://www.innodb.com/ibman.php#Savepoints for the syntax.
You can now create column prefix keys like in CREATE TABLE t (a BLOB, INDEX (a(10))).
You can also use O_DIRECT as the innodb_flush_method on the latest versions of Linux and FreeBSD. Beware of possible bugs in those operating systems, though.
Fixed the checksum calculation of data pages. Previously most OS file system corruption went unnoticed. Note that if you downgrade from version >= 4.0.14 to an earlier version < 4.0.14 then in the first startup(s) InnoDB will print warnings:
InnoDB: Warning: An inconsistent page in the doublewrite buffer InnoDB: space id 2552202359 page number 8245, 127'th page in dblwr buf.
but that is not dangerous and can be ignored.
Modified the buffer pool replacement algorithm so that it tries to flush modified pages if there are no replaceable pages in the last 10 % of the LRU list. This can reduce disk i/o if the workload is a mixture of reads and writes.
The buffer pool checkpoint flush algorithm now tries to flush also close neighbors of the page at the end of the flush list. This can speed up database shutdown, and can also speed up disk writes if InnoDB log files are very small compared to the buffer pool size.
In 4.0.13 we made SHOW INNODB STATUS to print detailed info on the latest UNIQUE KEY error, but storing that info could slow down REPLACE significantly. We no longer store or print the info.
Fixed a bug: SET FOREIGN_KEY_CHECKS=0 was not replicated properly in the MySQL replication. The fix will not be backported to 3.23.
Fixed a bug: the parameter innodb_max_dirty_pages_pct forgot to take into account the free pages in the buffer pool. This could lead to excessive flushing even though there were lots of free pages in the buffer pool. Workaround: SET GLOBAL innodb_max_dirty_pages_pct = 100.
Fixed a bug: if there were big index scans then a file read request could starve and InnoDB could assert because of a very long semaphore wait.
Fixed a bug: if AUTOCOMMIT=1 then inside LOCK TABLES MySQL failed to do the commit after an updating SQL statement if binlogging was not on, and for SELECT statements did not commit regardless of binlogging state.
Fixed a bug: InnoDB could make the index page directory corrupt in the first B-tree page splits after a mysqld startup. A symptom would be an assertion in page0page.c, in function page_dir_find_slot().
Fixed a bug: if in a FOREIGN KEY with an UPDATE CASCADE clause the parent column was of a different internal storage length than the child column, then a cascaded update would make the column length wrong in the child table and corrupt the child table. Because of MySQL's 'silent column specification changes' a fixed-length CHAR column can change internally to a VARCHAR and cause this error.
Fixed a bug: if a non-latin1 character set was used and if in a FOREIGN KEY the parent column was of a different internal storage length than the child column, then all inserts to the child table would fail in a foreign key error.
Fixed a bug: InnoDB could complain that it cannot find the clustered index record, or in rare cases return an extraneous row if a rollback, purge, and a SELECT coincided.
Fixed a possible hang over the btr0sea.c latch if SELECT was used inside LOCK TABLES.
Fixed a bug: contrary to what the release note of 4.0.13 said, the group commit still did not work if the MySQL binlogging was on.
Fixed a bug: os_event_wait() did not work properly in Unix, which might have caused starvation in various log operations.
Fixed a bug: if a single DELETE statement first managed to delete some rows and then failed in a FOREIGN KEY error or a 'Table is full error', MySQL did not roll back the whole SQL statement as it should, and also wrote the failed statement to the binlog, reporting there a non-zero error_code.
Fixed a bug: the maximum allowed number of columns in a table is 1000, but InnoDB did not check that limit in CREATE TABLE, and a subsequent INSERT or SELECT from that table could cause an assertion.
Changed the default value of innodb_flush_log_at_trx_commit from 0 to 1. If you have not specified it explicitly in your my.cnf, and your application runs much slower with this new release, it is because the value 1 causes a log flush to disk at each transaction commit.
Fixed a bug: InnoDB forgot to call pthread_mutex_destroy() when a table was dropped. That could cause memory leakage on FreeBSD and other non-Linux Unixes.
Fixed a bug: MySQL could erroneously return 'Empty set' if InnoDB estimated an index range size to 0 records though the range was not empty; MySQL also failed to do the next-key locking in the case of an empty index range.
Fixed a bug: GROUP BY and DISTINCT could treat NULL values inequal.
InnoDB now supports ALTER TABLE DROP FOREIGN KEY. You have to use SHOW CREATE TABLE to find the internally generated foreign key ID when you want to drop a foreign key.
SHOW INNODB STATUS now prints detailed information of the latest detected FOREIGN KEY and UNIQUE KEY errors. If you do not understand why InnoDB gives the error 150 from a CREATE TABLE, you can use this statement to study the reason.
ANALYZE TABLE now works also for InnoDB type tables. It makes 10 random dives to each of the index trees and updates index cardinality estimates accordingly. Note that since it is only an estimate, repeated runs of ANALYZE TABLE may produce different numbers. MySQL uses index cardinality estimates only in join optimization. If some join is not optimized in the right way, you may try using ANALYZE TABLE.
InnoDB group commit capability now works also when MySQL binlogging is switched on. There have to be > 2 client threads for the group commit to become active.
Changed the default value of innodb_flush_log_at_trx_commit from 0 to 1. If you have not specified it explicitly in your my.cnf, and your application runs much slower with this new release, it is because the value 1 causes a log flush to disk at each transaction commit.
Added a new global settable MySQL system variable innodb_max_dirty_pages_pct. It is an integer in the range 0 - 100. The default is 90. The main thread in InnoDB tries to flush pages from the buffer pool so that at most this many percents are not yet flushed at any time.
If innodb_force_recovery=6, do not let InnoDB do repair of corrupt pages based on the doublewrite buffer.
InnoDB start-up now happens faster because it does not set the memory in the buffer pool to zero.
Fixed a bug: The InnoDB parser for FOREIGN KEY definitions was confused by the keywords 'foreign key' inside MySQL comments.
Fixed a bug: If you dropped a table to which there was a FOREIGN KEY reference, and later created the same table with non-matching column types, InnoDB could assert in dict0load.c, in function dict_load_table().
Fixed a bug: GROUP BY and DISTINCT could treat NULL values as not equal. MySQL also failed to do the next-key locking in the case of an empty index range.
Fixed a bug: Do not commit the current transaction when a MyISAM table is updated; this also makes CREATE TABLE not to commit an InnoDB transaction, even when binlogging is enabled.
Fixed a bug: We did not allow ON DELETE SET NULL to modify the same table where the delete was made; we can allow it because that cannot produce infinite loops in cascaded operations.
Fixed a bug: Allow HANDLER PREV and NEXT also after positioning the cursor with a unique search on the primary key.
Fixed a bug: If MIN() or MAX() resulted in a deadlock or a lock wait timeout, MySQL did not return an error, but returned NULL as the function value.
Fixed a bug: InnoDB forgot to call pthread_mutex_destroy() when a table was dropped. That could cause memory leakage on FreeBSD and other non-Linux Unix systems.
InnoDB now supports up to 64 GB of buffer pool memory in a Windows 32-bit Intel computer. This is possible because InnoDB can use the AWE extension of Windows to address memory over the 4 GB limit of a 32-bit process. A new startup variable innodb_buffer_pool_awe_mem_mb enables AWE and sets the size of the buffer pool in megabytes.
Reduced the size of buffer headers and the lock table. InnoDB uses 2 % less memory.
Fixed a major bug in InnoDB query optimization: queries of type SELECT ... WHERE indexcolumn < x and SELECT ... WHERE indexcolumn > x could cause a table scan even if the selectivity would have been very good.
Fixed a potential bug if MySQL calls store_lock with TL_IGNORE in the middle of a query.
In crash recovery InnoDB now prints the progress in percents of a transaction rollback.
Fixed a bug/feature: if your application program used mysql_use_result(), and used >= 2 connections to send SQL queries, it could deadlock on the adaptive hash S-latch in btr0sea.c. Now mysqld releases the S-latch whenever it passes data from a SELECT to the client.
Fixed a bug: MySQL could erroneously return 'Empty set' if InnoDB estimated an index range size to 0 records though the range was not empty; MySQL also failed to do the next-key locking in the case of an empty index range.
Fixed a bug introduced in 4.0.10: SELECT ... FROM ... ORDER BY ... DESC could hang in an infinite loop.
An outstanding bug: SET FOREIGN_KEY_CHECKS=0 is not replicated properly in the MySQL replication.
In INSERT INTO t1 SELECT ... FROM t2 WHERE ... MySQL previously set a table level read lock on t2. This lock is now removed.
Increased SHOW INNODB STATUS max printed length to 200 KB.
Fixed a major bug in InnoDB query optimization: queries of type SELECT ... WHERE indexcolumn < x and SELECT ... WHERE indexcolumn > x could cause a table scan even if the selectivity would have been very good.
Fixed a bug: purge could cause a hang in a BLOB table where the primary key index tree was of height 1. Symptom: semaphore waits caused by an X-latch set in btr_free_externally_stored_field().
Fixed a bug: using InnoDB HANDLER commands on a fresh handle crashed mysqld in ha_innobase::change_active_index().
Fixed a bug: if MySQL estimated a query in the middle of a SELECT statement, InnoDB could hang on the adaptive hash index latch in btr0sea.c.
Fixed a bug: InnoDB could report table corruption and assert in page_dir_find_owner_slot() if an adaptive hash index search coincided with purge or an insert.
Fixed a bug: some file system snapshot tool in Windows 2000 could cause an InnoDB file write to fail with error 33 ERROR_LOCK_VIOLATION. In synchronous writes InnoDB now retries the write 100 times at 1 second intervals.
Fixed a bug: REPLACE INTO t1 SELECT ... did not work if t1 has an auto-inc column.
An outstanding bug: SET FOREIGN_KEY_CHECKS=0 is not replicated properly in the MySQL replication.
In INSERT INTO t1 SELECT ... FROM t2 WHERE ... MySQL previously set a table level read lock on t2. This lock is now removed.
Fixed a bug: if the combined size of InnoDB log files was >= 2 GB in a 32-bit computer, InnoDB would write log in a wrong position. That could make crash recovery and InnoDB Hot Backup to fail in log scan.
Fixed a bug: index cursor restoration could theoretically fail.
Fixed a bug: an assertion in btr0sea.c, in function btr_search_info_update_slow could theoretically fail in a race of 3 threads.
Fixed a bug: purge could cause a hang in a BLOB table where the primary key index tree was of height 1. Symptom: semaphore waits caused by an X-latch set in btr_free_externally_stored_field().
Fixed a bug: if MySQL estimated a query in the middle of a SELECT statement, InnoDB could hang on the adaptive hash index latch in btr0sea.c.
Fixed a bug: InnoDB could report table corruption and assert in page_dir_find_owner_slot() if an adaptive hash index search coincided with purge or an insert.
Fixed a bug: some file system snapshot tool in Windows 2000 could cause an InnoDB file write to fail with error 33 ERROR_LOCK_VIOLATION. In synchronous writes InnoDB now retries the write 100 times at 1 second intervals.
An outstanding bug: SET FOREIGN_KEY_CHECKS=0 is not replicated properly in the MySQL replication. The fix will appear in 4.0.11 and will probably not be backported to 3.23.
Fixed bug in InnoDB page0cur.c in function page_cur_search_with_match which caused InnoDB to remain on the same page forever. This bug is evident only in tables with more than one page.
Removed the warning message: 'InnoDB: Out of memory in additional memory pool.'
Fixed a bug: if the combined size of InnoDB log files was >= 2 GB in a 32-bit computer, InnoDB would write log in a wrong position. That could make crash recovery and InnoDB Hot Backup to fail.
Fixed a bug: index cursor restoration could theoretically fail.
InnoDB now supports also FOREIGN KEY (...) REFERENCES ...(...) [ON UPDATE CASCADE | ON UPDATE SET NULL | ON UPDATE RESTRICT | ON UPDATE NO ACTION].
Tables and indexes now reserve 4 % less space in the tablespace. Also existing tables reserve less space. By upgrading to 4.0.8 you will see more free space in "InnoDB free" in SHOW TABLE STATUS.
Fixed bugs: updating the PRIMARY KEY of a row would generate a foreign key error on all FOREIGN KEYs which referenced secondary keys of the row to be updated. Also, if a referencing FOREIGN KEY constraint only referenced the first columns in an index, and there were more columns in that index, updating the additional columns generated a foreign key error.
Fixed a bug: if an index contains some column twice, and that column is updated, the table will become corrupt. From now on InnoDB prevents creation of such indexes.
Fixed a bug: removed superfluous error 149 and 150 printouts from the .err log when a locking SELECT caused a deadlock or a lock wait timeout.
Fixed a bug: an assertion in btr0sea.c, in function btr_search_info_update_slow could theoretically fail in a race of 3 threads.
Fixed a bug: one could not switch a session transaction isolation level back to REPEATABLE READ after setting it to something else.
Since innodb_log_arch_dir has no relevance under MySQL, there is no need to specify it any more in my.cnf.
LOAD DATA INFILE in AUTOCOMMIT=1 mode no longer does implicit commits for each 1 MB of written binlog.
Fixed a bug introduced in 4.0.4: LOCK TABLES ... READ LOCAL should not set row locks on the rows read. This caused deadlocks and lock wait timeouts in mysqldump.
Fixed two bugs introduced in 4.0.4: in AUTO_INCREMENT, REPLACE could cause the counter to be left 1 too low. A deadlock or a lock wait timeout could cause the same problem.
Fixed a bug: TRUNCATE on a TEMPORARY table crashed InnoDB.
Fixed a bug introduced in 4.0.5: if binlogging was not switched on, INSERT INTO ... SELECT ... or CREATE TABLE ... SELECT ... could cause InnoDB to hang on a semaphore created in btr0sea.c, line 128. Workaround: switch binlogging on.
Fixed a bug: in replication issuing SLAVE STOP in the middle of a multiple-statement transaction could cause that SLAVE START would only perform a part of the transaction. A similar error could occur if the slave crashed and was restarted.
Fixed a bug: the InnoDB range estimator greatly exaggerated the size of a short index range if the paths to the endpoints of the range in the index tree happened to branch already in the root. This could cause unnecessary table scans in SQL queries.
Fixed a bug: ORDER BY could fail if you had not created a primary key to a table, but had defined several indexes of which at least one was a UNIQUE index with all its columns declared as NOT NULL.
Fixed a bug: a lock wait timeout in connection with ON DELETE CASCADE could cause corruption in indexes.
Fixed a bug: if a SELECT was done with a unique key from a primary index, and the search matched to a delete-marked record, InnoDB could erroneously return the NEXT record.
Fixed a bug introduced in 3.23.53: LOCK TABLES ... READ LOCAL should not set row locks on the rows read. This caused deadlocks and lock wait timeouts in mysqldump.
Fixed a bug: if an index contains some column twice, and that column is updated, the table will become corrupt. From now on InnoDB prevents creation of such indexes.
InnoDB now supports also transaction isolation levels READ COMMITTED and READ UNCOMMITTED. READ COMMITTED more closely emulates Oracle and makes porting of applications from Oracle to MySQL easier.
Deadlock resolution is now selective: we try to pick as victims transactions with less modified or inserted rows.
FOREIGN KEY definitions are now aware of the lower_case_table_names setting in my.cnf.
SHOW CREATE TABLE does not output the database name to a FOREIGN KEY definition if the referred table is in the same database as the table.
InnoDB does a consistency check to most index pages before writing them to a datafile.
If you set innodb_force_recovery > 0, InnoDB tries to jump over corrupt index records and pages when doing SELECT * FROM table. This helps in dumping.
InnoDB now again uses asynchronous unbuffered I/O in Windows 2000 and XP; only unbuffered simulated async I/O in NT, 95/98/ME.
Fixed a bug: the InnoDB range estimator greatly exaggerated the size of a short index range if the paths to the endpoints of the range in the index tree happened to branch already in the root. This could cause unnecessary table scans in SQL queries. The fix will also be backported to 3.23.54.
Fixed a bug present in 3.23.52, 4.0.3, 4.0.4: InnoDB startup could take very long or even crash on some Windows 95/98/ME computers.
Fixed a bug: the AUTO-INC lock was held to the end of the transaction if it was granted after a lock wait. This could cause unnecessary deadlocks.
Fixed a bug: if SHOW INNODB STATUS, innodb_monitor, or innodb_lock_monitor had to print several hundred transactions in one report, and the output became truncated, InnoDB would hang, printing to the error log many waits for a mutex created at srv0srv.c, line 1621.
Fixed a bug: SHOW INNODB STATUS on Unix always reported average file read size as 0 bytes.
Fixed a potential bug in 4.0.4: InnoDB now does ORDER BY ... DESC like MyISAM.
Fixed a bug: DROP TABLE could cause crash or a hang if there was a rollback concurrently running on the table. The fix will be backported to 3.23 only if this appears a real problem for users.
Fixed a bug: ORDER BY could fail if you had not created a primary key to a table, but had defined several indexes of which at least one was a UNIQUE index with all its columns declared as NOT NULL.
Fixed a bug: a lock wait timeout in connection with ON DELETE CASCADE could cause corruption in indexes.
Fixed a bug: if a SELECT was done with a unique key from a primary index, and the search matched to a delete-marked record, InnoDB could return the NEXT record.
Outstanding bugs: in 4.0.4 two bugs were introduced to AUTO_INCREMENT. REPLACE can cause the counter to be left 1 too low. A deadlock or a lock wait timeout can cause the same problem. These will be fixed in 4.0.6.
We again use unbuffered disk I/O to datafiles in Windows. Windows XP and Windows 2000 read performance seems to be very poor with normal I/O.
Tuned range estimator so that index range scans are preferred over full index scans.
Allow dropping and creating a table even if innodb_force_recovery is set. One can use this to drop a table which would cause a crash in rollback or purge, or if a failed table import causes a runaway rollback in recovery.
Fixed a bug present in 3.23.52, 4.0.3, 4.0.4: InnoDB startup could take very long or even crash on some Windows 95/98/ME computers.
Fixed a bug: fast shutdown (which is the default) sometimes was slowed down by purge and insert buffer merge.
Fixed a bug: doing a big SELECT from a table where no rows were visible in a consistent read could cause a very long (> 600 seconds) semaphore wait in btr0cur.c line 310.
Fixed a bug: the AUTO-INC lock was held to the end of the transaction if it was granted after a lock wait. This could cause unnecessary deadlocks.
Fixed a bug: if you created a temporary table inside LOCK TABLES, and used that temporary table, that caused an assertion failure in ha_innobase.cc.
Fixed a bug: if SHOW INNODB STATUS, innodb_monitor, or innodb_lock_monitor had to print several hundred transactions in one report, and the output became truncated, InnoDB would hang, printing to the error log many waits for a mutex created at srv0srv.c, line 1621.
Fixed a bug: SHOW INNODB STATUS on Unix always reported average file read size as 0 bytes.
We again use unbuffered disk I/O in Windows. Windows XP and Windows 2000 read performance seems to be very poor with normal I/O.
Increased the max key length of InnoDB tables from 500 to 1024 bytes.
Increased the table comment field in SHOW TABLE STATUS so that up to 16000 characters of foreign key definitions can be printed there.
The auto-increment counter is no longer incremented if an insert of a row immediately fails in an error.
Allow dropping and creating a table even if innodb_force_recovery is set. One can use this to drop a table which would cause a crash in rollback or purge, or if a failed table import causes a runaway rollback in recovery.
Fixed a bug: Using ORDER BY primarykey DESC in 4.0.3 causes an assertion failure in btr0pcur.c, line 203.
Fixed a bug: fast shutdown (which is the default) sometimes was slowed down by purge and insert buffer merge.
Fixed a bug: doing a big SELECT from a table where no rows were visible in a consistent read could cause a very long (> 600 seconds) semaphore wait in btr0cur.c line 310.
Fixed a bug: if the MySQL query cache was used, it did not get invalidated by a modification done by ON DELETE CASCADE or ...SET NULL.
Fixed a bug: if you created a temporary table inside LOCK TABLES, and used that temporary table, that caused an assertion failure in ha_innodb.cc.
Fixed a bug: if you set innodb_flush_log_at_trx_commit to 1, SHOW VARIABLES would show its value as 16 million.
Removed unnecessary deadlocks when inserts have to wait for a locking read, update, or delete to release its next-key lock.
The MySQL HANDLER SQL commands now work also for InnoDB type tables. InnoDB does the HANDLER reads always as consistent reads. HANDLER is a direct access path to read individual indexes of tables. In some cases HANDLER can be used as a substitute of server-side cursors.
Fixed a bug in 4.0.2: even a simple insert could crash the AIX version.
Fixed a bug: if you used in a table name characters whose code is > 127, in DROP TABLE InnoDB could assert on line 155 of pars0sym.c.
Compilation from source now provides a working version both on HP-UX-11 and HP-UX-10.20. The source of 4.0.2 worked only on 11, and the source of 3.23.52 only on 10.20.
Fixed a bug: if compiled on 64-bit Solaris, InnoDB produced a bus error at startup.
The feature set of 3.23 will be frozen from this version on. New features will go the 4.0 branch, and only bug fixes will be made to the 3.23 branch.
Many CPU-bound join queries now run faster. On Windows also many other CPU-bound queries run faster.
A new SQL command SHOW INNODB STATUS returns the output of the InnoDB Monitor to the client. The InnoDB Monitor now prints detailed information on the latest detected deadlock.
InnoDB made the SQL query optimizer to avoid too much index-only range scans and choose full table scans instead. This is now fixed.
BEGIN and COMMIT are now added in the binlog around transactions. The MySQL replication now respects transaction borders: a user will no longer see half transactions in replication slaves.
A replication slave now prints in crash recovery the last master binlog position it was able to recover to.
A new setting innodb_flush_log_at_trx_commit=2 makes InnoDB to write the log to the operating system file cache at each commit. This is almost as fast as the setting innodb_flush_log_at_trx_commit=0, and the setting 2 also has the nice feature that in a crash where the operating system does not crash, no committed transaction is lost. If the operating system crashes or there is a power outage, then the setting 2 is no safer than the setting 0.
Added checksum fields to log blocks.
SET FOREIGN_KEY_CHECKS=0 helps in importing tables in an arbitrary order which does not respect the foreign key rules.
SET UNIQUE_CHECKS=0 speeds up table imports into InnoDB if you have UNIQUE constraints on secondary indexes. This flag should be used only if you are certain that the input records contain no UNIQUE constraint violations.
SHOW TABLE STATUS now lists also possible ON DELETE CASCADE or ON DELETE SET NULL in the comment field of the table.
When CHECK TABLE is run on any InnoDB type table, it now checks also the adaptive hash index for all tables.
If you defined ON DELETE CASCADE or SET NULL and updated the referenced key in the parent row, InnoDB deleted or updated the child row. This is now changed to conform to SQL-92: you get the error 'Cannot delete parent row'.
Improved the auto-increment algorithm: now the first insert or SHOW TABLE STATUS initializes the auto-increment counter for the table. This removes almost all surprising deadlocks caused by SHOW TABLE STATUS.
Aligned some buffers used in reading and writing to datafiles. This allows using unbuffered raw devices as datafiles in Linux.
Fixed a bug: If you updated the primary key of a table so that only the case of characters changed, that could cause assertion failures, mostly in page0page.ic line 515.
Fixed a bug: If you delete or update a row referenced in a foreign key constraint and the foreign key check has to wait for a lock, then the check may report an erroneous result. This affects also the ON DELETE... operation.
Fixed a bug: A deadlock or a lock wait timeout error in InnoDB causes InnoDB to roll back the whole transaction, but MySQL could still write the earlier SQL statements to the binlog, even though InnoDB rolled them back. This could, for example, cause replicated databases to get out-of-sync.
Fixed a bug: If the database happened to crash in the middle of a commit, then the recovery might leak tablespace pages.
Fixed a bug: If you specified a non-latin1 character set in my.cnf, then, in contrary to what is stated in the manual, in a foreign key constraint a string type column had to have the same length specification in the referencing table and the referenced table.
Fixed a bug: DROP TABLE or DROP DATABASE could fail if there simultaneously was a CREATE TABLE running.
Fixed a bug: If you configured the buffer pool bigger than 2 GB in a 32-bit computer, InnoDB would assert in buf0buf.ic line 214.
Fixed a bug: on 64-bit computers updating rows which contained the SQL NULL in some column could cause the undo log and the ordinary log to become corrupt.
Fixed a bug: innodb_log_monitor caused a hang if it suppressed lock prints for a page.
Fixed a bug: in the HP-UX-10.20 version mutexes would leak and cause race conditions and crashes in any part of InnoDB code.
Fixed a bug: if you ran in the AUTOCOMMIT mode, executed a SELECT, and immediately after that a RENAME TABLE, then RENAME would fail and MySQL would complain about error 1192.
Fixed a bug: if compiled on 64-bit Solaris, InnoDB produced a bus error at startup.
InnoDB is essentially the same as InnoDB-3.23.51.
If no innodb_data_file_path is specified, InnoDB at the database creation now creates a 10 MB auto-extending datafile ibdata1 to the datadir of MySQL. In 4.0.1 the file was 64 MB and not auto-extending.
Fixed a bug: a join could result in a seg fault in copying of a BLOB or TEXT column if some of the BLOB or TEXT columns in the table contained SQL NULL values.
Fixed a bug: if you added self-referential foreign key constraints with ON DELETE CASCADE to tables and a row deletion caused InnoDB to attempt the deletion of the same row twice because of a cascading delete, then you got an assertion failure.
Fixed a bug: if you use MySQL 'user level locks' and close a connection, then InnoDB may assert in ha_innobase.cc, line 302.
InnoDB now supports an auto-extending last datafile. You do not need to preallocate the whole datafile at the database startup.
Made several changes to facilitate the use of the InnoDB Hot Backup tool. It is a separate non-free tool you can use to take online backups of your database without shutting down the server or setting any locks.
If you want to run the InnoDB Hot Backup tool on an auto-extending datafile you have to upgrade it to version ibbackup-0.35.
The log scan phase in crash recovery will now run much faster.
Starting from this server version, the hot backup tool truncates unused ends in the backup InnoDB datafiles.
To allow the hot backup tool to work, on Windows we no longer use unbuffered I/O or native async I/O; instead we use the same simulated async I/O as on Unix.
You can now define the ON DELETE CASCADE or ON DELETE SET NULL clause on foreign keys.
FOREIGN KEY constraints now survive ALTER TABLE and CREATE INDEX.
We suppress the FOREIGN KEY check if any of the column values in the foreign key or referenced key to be checked is the SQL NULL. This is compatible with Oracle, for example.
SHOW CREATE TABLE now lists also foreign key constraints. Also mysqldump no longer forgets about foreign keys in table definitions.
You can now add a new foreign key constraint with ALTER TABLE ... ADD CONSTRAINT FOREIGN KEY (...) REFERENCES ... (...).
FOREIGN KEY definitions now allow backquotes around table and column names.
MySQL command SET TRANSACTION ISOLATION LEVEL ... has now the following effect on InnoDB tables: if a transaction is defined as SERIALIZABLE then InnoDB conceptually adds LOCK IN SHARE MODE to all consistent reads. If a transaction is defined to have any other isolation level, then InnoDB obeys its default locking strategy which is REPEATABLE READ.
SHOW TABLE STATUS no longer sets an x-lock at the end of an auto-increment index if the auto-increment counter has already been initialized. This removes in almost all cases the surprising deadlocks caused by SHOW TABLE STATUS.
Fixed a bug: in a CREATE TABLE statement the string 'foreign' followed by a non-space character confused the FOREIGN KEY parser and caused table creation to fail with errno 150.
Fixed a bug: if you called DROP DATABASE for a database on which there simultaneously were running queries, the MySQL server could crash or hang. Crashes fixed, but a full fix has to wait some changes in the MySQL layer of code.
Fixed a bug: on Windows one had to put the database name in lowercase for DROP DATABASE to work. Fixed in 3.23.49: case no longer matters on Windows. On Unix, the database name remains case sensitive.
Fixed a bug: if one defined a non-latin1 character set as the default character set, then definition of foreign key constraints could fail in an assertion failure in dict0crea.c, reporting an internal error 17.
Tuned the SQL optimizer to favor more often index searches over table scans.
Fixed a performance problem when several large SELECT queries are run concurrently on a multiprocessor Linux computer. Large CPU-bound SELECT queries will now also generally run faster on all platforms.
If MySQL binlogging is used, InnoDB now prints after crash recovery the latest MySQL binlog file name and the position in that file (= byte offset) InnoDB was able to recover to. This is useful, for example, when resynchronizing a master and a slave database in replication.
Added better error messages to help in installation problems.
One can now recover also MySQL temporary tables which have become orphaned inside the InnoDB tablespace.
InnoDB now prevents a FOREIGN KEY declaration where the signedness is not the same in the referencing and referenced integer columns.
Fixed a bug: calling SHOW CREATE TABLE or SHOW TABLE STATUS could cause memory corruption and make mysqld to crash. Especially at risk was mysqldump, because it calls frequently SHOW CREATE TABLE.
Fixed a bug: if on Unix you did an ALTER TABLE to an InnoDB table and simultaneously did queries to it, mysqld could crash with an assertion failure in row0row.c, line 474.
Fixed a bug: if inserts to several tables containing an auto-inc column were wrapped inside one LOCK TABLES, InnoDB asserted in lock0lock.c.
In 3.23.47 we allowed several NULLS in a UNIQUE secondary index. But CHECK TABLE was not relaxed: it reports the table as corrupt. CHECK TABLE no longer complains in this situation.
Fixed a bug: on Sparc and other high-endian processors SHOW VARIABLES showed innodb_flush_log_at_trx_commit and other boolean-valued startup parameters always OFF even if they were switched on.
Fixed a bug: if you ran mysqld-max-nt as a service on Windows NT/2000, the service shutdown did not always wait long enough for the InnoDB shutdown to finish.
Recovery happens now faster, especially in a lightly loaded system, because background checkpointing has been made more frequent.
InnoDB allows now several similar key values in a UNIQUE secondary index if those values contain SQL NULLs. Thus the convention is now the same as in MyISAM tables.
InnoDB gives a better row count estimate for a table which contains BLOBs.
In a FOREIGN KEY constraint InnoDB is now case-insensitive to column names, and in Windows also to table names.
InnoDB allows a FOREIGN KEY column of CHAR type to refer to a column of VARCHAR type, and vice versa. MySQL silently changes the type of some columns between CHAR and VARCHAR, and these silent changes do not hinder FOREIGN KEY declaration any more.
Recovery has been made more resilient to corruption of log files.
Unnecessary statistics calculation has been removed from queries which generate a temporary table. Some ORDER BY and DISTINCT queries will now run much faster.
MySQL now knows that the table scan of an InnoDB table is done through the primary key. This will save a sort in some ORDER BY queries.
The maximum key length of InnoDB tables is again restricted to 500 bytes. The MySQL interpreter is not able to handle longer keys.
The default value of innodb_lock_wait_timeout was changed from infinite to 50 seconds, the default value of innodb_file_io_threads from 9 to 4.
InnoDB is the same as in 3.23.47.
In 4.0.0 the MySQL interpreter did not know the syntax LOCK IN SHARE MODE. This has been fixed.
In 4.0.0 multiple-table delete did not work for transactional tables. This has been fixed.
This is a bugfix release.
In versions 3.23.42-.44 when creating a table on Windows you have to use lowercase letters in the database name to be able to access the table. Fixed in 3.23.45.
InnoDB now flushes stdout and stderr every 10 seconds: if these are redirected to files, the file contents can be better viewed with an editor.
Fixed an assertion failure in .44, in trx0trx.c, line 178 when you drop a table which has the .frm file but does not exist inside InnoDB.
Fixed a bug in the insert buffer. The insert buffer tree could get into an inconsistent state, causing a crash, and also crashing the recovery. This bug could appear especially in large table imports or alterations.
Fixed a bug in recovery: InnoDB could go into an infinite loop constantly printing a warning message that it cannot find free blocks from the buffer pool.
Fixed a bug: when you created a temporary table of the InnoDB type, and then used ALTER TABLE to it, the MySQL server could crash.
Prevented creation of MySQL system tables 'mysql.user', 'mysql.host', or 'mysql.db', in the InnoDB type.
Fixed a bug which can cause an assertion failure in 3.23.44 in srv0srv.c, line 1728.
You can define foreign key constraints on InnoDB tables. An example: FOREIGN KEY (col1) REFERENCES table2(col2).
You can create > 4 GB datafiles in those file systems that allow it.
Improved InnoDB monitors, including a new innodb_table_monitor which allows you to print the contents of the InnoDB internal data dictionary.
DROP DATABASE will now work also for InnoDB tables.
Accent characters in the default character set latin1 will be ordered according to the MySQL ordering.<br> NOTE: if you are using latin1 and have inserted characters whose code is > 127 to an indexed CHAR column, you should run CHECK TABLE on your table when you upgrade to 3.23.43, and drop and reimport the table if CHECK TABLE reports an error!
InnoDB will calculate better table cardinality estimates.
Change in deadlock resolution: in .43 a deadlock rolls back only the SQL statement, in .44 it will roll back the whole transaction.
Deadlock, lock wait timeout, and foreign key constraint violations (no parent row, child rows exist) now return native MySQL error codes 1213, 1205, 1216, 1217, respectively.
A new my.cnf parameter innodb_thread_concurrency helps in performance tuning in high concurrency environments.
A new my.cnf option innodb_force_recovery will help you in dumping tables from a corrupted database.
A new my.cnf option innodb_fast_shutdown will speed up shutdown. Normally InnoDB does a full purge and an insert buffer merge at shutdown.
Raised maximum key length to 7000 bytes from a previous limit of 500 bytes.
Fixed a bug in replication of auto-inc columns with multiline inserts.
Fixed a bug when the case of letters changes in an update of an indexed secondary column.
Fixed a hang when there are > 24 datafiles.
Fixed a crash when MAX(col) is selected from an empty table, and col is a not the first column in a multi-column index.
Fixed a bug in purge which could cause crashes.
Fixed a bug which corrupted the table if the primary key of a > 8000-byte row was updated.
There are now 3 types of InnoDB Monitors: innodb_monitor, innodb_lock_monitor, and innodb_tablespace_monitor. innodb_monitor now prints also buffer pool hit rate and the total number of rows inserted, updated, deleted, read.
Fixed a bug in RENAME TABLE.
Fixed a bug in replication with an auto-increment column.
Support for < 4 GB rows. The previous limit was 8000 bytes.
Use the doublewrite file flush method.
Raw disk partitions supported as datafiles.
InnoDB Monitor.
Several hang bugs fixed and an ORDER BY bug ('Sort aborted') fixed.
CHECK TABLE now works for InnoDB tables.
A new my.cnf parameter innodb_unix_file_flush_method introduced. It can be used to tune disk write performance.
An auto-increment column now gets new values past the transaction mechanism. This saves CPU time and eliminates transaction deadlocks in new value assignment.
Several bug fixes, most notably the rollback bug in 3.23.38.
Contact information of Innobase Oy, producer of the InnoDB engine. Web site: http://www.innodb.com/. Email: <sales@innodb.com>
phone: 358-9-6969 3250 (office) 358-40-5617367 (mobile) Innobase Oy Inc. World Trade Center Helsinki Aleksanterinkatu 17 P.O.Box 800 00101 Helsinki Finland
Table of Contents
BerkeleyDB, available at http://www.sleepycat.com/ has provided MySQL with a transactional storage engine. Support for this storage engine is included in the MySQL source distribution starting from version 3.23.34 and is activated in the MySQL-Max binary. This storage engine is typically called BDB for short.
BDB tables may have a greater chance of surviving crashes and are also capable of COMMIT and ROLLBACK operations on transactions. The MySQL source distribution comes with a BDB distribution that has a couple of small patches to make it work more smoothly with MySQL. You can't use a non-patched BDB version with MySQL.
We at MySQL AB are working in close cooperation with Sleepycat to keep the quality of the MySQL/BDB interface high.
When it comes to supporting BDB tables, we are committed to help our users to locate the problem and help creating a reproducible test case for any problems involving BDB tables. Any such test case will be forwarded to Sleepycat who in turn will help us find and fix the problem. As this is a two-stage operation, any problems with BDB tables may take a little longer for us to fix than for other storage engines. However, as the BerkeleyDB code itself has been used by many other applications than MySQL, we don't envision any big problems with this. See Support.
If you have downloaded a binary version of MySQL that includes support for BerkeleyDB, simply follow the instructions for installing a binary version of MySQL. See Installing binary. See mysqld-max.
To compile MySQL with Berkeley DB support, download MySQL Version 3.23.34 or newer and configure MySQL with the --with-berkeley-db option. See Installing source.
cd /path/to/source/of/mysql-3.23.34 ./configure --with-berkeley-db
Please refer to the manual provided with the BDB distribution for more updated information.
Even though Berkeley DB is in itself very tested and reliable, the MySQL interface is still considered gamma quality. We are actively improving and optimizing it to make it stable very soon.
If you are running with AUTOCOMMIT=0 then your changes in BDB tables will not be updated until you execute COMMIT. Instead of commit you can execute ROLLBACK to forget your changes. See COMMIT.
If you are running with AUTOCOMMIT=1 (the default), your changes will be committed immediately. You can start an extended transaction with the BEGIN WORK SQL command, after which your changes will not be committed until you execute COMMIT (or decide to ROLLBACK the changes).
The following options to mysqld can be used to change the behavior of BDB tables:
Option | Description |
--bdb-home=directory | Base directory for BDB tables. This should be the same directory you use for --datadir. |
--bdb-lock-detect=# | Berkeley lock detection method. One of (DEFAULT, OLDEST, RANDOM, or YOUNGEST). |
--bdb-logdir=directory | Berkeley DB log file directory. |
--bdb-no-sync | Don't synchronously flush logs. |
--bdb-no-recover | Don't start Berkeley DB in recover mode. |
--bdb-shared-data | Start Berkeley DB in multi-process mode (Don't use DB_PRIVATE when initializing Berkeley DB) |
--bdb-tmpdir=directory | Berkeley DB temporary file directory. |
--skip-bdb | Disable usage of BDB tables. |
-O bdb_max_lock=1000 | Set the maximum number of locks possible. See bdb_max_lock. |
If you use --skip-bdb, MySQL will not initialize the Berkeley DB library and this will save a lot of memory. You cannot use BDB tables if you are using this option. If you try to create a BDB table, MySQL will instead create a MyISAM table.
Normally you should start mysqld without --bdb-no-recover if you intend to use BDB tables. This may, however, give you problems when you try to start mysqld if the BDB log files are corrupted. See Starting server.
With bdb_max_lock you can specify the maximum number of locks (10000 by default) you can have active on a BDB table. You should increase this if you get errors of type bdb: Lock table is out of available locks or Got error 12 from ... when you have do long transactions or when mysqld has to examine a lot of rows to calculate the query.
You may also want to change binlog_cache_size and max_binlog_cache_size if you are using big multi-line transactions. See COMMIT.
To be able to rollback transactions, the BDB storage engine maintains log files. For maximum performance you should place these on another disk than your databases by using the --bdb-logdir option.
MySQL performs a checkpoint each time a new BDB log file is started, and removes any log files that are not needed for current transactions. One can also run FLUSH LOGS at any time to checkpoint the Berkeley DB tables.
For disaster recovery, one should use table backups plus MySQL's binary log. See Backup.
Warning: If you delete old log files that are in use, BDB will not be able to do recovery at all and you may lose data if something goes wrong.
MySQL requires a PRIMARY KEY in each BDB table to be able to refer to previously read rows. If you don't create one, MySQL will create an maintain a hidden PRIMARY KEY for you. The hidden key has a length of 5 bytes and is incremented for each insert attempt.
If all columns you access in a BDB table are part of the same index or part of the primary key, then MySQL can execute the query without having to access the actual row. In a MyISAM table the above holds only if the columns are part of the same index.
The PRIMARY KEY will be faster than any other key, as the PRIMARY KEY is stored together with the row data. As the other keys are stored as the key data + the PRIMARY KEY, it's important to keep the PRIMARY KEY as short as possible to save disk and get better speed.
LOCK TABLES works on BDB tables as with other tables. If you don't use LOCK TABLE, MySQL will issue an internal multiple-write lock on the table to ensure that the table will be properly locked if another thread issues a table lock.
Internal locking in BDB tables is done on page level.
SELECT COUNT(*) FROM table_name is slow as BDB tables doesn't maintain a count of the number of rows in the table.
Sequential scanning is slower than with MyISAM tables as the data in BDB tables stored in B-trees and not in a separate datafile.
The application must always be prepared to handle cases where any change of a BDB table may make an automatic rollback and any read may fail with a deadlock error.
Keys are not prefix or suffix-compressed like keys in MyISAM tables. In other words, the key information will take a little more space in BDB tables compared to MyISAM tables.
There are often holes in the BDB table to allow you to insert new rows in the middle of the key tree. This makes BDB tables somewhat larger than MyISAM tables.
The optimizer needs to know an approximation of the number of rows in the table. MySQL solves this by counting inserts and maintaining this in a separate segment in each BDB table. If you don't issue a lot of DELETE or ROLLBACK statements, this number should be accurate enough for the MySQL optimizer, but as MySQL only stores the number on close, it may be incorrect if MySQL dies unexpectedly. It should not be fatal even if this number is not 100% correct. One can update the number of rows by executing ANALYZE TABLE or OPTIMIZE TABLE. See ANALYZE TABLE . See OPTIMIZE TABLE.
If you get full disk with a BDB table, you will get an error (probably error 28) and the transaction should roll back. This is in contrast with MyISAM and ISAM tables where mysqld will wait for enough free disk before continuing.
It's very slow to open many BDB tables at the same time. If you are going to use BDB tables, you should not have a very big table cache (like >256) and you should use --no-auto-rehash with the mysql client. We plan to partly fix this in 4.0.
SHOW TABLE STATUS doesn't yet provide that much information for BDB tables.
Optimize performance.
Change to not use page locks at all when we are scanning tables.
Currently we know that the BDB storage engine works with the following operating systems:
Linux 2.x Intel
Sun Solaris (SPARC and x86)
FreeBSD 4.x/5.x (x86, sparc64)
IBM AIX 4.3.x
SCO OpenServer
SCO UnixWare 7.1.x
It doesn't work with the following operating systems:
Linux 2.x Alpha
Linux 2.x AMD64
Linux 2.x IA-64
Linux 2.x s390
Max OS X
Note: The above list is not complete; we will update it as we receive more information.
If you build MySQL with support for BDB tables and get the following error in the log file when you start mysqld:
bdb: architecture lacks fast mutexes: applications cannot be threaded Can't init databases
This means that BDB tables are not supported for your architecture. In this case you must rebuild MySQL without BDB table support.
Here follows the restrictions you have when using BDB tables:
BDB tables store in the .db file the path to the file as it was created. (This was done to be able to detect locks in a multi-user environment that supports symlinks).
The effect of this is that BDB tables are not movable between directories!
When taking backups of BDB tables, you have to either use mysqldump or take a backup of all table_name.db files and the BDB log files. The BDB log files are the files in the base data directory named log.XXXXXXXXXX (ten digits); The BDB storage engine stores unfinished transactions in the log files and requires these logs to be present when mysqld starts.
If you get the following error in the hostname.err log when starting mysqld:
bdb: Ignoring log file: .../log.XXXXXXXXXX: unsupported log version #
it means that the new BDB version doesn't support the old log file format. In this case you have to delete all BDB logs from your database directory (the files with names that have the format log.XXXXXXXXXX) and restart mysqld. We would also recommend you to do a mysqldump --opt of your old BDB tables, delete the old tables, and restore the dump.
If you are not running in auto-commit mode and delete a table that is referenced in another transaction, you may get the following error messages in your MySQL error log:
001119 23:43:56 bdb: Missing log fileid entry 001119 23:43:56 bdb: txn_abort: Log undo failed for LSN: 1 3644744: Invalid
This is not fatal but we don't recommend that you delete tables if you are not in auto-commit mode, until this problem is fixed (the fix is not trivial).
The deprecated ISAM table type will disappear in MySQL version 5.0. In MySQL 4.1 it's included in the source but not compiled anymore. MyISAM is a better implementation of this table handler and you should convert all ISAM tables to MySAM tables as soon as possible.
ISAM uses a B-tree index. The index is stored in a file with the .ISM extension, and the data is stored in a file with the .ISD extension. You can check/repair ISAM tables with the isamchk utility. See Crash recovery.
ISAM has the following features/properties:
Compressed and fixed-length keys
Fixed and dynamic record length
16 keys with 16 key parts/key
Max key length 256 (default)
Data is stored in machine format; this is fast, but is machine/OS dependent.
Most of the things true for MyISAM tables are also true for ISAM tables. See MyISAM tables. The major differences compared to MyISAM tables are:
ISAM tables are not binary portable across OS/Platforms.
Can't handle tables > 4G.
Only support prefix compression on strings.
Smaller key limits.
Dynamic tables get more fragmented.
Tables are compressed with pack_isam rather than with myisampack.
If you want to convert an ISAM table to a MyISAM table so that you can use utilities such as mysqlcheck, use an ALTER TABLE statement:
mysql> ALTER TABLE tbl_name TYPE = MYISAM;
The embedded MySQL versions doesn't support ISAM tables.
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MaxDB is an enterprise level database. MaxDB is the new name of a database management system formerly called SAP DB.
The history of SAP DB goes back to the early 1980s when it was developed as a commercial product (Adabas). The database has changed names several times since then. When SAP AG, a Walldorf, Germany, based company, took over the development of that database system, it was called SAP DB.
SAP developed that database system to serve as a storage system for all heavy-duty SAP applications, namely R/3. SAP DB was meant to provide an alternative to third-party database systems like Oracle, Microsoft SQL Server, or DB2 by IBM. In October 2000, SAP AG released SAP DB under the GNU GPL license (see GPL license), thus making it open source software. In October 2003, more than 2,000 customers of SAP AG were using SAP DB as their main database system, and more than another 2,000 customers were using it as a separate database system besides their main database, as part of the APO/LiveCache solution.
In May 2003, a technology partnership was formed between MySQL AB and SAP AG. That partnership entitles MySQL AB to further develop SAP DB, rename it, and sell commercial licenses of the renamed SAP DB to customers who do not want to be bound to the restrictions imposed to them when using that database system under the GNU GPL (see GPL license). In August 2003, SAP DB was renamed to MaxDB by MySQL AB.
MaxDB can be used under the same licenses available for the other products distributed by MySQL AB (MySQL licenses). Thus, MaxDB will be available under the GNU General Public License (GPL license), and a commercial license (Licensing and Support).
MySQL will offer MaxDB support to non-SAP customers.
The first rebranded version will be MaxDB 7.5.00 that will be released in late 2003.
MaxDB operates as a client/server product. It was developed to meet the demands of installations processing a high volume of online transactions. Both online backup and expansion of the database are supported. Microsoft Clustered Server is supported directly for multiple server implementations; other failover solutions must be scripted manually. Database management tools are provided in both Windows and browser-based implementations.
The following list provides a short summary of the main differences between MaxDB and MySQL; it is not complete.
MaxDB runs as a client/server system. MySQL can run as a client/server system or as an embedded system.
MaxDB might not run on all platforms supported by MySQL. For example, MaxDB does not run on IBM's OS/2.
MaxDB uses a proprietary network protocol for client/server communication, while MySQL uses either TCP/IP (with or without SSL encryption), sockets (under Unix-like systems), or named pipes (under Windows NT-family systems).
MaxDB supports stored procedures. For MySQL, stored procedures are implemented in version 5.0. MaxDB also supports programming of triggers through an SQL extension, which is scheduled for MySQL 5.1. MaxDB contains a debugger for stored procedure languages, can cascade nested triggers, and supports multiple triggers per action and row.
MaxDB is distributed containing user interfaces that are text-based, graphical, or web-based. MySQL is distributed with text-based user interfaces only; a graphical user interface (MySQL Control Center) is shipped separately from the main distributions. Web-based user interfaces for MySQL are offered by third parties.
MaxDB supports a number of programming interfaces also supported by MySQL. However, MaxDB does not support RDO, ADO, or .NET, all of which are supported by MySQL. MaxDB supports embedded SQL only with C/C++.
MaxDB contains administrative features that MySQL does not have: Job scheduling by time, event, and alert, and sending messages to a database administrator on alert thresholds.
The following features will be included in MaxDB versions to be released shortly after the first 7.5.00 version. These features will allow interoperation between MaxDB and MySQL:
There will be a MySQL proxy enabling one to connect to MaxDB using the MySQL protocol. This makes it possible to use MySQL client programs for MaxDB, like the mysql command-line user interface, the mysqldump dump utility, or the mysqlimport import program. Using mysqldump, one can easily dump data from one database system and export (or even pipe) those data to the other database system.
Replication between MySQL and MaxDB will be supported in both directions. That is, either MySQL or MaxDB can be used as the master replication server. The long-range plan is to converge and extend the replication syntax so that both database systems understand the same syntax. See Replication Intro.
The main page for information about MaxDB is http://www.mysql.com/maxdb. Eventually, all information available at http://www.sapdb.org will be moved there.
Like MySQL, MaxDB has a number of reserved words that have special meanings. Normally, they cannot be used as names of identifiers, such as database or table names. The following table lists reserved words in MaxDB, indicates the context in which those words are used, and indicates whether or not they have counterparts in MySQL. If such a counterpart exists, the meaning in MySQL might be identical, or differing in some aspects. The main purpose is to list in which respects MaxDB differs from MySQL; therefore, this list is not complete.
For the list of reserved words in MySQL, see See Reserved words.
Reserved in MaxDB | Context of usage in MaxDB | MySQL counterpart |
@ | May prefix identifier, like ``@table'' | Not allowed |
ADDDATE() | SQL function | ADDDATE(); new in MySQL version 4.1.1 |
ADDTIME() | SQL function | ADDTIME(); new in MySQL version 4.1.1 |
ALPHA | SQL function | Nothing comparable |
ARRAY | Data type | Not implemented |
ASCII() | SQL function | ASCII(), but implemented with a different meaning |
AUTOCOMMIT | Transactions; ON by default | Transactions; OFF by default |
BOOLEAN | Column types; BOOLEAN accepts as values only TRUE, FALSE, and NULL | BOOLEAN was added in MySQL version 4.1.0; it is a synonym for BOOL which is mapped to TINYINT(1). It accepts integer values in the same range as TINYINT as well as NULL. TRUE and FALSE can be used as aliases for 1 and 0. |
CHECK | CHECK TABLE | CHECK TABLE; similar, but not identical usage |
COLUMN | Column types | COLUMN; noise word |
CHAR() | SQL function | CHAR(); identical syntax; similar, not identical usage |
COMMIT | Implicit commits of transactions happen when data definition queries are being issued | Implicit commits of transactions happen when data definition queries are being issued, but also with a number of other queries |
COSH() | SQL function | Nothing comparable |
COT() | SQL function | COT(); identical syntax and implementation |
CREATE | SQL, data definition language | CREATE |
DATABASE | SQL function | DATABASE(); DATABASE is used in a different context, for example CREATE DATABASE |
DATE() | SQL function | CURRENT_DATE |
DATEDIFF() | SQL function | DATEDIFF(); new in MySQL version 4.1.1 |
DAY() | SQL function | Nothing comparable |
DAYOFWEEK() | SQL function | DAYOFWEEK(); the first day (1) by default is Monday in MaxDB, and Sunday in MySQL |
DISTINCT | SQL functions AVG, MAX, MIN, SUM | DISTINCT; but used in a different context: SELECT DISTINCT |
DROP | inter alia in DROP INDEX | DROP INDEX; similar, but not identical usage |
EBCDIC() | SQL function | Nothing comparable |
EXPAND() | SQL function | Nothing comparable |
EXPLAIN | Optimization | EXPLAIN; similar, but not identical usage |
FIXED() | SQL function | Nothing comparable |
FLOAT() | SQL function | Nothing comparable |
HEX() | SQL function | HEX(); similar, but not identical usage |
INDEX() | SQL function | INSTR() or LOCATE(); similar, but not identical syntaxes and meanings |
INDEX | USE INDEX, IGNORE INDEX and similar hints are being used right after SELECT, like SELECT ... USE INDEX | USE INDEX, IGNORE INDEX and similar hints are being used in the FROM clause of a SELECT query, like in SELECT ... FROM ... USE INDEX |
INITCAP() | SQL function | Nothing comparable |
LENGTH() | SQL function | LENGTH(); identical syntax, but slightly different implementation |
LFILL() | SQL function | Nothing comparable |
LIKE | Comparisons | LIKE; but the extended LIKE MaxDB provides rather resembles the MySQL REGEX |
LIKE wildcards | MaxDB supports ``%'', ``_'', ``ctrl+underline'', ``ctrl+up arrow'', ``*'', and ``?'' as wildcards in a LIKE comparison | MySQL supports ``%'', and ``_'' as wildcards in a LIKE comparison |
LPAD() | SQL function | LPAD(); slightly different implementation |
LTRIM() | SQL function | LTRIM(); slightly different implementation |
MAKEDATE() | SQL function | MAKEDATE(); new in MySQL version 4.1.1 |
MAKETIME() | SQL function | MAKETIME(); new in MySQL version 4.1.1 |
MAPCHAR() | SQL function | Nothing comparable |
MICROSECOND() | SQL function | MICROSECOND(); new in MySQL version 4.1.1 |
NOROUND() | SQL function | Nothing comparable |
NULL | Column types; comparisons | NULL; MaxDB supports special NULL values that are returned by arithmetic operations that lead to an overflow or a division by zero; MySQL does not support such special values |
PI | SQL function | PI(); identical syntax and implementation, but parantheses are mandatory |
REF | Data type | Nothing comparable |
RFILL() | SQL function | Nothing comparable |
ROWNO | Predicate in WHERE clause | Similar to LIMIT clause |
RPAD() | SQL function | RPAD(); slightly different implementation |
RTRIM() | SQL function | RTRIM(); slightly different implementation |
SEQUENCE | CREATE SEQUENCE, DROP SEQUENCE | AUTO_INCREMENT; similar concept, but differing implementation |
SINH() | SQL function | Nothing comparable |
SOUNDS() | SQL function | SOUNDEX(); slightly different syntax |
STATISTICS | UPDATE STATISTICS | ANALYZE; similar concept, but differing implementation |
SUBSTR() | SQL function | SUBSTRING(); slightly different implementation |
SUBTIME() | SQL function | SUBTIME(); new in MySQL version 4.1.1 |
SYNONYM | Data definition language: CREATE [PUBLIC] SYNONYM, RENAME SYNONYM, DROP SYNONYM | Nothing comparable |
TANH() | SQL function | Nothing comparable |
TIME() | SQL function | CURRENT_TIME |
TIMEDIFF() | SQL function | TIMEDIFF(); new in MySQL version 4.1.1 |
TIMESTAMP() | SQL function | TIMESTAMP(); new in MySQL version 4.1.1 |
TIMESTAMP() as argument to DAYOFMONTH() and DAYOFYEAR() | SQL function | Nothing comparable |
TIMEZONE() | SQL function | Nothing comparable |
TRANSACTION() | Returns the ID of the current transaction | Nothing comparable |
TRANSLATE() | SQL function | REPLACE(); identical syntax and implementation |
TRIM() | SQL function | TRIM(); slightly different implementation |
TRUNC() | SQL function | TRUNCATE(); slightly different syntax and implementation |
USE | mysql commandline user interface command | USE |
USER | SQL function | USER(); identical syntax, but slightly different implementation, and parantheses are mandatory |
UTC_DIFF() | SQL function | UTC_DATE(); provides a means to calculate the result of UTC_DIFF() |
VALUE() | SQL function, alias for COALESCE() | COALESCE(); identical syntax and implementation |
VARIANCE() | SQL function | Nothing comparable |
WEEKOFYEAR() | SQL function | WEEKOFYEAR(); new in MySQL version 4.1.1 |
Table of Contents
Improved handling of character sets is one of the features added to MySQL in Version 4.1. This chapter explains:
What are character sets and collations
The multi-level default system
New syntax in MySQL 4.1
Affected functions and operations
The meaning of each individual character set and collation
The features described here are as implemented in MySQL 4.1.1. (MySQL 4.1.0 has some but not all of these features, and some of them are implemented differently.)
Character set support currently is included in the MySISAM and MEMORY (HEAP) storage engines. The InnoDB storage engine does not yet include it. ISAM does not; there are no plans to do so.
A character set is a set of symbols and encodings. A collation is a set of rules for comparing characters in a character set. Let's make the distinction clear with an example of an imaginary character set.
Suppose we had an alphabet with four letters: A, B, a, b. We give each letter a number: A = 0, B = 1, a = 2, c = 3. The letter A is a symbol, the number 0 is the encoding for A, and the combination of all four letters and their encodings is a character set.
Now, suppose we want to compare two string values, A and B. The simplest way to do this is to look at the encodings --- 0 for A and 1 for B --- and because 0 is less than 1, we say A is less than B. Now, what we've just done is apply a collation to our character set. The collation is a set of rules (only one rule in this case): ``compare the encodings''. We call this simplest of all possible collations a binary collation.
But what if we want to say that the lowercase and uppercase letters are equivalent? Then we would have at least two rules: (1) treat the lowercase letters a and b as equivalent to A and B; (2) then compare the encodings. We call this a case insensitive collation. It's a little more complex than a binary collation.
In real life, most character sets have many characters: not just A and B but whole alphabets, sometimes multiple alphabets or eastern writing systems with thousands of characters, along with many special symbols and punctuation marks. Also in real life, most collations have many rules: not just case insensitivity but also accent insensitivity (an ``accent'' is a mark attached to a character as in German Ö) and multiple-character mappings (such as the rule that Ö = OE in one of the two German collations).
MySQL 4.1 can do these things for you:
Store strings using a variety of character sets
Compare strings using a variety of collations
Mix strings with different character sets or collations in the same server, the same database, or even the same table
Allow specification of character set and collation at any level
In these respects, not only is MySQL 4.1 far more flexible than MySQL 4.0, it also is far ahead of other DBMSs. However, to use the new features effectively, you will need to learn what character sets and collations are available, how to change their defaults, and what the various string operators do with them.
A character set always has at least one collation. It may have several collations.
For example, character set latin1 (``ISO-8859-1 West European'') has the following collations:
Collation | Meaning |
latin1_bin | Binary according to latin1 encoding |
latin1_danish_ci | Danish/Norwegian |
latin1_german1_ci | German DIN-1 |
latin1_german2_ci | German DIN-2 |
latin1_spanish_ci | Modern Spanish |
latin1_swedish_ci | Swedish/Finnish |
latin1_general_ci | Multilingual |
Notes:
Two different character sets can't have the same collation.
Each character set has one collation that is the default collation. For example, the default collation for latin1 is latin1_swedish_ci.
Notice that there is a convention for collation names: They start with the name of the character set they are associated with, they usually include a language name, and they end with _ci (case insensitive), _cs (case sensitive), or _bin (binary).
Table of Contents
There are default settings for character sets and collations at four levels: server, database, table, connection. The following description may appear complex, but it's been found in practice that multi-level defaulting leads to natural and obvious results.
The MySQL Server has a server character set and a server collation, which may not be null.
MySQL determines the server character set and server collation thus:
According to the option settings in effect when the server starts.
At this level, the decision is simple. The server character set and collation depend on the options that you use when you start mysqld. You can use --default-character-set=character_set_name for the character set, and along with it you can add --default-collation=collation_name for the collation. If you don't specify a character set, that is the same as saying --default-character-set=latin1. If you specify only a character set (for instance, latin1) but not a collation, that is the same as saying --default-charset=latin1 --collation=latin1_swedish_ci because latin1_swedish_ci is the default collation for latin1. Therefore the following three commands all have the same effect:
shell> mysqld shell> mysqld --default-character-set=latin1 shell> mysqld --default-character-set=latin1 --default-collation=latin1_swedish_ci
One way to change the settings is by recompiling. If you want to change the default server character set and collation when building from sources, use: --with-character-set and --with-collation as arguments for configure. For example:
shell> ./configure --with-character-set=latin1
or:
shell> ./configure --with-character-set=latin1 --with-collation=latin1_german1_ci
Both mysqld and configure check that the character set/collation combination is valid. Each program displays an error message and terminates if the combination is not valid.
Every database has a database character set and a database collation, which may not be null. The CREATE DATABASE and ALTER DATABASE commands now have optional clauses for specifying the database character set and collation:
CREATE DATABASE db_name [DEFAULT CHARACTER SET character_set_name [COLLATE collation_name]] ALTER DATABASE db_name [DEFAULT CHARACTER SET character_set_name [COLLATE collation_name]]
Example:
CREATE DATABASE db_name DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci;
MySQL chooses the database character set and database collation thus:
If both CHARACTER SET X and COLLATE Y were specified, then character set X and collation Y.
If CHARACTER SET X was specified without COLLATE, then character set X and its default collation.
Otherwise, the server character set and server collation.
MySQL's CREATE DATABASE ... DEFAULT CHARACTER SET ... syntax is analogous to the standard-SQL CREATE SCHEMA ... CHARACTER SET ... syntax. Because of this, it is possible to create databases with different character sets and collations, on the same MySQL server.
The database character set and collation are used as default values if the table character set and collation are not specified in CREATE TABLE statements. They have no other purpose.
Every table has a table character set and a table collation, which may not be null. The CREATE TABLE and ALTER TABLE statements now have optional clauses for specifying the table character set and collation:
CREATE TABLE table_name ( column_list ) [DEFAULT CHARACTER SET character_set_name [COLLATE collation_name]] ALTER TABLE table_name [DEFAULT CHARACTER SET character_set_name] [COLLATE collation_name]
Example:
CREATE TABLE t1 ( ... ) DEFAULT CHARACTER SET latin1 COLLATE latin1_danish_ci;
MySQL chooses the table character set and collation thus:
If both CHARACTER SET X and COLLATE Y were specified, then character set X and collation Y.
If CHARACTER SET X was specified without COLLATE, then character set X and its default collation.
Otherwise, the database character set and collation.
The table character set and collation are used as default values, if the column character set and collation are not specified in individual column definitions. The table character set and collation are MySQL extensions; there are no such things in standard SQL.
Every ``character'' column (that is, a column of type CHAR, VARCHAR, or TEXT) has a column character set and a column collation, which may not be null. Column definition syntax now has optional clauses for specifying the column character set and collation:
column_name {CHAR | VARCHAR | TEXT} (column_length) [CHARACTER SET character_set_name [COLLATE collation_name]]
Example:
CREATE TABLE Table1 ( column1 VARCHAR(5) CHARACTER SET latin1 COLLATE latin1_german1_ci );
MySQL chooses the column character set and collation thus:
If both CHARACTER SET X and COLLATE Y were specified, then character set X and collation Y.
If CHARACTER SET X was specified without COLLATE, then character set X and its default collation.
Otherwise, the table character set and collation.
The CHARACTER SET and COLLATE clauses are standard SQL.
The following examples show how MySQL determines default character set and collation values.
CREATE TABLE t1 ( c1 CHAR(10) CHARACTER SET latin1 COLLATE latin1_german1_ci ) DEFAULT CHARACTER SET latin2 COLLATE latin2_bin;
Here you have a column with a latin1 character set and a latin1_german1_ci collation. The definition is explicit, so that's straightforward. Notice that there's no problem storing a latin1 column in a latin2 table.
CREATE TABLE t1 ( c1 CHAR(10) CHARACTER SET latin1 ) DEFAULT CHARACTER SET latin1 COLLATE latin1_danish_ci;
This time we have a column with a latin1 character set and a default collation. Now, although it might seem natural, the default collation is not taken from the table level. Instead, because the default collation for latin1 is always latin1_swedish_ci, column c1 will have a collation of latin1_swedish_ci (not latin1_danish_ci).
CREATE TABLE t1 ( c1 CHAR(10) ) DEFAULT CHARACTER SET latin1 COLLATE latin1_danish_ci;
We have a column with a default character set and a default collation. In this circumstance, MySQL looks up to the table level for inspiration in determining the column character set and collation. So the character set for column c1 is latin1 and its collation is latin1_danish_ci.
CREATE DATABASE d1 DEFAULT CHARACTER SET latin2 COLLATE latin2_czech_ci; USE d1; CREATE TABLE t1 ( c1 CHAR(10) );
We create a column without specifying its character set and collation. We're also not specifying a character set and a collation at the table level. In this circumstance, MySQL looks up to the database level for inspiration. (The database's settings become the table's settings, and thereafter become the column's setting.) So the character set for column c1 is latin2 and its collation is latin2_czech_ci.
Every connection has connection character sets and connection collations, which may not be null. There are actually two connection character sets, which we will call ``connection/literals'' and ``connection/results'' when it is necessary to distinguish them.
Consider what a ``connection'' is: It's what you make when you connect to the server. The client sends SQL statements, such as queries, over the connection to the server. The server sends responses, such as result sets, over the connection back to the client. This leads to several questions, such as: (a) what character set is the query in when it leaves the client? (b) what character set should the server translate a query to after receiving it? (c) what character set should the server translate to before shipping result sets or error messages back to the client? You can fine-tune the setting for these things, or you can depend on the defaults (in which case, you can skip this section).
There are two statements that affect the connection character sets:
SET NAMES 'character_set_name' SET CHARACTER SET character_set_name
SET NAMES indicates what is in the SQL statement that the client sends. Thus, SET NAMES 'cp1251' tells the server ``future incoming messages from this client will be in character set cp1251'' and the server is free to translate to its own character set, if appropriate.
SET CHARACTER SET indicates what is in the SQL statement that the client sends, and also what is in the result set that the server sends back to the client. Thus, SET CHARACTER SET includes SET NAMES, and also specifies what character set the column values will have if, for example, you use a SELECT statement.
EXAMPLE: Suppose that column1 is defined as CHAR(5) CHARACTER SET latin2. If you do not say SET CHARACTER SET, then for SELECT column1 FROM t the server will send back all the values for column1 using character set latin2. If on the other hand you say SET CHARACTER SET latin1 then the server will, just before sending back, convert the latin2 values to latin1. Such conversion is slow and may be lossy.
When you execute SET NAMES or SET CHARACTER SET, you are also changing the ``connection collation''. However, the connection collation exists for consistency only. Usually its value doesn't matter.
With the mysql client, it is not necessary to execute SET NAMES every time you start up. You can add the --default-character-set option setting to your mysql statement line, or in your option file. For example, the following option file setting will change the connection character set each time you run mysql:
[mysql] default-character-set=character_set_name
Every character string literal has a character set and a collation, which may not be null.
A character string literal may have an optional character set introducer and COLLATE clause:
[_character_set_name]'string' [COLLATE collation_name]
Examples:
SELECT 'string'; SELECT _latin1'string'; SELECT _latin1'string' COLLATE latin1_danish_ci;
The simple statement SELECT 'string' uses the connection/literal character set.
The _character_set_name expression is formally called an introducer. It tells the parser, ``the string that is about to follow is in character set X.'' Because this has confused people in the past, we emphasize that an introducer does not cause any conversion, it is strictly a signal that does not change the string's value. An introducer is also legal before standard hex literal and numeric hex literal notation (x'literal' and 0xnnnn), and before ? (parameter substitution when using prepared statements within a programming language interface).
Examples:
SELECT _latin1 x'AABBCC'; SELECT _latin1 0xAABBCC; SELECT _latin1 ?;
MySQL determines a literal's character set and collation thus:
If both _X and COLLATE Y were specified then the literal character set is X and the literal collation is Y
If _X is specified but COLLATE is not specified, then the literal character set is X and the literal collation is X's default collation
Otherwise, the connection/literals character set and collation.
Examples:
A string with latin1 character set and latin1_german1_ci collation:
SELECT _latin1'Müller' COLLATE latin1_german1_ci;
A string with latin1 character set and its default collation, that is, latin1_swedish_ci:
SELECT _latin1'Müller';
A string with the connection/literals character set and collation:
SELECT 'Müller';
Character set introducers and the COLLATE clause are implemented according to standard-SQL specifications.
With the COLLATE clause you can override whatever the default collation is for a comparison. COLLATE may be used in various parts of SQL queries. Here are some examples:
With ORDER BY:
SELECT k FROM t1 ORDER BY k COLLATE latin1_german2_ci;
With AS:
SELECT k COLLATE latin1_german2_ci AS k1 FROM t1 ORDER BY k1;
With GROUP BY:
SELECT k FROM t1 GROUP BY k COLLATE latin1_german2_ci;
With aggregate functions:
SELECT MAX(k COLLATE latin1_german2_ci) FROM t1;
With DISTINCT:
SELECT DISTINCT k COLLATE latin1_german2_ci FROM t1;
With WHERE:
SELECT * FROM t1 WHERE _latin1 'Müller' COLLATE latin1_german2_ci = k;
With HAVING:
SELECT k FROM t1 GROUP BY k HAVING k = _latin1 'Müller' COLLATE latin1_german2_ci;
The COLLATE clause has high precedence (higher than ||), so the expression
x || y COLLATE z
is equivalent to:
x || (y COLLATE z)
The BINARY operator is a shorthand for a COLLATE clause. For example, BINARY 'x' is equivalent to 'x' COLLATE y, where y is the name of an appropriate binary collation. For example, assuming that column a is of character set latin1, these two queries have the same effect:
SELECT * FROM t1 ORDER BY BINARY a; SELECT * FROM t1 ORDER BY a COLLATE latin1_bin;
Note: Every character set has a binary collation.
In the great majority of queries, it is obvious what collation MySQL uses to resolve a comparison operation. For example, in the following cases it should be clear that the collation will be ``the column collation of column x'':
SELECT x FROM T ORDER BY x; SELECT x FROM T WHERE x = x; SELECT DISTINCT x FROM T;
However, when multiple operands are involved, there can be ambiguity. For example:
SELECT x FROM T WHERE x = 'Y';
Should this query use the collation of the column x, or of the string literal 'Y'?
Standard SQL resolves such questions using what used to be called ``coercibility'' rules. The essence is: Because x and 'Y' both have collations, whose collation takes precedence? It's complex, but these rules would take care of most situations:
An explicit COLLATE clause has a coercibility of 0. (Not coercible at all.)
A concatenation of two strings with different collations has a coercibility of 1.
A column's collation has a coercibility of 2.
A literal's collation has a coercibility of 3.
Those rules resolve ambiguities thus:
Use the collation with the lowest coercibility value.
If both sides have the same coercibility, then it's an error if the collations aren't the same.
Examples:
column1 = 'A' | Use collation of column1 |
column1 = 'A' COLLATE x | Use collation of 'A' |
column1 COLLATE x = 'A' COLLATE y | Error |
The COERCIBILITY() function can be used to determine the coercibility of a string expression:
mysql> SELECT COERCIBILITY('A' COLLATE latin1_swedish_ci); -> 0 mysql> SELECT COERCIBILITY('A'); -> 3
Recall that each character set has one or more collations, and each collation is associated with one and only one character set. Therefore, the following statement causes an error message because the latin2_bin collation is not legal with the latin1 character set:
mysql> SELECT _latin1 'x' COLLATE latin2_bin; ERROR 1251: COLLATION 'latin2_bin' is not valid for CHARACTER SET 'latin1'
Suppose column X in table T has these latin1 column values:
Muffler Müller MX Systems MySQL
And suppose that the column values are retrieved using the following statement:
SELECT X FROM T ORDER BY X COLLATE collation_name;
The resulting order of the values for different collations is shown in this table:
latin1_swedish_ci | latin1_german1_ci | latin1_german2_ci |
Muffler | Muffler | Müller |
MX Systems | Müller | Muffler |
Müller | MX Systems | MX Systems |
MySQL | MySQL | MySQL |
The table is an example that shows what the effect would be if we used different collations in an ORDER BY clause. The character that's causing the trouble in this example is the U with two dots over it, which the Germans call U-umlaut, but we'll call it U-diaeresis.
The first column shows the result of the SELECT using the Swedish/Finnish collating rule, which says that U-diaeresis sorts with Y.
The second column shows the result of the SELECT using the German DIN-1 rule, which says that U-diaeresis sorts with U.
The third column shows the result of the SELECT using the German DIN-2 rule, which says that U-diaeresis sorts with UE.
Three different collations, three different results. That's what MySQL is here to handle. By using the appropriate collation, you can choose the sort order you want.
Table of Contents
This section describes operations that take character set information into account now.
MySQL has many operators and functions that return a string. This section answers the question: What is the character set and collation of such a string?
For simple functions that take a string input and return a string result as output, the output's character set and collation are the same as the principal input's. For example, UPPER(X) returns a string whose character string and collation are the same as that of X. The same applies for: INSTR(), LCASE(), LOWER(), LTRIM(), MID(), REPEAT(), REPLACE(), REVERSE(), RIGHT(), RPAD(), RTRIM(), SOUNDEX(), SUBSTRING(), TRIM(), UCASE(), UPPER(). (Also note: the REPLACE() function, unlike all other functions, ignores the collation of the string input and performs a case-insensitive comparison every time.)
For operations that combine multiple string inputs and return a single string output, SQL-99's ``aggregation rules'' apply. They are:
If explicit COLLATE X occurs, then use X
If explicit COLLATE X and COLLATE Y occur, then error
Otherwise, if all collations are X, then use X
Otherwise, the result has no collation
For example, with CASE ... WHEN a THEN b WHEN b THEN c COLLATE X END, the resultant collation is X. The same applies for: CONCAT(), GREATEST(), IF(), LEAST(), CASE, UNION, ||, ELT().
For operations that convert to character data, the result string's character set and collation are in the connection/literals character set and have the connection/literals collation. This applies for: CHAR(), CAST(), CONV(), FORMAT(). HEX(), SPACE().
CONVERT() provides a way to convert data between different character sets. The syntax is:
CONVERT(expr USING transcoding_name)
In MySQL, transcoding names are the same as the corresponding character set names.
Examples:
SELECT CONVERT(_latin1'Müller' USING utf8); INSERT INTO utf8table (utf8column) SELECT CONVERT(latin1field USING utf8) FROM latin1table;
CONVERT(... USING ...) is implemented according to the SQL-99 specification.
You may also use CAST() to convert a string to a different character set. The new format is:
CAST ( character_string AS character_data_type CHARACTER SET character_set_name )
Example:
SELECT CAST(_latin1'test' AS CHAR CHARACTER SET utf8);
You may not use a COLLATE clause inside a CAST(), but you may use it outside, that is, CAST(... COLLATE ...) is illegal but CAST(...) COLLATE ... is legal.
Example:
SELECT CAST(_latin1'test' AS CHAR CHARACTER SET utf8) COLLATE utf8_bin;
If you use CAST() without specifying CHARACTER SET, then the resulting character set and collation are the connection/literal character set and its default collation. If you use CAST() with CHARACTER SET X, then the resulting character set is X and the resulting collation is X's default collation.
The SHOW CHARACTER SET command shows all available character sets. It takes an optional LIKE clause that indicates which character set names to match.
For example:
mysql> SHOW CHARACTER SET LIKE 'latin%'; +---------+-----------------------------+-------------------+--------+ | Charset | Description | Default collation | Maxlen | +---------+-----------------------------+-------------------+--------+ | latin1 | ISO 8859-1 West European | latin1_swedish_ci | 1 | | latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 | | latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 | | latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 | +---------+-----------------------------+-------------------+--------+ 4 rows in set (0.00 sec)
Notes about the preceding listing:
The Maxlen column shows the maximum number of bytes used to store one character.
The output from SHOW COLLATION includes all available character sets. It takes an optional LIKE clause that indicates which collation names to match.
mysql> SHOW COLLATION LIKE 'latin1%'; +-------------------+---------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +-------------------+---------+----+---------+----------+---------+ | latin1_german1_ci | latin1 | 5 | | | 0 | | latin1_swedish_ci | latin1 | 8 | Yes | Yes | 0 | | latin1_danish_ci | latin1 | 15 | | | 0 | | latin1_german2_ci | latin1 | 31 | | Yes | 2 | | latin1_bin | latin1 | 47 | | Yes | 0 | | latin1_general_ci | latin1 | 48 | | | 0 | | latin1_general_cs | latin1 | 49 | | | 0 | | latin1_spanish_ci | latin1 | 94 | | | 0 | +-------------------+---------+----+---------+----------+---------+ 7 rows in set (0.00 sec)
The Default column indicates whether a collation is the default for its character set. Compiled indicates whether or not the character set is compiled into the server. Sortlen is related to the amount of memory required to sort strings expressed in the character set.
The following query shows a CREATE DATABASE statement that will create the given database. The result includes all database options. DEFAULT CHARACTER SET and COLLATE are supported. All database options are stored in a text file that can be found in the database directory.
mysql> SHOW CREATE DATABASE a; +----------+---------------------------------------------------------------------------------+ | Database | Create Database | +----------+---------------------------------------------------------------------------------+ | a | CREATE DATABASE `a` /*!40100 DEFAULT CHARACTER SET macce COLLATE macce_ci_ai */ | +----------+---------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
The SHOW COLUMNS statement now displays the collations of a table's columns, when invoked as SHOW FULL COLUMNS. Columns with CHAR, VARCHAR, or TEXT datatypes have non-NULL collations. Numeric and other non-character types have NULL collations. For example:
mysql> SHOW FULL COLUMNS FROM a; +-------+---------+-------------------+------+-----+---------+-------+ | Field | Type | Collation | Null | Key | Default | Extra | +-------+---------+-------------------+------+-----+---------+-------+ | a | char(1) | latin1_swedish_ci | YES | | NULL | | | b | int(11) | NULL | YES | | NULL | | +-------+---------+-------------------+------+-----+---------+-------+ 2 rows in set (0.02 sec)
The character set is not part of the display.
There are two new (as of MySQL version 4.1) character sets for storing Unicode data: ucs2 (the UCS-2 Unicode character set) and utf8 (the UTF8 encoding of the Unicode character set).
In UCS-2 (binary Unicode representation) every character is represented by a two-byte Unicode code with the most significant byte first. For example: "LATIN CAPITAL LETTER A" has the code 0x0041 and it's stored as a two byte sequence: 0x00 0x41. "CYRILLIC SMALL LETTER YERU" (Unicode 0x044B) is stored as a two byte sequence: 0x04 0x4B. For Unicode characters and their codes please refer to the Unicode Home Page.
Temporary restriction: UCS-2 can't (yet) be used as a client character set. That means that SET NAMES 'ucs2' will not work.
The UTF8 character set (transform Unicode representation) is an alternative way to store Unicode data. It is implemented according to RFC2279. The idea of the UTF8 character set is that various Unicode characters fit into byte sequences of different lengths.
Basic Latin letters, digits, and punctuation signs use one byte.
Most European and Middle East script letters fit into a two-byte sequence: extended Latin letters (with tilde, macron, acute, grave and other accents), Cyrillic, Greek, Armenian, Hebrew, Arabic, Syriac, and others.
Korean, Chinese and Japanese ideographs use three-byte sequences.
Currently, MySQL UTF8 support does not include four-byte sequences.
Tip: To save space with UTF8, use VARCHAR instead of CHAR. Otherwise, MySQL has to reserve 30 bytes for a CHAR(10) CHARACTER SET utf8 column, because that's the maximum possible length.
The metadata is the data about the data. Anything that describes the database, as opposed to being the contents of the database, is metadata. Thus column names, database names, user names, version names, and most of the string results from SHOW, are metadata.
All metadata must be in the same character set. (Otherwise, SHOW wouldn't work properly because different rows in the same column would be in different character sets.) On the other hand, metadata must include all characters in all languages. (Otherwise, users wouldn't be able to name columns and tables in their own languages.) In order to allow for both of these objectives, MySQL stores metadata in a Unicode character set, namely UTF8. This will not cause any disruption if you never use accented characters. But if you do, you should be aware that metadata is in UTF8.
This means that USER() (and its synonyms, SESSION_USER() and SYSTEM_USER()), CURRENT_USER(), and VERSION() functions will have the UTF8 character set by default.
This does NOT mean that the headers of columns and the results of DESCRIBE functions will be in the UTF8 character set by default. (When you say SELECT column1 FROM t the name column1 itself will be returned from the server to the client in the client's character set as determined by the SET NAMES statement.)
If you want the server to pass metadata results back in a non-UTF8 character set, then use SET CHARACTER SET to force the server to convert (see Charset-connection), or set the client to do the conversion. It is always more efficient to set the client to do the conversion, but this option will not be available for many clients until late in the MySQL 4.x product cycle.
If you are just using, for example, the USER() function for comparison or assignment within a single statement ... don't worry. MySQL will do some automatic conversion for you.
SELECT * FROM Table1 WHERE USER() = latin1_column;
This will work, because the contents of latin1_column are automatically converted to UTF8 before the comparison.
INSERT INTO Table1 (latin1_column) SELECT USER();
This will work, becaues the contents of USER() are automatically converted to latin1 before the assignment. Automatic conversion is not fully implemented yet, but should work correctly in a later version.
Although automatic conversion is not in the SQL standard, the SQL standard document does say that every character set is (in terms of supported characters) a ``subset'' of Unicode. Since it is a well-known principle that ``what applies to a superset can apply to a subset,'' we believe that a collation for Unicode can apply for comparisons with non-Unicode strings.
For SAP DB compatibility these two statements are the same:
CREATE TABLE t1 (f1 CHAR(n) UNICODE); CREATE TABLE t1 (f1 CHAR(n) CHARACTER SET ucs2);
In MySQL 4.1, character set configuration is stored in XML files, one file per character set. (In previous versions, this information was stored in .conf files.)
In MySQL-4.x and earlier, NCHAR and CHAR were synonymous. ANSI defines NCHAR or NATIONAL CHAR as a way to define that a CHAR column should use some predefined character set. MySQL uses utf8 as that predefined character set. For example, these column type declarations are equivalent:
CHAR(10) CHARACTER SET utf8 NATIONAL CHARACTER(10) NCHAR(10)
As are these:
VARCHAR(10) CHARACTER SET utf8 NATIONAL VARCHAR(10) NCHAR VARCHAR(10) NATIONAL CHARACTER VARYING(10) NATIONAL CHAR VARYING(10)
You can use N'literal' to create a string in national character set.
These two statements are equivalent:
SELECT N'some text'; SELECT _utf8'some text';
Now, what about upgrading from older versions of MySQL? MySQL 4.1 is almost upward compatible with MySQL 4.0 and earlier for the simple reason that almost all of the features are new, so there's nothing in earlier versions to conflict with. However, there are some differences and a few things to be aware of.
Most important: The ``MySQL 4.0 character set'' has the properties of both ``MySQL 4.1 character sets'' and ``MySQL 4.1 collations.'' You will have to unlearn this. Henceforth we will not bundle character set / collation properties in the same conglomerate object.
There is a special treatment of national character sets in MySQL 4.1. NCHAR is not the same as CHAR, and N'...' literals are not the same as '...' literals.
Finally, there is a different file format for storing information about character sets and collations. Make sure you have reinstalled the /share/mysql/charsets/ directory containing the new configuration files.
If you want to start mysqld from a 4.1.x distribution with data created by MySQL 4.0, you should start the server with the same character set and collation. In this case you won't need to reindex your data.
There are two ways to do so:
shell> ./configure --with-character-set=... --with-collation=... shell> ./mysqld --default-character-set=... --default-collation=...
If you used mysql with, for example, the MySQL 4.0 danish character set, you should now use the latin1 character set and the latin1_danish_ci collation:
shell> ./configure --with-character-set=latin1 --with-collation=latin1_danish_ci shell> ./mysqld --default-character-set=latin1 --default-collation=latin1_danish_ci
Use the table shown in the next section to find old 4.0 character set names and their 4.1 character set/collation pair equivalents.
ID | 4.0 Character Set | 4.1 Character Set | 4.1 Collation |
1 | big5 | big5 | big5_chinese_ci |
2 | czech | latin2 | latin2_czech_ci |
3 | dec8 | dec8 | dec8_swedish_ci |
4 | dos | cp850 | cp850_general_ci |
5 | german1 | latin1 | latin1_german1_ci |
6 | hp8 | hp8 | hp8_english_ci |
7 | koi8_ru | koi8r | koi8r_general_ci |
8 | latin1 | latin1 | latin1_swedish_ci |
9 | latin2 | latin2 | latin2_general_ci |
10 | swe7 | swe7 | swe7_swedish_ci |
11 | usa7 | ascii | ascii_general_ci |
12 | ujis | ujis | ujis_japanese_ci |
13 | sjis | sjis | sjis_japanese_ci |
14 | cp1251 | cp1251 | cp1251_bulgarian_ci |
15 | danish | latin1 | latin1_danish_ci |
16 | hebrew | hebrew | hebrew_general_ci |
17 | win1251 | (removed) | (removed) |
18 | tis620 | tis620 | tis620_thai_ci |
19 | euc_kr | euckr | euckr_korean_ci |
20 | estonia | latin7 | latin7_estonian_ci |
21 | hungarian | latin2 | latin2_hungarian_ci |
22 | koi8_ukr | koi8u | koi8u_ukrainian_ci |
23 | win1251ukr | cp1251 | cp1251_ukrainian_ci |
24 | gb2312 | gb2312 | gb2312_chinese_ci |
25 | greek | greek | greek_general_ci |
26 | win1250 | cp1250 | cp1250_general_ci |
27 | croat | latin2 | latin2_croatian_ci |
28 | gbk | gbk | gbk_chinese_ci |
29 | cp1257 | cp1257 | cp1257_lithuanian_ci |
30 | latin5 | latin5 | latin5_turkish_ci |
31 | latin1_de | latin1 | latin1_german2_ci |
Table of Contents
Here is an annotated list of character sets and collations that MySQL supports. Because options and installation settings differ, some sites will not have all items in the list, and some sites will have items that are not on the list because defining new character sets or collations is straightforward.
MySQL supports 70+ collations for 30+ character sets.
mysql> SHOW CHARACTER SET; +----------+-----------------------------+---------------------+--------+ | Charset | Description | Default collation | Maxlen | +----------+-----------------------------+---------------------+--------+ | big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 | | dec8 | DEC West European | dec8_swedish_ci | 1 | | cp850 | DOS West European | cp850_general_ci | 1 | | hp8 | HP West European | hp8_english_ci | 1 | | koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 | | latin1 | ISO 8859-1 West European | latin1_swedish_ci | 1 | | latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 | | swe7 | 7bit Swedish | swe7_swedish_ci | 1 | | ascii | US ASCII | ascii_general_ci | 1 | | ujis | EUC-JP Japanese | ujis_japanese_ci | 3 | | sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 | | cp1251 | Windows Cyrillic | cp1251_bulgarian_ci | 1 | | hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 | | tis620 | TIS620 Thai | tis620_thai_ci | 1 | | euckr | EUC-KR Korean | euckr_korean_ci | 2 | | koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 | | gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 | | greek | ISO 8859-7 Greek | greek_general_ci | 1 | | cp1250 | Windows Central European | cp1250_general_ci | 1 | | gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 | | latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 | | armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 | | utf8 | UTF-8 Unicode | utf8_general_ci | 3 | | ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 | | cp866 | DOS Russian | cp866_general_ci | 1 | | keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 | | macce | Mac Central European | macce_general_ci | 1 | | macroman | Mac West European | macroman_general_ci | 1 | | cp852 | DOS Central European | cp852_general_ci | 1 | | latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 | | cp1256 | Windows Arabic | cp1256_general_ci | 1 | | cp1257 | Windows Baltic | cp1257_general_ci | 1 | | binary | Binary pseudo charset | binary | 1 | +----------+-----------------------------+---------------------+--------+ 33 rows in set (0.01 sec)
NB: ALL CHARACTER SETS HAVE A BINARY COLLATION. WE HAVE NOT INCLUDED THE BINARY COLLATION IN ALL THE DESCRIPTIONS THAT FOLLOW.
There are our two Unicode character sets. You can store texts in about 650 languages using these character sets. We have not added a large number of collations for these two new sets yet, but that will be happening soon. Now they have default case-insensitive accent-insensitive collations, plus the binary collation.
+---------+-----------------+-------------------+--------+ | Charset | Description | Default collation | Maxlen | +---------+-----------------+-------------------+--------+ | utf8 | UTF-8 Unicode | utf8_general_ci | 3 | | ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 | +---------+-----------------+-------------------+--------+
+----------+-----------------------------+---------------------+--------+ | Charset | Description | Default collation | Maxlen | +----------+-----------------------------+---------------------+--------+ | dec8 | DEC West European | dec8_swedish_ci | 1 | | hp8 | HP West European | hp8_english_ci | 1 | +----------+-----------------------------+---------------------+--------+
+----------+-----------------------------+---------------------+--------+ | Charset | Description | Default collation | Maxlen | +----------+-----------------------------+---------------------+--------+ | armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 | | cp1256 | Windows Arabic | cp1256_general_ci | 1 | | hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 | | greek | ISO 8859-7 Greek | greek_general_ci | 1 | | latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 | | geostd8 | Georgian | geostd8_general_ci | 1 | +----------+-----------------------------+---------------------+--------+
The Asian character sets that we support include Chinese, Japanese, Korean, and Thai. These can be complicated. For example, the Chinese sets have to allow for thousands of different characters.
+----------+-----------------------------+---------------------+--------+ | Charset | Description | Default collation | Maxlen | +----------+-----------------------------+---------------------+--------+ | big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 | | gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 | | gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 | | euckr | EUC-KR Korean | euckr_korean_ci | 2 | | ujis | EUC-JP Japanese | ujis_japanese_ci | 3 | | sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 | | tis620 | TIS620 Thai | tis620_thai_ci | 1 | +----------+-----------------------------+---------------------+--------+
The Baltic character sets cover Estonian, Latvian, and Lithuanian languages. There are two Baltic character sets currently supported:
latin7 (ISO 8859-13 Baltic):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | latin7_estonian_cs | latin7 | 20 | | | 0 | | latin7_general_ci | latin7 | 41 | Yes | | 0 | | latin7_general_cs | latin7 | 42 | | | 0 | | latin7_bin | latin7 | 79 | | | 0 | +----------------------+----------+----+---------+----------+---------+
cp1257 (Windows Baltic):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | cp1257_lithuanian_ci | cp1257 | 29 | | | 0 | | cp1257_bin | cp1257 | 58 | | | 0 | | cp1257_general_ci | cp1257 | 59 | Yes | | 0 | +----------------------+----------+----+---------+----------+---------+
Here are the Cyrillic character sets and collations for use with Belarusian, Bulgarian, Russian, Ukrainian languages.
cp1251 (Windows Cyrillic):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | cp1251_bulgarian_ci | cp1251 | 14 | | | 0 | | cp1251_ukrainian_ci | cp1251 | 23 | | | 0 | | cp1251_bin | cp1251 | 50 | | | 0 | | cp1251_general_ci | cp1251 | 51 | Yes | | 0 | | cp1251_general_cs | cp1251 | 52 | | | 0 | +----------------------+----------+----+---------+----------+---------+
cp866 (DOS Russian):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | cp866_general_ci | cp866 | 36 | Yes | | 0 | | cp866_bin | cp866 | 68 | | | 0 | +----------------------+----------+----+---------+----------+---------+
koi8r (KOI8-R Relcom Russian, primarily used in Russia on Unix):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | koi8r_general_ci | koi8r | 7 | Yes | | 0 | | koi8r_bin | koi8r | 74 | | | 0 | +----------------------+----------+----+---------+----------+---------+
koi8u (KOI8-U Ukrainian, primarily used in Ukraine on Unix):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | koi8u_general_ci | koi8u | 22 | Yes | | 0 | | koi8u_bin | koi8u | 75 | | | 0 | +----------------------+----------+----+---------+----------+---------+
We have some support for character sets used in The Czech Republic, Slovakia, Hungary, Romania, Slovenia, Croatia, and Poland.
cp1250 (Windows Central European):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | cp1250_general_ci | cp1250 | 26 | Yes | | 0 | | cp1250_czech_ci | cp1250 | 34 | | Yes | 2 | | cp1250_bin | cp1250 | 66 | | | 0 | +----------------------+----------+----+---------+----------+---------+
cp852 (DOS Central European):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | cp852_general_ci | cp852 | 40 | Yes | | 0 | | cp852_bin | cp852 | 81 | | | 0 | +----------------------+----------+----+---------+----------+---------+
macce (Mac Central European):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | macce_general_ci | macce | 38 | Yes | | 0 | | macce_bin | macce | 43 | | | 0 | +----------------------+----------+----+---------+----------+---------+
latin2 (ISO 8859-2 Central European):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | latin2_czech_ci | latin2 | 2 | | Yes | 4 | | latin2_general_ci | latin2 | 9 | Yes | | 0 | | latin2_hungarian_ci | latin2 | 21 | | | 0 | | latin2_croatian_ci | latin2 | 27 | | | 0 | | latin2_bin | latin2 | 77 | | | 0 | +----------------------+----------+----+---------+----------+---------+
keybcs2 (DOS Kamenicky Czech-Slovak):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | keybcs2_general_ci | keybcs2 | 37 | Yes | | 0 | | keybcs2_bin | keybcs2 | 73 | | | 0 | +----------------------+----------+----+---------+----------+---------+
West European Character Sets cover most West European languages, such as French, Spanish, Catalan, Basque, Portuguese, Italian, Albanian, Dutch, German, Danish, Swedish, Norwegian, Finnish, Faroese, Icelandic, Irish, Scottish, and English.
latin1 (ISO 8859-1 West European):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | latin1_german1_ci | latin1 | 5 | | | 0 | | latin1_swedish_ci | latin1 | 8 | Yes | Yes | 0 | | latin1_danish_ci | latin1 | 15 | | | 0 | | latin1_german2_ci | latin1 | 31 | | Yes | 2 | | latin1_bin | latin1 | 47 | | Yes | 0 | | latin1_general_ci | latin1 | 48 | | | 0 | | latin1_general_cs | latin1 | 49 | | | 0 | | latin1_spanish_ci | latin1 | 94 | | | 0 | +----------------------+----------+----+---------+----------+---------+
The latin1_swedish_ci collation is the default that probably is used by the majority of MySQL customers. It is constantly stated that this is based on the Swedish/Finnish collation rules, but you will find Swedes and Finns who disagree with that statement.
The latin1_german1_ci and latin1_german2_ci collations are based on the DIN-1 and DIN-2 standards, where DIN stands for Deutsches Institut für Normung (that is, the German answer to ANSI). DIN-1 is called the dictionary collation and DIN-2 is called the phone-book collation.
latin1_german1_ci (dictionary) rules:
Ä = A, Ö = O, Ü = U, ß = s
latin1_german2_ci (phone-book) rules:
Ä = AE, Ö = OE, Ü = UE, ß = ss
In the latin1_spanish_ci collation, Ñ (N-tilde) is a separate letter between N and O.
macroman (Mac West European):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | macroman_general_ci | macroman | 39 | Yes | | 0 | | macroman_bin | macroman | 53 | | | 0 | +----------------------+----------+----+---------+----------+---------+
cp850 (DOS West European):
+----------------------+----------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +----------------------+----------+----+---------+----------+---------+ | cp850_general_ci | cp850 | 4 | Yes | | 0 | | cp850_bin | cp850 | 80 | | | 0 | +----------------------+----------+----+---------+----------+---------+
Table of Contents
MySQL 4.1 introduces spatial extensions to allow the generation, storage, and analysis of geographic features. Currently, these features are available for MyISAM tables only.
This chapter covers the following topics:
The basis of these spatial extensions in the OpenGIS geometry model
Data formats for representing spatial data
How to use spatial data in MySQL
Use of indexing for spatial data
MySQL differences from the OpenGIS specification
MySQL implements spatial extensions following the specification of the Open GIS Consortium (OGC). This is an international consortium of more than 250 companies, agencies, and universities participating in the development of publicly available conceptual solutions that can be useful with all kinds of applications that manage spatial data. The OGC maintains a web site at http://www.opengis.org/.
In 1997, the Open GIS Consortium published the OpenGIS (R) Simple Features Specifications For SQL, a document that proposes several conceptual ways for extending an SQL RDBMS to support spatial data. This specification is available from the Open GIS web site at http://www.opengis.org/docs/99-049.pdf. It contains additional information relevant to this chapter.
MySQL implements a subset of the SQL with Geometry Types environment proposed by OGC. This term refers to an SQL environment that has been extended with a set of geometry types. A geometry-valued SQL column is implemented as a column that has a geometry type. The specifications describe a set of SQL geometry types, as well as functions on those types to create and analyze geometry values.
A geographic feature is anything in the world that has a location. A feature can be:
An entity. For example, a mountain, a pond, a city.
A space. For example, a postcode area, the tropics.
A definable location. For example, a crossroad, as a particular place where two streets intersect.
You can also find documents that use the term geospatial feature to refer to geographic features.
Geometry is another word that denotes a geographic feature. Originally the word geometry means measurement of the earth. Another meaning comes from cartography, referring to the geometric features that cartographers use to map the world.
This chapter uses all of these terms synonymously: geographic feature, geospatial feature, feature, or geometry. The term most commonly used here is geometry.
Let's define a geometry as a point or an aggregate of points representing anything in the world that has a location.
Table of Contents
The set of geometry types proposed by OGC's SQL with Geometry Types environment is based on the OpenGIS Geometry Model. In this model, each geometric object has the following general properties:
It is associated with a Spatial Reference System, which describes the coordinate space in which the object is defined.
It belongs to some geometry class.
A geometry value has the following properties:
Its type. Each geometry belongs to one of the instantiable classes in the hierarchy.
Its SRID, or Spatial Reference Identifier. This value identifies the geometry's associated Spatial Reference System that describes the coordinate space in which the geometry object is defined.
Its coordinates in its Spatial Reference System, represented as double-precision (8-byte) numbers. All non-empty geometries include at least one pair of (X,Y) coordinates. Empty geometries contain no coordinates.
Coordinates are related to the SRID. For example, in different coordinate systems, the distance between two objects may differ even when objects have the same coordinates, because the distance on the planar coordinate system and the distance on the geocentric system (coordinates on the Earth's surface) are different things.
Its interior, boundary, and exterior.
Every geometry occupies some position in space. The exterior of a geometry is all space not occupied by the geometry. The interior is the space occupied by the geometry. The boundary is the interface between the geometry's interior and exterior.
Its MBR (Minimum Bounding Rectangle), or Envelope. This is the bounding geometry, formed by the minimum and maximum (X,Y) coordinates:
((MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY))
The quality of being simple or non-simple. Geometry values of types (LineString, MultiPoint, MultiLineString) are either simple or non-simple. Each type determines its own assertions for being simple or non-simple.
The quality of being closed or not closed. Geometry values of types (LineString, MultiString) are either closed or not closed. Each type determines its own assertions for being closed or not closed.
The quality of being empty or not empty A geometry is empty if it does not have any points. Exterior, interior and boundary of an empty geometry are not defined (that is, they are represented by a NULL value). An empty geometry is defined to be always simple and has an area of 0.
Its dimension. A geometry can have a dimension of -1, 0, 1, or 2:
-1 for empty geometry.
0 for geometry with no length and no area.
1 for geometry with non-zero length and zero area.
2 for geometry with non-zero area.
Point objects have a dimension of zero. LineString objects have a dimension of 1. Polygon objects have a dimension of 2. The dimensions of MultiPoint, MultiLineString, and MultiPolygon objects are the same as the dimensions of the elements they consist of.
Imagine a large-scale map of the world with many cities. A point could represent each city.
On a city map, a Point could represent a bus stop.
X-coordinate value.
Y-coordinate value.
Point is defined as a zero-dimensional geometry.
The boundary of a Point is the empty set.
A Curve has the coordinates of its points.
A Curve is defined as a one-dimensional geometry.
A Curve is simple if it does not pass through the same point twice.
A Curve is closed if its start point is equal to its end point.
The boundary of a closed Curve is empty.
The boundary of a non-closed Curve consists of its two end points.
A Curve that is simple and closed is a LinearRing.
On a world map, LineString objects could represent rivers.
In a city map, LineString objects could represent streets.
A LineString has coordinates of segments, defined by each consecutive pair of points.
A LineString is a Line if it consists of exactly two points.
A LineString is a LinearRing if it's both closed and simple.
A Surface is defined as a two-dimensional geometry.
The OpenGIS specification defines a simple Surface as a geometry that consists of a single ``patch'' that is associated with a single exterior boundary and zero or more interior boundaries.
The boundary of a simple Surface is the set of closed curves corresponding to its exterior and interior boundaries.
The boundary of a Polygon consists of a set of LinearRing objects (that is, LineString objects that are both simple and closed) that make up its exterior and interior boundaries.
A Polygon has no rings which cross. The rings in the boundary of a Polygon may intersect at a Point, but only as a tangent.
A Polygon has no lines, spikes, or punctures.
A Polygon has an interior which is a connected point set.
A Polygon may have holes. The exterior of a Polygon with holes is not connected. Each hole defines a connected component of the exterior.
The above assertions make a Polygon a simple geometry.
On a world map, a Multipoint could represent a chain of small islands.
On a city map, a Multipoint could represent the outlets for a ticket office.
A MultiPoint is a zero-dimensional geometry.
A MultiPoint is simple if no two of its Point values are equal (have identical coordinate values).
A MultiPoint's boundary is the empty set.
A MultiCurve is a one-dimensional geometry.
A MultiCurve is simple if and only if all of its elements are simple, the only intersections between any two elements occur at points that are on the boundaries of both elements.
A MultiCurve boundary is obtained by applying the ``mod 2 union rule'' (also known as the odd-even rule): A point is in the boundary of a MultiCurve if it is in the boundaries of an odd number of MultiCurve elements.
A MultiCurve is closed if all of its elements are closed.
A closed MultiCurve's boundary is always empty.
On a region map, a MultiLineString could represent a river system or a highway system.
Two MultiSurface surfaces have no interiors which intersect.
Two MultiSurface elements have boundries which intersect at most at a finite number of points.
A MultiPolygon has no two Polygon elements with interiors that intersect.
A MultiPolygon has no two Polygon elements that cross (crossing is also forbidden by the previous assertion), or that touch at an infinite number of points.
A MultiPolygon may not have cut lines, spikes or punctures. A MultiPolygon is a regular, closed point set.
A MultiPolygon which has more than one Polygon has an interior which is not connected. The number of connected components of the interior of a MultiPolygon is equal to the number of Polygon values in the MultiPolygon.
A MultiPolygon is a two-dimensional geometry.
A MultiPolygon boundary is a set of closed curves (LineString values) corresponding to the boundaries of its Polygon elements.
Each Curve in the boundary of the MultiPolygon is in the boundary of exactly one Polygon element.
Every Curve in the boundary of an Polygon element is in the boundary of the MultiPolygon.
The geometry classes define a hierarchy as follows:
Geometry (non-instantiable)
Point (instantiable)
Curve (non-instantiable)
LineString (instantiable)
Line
LinearRing
Surface (non-instantiable)
Polygon (instantiable)
GeometryCollection (instantiable)
MultiPoint (instantiable)
MultiCurve (non-instantiable)
MultiLineString (instantiable)
MultiSurface (non-instantiable)
MultiPolygon (instantiable)
It is not possible to create objects in non-instantiable classes. It is possible to create objects in instantiable classes. All classes have properties, and instantiable classes may also have assertions (rules that define valid class instances).
Geometry is the base class. It's an abstract class. The instantiable subclasses of Geometry are restricted to zero-, one-, and two-dimensional geometric objects that exist in two-dimensional coordinate space. All instantiable geometry classes are defined so that valid instances of a geometry class are topologically closed (that is, all defined geometries include their boundary).
The base Geometry class has subclasses for Point, Curve, Surface and GeometryCollection:
Point represents zero-dimensional objects.
Curve represents one-dimensional objects, and has subclass LineString, with sub-subclasses Line and LinearRing.
Surface is designed for two-dimensional objects and has subclass Polygon.
GeometryCollection has specialized zero-, one-, and two-dimensional collection classes named MultiPoint, MultiLineString, and MultiPolygon for modelling geometries corresponding to collections of Points, LineStrings, and Polygons, respectively. MultiCurve and MultiSurface are introduced as abstract superclasses that generalize the collection interfaces to handle Curves and Surfaces.
Geometry, Curve, Surface, MultiCurve, and MultiSurface are defined as non-instantiable classes. They define a common set of methods for their subclasses and are included for extensibility.
Point, LineString, Polygon, GeometryCollection, MultiPoint, MultiLineString, and MultiPolygon are instantiable classes.
Geometry is the root class of the hierarchy. It is a non-instantiable class but has a number of properties that are common to all geometry values created from any of the Geometry subclasses. These properties are described in the following list. (Particular subclasses have their own specific properties, described later.)
A Curve is a one-dimensional geometry, usually represented by a sequence of points. Particular subclasses of Curve define the type of interpolation between points. Curve is a non-instantiable class.
A Surface is a two-dimensional geometry. It is a non-instantiable class. Its only instantiable subclass is Polygon.
A Polygon is a planar Surface representing a multisided geometry. It is defined by a single exterior boundary and zero or more interior boundaries, where each interior boundary defines a hole in the Polygon.
A GeometryCollection is a geometry that is a collection of one or more geometries of any class.
All the elements in a GeometryCollection must be in the same Spatial Reference System (that is, in the same coordinate system). There are no other constraints on the elements of a GeometryCollection, although the subclasses of GeometryCollection described in the following sections may restrict membership. Retrictions may be based on:
Element type (for example, a MultiPoint may contain only Point elements)
Dimension
Constraints on the degree of spatial overlap between elements
A MultiPoint is a geometry collection composed of Point elements. The points are not connected or ordered in any way.
A MultiCurve is a geometry collection composed of Curve elements. MultiCurve is a non-instantiable class.
A MultiLineString is a MultiCurve geometry collection composed of LineString elements.
A MultiSurface is a geometry collection composed of surface elements. MultiSurface is a non-instantiable class. Its only instantiable subclass is MultiPolygon.
Table of Contents
This section describes the standard spatial data formats that are used to represent geometry objects in queries. They are:
Well-Known Text (WKT) format
Well-Known Binary (WKB) format
Internally, MySQL stores geometry values in a format that is not identical to either WKT or WKB format.
The Well-Known Text (WKT) representation of Geometry is designed to exchange geometry data in ASCII form.
Examples of WKT representations of geometry objects are:
A Point:
POINT(15 20)
Note that point coordinates are specified with no separating comma.
A LineString with four points:
LINESTRING(0 0, 10 10, 20 25, 50 60)
A Polygon with one exterior ring and one interior ring:
POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7, 5 5))
A MultiPoint with three Point values:
MULTIPOINT(0 0, 20 20, 60 60)
A MultiLineString with two LineString values:
MULTILINESTRING((10 10, 20 20), (15 15, 30 15))
A MultiPolygon with two Polygon values:
MULTIPOLYGON(((0 0,10 0,10 10,0 10,0 0)),((5 5,7 5,7 7,5 7, 5 5)))
A GeometryCollection consisting of two Point values and one LineString:
GEOMETRYCOLLECTION(POINT(10 10), POINT(30 30), LINESTRING(15 15, 20 20))
A Backus-Naur grammar that specifies the formal production rules for writing WKT values may be found in the OGC specification document referenced near the beginning of this chapter.
The Well-Known Binary (WKB) representation for geometric values is defined by the OpenGIS specifications. It is also defined in the ISO ``SQL/MM Part 3: Spatial'' standard.
WKB is used to exchange geometry data as binary streams represented by BLOB values containing geometric WKB information.
WKB uses 1-byte unsigned integers, 4-byte unsigned integers, and 8-byte double-precision numbers (IEEE 754 format). A byte is 8 bits.
For example, a WKB value that corresponds to POINT(1 1) consists of this sequence of 21 bytes (each represented here by two hex digits):
0101000000000000000000F03F000000000000F03F
The sequence may be broken down into these components:
Byte order : 01 WKB type : 01000000 X : 000000000000F03F Y : 000000000000F03F
Component representation is as follows:
The byte order may be either 0 or 1 to indicate little-endian or big-endian storage. The little-endian and big-endian byte orders are also known as Network Data Representation (NDR) and External Data Representation (XDR), respectively.
The WKB type is a code that indicates the geometry type. Values from 1 through 7 indicate Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, and GeometryCollection.
A Point value has X and Y coordinates, each represented as a double-precision value.
WKB values for more complex geometry values are represented by more complex data structures, as detailed in the OpenGIS specification.
Table of Contents
This section describes the datatypes you can use for representing spatial data in MySQL, and the functions available for creating and retrieving spatial values.
MySQL has datatypes that correspond to OpenGIS classes. Some of these types hold single geometry values:
GEOMETRY
POINT
LINESTRING
POLYGON
GEOMETRY can store geometry values of any type. The other single-value types, POINT and LINESTRING and POLYGON, restrict their values to a particular geometry type.
The other datatypes hold collections of values:
MULTIPOINT
MULTILINESTRING
MULTIPOLYGON
GEOMETRYCOLLECTION
GEOMETRYCOLLECTION can store a collection of objects of any type. The other collection types, MULTIPOINT and MULTILINESTRING and MULTIPOLYGON and GEOMETRYCOLLECTION, restrict collection members to those having a particular geometry type.
This section describes how to create spatial values using Well-Known Text and Well-Known Binary functions that are defined in the OpenGIS standard, and using MySQL-specific functions.
MySQL provides a number of functions that take as input parameters a Well-Known Text representation (and, optionally, a spatial reference system identifier (SRID)), and return the corresponding geometry.
GeomFromText() accepts a WKT of any geometry type as its first argument. An implementation also provides type-specific construction functions for construction of geometry values of each geometry type.
GeomFromText(wkt[,srid]) , GeometryFromText(wkt[,srid]) | Constructs a geometry value of any type using its WKT representation and SRID. |
PointFromText(wkt[,srid]) | Constructs a POINT value using its WKT representation and SRID. |
LineFromText(wkt[,srid]) , LineStringFromText(wkt[,srid]) | Constructs a LINESTRING value using its WKT representation and SRID. |
PolyFromText(wkt[,srid]) , PolygonFromText(wkt[,srid]) | Constructs a POLYGON value using its WKT representation and SRID. |
MPointFromText(wkt[,srid]) , MultiPointFromText(wkt[,srid]) | Constructs a MULTIPOINT value using its WKT representation and SRID. |
MLineFromText(wkt[,srid]) , MultiLineStringFromText(wkt[,srid]) | Constructs a MULTILINESTRING value using its WKT representation and SRID. |
MPolyFromText(wkt[,srid]) , MultiPolygonFromText(wkt[,srid]) | Constructs a MULTIPOLYGON value using its WKT representation and SRID. |
GeomCollFromText(wkt[,srid]) , GeometryCollectionFromText(wkt[,srid]) | Constructs a GEOMETRYCOLLECTION value using its WKT representation and SRID. |
The OpenGIS specification also describes optional functions for constructing Polygon or MultiPolygon values based on the WKT representation of a collection of rings or closed LineString values. These values may intersect. MySQL does not implement these functions:
BdPolyFromText(wkt,srid) | Constructs a Polygon value from a MultiLineString value in WKT format containing an arbitrary collection of closed LineString values. |
BdMPolyFromText(wkt,srid) | Constructs a MultiPolygon value from a MultiLineString value in WKT format containing an arbitrary collection of closed LineString values. |
MySQL provides a number of functions that take as input parameters a BLOB containing a Well-Known Binary representation (and, optionally, a spatial reference system identifier (SRID)), and return the corresponding geometry.
GeomFromWKT() accepts a WKB of any geometry type as its first argument. An implementation also provides type-specific construction functions for construction of geometry values of each geometry type.
GeomFromWKB(wkb[,srid]) , GeometryFromWKB(wkt[,srid]) | Constructs a geometry value of any type using its WKB representation and SRID. |
PointFromWKB(wkb[,srid]) | Constructs a POINT value using its WKB representation and SRID. |
LineFromWKB(wkb[,srid]) , LineStringFromWKB(wkb[,srid]) | Constructs a LINESTRING value using its WKB representation and SRID. |
PolyFromWKB(wkb[,srid]) , PolygonFromWKB(wkb[,srid]) | Constructs a POLYGON value using its WKB representation and SRID. |
MPointFromWKB(wkb[,srid]) , MultiPointFromWKB(wkb[,srid]) | Constructs a MULTIPOINT value using its WKB representation and SRID. |
MLineFromWKB(wkb[,srid]) , MultiLineStringFromWKB(wkb[,srid]) | Constructs a MULTILINESTRING value using its WKB representation and SRID. |
MPolyFromWKB(wkb[,srid]) , MultiPolygonFromWKB(wkb[,srid]) | Constructs a MULTIPOLYGON value using its WKB representation and SRID. |
GeomCollFromWKB(wkb[,srid]) , GeometryCollectionFromWKB(wkt[,srid]) | Constructs a GEOMETRYCOLLECTION value using its WKB representation and SRID. |
The OpenGIS specification also describes optional functions for constructing Polygon or MultiPolygon values based on the WKB representation of a collection of rings or closed LineString values. These values may intersect. MySQL does not implement these functions:
BdPolyFromWKB(wkb,srid) | Constructs a Polygon value from a MultiLineString value in WKB format containing an arbitrary collection of closed LineString values. |
BdMPolyFromWKB(wkb,srid) | Constructs a MultiPolygon value from a MultiLineString value in WKB format containing an arbitrary collection of closed LineString values. |
Note: MySQL does not implement the functions listed in this section.
MySQL provides a set of useful functions for creating geometry WKB representations. The functions described in this section are MySQL extensions to the OpenGIS specifications. The results of these functions are BLOB values containing WKB representations of geometry values with no SRID. The results of these functions can be substituted as the first argument for any function in the GeomFromWKB() function family.
Point(x,y) | Constructs a WKB Point using its coordinates. |
MultiPoint(pt1,pt2,...) | Constructs a WKB MultiPoint value using WKB Point arguments. If any argument is not a WKBPoint, the return value is NULL. |
LineString(pt1,pt2,...) | Constructs a WKB LineString value from a number of WKB Point arguments. If any argument is not a WKB Point, the return value is NULL. If the number of Point arguments is less than two, the return value is NULL. |
MultiLineString(ls1,ls2,...) | Constructs a WKB MultiLineString value using using WBK LineString arguments. If any argument is not a LineString, the return value is NULL. |
Polygon(ls1,ls2,...) | Constructs a WKB Polygon value from a number of WKB LineString arguments. If any argument does not represent the WKB of a LinearRing (that is, not a closed and simple LineString) the return value is NULL. |
MultiPolygon(poly1,poly2,...) | Constructs a WKB MultiPolygon value from a set of WKB Polygon arguments. If any argument is not a WKB Polygon, the rerurn value is NULL. |
GeometryCollection(g1,g2,...) | Constucts a WKB GeometryCollection. If any argument is not a well-formed WKB representation of a geometry, the return value is NULL. |
MySQL provides a standard way of creating spatial columns for geometry types, for example, with CREATE TABLE or ALTER TABLE. Currently, spatial columns are supported only for MyISAM tables.
Use the CREATE TABLE statement to create a table with a spatial column:
mysql> CREATE TABLE geom (g GEOMETRY); Query OK, 0 rows affected (0.02 sec)
Use the ALTER TABLE statement to add or drop a spatial column to or from an existing table:
mysql> ALTER TABLE geom ADD pt POINT; Query OK, 0 rows affected (0.00 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> ALTER TABLE geom DROP pt; Query OK, 0 rows affected (0.00 sec) Records: 0 Duplicates: 0 Warnings: 0
After you have created spatial columns, you can populate them with spatial data.
Values should be stored in internal geometry format, but you can convert them to that format from either Well-Known Text (WKT) or Well-Known Binary (WKB) format. The following examples demonstrate how to insert geometry values into a table by converting WKT values into internal geometry format.
You can perform the conversion directly in the INSERT statement:
INSERT INTO geom VALUES (GeomFromText('POINT(1 1)')); SET @g = 'POINT(1 1)'; INSERT INTO geom VALUES (GeomFromText(@g));
Or you can perform the conversion prior to the INSERT:
SET @g = GeomFromText('POINT(1 1)'); INSERT INTO geom VALUES (@g);
The following examples insert more complex geometries into the table:
SET @g = 'LINESTRING(0 0,1 1,2 2)'; INSERT INTO geom VALUES (GeomFromText(@g)); SET @g = 'POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7, 5 5))'; INSERT INTO geom VALUES (GeomFromText(@g)); SET @g = 'GEOMETRYCOLLECTION(POINT(1 1),LINESTRING(0 0,1 1,2 2,3 3,4 4))'; INSERT INTO geom VALUES (GeomFromText(@g));
The preceding examples all use GeomFromText() to create geometry values. You can also use type-specific functions:
SET @g = 'POINT(1 1)'; INSERT INTO geom VALUES (PointFromText(@g)); SET @g = 'LINESTRING(0 0,1 1,2 2)'; INSERT INTO geom VALUES (LineStringFromText(@g)); SET @g = 'POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7, 5 5))'; INSERT INTO geom VALUES (PolygonFromText(@g)); SET @g = 'GEOMETRYCOLLECTION(POINT(1 1),LINESTRING(0 0,1 1,2 2,3 3,4 4))'; INSERT INTO geom VALUES (GeomCollFromText(@g));
Note that if a client application program wants to use WKB representations of geometry values, it is responsible for sending correctly formed WKB in queries to the server. However, there are several ways of satisfying this requirement. For example:
Inserting a POINT(1 1) value with hex literal syntax:
mysql> INSERT INTO geom VALUES -> (GeomFromWKB(0x0101000000000000000000F03F000000000000F03F));
An ODBC application can send a WKB representation, binding it to a placeholder using an argument of BLOB type:
INSERT INTO geom VALUES (GeomFromWKB(?))
Other programming interfaces may support a similar placeholder mechanism.
In a C program, you can escape a binary value using mysql_real_escape_string() and include the result in a query string that is sent to the server. See mysql_real_escape_string().
Geometry values stored in a table can be fetched in internal format. You can also convert them into WKT or WKB format.
Fetching geometry values using internal format can be useful in table-to-table transfers:
CREATE TABLE geom2 (g GEOMETRY) SELECT g FROM geom;
The AsText() function converts a geometry from internal format into a WKT string.
mysql> SELECT AsText(g) FROM geom; +-------------------------+ | AsText(p1) | +-------------------------+ | POINT(1 1) | | LINESTRING(0 0,1 1,2 2) | +-------------------------+
Table of Contents
After populating spatial columns with values, you are ready to query and analyze them. MySQL provides a set of functions to perform various operations on spatial data. These functions can be grouped into four major categories according to the type of operation they perform:
Functions that convert geometries between various formats
Functions that provide access to qualitative or quantitative properties of a geometry
Functions that describe relations between two geometries
Functions that create new geometries from existing ones
Spatial analysis functions can be used in many contexts, such as:
Any interactive SQL program, like mysql or MySQLCC
Application programs written in any language that supports a MySQL client API
MySQL supports the following functions for converting geometry values between internal format and either WKT or WKB format:
GeomFromText(wkt[,srid]) | Converts a string value from its WKT representation into internal geometry format and returns the result. A number of type-specific functions are also supported, such as PointFromText() and LineFromText(); see GIS WKT Functions. |
GeomFromWKB(wkb[,srid]) | Converts a binary value from its WKB representation into internal geometry format and returns the result. A number of type-specific functions are also supported, such as PointFromWKB() and LineFromWKB(); see GIS WKB Functions. |
AsText(g) |
Converts a value in internal geometry format to its WKT representation
and returns the string result.
mysql> SET @g = 'LineString(1 1,2 2,3 3)'; mysql> SELECT AsText(GeomFromText(@g)); +--------------------------+ | AsText(GeomFromText(@G)) | +--------------------------+ | LINESTRING(1 1,2 2,3 3) | +--------------------------+ |
AsBinary(g) | Converts a value in internal geometry format to its WKB representation and returns the binary result. |
Each function that belongs to this group takes a geometry value as its argument and returns some quantitive or qualitive property of the geometry. Some functions restrict their argument type. Such functions return NULL if the argument is of an incorrect geometry type. For example, Area() returns NULL if the object type is neither Polygon nor MultiPolygon.
The functions listed in this ssection do not restrict their argument and accept a geometry value of any type.
GeometryType(g) |
Returns as a string the name of the geometry type of which
the geometry instance g is a member.
The name will correspond to one of the instantiable Geometry subclasses.
mysql> SELECT GeometryType(GeomFromText('POINT(1 1)')); +------------------------------------------+ | GeometryType(GeomFromText('POINT(1 1)')) | +------------------------------------------+ | POINT | +------------------------------------------+ |
Dimension(g) |
Returns the inherent dimension of the geometry value g. The result
can be -1, 0, 1, or 2. (The meaning of these values is given in
GIS class geometry.)
mysql> SELECT Dimension(GeomFromText('LineString(1 1,2 2)')); +------------------------------------------------+ | Dimension(GeomFromText('LineString(1 1,2 2)')) | +------------------------------------------------+ | 1 | +------------------------------------------------+ |
SRID(g) |
Returns an integer indicating the Spatial Reference System ID for the geometry
value g.
mysql> SELECT SRID(GeomFromText('LineString(1 1,2 2)',101)); +-----------------------------------------------+ | SRID(GeomFromText('LineString(1 1,2 2)',101)) | +-----------------------------------------------+ | 101 | +-----------------------------------------------+ |
Envelope(g) |
Returns the Minimum Bounding Rectangle (MBR) for the geometry value g.
The result is returned as a polygon value.
mysql> SELECT AsText(Envelope(GeomFromText('LineString(1 1,2 2)'))); +-------------------------------------------------------+ | AsText(Envelope(GeomFromText('LineString(1 1,2 2)'))) | +-------------------------------------------------------+ | POLYGON((1 1,2 1,2 2,1 2,1 1)) | +-------------------------------------------------------+The polygon is defined by the corner points of the bounding box: POLYGON((MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY)) |
The OpenGIS specification also defines the following functions, which MySQL does not implement:
Boundary(g) | Returns a geometry that is the closure of the combinatorial boundary of the geometry value g. |
IsEmpty(g) | Returns 1 if the geometry value g is the empty geometry, 0 if it is not empty, and -1 if the argument is NULL. If the geometry is empty, it represents the empty point set. |
IsSimple(g) | Currently, this function is a placeholder and should not be used. If implemented, its behavior will be as described in the next paragraph. Returns 1 if the geometry value g has no anomalous geometric points, such as self intersection or self tangency. IsSimple() returns 0 if the argument is not simple, and -1 if it is NULL. The description of each instantiable geometric class given earlier in the chapter includes the specific conditions that cause an instance of that class to be classified as not simple. |
A Point consists of X and Y coordinates, which may be obtained using the following functions:
X(p) |
Returns the X-coordinate value for the point p as a double-precision
number.
mysql> SELECT X(GeomFromText('Point(56.7 53.34)')); +--------------------------------------+ | X(GeomFromText('Point(56.7 53.34)')) | +--------------------------------------+ | 56.7 | +--------------------------------------+ |
Y(p) |
Returns the Y-coordinate value for the point p as a double-precision
number.
mysql> SELECT Y(GeomFromText('Point(56.7 53.34)')); +--------------------------------------+ | Y(GeomFromText('Point(56.7 53.34)')) | +--------------------------------------+ | 53.34 | +--------------------------------------+ |
A LineString consists of Point values. You can extract particular points of a LineString, count the number of points that it contains, or obtain its length.
EndPoint(ls) |
Returns the Point that is the end point of the LineString value
ls.
mysql> SELECT AsText(EndPoint(GeomFromText('LineString(1 1,2 2,3 3)'))); +------------------------------------------------------------+ | AsText(EndPoint(GeomFromText('LineString(1 1,2 2,3 3)'))) | +------------------------------------------------------------+ | POINT(3 3) | +------------------------------------------------------------+ |
GLength(ls) |
Returns as a double-precision number the length of the LineString
value ls in its associated spatial reference.
mysql> SELECT GLength(GeomFromText('LineString(1 1,2 2,3 3)')); +--------------------------------------------------+ | GLength(GeomFromText('LineString(1 1,2 2,3 3)')) | +--------------------------------------------------+ | 2.8284271247462 | +--------------------------------------------------+ |
IsClosed(ls) |
Returns 1 if the LineString value ls is closed
(that is, its StartPoint() and EndPoint() values are the same).
Returns 0 if ls is not closed, and -1 if it is NULL.
mysql> SELECT IsClosed(GeomFromText('LineString(1 1,2 2,3 3)')); +---------------------------------------------------+ | IsClosed(GeomFromText('LineString(1 1,2 2,3 3)')) | +---------------------------------------------------+ | 0 | +---------------------------------------------------+ |
NumPoints(ls) |
Returns the number of points in the LineString value ls.
mysql> SELECT NumPoints(GeomFromText('LineString(1 1,2 2,3 3)')); +----------------------------------------------------+ | NumPoints(GeomFromText('LineString(1 1,2 2,3 3)')) | +----------------------------------------------------+ | 3 | +----------------------------------------------------+ |
PointN(ls,n) |
Returns the n-th point in the Linestring value ls.
Point numbers begin at 1.
mysql> SELECT AsText(PointN(GeomFromText('LineString(1 1,2 2,3 3)'),2)); +-----------------------------------------------------------+ | AsText(PointN(GeomFromText('LineString(1 1,2 2,3 3)'),2)) | +-----------------------------------------------------------+ | POINT(2 2) | +-----------------------------------------------------------+ |
StartPoint(ls) |
Returns the Point that is the start point of the LineString value
ls.
mysql> SELECT AsText(StartPoint(GeomFromText('LineString(1 1,2 2,3 3)'))); +-------------------------------------------------------------+ | AsText(StartPoint(GeomFromText('LineString(1 1,2 2,3 3)'))) | +-------------------------------------------------------------+ | POINT(1 1) | +-------------------------------------------------------------+ |
The OpenGIS specification also defines the following function, which MySQL does not implement:
IsRing(ls) | Returns 1 if the LineString value ls is closed (that is, its StartPoint() and EndPoint() values are the same) and is simple (does not pass through the same point more than once). Returns 0 if ls is not a ring, and -1 if it is NULL. |
GLength(mls) |
Returns as a double-precision number
the length of the MultiLineString value mls. The length of
mls is equal to the sum of the lengths of its elements.
mysql> SELECT GLength(GeomFromText('MultiLineString((1 1,2 2,3 3),(4 4,5 5))')); +-------------------------------------------------------------------+ | GLength(GeomFromText('MultiLineString((1 1,2 2,3 3),(4 4,5 5))')) | +-------------------------------------------------------------------+ | 4.2426406871193 | +-------------------------------------------------------------------+ |
IsClosed(mls) |
Returns 1 if the MultiLineString value mls is closed
(that is, the StartPoint() and EndPoint() values are the same
for each LineString in mls).
Returns 0 if mls is not closed, and -1 if it is NULL.
mysql> SELECT IsClosed(GeomFromText('MultiLineString((1 1,2 2,3 3),(4 4,5 5))')); +--------------------------------------------------------------------+ | IsClosed(GeomFromText('MultiLineString((1 1,2 2,3 3),(4 4,5 5))')) | +--------------------------------------------------------------------+ | 0 | +--------------------------------------------------------------------+ |
Area(poly) |
Returns as a double-precision number the area of the Polygon value
poly, as measured in its spatial reference system.
mysql> SELECT Area(GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))')); +----------------------------------------------------------------------------+ | Area(GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))')) | +----------------------------------------------------------------------------+ | 8 | +----------------------------------------------------------------------------+ |
NumInteriorRings(poly) |
Returns the number of interior rings in the Polygon value poly.
mysql> SELECT NumInteriorRings(GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))')); +----------------------------------------------------------------------------------------+ | NumInteriorRings(GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))')) | +----------------------------------------------------------------------------------------+ | 1 | +----------------------------------------------------------------------------------------+ |
ExteriorRing(poly) |
Returns the exterior ring of the Polygon value poly
as a LineString.
mysql> SELECT AsText(ExteriorRing(GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))'))); +--------------------------------------------------------------------------------------------+ | AsText(ExteriorRing(GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))'))) | +--------------------------------------------------------------------------------------------+ | LINESTRING(0 0,0 3,3 3,3 0,0 0) | +--------------------------------------------------------------------------------------------+ |
InteriorRingN(poly,n) |
Returns the n-th interior ring for the Polygon value
poly as a LineString.
Ring numbers begin at 1.
mysql> SELECT AsText(InteriorRingN(GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))'),1)); +-----------------------------------------------------------------------------------------------+ | AsText(InteriorRingN(GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))'),1)) | +-----------------------------------------------------------------------------------------------+ | LINESTRING(1 1,1 2,2 2,2 1,1 1) | +-----------------------------------------------------------------------------------------------+ |
Area(mpoly) |
Returns as a double-precision number the area of the MultiPolygon
value mpoly, as measured in its spatial reference system.
mysql> SELECT Area(GeomFromText('MultiPolygon(((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1)))')); +-----------------------------------------------------------------------------------+ | Area(GeomFromText('MultiPolygon(((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1)))')) | +-----------------------------------------------------------------------------------+ | 8 | +-----------------------------------------------------------------------------------+ |
The OpenGIS specification also defines the following functions, which MySQL does not implement:
NumGeometries(gc) |
Returns the number of geometries in the GeometryCollection value
gc.
mysql> SELECT NumGeometries(GeomFromText('GeometryCollection(Point(1 1),LineString(2 2, 3 3))')); +------------------------------------------------------------------------------------+ | NumGeometries(GeomFromText('GeometryCollection(Point(1 1),LineString(2 2, 3 3))')) | +------------------------------------------------------------------------------------+ | 2 | +------------------------------------------------------------------------------------+ |
GeometryN(gc,n) |
Returns the n-th geometry in the GeometryCollection value
gc. Geometry numbers begin at 1.
mysql> SELECT AsText(GeometryN(GeomFromText('GeometryCollection(Point(1 1),LineString(2 2, 3 3))'),1)); +------------------------------------------------------------------------------------------+ | AsText(GeometryN(GeomFromText('GeometryCollection(Point(1 1),LineString(2 2, 3 3))'),1)) | +------------------------------------------------------------------------------------------+ | POINT(1 1) | +------------------------------------------------------------------------------------------+ |
In the section Geometry property functions, we've already discussed some functions that can construct new geometries from the existing ones:
Envelope(g)
StartPoint(ls)
EndPoint(ls)
PointN(ls,n)
ExteriorRing(poly)
InteriorRingN(poly,n)
GeometryN(gc,n)
OpenGIS proposes a number of other functions that can produce geometries. They are designed to implement Spatial Operators.
These functions are not implemented in MySQL. They may appear in future releases.
Intersection(g1,g2) | Returns a geometry that represents the point set intersection of the geometry values g1 with g2. |
Union(g1,g2) | Returns a geometry that represents the point set union of the geometry values g1 and g2. |
Difference(g1,g2) | Returns a geometry that represents the point set difference of the geometry value g1 with g2. |
SymDifference(g1,g2) | Returns a geometry that represents the point set symmetric difference of the geometry value g1 with g2. |
Buffer(g,d) | Returns a geometry that represents all points whose distance from the geometry value g is less than or equal to a distance of d. |
ConvexHull(g) | Returns a geometry that represents the convex hull of the geometry value g. |
The functions described in these sections take two geometries as input parameters and return a qualitive or quantitive relation between them.
MySQL provides some functions that can test relations between mininal bounding rectangles of two geometries g1 and g2. They include:
MBRContains(g1,g2) |
Returns 1 or 0 to indicate whether or not the Minimum Bounding Rectangle of
g1 contains the Minimum Bounding Rectangle of g2.
mysql> SET @g1 = GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0))'); mysql> SET @g2 = GeomFromText('Point(1 1)'); mysql> SELECT MBRContains(@g1,@g2), MBRContains(@g2,@g1); ----------------------+----------------------+ | MBRContains(@g1,@g2) | MBRContains(@g2,@g1) | +----------------------+----------------------+ | 1 | 0 | +----------------------+----------------------+ |
MBRWithin(g1,g2) |
Returns 1 or 0 to indicate whether or not the Minimum Bounding Rectangle
of g1 is within the Minimum Bounding Rectangle of g2.
mysql> SET @g1 = GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0))'); mysql> SET @g2 = GeomFromText('Polygon((0 0,0 5,5 5,5 0,0 0))'); mysql> SELECT MBRWithin(@g1,@g2), MBRWithin(@g2,@g1); +--------------------+--------------------+ | MBRWithin(@g1,@g2) | MBRWithin(@g2,@g1) | +--------------------+--------------------+ | 1 | 0 | +--------------------+--------------------+ |
MBRDisjoint(g1,g2) | Returns 1 or 0 to indicate whether or not the Minimum Bounding Rectangles of the two geometries g1 and g2 are disjoint (do not intersect). |
MBREquals(g1,g2) | Returns 1 or 0 to indicate whether or not the Minimum Bounding Rectangles of the two geometries g1 and g2 are the same. |
MBRIntersects(g1,g2) | Returns 1 or 0 to indicate whether or not the Minimum Bounding Rectangles of the two geometries g1 and g2 intersect. |
MBROverlaps(g1,g2) | Returns 1 or 0 to indicate whether or not the Minimum Bounding Rectangles of the two geometries g1 and g2 overlap. |
MBRTouches(g1,g2) | Returns 1 or 0 to indicate whether or not the Minimum Bounding Rectangles of the two geometries g1 and g2 touch. |
The OpenGIS specification defines the following functions, which MySQL does not implement. They may appear in future releases. If implemented, they will provide full support for spatial analysis, not just MBR-based support.
The functions operate on two geometry values g1 and g2.
Contains(g1,g2) | Returns 1 or 0 to indicate whether or not g1 completely contains g2. |
Crosses(g1,g2) |
Returns 1 if g1 spatially crosses g2.
Returns NULL if g1 is a Polygon or a MultiPolygon,
or if g2 is a Point or a MultiPoint.
Otherwise, returns 0.
The term spatially crosses denotes a spatial relation between two given
geometries that has the following properties:
|
Disjoint(g1,g2) | Returns 1 or 0 to indicate whether or not g1 is spatially disjoint from (does not intersect) g2. |
Equals(g1,g2) | Returns 1 or 0 to indicate whether or not g1 is spatially equal to g2. |
Intersects(g1,g2) | Returns 1 or 0 to indicate whether or not g1 spatially intersects g2. |
Overlaps(g1,g2) | Returns 1 or 0 to indicate whether or not g1 spatially overlaps g2. The term spatially overlaps is used if two geometries intersect and their intersection results in a geometry of the same dimension but not equal to either of the given geometries. |
Touches(g1,g2) | Returns 1 or 0 to indicate whether or not g1 spatially touches g2. Two geometries spatially touch if the interiors of the geometries do not intersect, but the boundary of one of the geometries intersects either the boundary or the interior of the other. |
Within(g1,g2) | Returns 1 or 0 to indicate whether or not g1 is spatially within g2. |
Distance(g1,g2) | Returns as a double-precision number the shortest distance between any two points in the two geometries. |
Related(g1,g2,pattern_matrix) | Returns 1 or 0 to indicate whether or not the spatial relationship specified by pattern_matrix exists between g1 and g2. Returns -1 if the arguments are NULL. The pattern matrix is a string. Its specification will be noted here if this function is implemented. |
Table of Contents
Search operations in non-spatial databases can be optimized using indexes. This is true for spatial databases as well. With the help of a great variety of multi-dimensional indexing methods that have already been designed, it's possible to optimize spatial searches. The most typical of these are:
Point queries that search for all objects that contain a given point
Region queries that search for all objects that overlap a given region
MySQL uses R-Trees with quadratic splitting to index spatial columns. A spatial index is built using the MBR of a geometry. For most geometries, the MBR is a minimum rectangle that surrounds the geometries. For a horizontal or a vertical linestring, the MBR is a rectangle degenerated into the linestring. For a point, the MBR is a rectangle degenerated into the point.
MySQL can create spatial indexes using syntax similar to that for creating regular indexes, but extended with the SPATIAL keyword. Spatial columns that are indexed currently must be declared NOT NULL. The following examples demonstrate how to create spatial indexes.
With CREATE TABLE:
mysql> CREATE TABLE geom (g GEOMETRY NOT NULL, SPATIAL INDEX(g));
With ALTER TABLE:
mysql> ALTER TABLE geom ADD SPATIAL INDEX(g);
With CREATE INDEX:
mysql> CREATE SPATIAL INDEX sp_index ON geom (g);
To drop spatial indexes, use ALTER TABLE or DROP INDEX:
With ALTER TABLE:
mysql> ALTER TABLE geom DROP INDEX g;
With DROP INDEX:
mysql> DROP INDEX sp_index ON geom;
Example: Suppose that a table geom contains more than 32000 geometries, which are stored in the column g of type GEOMETRY. The table also has an AUTO_INCREMENT column fid for storing object ID values.
mysql> SHOW FIELDS FROM geom; +-------+----------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+----------+------+-----+---------+----------------+ | fid | int(11) | | PRI | NULL | auto_increment | | g | geometry | | | | | +-------+----------+------+-----+---------+----------------+ 2 rows in set (0.00 sec) mysql> SELECT COUNT(*) FROM geom; +----------+ | count(*) | +----------+ | 32376 | +----------+ 1 row in set (0.00 sec)
To add a spatial index on the column g, use this statement:
mysql> ALTER TABLE geom ADD SPATIAL INDEX(g); Query OK, 32376 rows affected (4.05 sec) Records: 32376 Duplicates: 0 Warnings: 0
The optimizer investigates whether available spatial indexes can be involved in the search for queries that use a function such as MBRContains() or MBRWithin() in the WHERE clause. For example, let's say we want to find all objects that are in the given rectangle:
mysql> SELECT fid,AsText(g) FROM geom WHERE mysql> MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g); +-----+-----------------------------------------------------------------------------+ | fid | AsText(g) | +-----+-----------------------------------------------------------------------------+ | 21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30333.8 15828.8) | | 22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8,30334 15871.4) | | 23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4,30334 15914.2) | | 24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4,30273.4 15823) | | 25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882.4,30274.8 15866.2) | | 26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4,30275 15918.2) | | 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946.8,30320.4 15938.4) | | 1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136.4,30240 15127.2) | | 2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136,30210.4 15121) | | 3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,30169 15113) | | 4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30157 15111.6) | | 5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4,30194.2 15075.2) | | 6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,30244.6 15077) | | 7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8,30201.2 15049.4) | | 10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6,30189.6 15019) | | 11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2,30151.2 15009.8) | | 13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,30114.6 15067.8) | | 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30278 15134) | | 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30259 15083.4) | | 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4,30128.8 15001) | +-----+-----------------------------------------------------------------------------+ 20 rows in set (0.00 sec)
Now let's check the way this query is executed, using EXPLAIN:
mysql> EXPLAIN SELECT fid,AsText(g) FROM geom WHERE mysql> MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g); +----+-------------+-------+-------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | geom | range | g | g | 32 | NULL | 50 | Using where | +----+-------------+-------+-------+---------------+------+---------+------+------+-------------+ 1 row in set (0.00 sec)
Now let's check what would happen if we didn't have a spatial index:
mysql> EXPLAIN SELECT fid,AsText(g) FROM g IGNORE INDEX (g) WHERE mysql> MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g); +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | 1 | SIMPLE | geom | ALL | NULL | NULL | NULL | NULL | 32376 | Using where | +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ 1 row in set (0.00 sec)
Let's execute the above query, ignoring the spatial key we have:
mysql> SELECT fid,AsText(g) FROM geom IGNORE INDEX (g) WHERE mysql> MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g); +-----+-----------------------------------------------------------------------------+ | fid | AsText(g) | +-----+-----------------------------------------------------------------------------+ | 1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136.4,30240 15127.2) | | 2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136,30210.4 15121) | | 3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,30169 15113) | | 4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30157 15111.6) | | 5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4,30194.2 15075.2) | | 6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,30244.6 15077) | | 7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8,30201.2 15049.4) | | 10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6,30189.6 15019) | | 11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2,30151.2 15009.8) | | 13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,30114.6 15067.8) | | 21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30333.8 15828.8) | | 22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8,30334 15871.4) | | 23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4,30334 15914.2) | | 24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4,30273.4 15823) | | 25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882.4,30274.8 15866.2) | | 26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4,30275 15918.2) | | 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30278 15134) | | 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30259 15083.4) | | 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4,30128.8 15001) | | 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946.8,30320.4 15938.4) | +-----+-----------------------------------------------------------------------------+ 20 rows in set (0.46 sec)
When the index is not used, the execution time for this query rises from 0.00 seconds to 0.46 seconds.
In future releases, spatial indexes may also be used for optimizing other functions. See Functions for testing spatial relations between geometric objects.
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Additional Metadata Views | OpenGIS specifications propose several additional metadata views. For example, a system view named GEOMETRY_COLUMNS contains a description of geometry columns, one row for each geometry column in the database. |
The OpenGIS function Length() on LineString and MultiLineString currently should be called in MySQL as GLength() | The problem is that there is an existing SQL function Length() which calculates the length of string values, and sometimes it's not possible to distinguish whether the function is called in a textual or spatial context. We need either to solve this somehow, or decide on another function name. |
Table of Contents
Stored procedures and functions are a new feature in MySQL version 5.0. A stored procedure is a set of SQL commands that can be stored in the server. Once this has been done, clients don't need to keep re-issuing the individual commands but can refer to the stored procedure instead.
Stored procedures can provide improved performance as less information needs to be sent between the server and the client. The trade-off is that this does increase the load on the database server system, as more of the work is done on the server side and less on the client (application) side. And often, there are multiple client machines (such as web servers) but only one or a few database servers.
Stored procedures also allow you to have libraries of functions in the database server. However, modern application languages already allow such design internally with for instance classes, and using these client application language features is beneficial for the programmer even outside the scope of database use.
Some situations where stored procedures can be particularly useful:
When multiple client applications are written in different languages or work on different platforms, but need to perform the same database operations.
When security is paramount. Banks, for instance, use stored procedures for all common operations. This provides a consistent and secure environment, and procedures can ensure that each operation is properly logged. In such a setup, applications and users would not get any access to the database tables directly, but may only execute specific stored procedures.
MySQL follows the SQL:2003 syntax for stored procedures, which is also used by IBM's DB2. Compatibility support for other stored procedure languages (PL/SQL, T-SQL) may be added later.
The MySQL implementation of stored procedures is still in progress. All syntax described in this chapter is supported and any limitations and extensions are documented where appropriate.
Stored procedures require the proc table in the mysql database. This table is created during the MySQL 5.0 installation procedure. If you are upgrading to MySQL 5.0 from an earlier version, be sure to update your grant tables to make sure the proc table exists. See Upgrading-grant-tables.
Table of Contents
Stored procedures and functions are routines that are created with CREATE PROCEDURE and CREATE FUNCTION statements. A procedure is invoked using a CALL statement, and can only pass back values using output variables. Functions may return a scalar value and can be called from inside a statement just like any other function (that is, by invoking the function's name). Stored routines may call other stored routines. A routine is either a procedure or a function.
At present, MySQL only preserves context for the default database. That is, if you say USE dbname within a procedure, the original default database is restored upon routine exit. A routine inherits the default database from the caller, so generally routines should either issue a USE dbname statement, or specify all tables with an explicit database reference, e.g. dbname.tablename.
MySQL supports the very useful extension that allows the use of regular SELECT statements (that is, without using cursors or local variables) inside a stored procedure. The result set of such a query is simply sent directly to the client. Multiple SELECT statements generate multiple result sets, so the client must use a MySQL client library that supports multiple result sets. This means the client must use a client library from a version of MySQL at least as recent as 4.1.
This following section describes the syntax used to create, alter, drop, and query stored procedures and functions.
CREATE PROCEDURE sp_name ([parameter[,...]]) [characteristic ...] routine_body CREATE FUNCTION sp_name ([parameter[,...]]) [RETURNS type] [characteristic ...] routine_body parameter: [ IN | OUT | INOUT ] param_name type type: Any valid MySQL data type characteristic: LANGUAGE SQL | [NOT] DETERMINISTIC | SQL SECURITY {DEFINER | INVOKER} | COMMENT string routine_body: Valid SQL procedure statement(s)
The RETURNS clause may be specified for a only FUNCTION. It is used to indicate the return type of the function, and the function body must contain a RETURN value statement.
The parameter list enclosed within parentheses must always be present. If there are no parameters, an empty parameter list of () should be used. Each parameter is an IN parameter by default. To specify otherwise for a parameter, use the keyword OUT or INOUT before the parameter name. Specifying IN, OUT, or INOUT is only valid for a PROCEDURE.
The CREATE FUNCTION statement is used in earlier versions of MySQL to support UDFs (User Defined Functions). See Adding functions. UDFs continue to be supported, even with the existence of stored functions. A UDF can be regarded as an external stored function. However, do note that stored functions share their namespace with UDFs.
A framework for external stored procedures will be introduced in the near future. This will allow you to write stored procedures in languages other than SQL. Most likely, one of the first languages to be supported will be PHP, as the core PHP engine is small, thread-safe, and can easily be embedded. As the framework will be public, it is expected that many other languages will also be supported.
A function is considered ``deterministic'' if it always returns the same result for the same input parameters, and ``not deterministic'' otherwise. Currently, the DETERMINISTIC characteristic is accepted, but not yet used by the optimizer.
The SQL SECURITY characteristic can be used to specify whether the routine should be executed using the permissions of the user who creates the routine, or the user who invokes it. The default value is DEFINER. This feature is new in SQL:2003.
MySQL does not yet use the GRANT EXECUTE privilege. So for now, if a procedure p1() mentions table t1, the caller must have privileges on table t1 in order to call procedure p1() successfully.
MySQL stores the sql_mode settings in effect at the time a routine is created, and will always execute routines with these settings in force.
The COMMENT clause is a MySQL extension, and may be used to describe the stored procedure. This information is displayed by the SHOW CREATE PROCEDURE and SHOW CREATE FUNCTION statements.
MySQL allows routines to contain DDL statements (such as CREATE and DROP) and SQL transaction statements (such as COMMIT). This is not required by the standard and is therefore implementation-specific.
NOTE: Currently, stored FUNCTIONs may not contain references to tables. Please note that this includes some SET statements, but excludes some SELECT statements. This limitation will be lifted as soon as possible.
The following is an example of a simple stored procedure that uses an OUT parameter. The example uses the mysql client delimiter command to change the statement delimiter prior to defining the procedure. This allows the ; delimiter used in the procedure body to be passed through to the server rather than being interpreted by mysql itself.
mysql> delimiter | mysql> CREATE PROCEDURE simpleproc (OUT param1 INT) -> BEGIN -> SELECT COUNT(*) INTO param1 FROM t; -> END -> | Query OK, 0 rows affected (0.00 sec) mysql> CALL simpleproc(@a)| Query OK, 0 rows affected (0.00 sec) mysql> SELECT @a| +------+ | @a | +------+ | 3 | +------+ 1 row in set (0.00 sec)
The following is an example of a function that takes a parameter, performs an operation using an SQL function, and returns the result:
mysql> delimiter | mysql> CREATE FUNCTION hello (s CHAR(20)) RETURNS CHAR(50) -> RETURN CONCAT('Hello, ',s,'!'); -> | Query OK, 0 rows affected (0.00 sec) mysql> SELECT hello('world')| +----------------+ | hello('world') | +----------------+ | Hello, world! | +----------------+ 1 row in set (0.00 sec)
ALTER {PROCEDURE | FUNCTION} sp_name [characteristic ...] characteristic: NAME newname | SQL SECURITY {DEFINER | INVOKER} | COMMENT string
This command can be used to rename a stored procedure or function, and to change its characteristics. More than one change may be specified in an ALTER PROCEDURE or ALTER FUNCTION statement.
DROP {PROCEDURE | FUNCTION} [IF EXISTS] sp_name
This command is used to delete a stored procedure or function. That is, the specified routine is removed from the server.
The IF EXISTS clause is a MySQL extension. It prevents an error from occurring if the procedure or function does not exist. A warning is produced that can be viewed with SHOW WARNINGS.
SHOW {PROCEDURE | FUNCTION} STATUS [LIKE pattern]
This command is a MySQL extension. It returns characteristics of routines, such as the name, type, creator, creation and modification dates. If no pattern is specified, the information for all stored procedures or all stored functions is listed, depending on which statement you use.
CALL sp_name([parameter[,...]])
The CALL command is used to invoke a routine that was defined previously with CREATE PROCEDURE.
[begin_label:] BEGIN statement(s) END [end_label]
Stored routines may contain multiple statements, using a BEGIN ... END compound statement.
begin_label and end_label must be the same, if both are specified.
Please note that the optional [NOT] ATOMIC clause is not yet supported. This means that no transactional savepoint is set at the start of the instruction block and the BEGIN clause used in this context has no effect on the current transaction.
Multiple statements requires that a client is able to send query strings containing ;. This is handled in the mysql command-line client with the delimiter command. Changing the ; end-of-query delimiter (for example, to |) allows ; to be used in a routine body.
The DECLARE statement is used to define various items local to a routine: local variables (see Variables in Stored Procedures), conditions and handlers (see Conditions and Handlers) and cursors (see Cursors). SIGNAL and RESIGNAL statements are not currently supported.
DECLARE may only be used inside a BEGIN ... END compound statement and must be at its start, before any other statements.
You may declare and use variables within a routine.
DECLARE var_name[,...] type [DEFAULT value]
This command is used to declare local variables. The scope of a variable is within the BEGIN ... END block.
SET variable = expression [,...]
The SET statement in stored procedures is an extended version of the general SET command. Referenced variables may be ones declared inside a routine, or global server variables.
The SET statement in stored procedures is implemented as part of the pre-existing SET syntax. This allows an extended syntax of SET a=x, b=y, ... where different variable types (locally declared variables, server variables, and global and session server variables) can be mixed. This also allows combinations of local variables and some options that only make sense for global/system variables; in that case the options are accepted but ignored.
Certain conditions may require specific handling. These conditions can relate to errors, as well as general flow control inside a routine.
DECLARE condition_name CONDITION FOR condition_value condition_value: SQLSTATE [VALUE] sqlstate_value | mysql_error_code
This statement specifies conditions that will need specific handling. It associates a name with a specified error condition. The name can subsequently be used in a DECLARE HANDLER statement. See DECLARE Handlers.
In addition to SQLSTATE values, MySQL error codes are also supported.
DECLARE handler_type HANDLER FOR condition_value[,...] sp_statement handler_type: CONTINUE | EXIT | UNDO condition_value: SQLSTATE [VALUE] sqlstate_value | condition_name | SQLWARNING | NOT FOUND | SQLEXCEPTION | mysql_error_code
This statement specifies handlers that each may deal with one or more conditions. If one of these conditions occurs, the specified statement is executed.
For a CONTINUE handler, execution of the current routine continues after execution of the handler statement. For an EXIT handler, execution of the current BEGIN...END compound statement is terminated. The UNDO handler_type is not yet supported. UNDO currently behaves like CONTINUE.
SQLWARNING is shorthand for all SQLSTATE codes that begin with 01.
NOT FOUND is shorthand for all SQLSTATE codes that begin with 02.
EXCEPTION is shorthand for all SQLSTATE codes not caught by SQLWARNING or NOT FOUND.
In addition to SQLSTATE values, MySQL error codes are also supported.
For example:
mysql> CREATE TABLE test.t (s1 int,primary key (s1)); Query OK, 0 rows affected (0.00 sec) mysql> delimiter | mysql> CREATE PROCEDURE handlerdemo () -> BEGIN -> DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' SET @x2 = 1; -> set @x = 1; -> INSERT INTO test.t VALUES (1); -> set @x = 2; -> INSERT INTO test.t VALUES (1); -> SET @x = 3; -> END; -> | Query OK, 0 rows affected (0.00 sec) mysql> CALL handlerdemo()| Query OK, 0 rows affected (0.00 sec) mysql> SELECT @x| +------+ | @x | +------+ | 3 | +------+ 1 row in set (0.00 sec)
Notice that @x is 3, which shows that MySQL executed to the end of the procedure. If the line DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' SET @x2 = 1; had not been present, MySQL would have taken the default (EXIT) path after the second INSERT failed due to the PRIMARY KEY constraint, and SELECT @x would have returned 2.
Simple cursors are supported inside stored procedures and functions. The syntax is as in embedded SQL. Cursors are currently asensitive, read-only, and non-scrolling. Asensitive means that the server may or may not make a copy of its result table.
For example:
CREATE PROCEDURE curdemo() BEGIN DECLARE done INT DEFAULT 0; DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1; DECLARE cur1 CURSOR FOR SELECT id,data FROM test.t1; DECLARE cur2 CURSOR FOR SELECT i FROM test.t2; DECLARE a CHAR(16); DECLARE b,c INT; OPEN cur1; OPEN cur2; REPEAT FETCH cur1 INTO a, b; FETCH cur2 INTO c; IF NOT done THEN IF b < c THEN INSERT INTO test.t3 VALUES (a,b); ELSE INSERT INTO test.t3 VALUES (a,c); END IF; END IF; UNTIL done END REPEAT; CLOSE cur1; CLOSE cur2; END
DECLARE cursor_name CURSOR FOR sql_statement
Multiple cursors may be defined in a routine, but each must have a unique name.
The IF, CASE, LOOP, WHILE, ITERATE, and LEAVE constructs are fully implemented.
These constructs may each contain either a single statement, or a block of statements using the BEGIN ... END compound statement. Constructs may be nested.
FOR loops are not currently supported.
IF search_condition THEN statement(s) [ELSEIF search_condition THEN statement(s)] ... [ELSE statement(s)] END IF
IF implements a basic conditional construct. If the search_condition evaluates to true, the corresponding SQL statement is executed. If no search_condition matches, the statement in the ELSE clause is executed.
Please note that there is also an IF() function. See Control flow functions.
CASE case_value WHEN when_value THEN statement [WHEN when_value THEN statement ...] [ELSE statement] END CASE
or
CASE WHEN search_condition THEN statement [WHEN search_condition THEN statement ...] [ELSE statement] END CASE
CASE implements a complex conditional construct. If a search_condition evaluates to true, the corresponding SQL statement is executed. If no search condition matches, the statement in the ELSE clause is executed.
Please note that the syntax of a CASE statement inside a stored procedure differs slightly from that of the SQL CASE expression. The CASE statement can not have an ELSE NULL clause, and the construct is terminated with END CASE instead of END. See Control flow functions.
[begin_label:] LOOP statement(s) END LOOP [end_label]
LOOP implements a simple loop construct, enabling repeated execution of a particular statement or group of statements. The statements within the loop are repeated until the loop is exited, usually this is accomplished with a LEAVE statement.
begin_label and end_label must be the same, if both are specified.
ITERATE label
ITERATE can only appear within LOOP, REPEAT, and WHILE statements. ITERATE means ``do the loop iteration again.''
For example:
CREATE PROCEDURE doiterate(p1 INT) BEGIN label1: LOOP SET p1 = p1 + 1; IF p1 < 10 THEN ITERATE label1; END IF; LEAVE label1; END LOOP label1; SET @x = p1; END
[begin_label:] REPEAT statement(s) UNTIL search_condition END REPEAT [end_label]
The statements within a REPEAT statement are repeated until the search_condition is true.
begin_label and end_label must be the same, if both are specified.
For example:
mysql> delimiter | mysql> CREATE PROCEDURE dorepeat(p1 INT) -> BEGIN -> SET @x = 0; -> REPEAT SET @x = @x + 1; UNTIL @x > p1 END REPEAT; -> END -> | Query OK, 0 rows affected (0.00 sec) mysql> CALL dorepeat(1000)| Query OK, 0 rows affected (0.00 sec) mysql> SELECT @x| +------+ | @x | +------+ | 1001 | +------+ 1 row in set (0.00 sec)
[begin_label:] WHILE search_condition DO statement(s) END WHILE [end_label]
The statements within a WHILE statement are repeated as long as the search_condition is true.
begin_label and end_label must be the same, if both are specified.
For example:
CREATE PROCEDURE dowhile() BEGIN DECLARE v1 INT DEFAULT 5; WHILE v1 > 0 DO ... SET v1 = v1 - 1; END WHILE; END
Table of Contents
This chapter describes the APIs available for MySQL, where to get them, and how to use them. The C API is the most extensively covered, as it was developed by the MySQL team, and is the basis for most of the other APIs.
Table of Contents
The C API code is distributed with MySQL. It is included in the mysqlclient library and allows C programs to access a database.
Many of the clients in the MySQL source distribution are written in C. If you are looking for examples that demonstrate how to use the C API, take a look at these clients. You can find these in the clients directory in the MySQL source distribution.
Most of the other client APIs (all except Connector/J) use the mysqlclient library to communicate with the MySQL server. This means that, for example, you can take advantage of many of the same environment variables that are used by other client programs, because they are referenced from the library. See Client-Side Scripts, for a list of these variables.
The client has a maximum communication buffer size. The size of the buffer that is allocated initially (16K bytes) is automatically increased up to the maximum size (the maximum is 16M). Because buffer sizes are increased only as demand warrants, simply increasing the default maximum limit does not in itself cause more resources to be used. This size check is mostly a check for erroneous queries and communication packets.
The communication buffer must be large enough to contain a single SQL statement (for client-to-server traffic) and one row of returned data (for server-to-client traffic). Each thread's communication buffer is dynamically enlarged to handle any query or row up to the maximum limit. For example, if you have BLOB values that contain up to 16M of data, you must have a communication buffer limit of at least 16M (in both server and client). The client's default maximum is 16M, but the default maximum in the server is 1M. You can increase this by changing the value of the max_allowed_packet parameter when the server is started. See Server parameters.
The MySQL server shrinks each communication buffer to net_buffer_length bytes after each query. For clients, the size of the buffer associated with a connection is not decreased until the connection is closed, at which time client memory is reclaimed.
For programming with threads, see Threaded clients. For creating a stand-alone application which includes the "server" and "client" in the same program (and does not communicate with an external MySQL server), see libmysqld.
MYSQL | This structure represents a handle to one database connection. It is used for almost all MySQL functions. |
MYSQL_RES | This structure represents the result of a query that returns rows (SELECT, SHOW, DESCRIBE, EXPLAIN). The information returned from a query is called the result set in the remainder of this section. |
MYSQL_ROW | This is a type-safe representation of one row of data. It is currently implemented as an array of counted byte strings. (You cannot treat these as null-terminated strings if field values may contain binary data, because such values may contain null bytes internally.) Rows are obtained by calling mysql_fetch_row(). |
MYSQL_FIELD | This structure contains information about a field, such as the field's name, type, and size. Its members are described in more detail here. You may obtain the MYSQL_FIELD structures for each field by calling mysql_fetch_field() repeatedly. Field values are not part of this structure; they are contained in a MYSQL_ROW structure. |
MYSQL_FIELD_OFFSET | This is a type-safe representation of an offset into a MySQL field list. (Used by mysql_field_seek().) Offsets are field numbers within a row, beginning at zero. |
my_ulonglong |
The type used for the number of rows and for mysql_affected_rows(),
mysql_num_rows(), and mysql_insert_id(). This type provides a
range of 0 to 1.84e19.
On some systems, attempting to print a value of type my_ulonglong
will not work. To print such a value, convert it to unsigned long
and use a %lu print format. Example:
printf ("Number of rows: %lu\n", (unsigned long) mysql_num_rows(result)); |
The MYSQL_FIELD structure contains the members listed here:
char * name | The name of the field, as a null-terminated string. | |||||||||||||||||||||||||||||||||||||||||||
char * table | The name of the table containing this field, if it isn't a calculated field. For calculated fields, the table value is an empty string. | |||||||||||||||||||||||||||||||||||||||||||
char * def | The default value of this field, as a null-terminated string. This is set only if you use mysql_list_fields(). | |||||||||||||||||||||||||||||||||||||||||||
enum enum_field_types type | The type of the field. The type value may be one of the following: |
| ||||||||||||||||||||||||||||||||||||||||||
unsigned int length | The width of the field, as specified in the table definition. | |||||||||||||||||||||||||||||||||||||||||||
unsigned int max_length | The maximum width of the field for the result set (the length of the longest field value for the rows actually in the result set). If you use mysql_store_result() or mysql_list_fields(), this contains the maximum length for the field. If you use mysql_use_result(), the value of this variable is zero. | |||||||||||||||||||||||||||||||||||||||||||
unsigned int flags | Different bit-flags for the field. The flags value may have zero or more of the following bits set: |
|
| |||||||||||||||||||||||||||||||||||||||||
unsigned int decimals | The number of decimals for numeric fields. |
The functions available in the C API are summarized here and described in greater detail in a later section. See C API functions.
Function | Description |
mysql_affected_rows() | Returns the number of rows changed/deleted/inserted by the last UPDATE, DELETE, or INSERT query. |
mysql_change_user() | Changes user and database on an open connection. |
mysql_character_set_name() | Returns the name of the default character set for the connection. |
mysql_close() | Closes a server connection. |
mysql_connect() | Connects to a MySQL server. This function is deprecated; use mysql_real_connect() instead. |
mysql_create_db() | Creates a database. This function is deprecated; use the SQL command CREATE DATABASE instead. |
mysql_data_seek() | Seeks to an arbitrary row number in a query result set. |
mysql_debug() | Does a DBUG_PUSH with the given string. |
mysql_drop_db() | Drops a database. This function is deprecated; use the SQL command DROP DATABASE instead. |
mysql_dump_debug_info() | Makes the server write debug information to the log. |
mysql_eof() | Determines whether the last row of a result set has been read. This function is deprecated; mysql_errno() or mysql_error() may be used instead. |
mysql_errno() | Returns the error number for the most recently invoked MySQL function. |
mysql_error() | Returns the error message for the most recently invoked MySQL function. |
mysql_escape_string() | Escapes special characters in a string for use in an SQL statement. |
mysql_fetch_field() | Returns the type of the next table field. |
mysql_fetch_field_direct() | Returns the type of a table field, given a field number. |
mysql_fetch_fields() | Returns an array of all field structures. |
mysql_fetch_lengths() | Returns the lengths of all columns in the current row. |
mysql_fetch_row() | Fetches the next row from the result set. |
mysql_field_seek() | Puts the column cursor on a specified column. |
mysql_field_count() | Returns the number of result columns for the most recent query. |
mysql_field_tell() | Returns the position of the field cursor used for the last mysql_fetch_field(). |
mysql_free_result() | Frees memory used by a result set. |
mysql_get_client_info() | Returns client version information as a string. |
mysql_get_client_version() | Returns client version information as an integer. |
mysql_get_host_info() | Returns a string describing the connection. |
mysql_get_server_version() | Returns version number of server as an integer (new in 4.1). |
mysql_get_proto_info() | Returns the protocol version used by the connection. |
mysql_get_server_info() | Returns the server version number. |
mysql_info() | Returns information about the most recently executed query. |
mysql_init() | Gets or initializes a MYSQL structure. |
mysql_insert_id() | Returns the ID generated for an AUTO_INCREMENT column by the previous query. |
mysql_kill() | Kills a given thread. |
mysql_list_dbs() | Returns database names matching a simple regular expression. |
mysql_list_fields() | Returns field names matching a simple regular expression. |
mysql_list_processes() | Returns a list of the current server threads. |
mysql_list_tables() | Returns table names matching a simple regular expression. |
mysql_num_fields() | Returns the number of columns in a result set. |
mysql_num_rows() | Returns the number of rows in a result set. |
mysql_options() | Sets connect options for mysql_connect(). |
mysql_ping() | Checks whether the connection to the server is working, reconnecting as necessary. |
mysql_query() | Executes an SQL query specified as a null-terminated string. |
mysql_real_connect() | Connects to a MySQL server. |
mysql_real_escape_string() | Escapes special characters in a string for use in an SQL statement, taking into account the current charset of the connection. |
mysql_real_query() | Executes an SQL query specified as a counted string. |
mysql_reload() | Tells the server to reload the grant tables. |
mysql_row_seek() | Seeks to a row offset in a result set, using value returned from mysql_row_tell(). |
mysql_row_tell() | Returns the row cursor position. |
mysql_select_db() | Selects a database. |
mysql_set_server_option() | Sets an option for the connection (like multi-statements). |
mysql_sqlstate() | Returns the SQLSTATE error code for the last error. |
mysql_shutdown() | Shuts down the database server. |
mysql_stat() | Returns the server status as a string. |
mysql_store_result() | Retrieves a complete result set to the client. |
mysql_thread_id() | Returns the current thread ID. |
mysql_thread_safe() | Returns 1 if the clients are compiled as thread-safe. |
mysql_use_result() | Initiates a row-by-row result set retrieval. |
mysql_warning_count() | Returns the warning count for the previous SQL statement. |
mysql_commit() | Commits the transaction (new in 4.1). |
mysql_rollback() | Rolls back the transaction (new in 4.1). |
mysql_autocommit() | Toggles autocommit mode on/off (new in 4.1). |
mysql_more_results() | Checks whether any more results exist (new in 4.1). |
mysql_next_result() | Returns/Initiates the next result in multi-query executions (new in 4.1). |
To connect to the server, call mysql_init() to initialize a connection handler, then call mysql_real_connect() with that handler (along with other information such as the hostname, username, and password). Upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1. This flag indicates, in the event that a query cannot be performed because of a lost connection, to try reconnecting to the server before giving up. When you are done with the connection, call mysql_close() to terminate it.
While a connection is active, the client may send SQL queries to the server using mysql_query() or mysql_real_query(). The difference between the two is that mysql_query() expects the query to be specified as a null-terminated string whereas mysql_real_query() expects a counted string. If the string contains binary data (which may include null bytes), you must use mysql_real_query().
For each non-SELECT query (for example, INSERT, UPDATE, DELETE), you can find out how many rows were changed (affected) by calling mysql_affected_rows().
For SELECT queries, you retrieve the selected rows as a result set. (Note that some statements are SELECT-like in that they return rows. These include SHOW, DESCRIBE, and EXPLAIN. They should be treated the same way as SELECT statements.)
There are two ways for a client to process result sets. One way is to retrieve the entire result set all at once by calling mysql_store_result(). This function acquires from the server all the rows returned by the query and stores them in the client. The second way is for the client to initiate a row-by-row result set retrieval by calling mysql_use_result(). This function initializes the retrieval, but does not actually get any rows from the server.
In both cases, you access rows by calling mysql_fetch_row(). With mysql_store_result(), mysql_fetch_row() accesses rows that have already been fetched from the server. With mysql_use_result(), mysql_fetch_row() actually retrieves the row from the server. Information about the size of the data in each row is available by calling mysql_fetch_lengths().
After you are done with a result set, call mysql_free_result() to free the memory used for it.
The two retrieval mechanisms are complementary. Client programs should choose the approach that is most appropriate for their requirements. In practice, clients tend to use mysql_store_result() more commonly.
An advantage of mysql_store_result() is that because the rows have all been fetched to the client, you not only can access rows sequentially, you can move back and forth in the result set using mysql_data_seek() or mysql_row_seek() to change the current row position within the result set. You can also find out how many rows there are by calling mysql_num_rows(). On the other hand, the memory requirements for mysql_store_result() may be very high for large result sets and you are more likely to encounter out-of-memory conditions.
An advantage of mysql_use_result() is that the client requires less memory for the result set because it maintains only one row at a time (and because there is less allocation overhead, mysql_use_result() can be faster). Disadvantages are that you must process each row quickly to avoid tying up the server, you don't have random access to rows within the result set (you can only access rows sequentially), and you don't know how many rows are in the result set until you have retrieved them all. Furthermore, you must retrieve all the rows even if you determine in mid-retrieval that you've found the information you were looking for.
The API makes it possible for clients to respond appropriately to queries (retrieving rows only as necessary) without knowing whether or not the query is a SELECT. You can do this by calling mysql_store_result() after each mysql_query() (or mysql_real_query()). If the result set call succeeds, the query was a SELECT and you can read the rows. If the result set call fails, call mysql_field_count() to determine whether a result was actually to be expected. If mysql_field_count() returns zero, the query returned no data (indicating that it was an INSERT, UPDATE, DELETE, etc.), and was not expected to return rows. If mysql_field_count() is non-zero, the query should have returned rows, but didn't. This indicates that the query was a SELECT that failed. See the description for mysql_field_count() for an example of how this can be done.
Both mysql_store_result() and mysql_use_result() allow you to obtain information about the fields that make up the result set (the number of fields, their names and types, etc.). You can access field information sequentially within the row by calling mysql_fetch_field() repeatedly, or by field number within the row by calling mysql_fetch_field_direct(). The current field cursor position may be changed by calling mysql_field_seek(). Setting the field cursor affects subsequent calls to mysql_fetch_field(). You can also get information for fields all at once by calling mysql_fetch_fields().
For detecting and reporting errors, MySQL provides access to error information by means of the mysql_errno() and mysql_error() functions. These return the error code or error message for the most recently invoked function that can succeed or fail, allowing you to determine when an error occurred and what it was.
In the descriptions here, a parameter or return value of NULL means NULL in the sense of the C programming language, not a MySQL NULL value.
Functions that return a value generally return a pointer or an integer. Unless specified otherwise, functions returning a pointer return a non-NULL value to indicate success or a NULL value to indicate an error, and functions returning an integer return zero to indicate success or non-zero to indicate an error. Note that ``non-zero'' means just that. Unless the function description says otherwise, do not test against a value other than zero:
if (result) /* correct */ ... error ... if (result < 0) /* incorrect */ ... error ... if (result == -1) /* incorrect */ ... error ...
When a function returns an error, the Errors subsection of the function description lists the possible types of errors. You can find out which of these occurred by calling mysql_errno(). A string representation of the error may be obtained by calling mysql_error().
Returns the number of rows changed by the last UPDATE, deleted by the last DELETE or inserted by the last INSERT statement. May be called immediately after mysql_query() for UPDATE, DELETE, or INSERT statements. For SELECT statements, mysql_affected_rows() works like mysql_num_rows().
An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records where updated for an UPDATE statement, no rows matched the WHERE clause in the query or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_affected_rows() was called prior to calling mysql_store_result(). Because mysql_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).
mysql_query(&mysql,"UPDATE products SET cost=cost*1.25 WHERE group=10"); printf("%ld products updated",(long) mysql_affected_rows(&mysql));
If one specifies the flag CLIENT_FOUND_ROWS when connecting to mysqld, mysql_affected_rows() will return the number of rows matched by the WHERE statement for UPDATE statements.
Note that when one uses a REPLACE command, mysql_affected_rows() will return 2 if the new row replaced and old row. This is because in this case one row was inserted after the duplicate was deleted.
Changes the user and causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that do not include an explicit database specifier.
This function was introduced in MySQL Version 3.23.3.
mysql_change_user() fails unless the connected user can be authenticated or if he doesn't have permission to use the database. In this case the user and database are not changed
The db parameter may be set to NULL if you don't want to have a default database.
Starting from MySQL 4.0.6 this command will always ROLLBACK any active transactions, close all temporary tables, unlock all locked tables and reset the state as if one had done a new connect. This will happen even if the user didn't change.
The same that you can get from mysql_real_connect().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
ER_UNKNOWN_COM_ERROR | The MySQL server doesn't implement this command (probably an old server). |
ER_ACCESS_DENIED_ERROR | The user or password was wrong. |
ER_BAD_DB_ERROR | The database didn't exist. |
ER_DBACCESS_DENIED_ERROR | The user did not have access rights to the database. |
ER_WRONG_DB_NAME | The database name was too long. |
if (mysql_change_user(&mysql, "user", "password", "new_database")) { fprintf(stderr, "Failed to change user. Error: %s\n", mysql_error(&mysql)); }
Closes a previously opened connection. mysql_close() also deallocates the connection handle pointed to by mysql if the handle was allocated automatically by mysql_init() or mysql_connect().
This function is deprecated. It is preferable to use mysql_real_connect() instead.
mysql_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_connect() must complete successfully before you can execute any of the other API functions, with the exception of mysql_get_client_info().
The meanings of the parameters are the same as for the corresponding parameters for mysql_real_connect() with the difference that the connection parameter may be NULL. In this case the C API allocates memory for the connection structure automatically and frees it when you call mysql_close(). The disadvantage of this approach is that you can't retrieve an error message if the connection fails. (To get error information from mysql_errno() or mysql_error(), you must provide a valid MYSQL pointer.)
Creates the database named by the db parameter.
This function is deprecated. It is preferable to use mysql_query() to issue an SQL CREATE DATABASE statement instead.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
if(mysql_create_db(&mysql, "my_database")) { fprintf(stderr, "Failed to create new database. Error: %s\n", mysql_error(&mysql)); }
Seeks to an arbitrary row in a query result set. The offset value is a row number and should be in the range from 0 to mysql_num_rows(stmt)-1.
This function requires that the result set structure contains the entire result of the query, so mysql_data_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().
Does a DBUG_PUSH with the given string. mysql_debug() uses the Fred Fish debug library. To use this function, you must compile the client library to support debugging. See Debugging server. See Debugging client.
The call shown here causes the client library to generate a trace file in /tmp/client.trace on the client machine:
mysql_debug("d:t:O,/tmp/client.trace");
Drops the database named by the db parameter.
This function is deprecated. It is preferable to use mysql_query() to issue an SQL DROP DATABASE statement instead.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
if(mysql_drop_db(&mysql, "my_database")) fprintf(stderr, "Failed to drop the database: Error: %s\n", mysql_error(&mysql));
Instructs the server to write some debug information to the log. For this to work, the connected user must have the SUPER privilege.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
This function is deprecated. mysql_errno() or mysql_error() may be used instead.
mysql_eof() determines whether the last row of a result set has been read.
If you acquire a result set from a successful call to mysql_store_result(), the client receives the entire set in one operation. In this case, a NULL return from mysql_fetch_row() always means the end of the result set has been reached and it is unnecessary to call mysql_eof(). When used with mysql_store_result(), mysql_eof() will always return true.
On the other hand, if you use mysql_use_result() to initiate a result set retrieval, the rows of the set are obtained from the server one by one as you call mysql_fetch_row() repeatedly. Because an error may occur on the connection during this process, a NULL return value from mysql_fetch_row() does not necessarily mean the end of the result set was reached normally. In this case, you can use mysql_eof() to determine what happened. mysql_eof() returns a non-zero value if the end of the result set was reached and zero if an error occurred.
Historically, mysql_eof() predates the standard MySQL error functions mysql_errno() and mysql_error(). Because those error functions provide the same information, their use is preferred over mysql_eof(), which is now deprecated. (In fact, they provide more information, because mysql_eof() returns only a boolean value whereas the error functions indicate a reason for the error when one occurs.)
The following example shows how you might use mysql_eof():
mysql_query(&mysql,"SELECT * FROM some_table"); result = mysql_use_result(&mysql); while((row = mysql_fetch_row(result))) { // do something with data } if(!mysql_eof(result)) // mysql_fetch_row() failed due to an error { fprintf(stderr, "Error: %s\n", mysql_error(&mysql)); }
However, you can achieve the same effect with the standard MySQL error functions:
mysql_query(&mysql,"SELECT * FROM some_table"); result = mysql_use_result(&mysql); while((row = mysql_fetch_row(result))) { // do something with data } if(mysql_errno(&mysql)) // mysql_fetch_row() failed due to an error { fprintf(stderr, "Error: %s\n", mysql_error(&mysql)); }
For the connection specified by mysql, mysql_errno() returns the error code for the most recently invoked API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL errmsg.h header file. Server error message numbers are listed in mysqld_error.h. In the MySQL source distribution you can find a complete list of error messages and error numbers in the file Docs/mysqld_error.txt. The server error codes also are listed at Error-returns.
Note that some functions like mysql_fetch_row() don't set mysql_errno() if they succeed.
A rule of thumb is that all functions that have to ask the server for information will reset mysql_errno() if they succeed.
An error code value for the last mysql_xxx call, if it failed. zero means no error occurred.
For the connection specified by mysql, mysql_error() returns a null-terminated string containing the error message for the most recently invoked API function that failed. If a function didn't fail, the return value of mysql_error() may be the previous error or an empty string to indicate no error.
A rule of thumb is that all functions that have to ask the server for information will reset mysql_error() if they succeed.
For functions that resets mysql_errno, the following two tests are equivalent:
if(mysql_errno(&mysql)) { // an error occurred } if(mysql_error(&mysql)[0] != '\0') { // an error occurred }
The language of the client error messages may be changed by recompiling the MySQL client library. Currently you can choose error messages in several different languages. See Languages.
A null-terminated character string that describes the error. An empty string if no error occurred.
Returns the definition of one column of a result set as a MYSQL_FIELD structure. Call this function repeatedly to retrieve information about all columns in the result set. mysql_fetch_field() returns NULL when no more fields are left.
mysql_fetch_field() is reset to return information about the first field each time you execute a new SELECT query. The field returned by mysql_fetch_field() is also affected by calls to mysql_field_seek().
If you've called mysql_query() to perform a SELECT on a table but have not called mysql_store_result(), MySQL returns the default blob length (8K bytes) if you call mysql_fetch_field() to ask for the length of a BLOB field. (The 8K size is chosen because MySQL doesn't know the maximum length for the BLOB. This should be made configurable sometime.) Once you've retrieved the result set, field->max_length contains the length of the largest value for this column in the specific query.
MYSQL_FIELD *field; while((field = mysql_fetch_field(result))) { printf("field name %s\n", field->name); }
Returns an array of all MYSQL_FIELD structures for a result set. Each structure provides the field definition for one column of the result set.
unsigned int num_fields; unsigned int i; MYSQL_FIELD *fields; num_fields = mysql_num_fields(result); fields = mysql_fetch_fields(result); for(i = 0; i < num_fields; i++) { printf("Field %u is %s\n", i, fields[i].name); }
Given a field number fieldnr for a column within a result set, returns that column's field definition as a MYSQL_FIELD structure. You may use this function to retrieve the definition for an arbitrary column. The value of fieldnr should be in the range from 0 to mysql_num_fields(result)-1.
unsigned int num_fields; unsigned int i; MYSQL_FIELD *field; num_fields = mysql_num_fields(result); for(i = 0; i < num_fields; i++) { field = mysql_fetch_field_direct(result, i); printf("Field %u is %s\n", i, field->name); }
Returns the lengths of the columns of the current row within a result set. If you plan to copy field values, this length information is also useful for optimization, because you can avoid calling strlen(). In addition, if the result set contains binary data, you must use this function to determine the size of the data, because strlen() returns incorrect results for any field containing null characters.
The length for empty columns and for columns containing NULL values is zero. To see how to distinguish these two cases, see the description for mysql_fetch_row().
An array of unsigned long integers representing the size of each column (not including any terminating null characters). NULL if an error occurred.
mysql_fetch_lengths() is valid only for the current row of the result set. It returns NULL if you call it before calling mysql_fetch_row() or after retrieving all rows in the result.
MYSQL_ROW row; unsigned long *lengths; unsigned int num_fields; unsigned int i; row = mysql_fetch_row(result); if (row) { num_fields = mysql_num_fields(result); lengths = mysql_fetch_lengths(result); for(i = 0; i < num_fields; i++) { printf("Column %u is %lu bytes in length.\n", i, lengths[i]); } }
Retrieves the next row of a result set. When used after mysql_store_result(), mysql_fetch_row() returns NULL when there are no more rows to retrieve. When used after mysql_use_result(), mysql_fetch_row() returns NULL when there are no more rows to retrieve or if an error occurred.
The number of values in the row is given by mysql_num_fields(result). If row holds the return value from a call to mysql_fetch_row(), pointers to the values are accessed as row[0] to row[mysql_num_fields(result)-1]. NULL values in the row are indicated by NULL pointers.
The lengths of the field values in the row may be obtained by calling mysql_fetch_lengths(). Empty fields and fields containing NULL both have length 0; you can distinguish these by checking the pointer for the field value. If the pointer is NULL, the field is NULL; otherwise, the field is empty.
A MYSQL_ROW structure for the next row. NULL if there are no more rows to retrieve or if an error occurred.
Note that error is not reset between calls to mysql_fetch_row()
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
MYSQL_ROW row; unsigned int num_fields; unsigned int i; num_fields = mysql_num_fields(result); while ((row = mysql_fetch_row(result))) { unsigned long *lengths; lengths = mysql_fetch_lengths(result); for(i = 0; i < num_fields; i++) { printf("[%.*s] ", (int) lengths[i], row[i] ? row[i] : "NULL"); } printf("\n"); }
Returns the number of columns for the most recent query on the connection.
The normal use of this function is when mysql_store_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.
MYSQL_RES *result; unsigned int num_fields; unsigned int num_rows; if (mysql_query(&mysql,query_string)) { // error } else // query succeeded, process any data returned by it { result = mysql_store_result(&mysql); if (result) // there are rows { num_fields = mysql_num_fields(result); // retrieve rows, then call mysql_free_result(result) } else // mysql_store_result() returned nothing; should it have? { if(mysql_field_count(&mysql) == 0) { // query does not return data // (it was not a SELECT) num_rows = mysql_affected_rows(&mysql); } else // mysql_store_result() should have returned data { fprintf(stderr, "Error: %s\n", mysql_error(&mysql)); } } }
An alternative is to replace the mysql_field_count(&mysql) call with mysql_errno(&mysql). In this case, you are checking directly for an error from mysql_store_result() rather than inferring from the value of mysql_field_count() whether the statement was a SELECT.
Sets the field cursor to the given offset. The next call to mysql_fetch_field() will retrieve the field definition of the column associated with that offset.
To seek to the beginning of a row, pass an offset value of zero.
Returns the position of the field cursor used for the last mysql_fetch_field(). This value can be used as an argument to mysql_field_seek().
Frees the memory allocated for a result set by mysql_store_result(), mysql_use_result(), mysql_list_dbs(), etc. When you are done with a result set, you must free the memory it uses by calling mysql_free_result().
Do not attempt to access a result set after freeing it.
Returns an integer that represents the client library version. The value has the format XYYZZ where X is the major version, YY is the release level, and ZZ is the version number within the release level. For example, a value of 40102 represents a client library version of 4.1.2.
Returns a string describing the type of connection in use, including the server hostname.
A number that represents the MySQL server version in format:
main_version*10000 + minor_version *100 + sub_version
For example, 4.1.0 is returned as 40100.
This is useful to quickly determine the version of the server in a client program to know if some capability exits.
Retrieves a string providing information about the most recently executed query, but only for the statements listed here. For other statements, mysql_info() returns NULL. The format of the string varies depending on the type of query, as described here. The numbers are illustrative only; the string will contain values appropriate for the query.
INSERT INTO ... SELECT ... | String format: Records: 100 Duplicates: 0 Warnings: 0 |
INSERT INTO ... VALUES (...),(...),(...)... | String format: Records: 3 Duplicates: 0 Warnings: 0 |
LOAD DATA INFILE ... | String format: Records: 1 Deleted: 0 Skipped: 0 Warnings: 0 |
ALTER TABLE | String format: Records: 3 Duplicates: 0 Warnings: 0 |
UPDATE | String format: Rows matched: 40 Changed: 40 Warnings: 0 |
Note that mysql_info() returns a non-NULL value for INSERT ... VALUES only for the multiple-row form of the statement (that is, only if multiple value lists are specified).
A character string representing additional information about the most recently executed query. NULL if no information is available for the query.
Allocates or initializes a MYSQL object suitable for mysql_real_connect(). If mysql is a NULL pointer, the function allocates, initializes, and returns a new object. Otherwise, the object is initialized and the address of the object is returned. If mysql_init() allocates a new object, it will be freed when mysql_close() is called to close the connection.
An initialized MYSQL* handle. NULL if there was insufficient memory to allocate a new object.
Returns the value generated for an AUTO_INCREMENT column by the previous INSERT or UPDATE statement. Use this function after you have performed an INSERT statement into a table that contains an AUTO_INCREMENT field.
More precisely, mysql_insert_id() is updated under these conditions:
INSERT statements that store a value into an AUTO_INCREMENT column. This is true whether the value is automatically generated by storing the special values NULL or 0 into the column, or is an explicit non-special value.
In the case of a multi-row INSERT statement, mysql_insert_id() returns the first automatically generated AUTO_INCREMENT value; if no such value is generated, it returns the last last explicit value inserted into the AUTO_INCREMENT column.
INSERT statements that generate an AUTO_INCREMENT value by inserting LAST_INSERT_ID(expr) into any column.
INSERT statements that generate an AUTO_INCREMENT value by updating any column to LAST_INSERT_ID(expr).
The value of mysql_insert_id() is not affected by statements such as SELECT that return a result set.
If the previous statement returned an error, the value of mysql_insert_id() is undefined.
Note that mysql_insert_id() returns 0 if the previous statement does not use an AUTO_INCREMENT value. If you need to save the value for later, be sure to call mysql_insert_id() immediately after the statement that generates the value.
The value of mysql_insert_id() is affected only by statements issued within the current client connection. It is not affected by statements issued by other clients.
Also note that the value of the SQL LAST_INSERT_ID() function always contains the most recently generated AUTO_INCREMENT value, and is not reset between statements because the value of that function is maintained in the server. Another difference is that LAST_INSERT_ID() is not updated if you set an AUTO_INCREMENT column to a specific non-special value.
The reason for the difference between LAST_INSERT_ID() and mysql_insert_id() is that LAST_INSERT_ID() is made easy to use in scripts while mysql_insert_id() tries to provide a little more exact information of what happens to the AUTO_INCREMENT column.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Returns a result set consisting of database names on the server that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters % or _, or may be a NULL pointer to match all databases. Calling mysql_list_dbs() is similar to executing the query SHOW databases [LIKE wild].
You must free the result set with mysql_free_result().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Returns a result set consisting of field names in the given table that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters % or _, or may be a NULL pointer to match all fields. Calling mysql_list_fields() is similar to executing the query SHOW COLUMNS FROM tbl_name [LIKE wild].
Note that it's recommended that you use SHOW COLUMNS FROM tbl_name instead of mysql_list_fields().
You must free the result set with mysql_free_result().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Returns a result set describing the current server threads. This is the same kind of information as that reported by mysqladmin processlist or a SHOW PROCESSLIST query.
You must free the result set with mysql_free_result().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Returns a result set consisting of table names in the current database that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters % or _, or may be a NULL pointer to match all tables. Calling mysql_list_tables() is similar to executing the query SHOW tables [LIKE wild].
You must free the result set with mysql_free_result().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Returns the number of columns in a result set.
Note that you can get the number of columns either from a pointer to a result set or to a connection handle. You would use the connection handle if mysql_store_result() or mysql_use_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether or not the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.
MYSQL_RES *result; unsigned int num_fields; unsigned int num_rows; if (mysql_query(&mysql,query_string)) { // error } else // query succeeded, process any data returned by it { result = mysql_store_result(&mysql); if (result) // there are rows { num_fields = mysql_num_fields(result); // retrieve rows, then call mysql_free_result(result) } else // mysql_store_result() returned nothing; should it have? { if (mysql_errno(&mysql)) { fprintf(stderr, "Error: %s\n", mysql_error(&mysql)); } else if (mysql_field_count(&mysql) == 0) { // query does not return data // (it was not a SELECT) num_rows = mysql_affected_rows(&mysql); } } }
An alternative (if you know that your query should have returned a result set) is to replace the mysql_errno(&mysql) call with a check if mysql_field_count(&mysql) is = 0. This will happen only if something went wrong.
Returns the number of rows in the result set.
The use of mysql_num_rows() depends on whether you use mysql_store_result() or mysql_use_result() to return the result set. If you use mysql_store_result(), mysql_num_rows() may be called immediately. If you use mysql_use_result(), mysql_num_rows() will not return the correct value until all the rows in the result set have been retrieved.
Can be used to set extra connect options and affect behavior for a connection. This function may be called multiple times to set several options.
mysql_options() should be called after mysql_init() and before mysql_connect() or mysql_real_connect().
The option argument is the option that you want to set; the arg argument is the value for the option. If the option is an integer, then arg should point to the value of the integer.
Possible options values:
Option | Argument type | Function |
MYSQL_OPT_CONNECT_TIMEOUT | unsigned int * | Connect timeout in seconds. |
MYSQL_OPT_READ_TIMEOUT | unsigned int * | Timeout for reads from server (works currently only on Windows on TCP/IP connections) |
MYSQL_OPT_WRITE_TIMEOUT | unsigned int * | Timeout for writes to server (works currently only on Windows on TCP/IP connections) |
MYSQL_OPT_COMPRESS | Not used | Use the compressed client/server protocol. |
MYSQL_OPT_LOCAL_INFILE | optional pointer to uint | If no pointer is given or if pointer points to an unsigned int != 0 the command LOAD LOCAL INFILE is enabled. |
MYSQL_OPT_NAMED_PIPE | Not used | Use named pipes to connect to a MySQL server on NT. |
MYSQL_INIT_COMMAND | char * | Command to execute when connecting to the MySQL server. Will automatically be re-executed when reconnecting. |
MYSQL_READ_DEFAULT_FILE | char * | Read options from the named option file instead of from my.cnf. |
MYSQL_READ_DEFAULT_GROUP | char * | Read options from the named group from my.cnf or the file specified with MYSQL_READ_DEFAULT_FILE. |
MYSQL_OPT_PROTOCOL | unsigned int * | Type of protocol to use. Should be one of the enum values of mysql_protocol_type defined in mysql.h. |
MYSQL_SHARED_MEMORY_BASE_NAME | char* | Named of of chared memory object for communication to server. Should be same as the option -shared-memory-base-name used for the mysqld server you want's to connect to. |
Note that the group client is always read if you use MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP.
The specified group in the option file may contain the following options:
Option | Description |
connect-timeout | Connect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server. |
compress | Use the compressed client/server protocol. |
database | Connect to this database if no database was specified in the connect command. |
debug | Debug options. |
disable-local-infile | Disable use of LOAD DATA LOCAL. |
host | Default hostname. |
init-command | Command to execute when connecting to MySQL server. Will automatically be re-executed when reconnecting. |
interactive-timeout | Same as specifying CLIENT_INTERACTIVE to mysql_real_connect(). See mysql_real_connect. |
local-infile[=(0|1)] | If no argument or argument != 0 then enable use of LOAD DATA LOCAL. |
max_allowed_packet | Max size of packet client can read from server. |
password | Default password. |
pipe | Use named pipes to connect to a MySQL server on NT. |
protocol=(TCP | SOCKET | PIPE | MEMORY) | Which protocol to use when connecting to server (New in 4.1) |
port | Default port number. |
return-found-rows | Tell mysql_info() to return found rows instead of updated rows when using UPDATE. |
shared-memory-base-name=name | Shared memory name to use to connect to server (default is "MySQL"). New in MySQL 4.1. |
socket | Default socket number. |
user | Default user. |
Note that timeout has been replaced by connect-timeout, but timeout will still work for a while.
For more information about option files, see Option files.
MYSQL mysql; mysql_init(&mysql); mysql_options(&mysql,MYSQL_OPT_COMPRESS,0); mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"odbc"); if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0)) { fprintf(stderr, "Failed to connect to database: Error: %s\n", mysql_error(&mysql)); }
The above requests the client to use the compressed client/server protocol and read the additional options from the odbc section in the my.cnf file.
Checks whether the connection to the server is working. If it has gone down, an automatic reconnection is attempted.
This function can be used by clients that remain idle for a long while, to check whether the server has closed the connection and reconnect if necessary.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Executes the SQL query pointed to by the null-terminated string query. The query must consist of a single SQL statement. You should not add a terminating semicolon (;) or \g to the statement.
mysql_query() cannot be used for queries that contain binary data; you should use mysql_real_query() instead. (Binary data may contain the \0 character, which mysql_query() interprets as the end of the query string.)
If you want to know if the query should return a result set or not, you can use mysql_field_count() to check for this. See mysql_field_count().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
mysql_real_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_real_connect() must complete successfully before you can execute any of the other API functions, with the exception of mysql_get_client_info().
The parameters are specified as follows:
The first parameter should be the address of an existing MYSQL structure. Before calling mysql_real_connect() you must call mysql_init() to initialize the MYSQL structure. You can change a lot of connect options with the mysql_options() call. See mysql_options().
The value of host may be either a hostname or an IP address. If host is NULL or the string "localhost", a connection to the local host is assumed. If the OS supports sockets (Unix) or named pipes (Windows), they are used instead of TCP/IP to connect to the server.
The user parameter contains the user's MySQL login ID. If user is NULL or the empty string "", the current user is assumed. Under Unix, this is the current login name. Under Windows ODBC, the current username must be specified explicitly. See ODBC administrator.
The passwd parameter contains the password for user. If passwd is NULL, only entries in the user table for the user that have a blank (empty) password field will be checked for a match. This allows the database administrator to set up the MySQL privilege system in such a way that users get different privileges depending on whether or not they have specified a password.
Note: Do not attempt to encrypt the password before calling mysql_real_connect(); password encryption is handled automatically by the client API.
db is the database name. If db is not NULL, the connection will set the default database to this value.
If port is not 0, the value will be used as the port number for the TCP/IP connection. Note that the host parameter determines the type of the connection.
If unix_socket is not NULL, the string specifies the socket or named pipe that should be used. Note that the host parameter determines the type of the connection.
The value of client_flag is usually 0, but can be set to a combination of the following flags in very special circumstances:
Flag name | Flag description |
CLIENT_COMPRESS | Use compression protocol. |
CLIENT_FOUND_ROWS | Return the number of found (matched) rows, not the number of affected rows. |
CLIENT_IGNORE_SPACE | Allow spaces after function names. Makes all functions names reserved words. |
CLIENT_INTERACTIVE | Allow interactive_timeout seconds (instead of wait_timeout seconds) of inactivity before closing the connection. The client's session wait_timeout variable will be set to the value of the session interactive_timeout variable. |
CLIENT_LOCAL_FILES | Enable LOAD DATA LOCAL handling. |
CLIENT_MULTI_STATEMENTS | Tell the server that the client may send multi-row-queries (separated with ;). If this flag is not set, multi-row-queries are disabled. New in 4.1. |
CLIENT_MULTI_RESULTS | Tell the server that the client can handle multiple-result sets from multi-queries or stored procedures. This is automatically set if CLIENT_MULTI_STATEMENTS is set. New in 4.1. |
CLIENT_NO_SCHEMA | Don't allow the db_name.tbl_name.col_name syntax. This is for ODBC. It causes the parser to generate an error if you use that syntax, which is useful for trapping bugs in some ODBC programs. |
CLIENT_ODBC | The client is an ODBC client. This changes mysqld to be more ODBC-friendly. |
CLIENT_SSL | Use SSL (encrypted protocol). This option should not be set by application programs; it is set internally in the client library. |
A MYSQL* connection handle if the connection was successful, NULL if the connection was unsuccessful. For a successful connection, the return value is the same as the value of the first parameter.
CR_CONN_HOST_ERROR | Failed to connect to the MySQL server. |
CR_CONNECTION_ERROR | Failed to connect to the local MySQL server. |
CR_IPSOCK_ERROR | Failed to create an IP socket. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_SOCKET_CREATE_ERROR | Failed to create a Unix socket. |
CR_UNKNOWN_HOST | Failed to find the IP address for the hostname. |
CR_VERSION_ERROR | A protocol mismatch resulted from attempting to connect to a server with a client library that uses a different protocol version. This can happen if you use a very old client library to connect to a new server that wasn't started with the --old-protocol option. |
CR_NAMEDPIPEOPEN_ERROR | Failed to create a named pipe on Windows. |
CR_NAMEDPIPEWAIT_ERROR | Failed to wait for a named pipe on Windows. |
CR_NAMEDPIPESETSTATE_ERROR | Failed to get a pipe handler on Windows. |
CR_SERVER_LOST | If connect_timeout > 0 and it took longer than connect_timeout seconds to connect to the server or if the server died while executing the init-command. |
MYSQL mysql; mysql_init(&mysql); mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"your_prog_name"); if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0)) { fprintf(stderr, "Failed to connect to database: Error: %s\n", mysql_error(&mysql)); }
By using mysql_options() the MySQL library will read the [client] and [your_prog_name] sections in the my.cnf file which will ensure that your program will work, even if someone has set up MySQL in some non-standard way.
Note that upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1. This flag indicates, in the event that a query cannot be performed because of a lost connection, to try reconnecting to the server before giving up.
This function is used to create a legal SQL string that you can use in a SQL statement. See String syntax.
The string in from is encoded to an escaped SQL string, taking into account the current character set of the connection. The result is placed in to and a terminating null byte is appended. Characters encoded are NUL (ASCII 0), \n, \r, \, ', ", and Control-Z (see Literals). (Strictly speaking, MySQL requires only that backslash and the quote character used to quote the string in the query be escaped. This function quotes the other characters to make them easier to read in log files.)
The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. (In the worst case, each character may need to be encoded as using two bytes, and you need room for the terminating null byte.) When mysql_real_escape_string() returns, the contents of to will be a null-terminated string. The return value is the length of the encoded string, not including the terminating null character.
char query[1000],*end; end = strmov(query,"INSERT INTO test_table values("); *end++ = '\''; end += mysql_real_escape_string(&mysql, end,"What's this",11); *end++ = '\''; *end++ = ','; *end++ = '\''; end += mysql_real_escape_string(&mysql, end,"binary data: \0\r\n",16); *end++ = '\''; *end++ = ')'; if (mysql_real_query(&mysql,query,(unsigned int) (end - query))) { fprintf(stderr, "Failed to insert row, Error: %s\n", mysql_error(&mysql)); }
The strmov() function used in the example is included in the mysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.
Executes the SQL query pointed to by query, which should be a string length bytes long. The query must consist of a single SQL statement. You should not add a terminating semicolon (;) or \g to the statement.
You must use mysql_real_query() rather than mysql_query() for queries that contain binary data, because binary data may contain the \0 character. In addition, mysql_real_query() is faster than mysql_query() because it does not call strlen() on the query string.
If you want to know if the query should return a result set or not, you can use mysql_field_count() to check for this. See mysql_field_count().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Asks the MySQL server to reload the grant tables. The connected user must have the RELOAD privilege.
This function is deprecated. It is preferable to use mysql_query() to issue an SQL FLUSH PRIVILEGES statement instead.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Sets the row cursor to an arbitrary row in a query result set. The offset value is a row offset that should be a value returned from mysql_row_tell() or from mysql_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_data_seek() instead.
This function requires that the result set structure contains the entire result of the query, so mysql_row_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().
The previous value of the row cursor. This value may be passed to a subsequent call to mysql_row_seek().
Returns the current position of the row cursor for the last mysql_fetch_row(). This value can be used as an argument to mysql_row_seek().
You should use mysql_row_tell() only after mysql_store_result(), not after mysql_use_result().
Causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that do not include an explicit database specifier.
mysql_select_db() fails unless the connected user can be authenticated as having permission to use the database.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Enables or disables an option for the connection. option can have one of the following values:
MYSQL_OPTION_MULTI_STATEMENTS_ON | Enable multi statement support. |
MYSQL_OPTION_MULTI_STATEMENTS_OFF | Disable multi statement support. |
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
ER_UNKNOWN_COM_ERROR | The server didn't support mysql_set_server_option() (which is the case that the server is older than 4.1.1) or the server didn't support the option one tried to set. |
Asks the database server to shut down. The connected user must have SHUTDOWN privileges.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Returns a null-terminated string containing the SQLSTATE error code for the last error. The error code consists of five characters. '00000' means ``no error''. The values are specified by ANSI SQL and ODBC. For a list of possible values, see Error-returns.
Note that not all MySQL errors are yet mapped to SQLSTATE's. The value 'HY000' (general error) is used for unmapped errors.
This function was added to MySQL 4.1.1.
See mysql_errno(). See mysql_error(). See mysql_stmt_sqlstate.
mysql_ssl_set() is used for establishing secure connections using SSL. It must be called before mysql_real_connect().
mysql_ssl_set() does nothing unless OpenSSL support is enabled in the client library.
mysql is the connection handler returned from mysql_init(). The other parameters are specified as follows:
key is the pathname to the key file.
cert is the pathname to the certificate file.
ca is the pathname to the certificate authority file.
capath is the pathname to a directory that contains trusted SSL CA certificates in pem format.
cipher is a list of allowable ciphers to use for SSL encryption.
Any unused SSL parameters may be given as NULL.
This function always returns 0. If SSL setup is incorrect, mysql_real_connect() will return an error when you attempt to connect.
Returns a character string containing information similar to that provided by the mysqladmin status command. This includes uptime in seconds and the number of running threads, questions, reloads, and open tables.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
You must call mysql_store_result() or mysql_use_result() for every query that successfully retrieves data (SELECT, SHOW, DESCRIBE, EXPLAIN).
You don't have to call mysql_store_result() or mysql_use_result() for other queries, but it will not do any harm or cause any notable performance if you call mysql_store_result() in all cases. You can detect if the query didn't have a result set by checking if mysql_store_result() returns 0 (more about this later one).
If you want to know if the query should return a result set or not, you can use mysql_field_count() to check for this. See mysql_field_count().
mysql_store_result() reads the entire result of a query to the client, allocates a MYSQL_RES structure, and places the result into this structure.
mysql_store_result() returns a null pointer if the query didn't return a result set (if the query was, for example, an INSERT statement).
mysql_store_result() also returns a null pointer if reading of the result set failed. You can check if an error occurred by checking if mysql_error() returns a non-empty string, if mysql_errno() returns non-zero, or if mysql_field_count() returns zero.
An empty result set is returned if there are no rows returned. (An empty result set differs from a null pointer as a return value.)
Once you have called mysql_store_result() and got a result back that isn't a null pointer, you may call mysql_num_rows() to find out how many rows are in the result set.
You can call mysql_fetch_row() to fetch rows from the result set, or mysql_row_seek() and mysql_row_tell() to obtain or set the current row position within the result set.
You must call mysql_free_result() once you are done with the result set.
mysql_store_result() resets mysql_error and mysql_errno if it succeeds.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Returns the thread ID of the current connection. This value can be used as an argument to mysql_kill() to kill the thread.
If the connection is lost and you reconnect with mysql_ping(), the thread ID will change. This means you should not get the thread ID and store it for later. You should get it when you need it.
You must call mysql_store_result() or mysql_use_result() for every query that successfully retrieves data (SELECT, SHOW, DESCRIBE, EXPLAIN).
mysql_use_result() initiates a result set retrieval but does not actually read the result set into the client like mysql_store_result() does. Instead, each row must be retrieved individually by making calls to mysql_fetch_row(). This reads the result of a query directly from the server without storing it in a temporary table or local buffer, which is somewhat faster and uses much less memory than mysql_store_result(). The client will allocate memory only for the current row and a communication buffer that may grow up to max_allowed_packet bytes.
On the other hand, you shouldn't use mysql_use_result() if you are doing a lot of processing for each row on the client side, or if the output is sent to a screen on which the user may type a ^S (stop scroll). This will tie up the server and prevent other threads from updating any tables from which the data is being fetched.
When using mysql_use_result(), you must execute mysql_fetch_row() until a NULL value is returned, otherwise, the unfetched rows will be returned as part of the result set for your next query. The C API will give the error Commands out of sync; you can't run this command now if you forget to do this!
You may not use mysql_data_seek(), mysql_row_seek(), mysql_row_tell(), mysql_num_rows(), or mysql_affected_rows() with a result returned from mysql_use_result(), nor may you issue other queries until the mysql_use_result() has finished. (However, after you have fetched all the rows, mysql_num_rows() will accurately return the number of rows fetched.)
You must call mysql_free_result() once you are done with the result set.
mysql_use_result() resets mysql_error and mysql_errno if it succeeds.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
Returns the number of warnings generated during execution of the previous SQL statement. Available from MySQL 4.1.
Returns true if more results exist from the currently executed query, and the application must call mysql_next_result() to fetch the results. Available from MySQL 4.1.
TRUE (1) if more results exist. FALSE (0) if no more results exist.
Note that in most cases one instead call mysql_next_result() to test if more result exists and initiate the next result set if it existed.
See C API multiple queries. See mysql_next_result.
If more query results exist, mysql_next_result() reads the next query results and returns the status back to application. Available from MySQL 4.1.
Note that you must call mysql_free_result() for the preceding query if it returned a result set.
After calling mysql_next_result() the state of the connection is as if you had called mysql_real_query() for the next query. This means that you can now call mysql_store_result(), mysql_warning_count(), mysql_affected_rows() ... on the connection.
If mysql_next_result() returns an error, no other statements will be executed and there is no more results to fetch.
0 if successful and there was more results -1 if no more results > 0 if an error occurred.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. For example if you didn't call mysql_use_result() for a previous result set. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
You should use mysql_real_escape_string() instead!
This function is identical to mysql_real_escape_string() except that mysql_real_escape_string() takes a connection handler as its first argument and escapes the string according to the current character set. mysql_escape_string() does not take a connection argument and does not respect the current charset setting.
unsigned int mysql_field_count(MYSQL *mysql)
If you are using a version of MySQL earlier than Version 3.22.24, you should use unsigned int mysql_num_fields(MYSQL *mysql) instead.
unsigned int mysql_num_fields(MYSQL_RES *result)
or:
unsigned int mysql_num_fields(MYSQL *mysql)
The second form doesn't work on MySQL Version 3.22.24 or newer. To pass a MYSQL* argument, you must use unsigned int mysql_field_count(MYSQL *mysql) instead.
MYSQL *mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, unsigned int port, const char *unix_socket, unsigned long client_flag)
unsigned long mysql_real_escape_string(MYSQL *mysql, char *to, const char *from, unsigned long length)
As of MySQL 4.1, the client/server protocol provides for the use of prepared statements. This capability uses the MYSQL_STMT statement handler data structure. Prepared execution is an efficient way to execute a statement more than once. The statement is first parsed to prepare it for execution. Then it is executed one or more times at a later time, using the statement handle returned by the prepare function.
Prepared execution is faster than direct execution for statements executed more than once, primarly because the query is parsed only once. In the case of direct execution, the query is parsed every time it is executed. Prepared execution also can provide a reduction of network traffic because for each execution of the prepared statement, it is necessary only to send the data for the parameters.
Another advantage of prepared statements is that it uses a binary protocol that makes data transfer between client and server more efficient. Prepared statements also can support input and output binding for multiple query execution.
Note: The API for prepared statements is still subject to revision. This information is provided for early adopters, but please be aware that the API may change.
Prepared statements mainly use the MYSQL_STMT and MYSQL_BIND data structures. A third structure, MYSQL_TIME, is used to transfer temporal data.
MYSQL_STMT | This structure represents a prepared statement. A statement is prepared by calling mysql_prepare(), which returns a statement handle, that is, a pointer to a MYSQL_STMT. The handle is used for all subsequent statement-related functions. The MYSQL_STMT structure has no members that are for application use. Multiple statement handles can be associated with a single connection. The limit on the number of handles depends on the available system resources. | |||||||||||||||||
MYSQL_BIND | This structure is used both for query input (data values sent to the server) and output (result values returned from the server). For input, it is used with mysql_bind_param() to bind parameter data values to buffers for use by mysql_execute(). For output, it is used with mysql_bind_result() to bind result set buffers for use in fetching rows with mysql_fetch(). The MYSQL_BIND structure contains the following members for use by application programs. Each is used both for input and for output, though sometimes for different purposes depending on the direction of data transfer. |
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MYSQL_TIME | This structure is used to send and receive DATE, TIME, DATETIME, and TIMESTAMP data directly to and from the server. This is done by setting the buffer_type member of a MYSQL_BIND structure to one of the temporal types, and setting the buffer member to point to a MYSQL_TIME structure. The MYSQL_TIME structure contains the following members: |
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The following table shows the allowable values that may be specified in the buffer_type member of MYSQL_BIND structures. The table also shows those SQL types that correspond most closely to each buffer_type value, and, for numeric and temporal types, the corresponding C type.
buffer_typeValue | SQL Type | C Type |
MYSQL_TYPE_TINY | TINYINT | char |
MYSQL_TYPE_SHORT | SMALLINT | short int |
MYSQL_TYPE_LONG | INT | long int |
MYSQL_TYPE_LONGLONG | BIGINT | long long int |
MYSQL_TYPE_FLOAT | FLOAT | float |
MYSQL_TYPE_DOUBLE | DOUBLE | double |
MYSQL_TYPE_TIME | TIME | MYSQL_TIME |
MYSQL_TYPE_DATE | DATE | MYSQL_TIME |
MYSQL_TYPE_DATETIME | DATETIME | MYSQL_TIME |
MYSQL_TYPE_TIMESTAMP | TIMESTAMP | MYSQL_TIME |
MYSQL_TYPE_STRING | CHAR | |
MYSQL_TYPE_VAR_STRING | VARCHAR | |
MYSQL_TYPE_TINY_BLOB | TINYBLOB/TINYTEXT | |
MYSQL_TYPE_BLOB | BLOB/TEXT | |
MYSQL_TYPE_MEDIUM_BLOB | MEDIUMBLOB/MEDIUMTEXT | |
MYSQL_TYPE_LONG_BLOB | LONGBLOB/LONGTEXT |
Implicit type conversion may be performed in both directions.
Note: The API for prepared statements is still subject to revision. This information is provided for early adopters, but please be aware that the API may change.
The functions available for prepared statement processing are summarized here and described in greater detail in a later section. See C API Prepared statement functions.
Function | Description |
mysql_bind_param() | Associates application data buffers with the parameter markers in a prepared SQL statement. |
mysql_bind_result() | Associates application data buffers with columns in the result set. |
mysql_execute() | Executes the prepared statement. |
mysql_fetch() | Fetches the next row of data from the result set and returns data for all bound columns. |
mysql_fetch_column() | Fetch data for one column of the current row of the result set. |
mysql_get_metadata() | Returns prepared statement metadata in the form of a result set. |
mysql_param_count() | Returns the number of parameters in a prepared SQL statement. |
mysql_param_result() | Return parameter metadata in the form of a result set. |
mysql_prepare() | Prepares an SQL string for execution. |
mysql_send_long_data() | Sends long data in chunks to server. |
mysql_stmt_affected_rows() | Returns the number of rows changes, deleted, or inserted by the last UPDATE, DELETE, or INSERT query. |
mysql_stmt_close() | Frees memory used by prepared statement. |
mysql_stmt_data_seek() | Seeks to an arbitrary row number in a statement result set. |
mysql_stmt_errno() | Returns the error number for the last statement execution. |
mysql_stmt_error() | Returns the error message for the last statement execution. |
mysql_stmt_free_result() | Free the resources allocated to the statement handle. |
mysql_stmt_num_rows() | Returns total rows from the statement buffered result set. |
mysql_stmt_reset() | Reset the statement buffers in the server. |
mysql_stmt_row_seek() | Seeks to a row offset in a statement result set, using value returned from mysql_stmt_row_tell(). |
mysql_stmt_row_tell() | Returns the statement row cursor position. |
mysql_stmt_sqlstate() | Returns the SQLSTATE error code for the last statement execution. |
mysql_stmt_store_result() | Retrieves the complete result set to the client. |
Call mysql_prepare() to prepare and initialize the statement handle, mysql_bind_param() to supply the parameter data, and mysql_execute() to execute the query. You can repeat the mysql_execute() by changing parameter values in the respective buffers supplied through mysql_bind_param().
If the query is a SELECT statement or any other query that produces a result set, mysql_prepare() will also return the result set metadata information in the form of a MYSQL_RES result set through mysql_get_metadata().
You can supply the result buffers using mysql_bind_result(), so that the mysql_fetch() will automatically return data to these buffers. This is row-by-row fetching.
You can also send the text or binary data in chunks to server using mysql_send_long_data(), by specifying the option is_long_data=1 or length=MYSQL_LONG_DATA or -2 in the MYSQL_BIND structure supplied with mysql_bind_param().
When statement execution has been completed, the statement handle must be closed using mysql_stmt_close() so that all resources associated with it can be freed.
If you obtained a SELECT statement's result set metadata by calling mysql_get_metadata(), you should also free it using mysql_free_result().
To prepare and execute a statement, an application follows these steps:
Call mysql_prepare() and pass it a string containing the SQL statement. For a successful prepare operation, mysql_prepare() returns a valid statement handle to the application.
If the query produces a result set, call mysql_get_metadata() to obtain the result set metadata. This metadata is itself in the form of result set, albeit a separate one from the one that contains the rows returned by the query. The metadata result set indicates how many columns are in the result and contains information about each column.
Set the values of any parameters using mysql_bind_param(). All parameters must be set. Otherwise, query execution will return an error or produce unexpected results.
Call mysql_execute() to execute the statement.
If the query produces a result set, bind the data buffers to use for retrieving the row values by calling mysql_bind_result().
Fetch the data into the buffers row by row by calling mysql_fetch() repeatedly until no more rows are found.
Repeat steps 3 through 6 as necessary, by changing the parameter values and re-executing the statement.
When mysql_prepare() is called, the MySQL client/server protocol performs these actions:
The server parses the query and sends the OK status back to the client by assigning a statement ID. It also sends total number of parameters, a column count, and its meta information if it is a result set oriented query. All syntax and semantics of the query are checked by the server during this call.
The client uses this statement ID for the further operations, so that the server can identify the statement from among its pool of statements. The client also allocates a statement handle with this ID and returns the handle to the application.
When mysql_execute() is called, the MySQL client/server protocol performs these actions:
The client uses the statement handle and sends the parameter data to the server.
The server identifies the statement using the ID provided by the client, replaces the parameter markers with the newly supplied data, and executes the query. If the query produces a result set, the server sends the data back to the client. Otherwise, it sends an OK status and total number of rows changed, deleted, or inserted.
When mysql_fetch() is called, the MySQL client/server protocol performs these actions:
The client reads the data from the packet row by row and places it into the application data buffers by doing the necessary conversions. If the application buffer type is same as that of the field type returned from the server, the conversions are straightforward.
You can get the statement error code, error message, and SQLSTATE value using mysql_stmt_errno(), mysql_stmt_error(), and mysql_stmt_sqlstate(), respectively.
To prepare and execute queries, use the following functions.
mysql_bind_param() is used to bind data for the parameter markers in the SQL statement that was passed to mysql_prepare(). It uses MYSQL_BIND structures to supply the data. bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain an element for each ? parameter marker that is present in the query.
Suppose you prepare the following statment:
INSERT INTO mytbl VALUES(?,?,?)
When you bind the parameters, the array of MYSQL_BIND structures must contain three elements, and can be declared like this:
MYSQL_BIND bind[3];
The members of each MYSQL_BIND element that should be set are described in C API Prepared statement datatypes.
CR_INVALID_BUFFER_USE | Indicates if the bind is to supply the long data in chunks and if the buffer type is non string or binary. |
CR_UNSUPPORTED_PARAM_TYPE | The conversion is not supported. Possibly the buffer_type value is illegal or is not one of the supported types. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
For the usage of mysql_bind_param(), refer to the Example from mysql_execute().
mysql_bind_result() is used to associate (bind) columns in the result set to data buffers and length buffers. When mysql_fetch() is called to fetch data, the MySQL client/server protocol places the data for the bound columns into the specified buffers.
Note that all columns must be bound to buffers prior to calling mysql_fetch(). bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain an element for each column of the result set. Otherwise, mysql_fetch() simply ignores the data fetch. Also, the buffers should be large enough to hold the data values, because the protocol doesn't return data values in chunks.
A column can be bound or rebound at any time, even after a result set has been partially retrieved. The new binding takes effect the next time mysql_fetch() is called. Suppose an application binds the columns in a result set and calls mysql_fetch(). The client/server protocol returns data in the bound buffers. Then suppose the application binds the columns to a different set of buffers. The protocol does not place data into the newly bound buffers until the next call to mysql_fetch() occurs.
To bind a column, an application calls mysql_bind_result() and passes the type, address, and the address of the length buffer. The members of each MYSQL_BIND element that should be set are described in C API Prepared statement datatypes.
CR_UNSUPPORTED_PARAM_TYPE | The conversion is not supported. Possibly the buffer_type value is illegal or is not one of the supported types. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
For the usage of mysql_bind_result(), refer to the Example from mysql_fetch().
mysql_execute() executes the prepared query associated with the statement handle. The currently bound parameter marker values are sent to server during this call, and the server replaces the markers with this newly supplied data.
If the statement is an UPDATE, DELETE, or INSERT, the total number of changed, deleted, or inserted rows can be found by calling mysql_stmt_affected_rows(). If this is a result set query such as SELECT, you must call mysql_fetch() to fetch the data prior to calling any other functions that result in query processing. For more information on how to fetch the results, refer to mysql_fetch().
Zero if execution was successful. Non-zero if an error occurred. The error code and message can be obtained by calling mysql_stmt_errno() and mysql_stmt_error().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
The following example demonstrates how to create and populate a table using mysql_prepare(), mysql_param_count(), mysql_bind_param(), mysql_execute(), and mysql_stmt_affected_rows(). The mysql variable is assumed to be a valid connection handle.
#define STRING_SIZE 50 #define DROP_SAMPLE_TABLE "DROP TABLE IF EXISTS test_table" #define CREATE_SAMPLE_TABLE "CREATE TABLE test_table(col1 INT,\ col2 VARCHAR(40),\ col3 SMALLINT,\ col4 TIMESTAMP)" #define INSERT_SAMPLE "INSERT INTO test_table(col1,col2,col3) VALUES(?,?,?)" MYSQL_STMT *stmt; MYSQL_BIND bind[3]; my_ulonglong affected_rows; int param_count; short small_data; int int_data; char str_data[STRING_SIZE]; unsigned long str_length; my_bool is_null; if (mysql_query(mysql, DROP_SAMPLE_TABLE)) { fprintf(stderr, " DROP TABLE failed\n"); fprintf(stderr, " %s\n", mysql_error(mysql)); exit(0); } if (mysql_query(mysql, CREATE_SAMPLE_TABLE)) { fprintf(stderr, " CREATE TABLE failed\n"); fprintf(stderr, " %s\n", mysql_error(mysql)); exit(0); } /* Prepare an INSERT query with 3 parameters */ /* (the TIMESTAMP column is not named; it will */ /* be set to the current date and time) */ stmt = mysql_prepare(mysql, INSERT_SAMPLE, strlen(INSERT_SAMPLE)); if (!stmt) { fprintf(stderr, " mysql_prepare(), INSERT failed\n"); fprintf(stderr, " %s\n", mysql_error(mysql)); exit(0); } fprintf(stdout, " prepare, INSERT successful\n"); /* Get the parameter count from the statement */ param_count= mysql_param_count(stmt); fprintf(stdout, " total parameters in INSERT: %d\n", param_count); if (param_count != 3) /* validate parameter count */ { fprintf(stderr, " invalid parameter count returned by MySQL\n"); exit(0); } /* Bind the data for all 3 parameters */ /* INTEGER PARAM */ /* This is a number type, so there is no need to specify buffer_length */ bind[0].buffer_type= MYSQL_TYPE_LONG; bind[0].buffer= (char *)&int_data; bind[0].is_null= 0; bind[0].length= 0; /* STRING PARAM */ bind[1].buffer_type= MYSQL_TYPE_VAR_STRING; bind[1].buffer= (char *)str_data; bind[1].buffer_length= STRING_SIZE; bind[1].is_null= 0; bind[1].length= &str_length; /* SMALLINT PARAM */ bind[2].buffer_type= MYSQL_TYPE_SHORT; bind[2].buffer= (char *)&small_data; bind[2].is_null= &is_null; bind[2].length= 0; /* Bind the buffers */ if (mysql_bind_param(stmt, bind)) { fprintf(stderr, " mysql_bind_param() failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Specify the data values for the first row */ int_data= 10; /* integer */ strncpy(str_data, "MySQL", STRING_SIZE); /* string */ str_length= strlen(str_data); /* INSERT SMALLINT data as NULL */ is_null= 1; /* Execute the INSERT statement - 1*/ if (mysql_execute(stmt)) { fprintf(stderr, " mysql_execute(), 1 failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Get the total number of affected rows */ affected_rows= mysql_stmt_affected_rows(stmt); fprintf(stdout, " total affected rows(insert 1): %ld\n", affected_rows); if (affected_rows != 1) /* validate affected rows */ { fprintf(stderr, " invalid affected rows by MySQL\n"); exit(0); } /* Specify data values for second row, then re-execute the statement */ int_data= 1000; strncpy(str_data, "The most popular open source database", STRING_SIZE); str_length= strlen(str_data); small_data= 1000; /* smallint */ is_null= 0; /* reset */ /* Execute the INSERT statement - 2*/ if (mysql_execute(stmt)) { fprintf(stderr, " mysql_execute, 2 failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Get the total rows affected */ affected_rows= mysql_stmt_affected_rows(stmt); fprintf(stdout, " total affected rows(insert 2): %ld\n", affected_rows); if (affected_rows != 1) /* validate affected rows */ { fprintf(stderr, " invalid affected rows by MySQL\n"); exit(0); } /* Close the statement */ if (mysql_stmt_close(stmt)) { fprintf(stderr, " failed while closing the statement\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); }
Note: For complete examples on the use of prepared statement functions, refer to the file tests/client_test.c. This file can be obtained from a MySQL source distribution or from the BitKeeper source repository.
mysql_fetch() returns the next row in the result set. It can be called only while the result set exists, that is, after a call to mysql_execute() that creates a result set or after mysql_stmt_store_result(), which is called after mysql_execute() to buffer the entire result set.
mysql_fetch() returns row data using the buffers bound by mysql_bind_result(). It returns the data in those buffers for all the columns in the current row set and the lengths are returned to the length pointer.
Note that all columns must be bound by the application before calling mysql_fetch().
If a fetched data value is a NULL value, the *is_null value of the corresponding MYSQL_BIND structure contains TRUE (1). Otherwise, the data and its length are returned in the *buffer and *length elements based on the buffer type specified by the application. Each numeric and temporal type has a fixed length, as listed in the following table. The length of the string types depends on the length of the actual data value, as indicated by data_length.
Type | Length |
MYSQL_TYPE_TINY | 1 |
MYSQL_TYPE_SHORT | 2 |
MYSQL_TYPE_LONG | 4 |
MYSQL_TYPE_LONGLONG | 8 |
MYSQL_TYPE_FLOAT | 4 |
MYSQL_TYPE_DOUBLE | 8 |
MYSQL_TYPE_TIME | sizeof(MYSQL_TIME) |
MYSQL_TYPE_DATE | sizeof(MYSQL_TIME) |
MYSQL_TYPE_DATETIME | sizeof(MYSQL_TIME) |
MYSQL_TYPE_TIMESTAMP | sizeof(MYSQL_TIME) |
MYSQL_TYPE_STRING | data length |
MYSQL_TYPE_VAR_STRING | data_length |
MYSQL_TYPE_TINY_BLOB | data_length |
MYSQL_TYPE_BLOB | data_length |
MYSQL_TYPE_MEDIUM_BLOB | data_length |
MYSQL_TYPE_LONG_BLOB | data_length |
Return Value | Description |
0 | Successful, the data has been fetched to application data buffers. |
1 | Error occurred. Error code and message can be obtained by calling mysql_stmt_errno() and mysql_stmt_error(). |
MYSQL_NO_DATA | No more rows/data exists |
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
CR_UNSUPPORTED_PARAM_TYPE | The buffer type is MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, but the datatype is not DATE, TIME, DATETIME, or TIMESTAMP. |
All other unsupported conversion errors are returned from mysql_bind_result(). |
The following example demonstrates how to fetch data from a table using mysql_get_metadata(), mysql_bind_result(), and mysql_fetch(). (This example expects to retrieve the two rows inserted by the example shown in mysql_execute().) The mysql variable is assumed to be a valid connection handle.
#define STRING_SIZE 50 #define SELECT_SAMPLE "SELECT col1, col2, col3, col4 FROM test_table" MYSQL_STMT *stmt; MYSQL_BIND bind[4]; MYSQL_RES *prepare_meta_result; MYSQL_TIME ts; unsigned long length[4]; int param_count, column_count, row_count; short small_data; int int_data; char str_data[STRING_SIZE]; my_bool is_null[4]; /* Prepare a SELECT query to fetch data from test_table */ stmt = mysql_prepare(mysql, SELECT_SAMPLE, strlen(SELECT_SAMPLE)); if (!stmt) { fprintf(stderr, " mysql_prepare(), SELECT failed\n"); fprintf(stderr, " %s\n", mysql_error(mysql)); exit(0); } fprintf(stdout, " prepare, SELECT successful\n"); /* Get the parameter count from the statement */ param_count= mysql_param_count(stmt); fprintf(stdout, " total parameters in SELECT: %d\n", param_count); if (param_count != 0) /* validate parameter count */ { fprintf(stderr, " invalid parameter count returned by MySQL\n"); exit(0); } /* Fetch result set meta information */ prepare_meta_result = mysql_get_metadata(stmt); if (!prepare_meta_result) { fprintf(stderr, " mysql_get_metadata(), returned no meta information\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Get total columns in the query */ column_count= mysql_num_fields(prepare_meta_result); fprintf(stdout, " total columns in SELECT statement: %d\n", column_count); if (column_count != 4) /* validate column count */ { fprintf(stderr, " invalid column count returned by MySQL\n"); exit(0); } /* Execute the SELECT query */ if (mysql_execute(stmt)) { fprintf(stderr, " mysql_execute(), failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Bind the result buffers for all 4 columns before fetching them */ /* INTEGER COLUMN */ bind[0].buffer_type= MYSQL_TYPE_LONG; bind[0].buffer= (char *)&int_data; bind[0].is_null= &is_null[0]; bind[0].length= &length[0]; /* STRING COLUMN */ bind[1].buffer_type= MYSQL_TYPE_VAR_STRING; bind[1].buffer= (char *)str_data; bind[1].buffer_length= STRING_SIZE; bind[1].is_null= &is_null[1]; bind[1].length= &length[1]; /* SMALLINT COLUMN */ bind[2].buffer_type= MYSQL_TYPE_SHORT; bind[2].buffer= (char *)&small_data; bind[2].is_null= &is_null[2]; bind[2].length= &length[2]; /* TIMESTAMP COLUMN */ bind[3].buffer_type= MYSQL_TYPE_TIMESTAMP; bind[3].buffer= (char *)&ts; bind[3].is_null= &is_null[3]; bind[3].length= &length[3]; /* Bind the result buffers */ if (mysql_bind_result(stmt, bind)) { fprintf(stderr, " mysql_bind_result() failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Now buffer all results to client */ if (mysql_stmt_store_result(stmt)) { fprintf(stderr, " mysql_stmt_store_result() failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Fetch all rows */ row_count= 0; fprintf(stdout, "Fetching results ...\n"); while (!mysql_fetch(stmt)) { row_count++; fprintf(stdout, " row %d\n", row_count); /* column 1 */ fprintf(stdout, " column1 (integer) : "); if (is_null[0]) fprintf(stdout, " NULL\n"); else fprintf(stdout, " %d(%ld)\n", int_data, length[0]); /* column 2 */ fprintf(stdout, " column2 (string) : "); if (is_null[1]) fprintf(stdout, " NULL\n"); else fprintf(stdout, " %s(%ld)\n", str_data, length[1]); /* column 3 */ fprintf(stdout, " column3 (smallint) : "); if (is_null[2]) fprintf(stdout, " NULL\n"); else fprintf(stdout, " %d(%ld)\n", small_data, length[2]); /* column 4 */ fprintf(stdout, " column4 (timestamp): "); if (is_null[3]) fprintf(stdout, " NULL\n"); else fprintf(stdout, " %04d-%02d-%02d %02d:%02d:%02d (%ld)\n", ts.year, ts.month, ts.day, ts.hour, ts.minute, ts.second, length[3]); fprintf(stdout, "\n"); } /* Validate rows fetched */ fprintf(stdout, " total rows fetched: %d\n", row_count); if (row_count != 2) { fprintf(stderr, " MySQL failed to return all rows\n"); exit(0); } /* Free the prepared result metadata */ mysql_free_result(prepare_meta_result); /* Close the statement */ if (mysql_stmt_close(stmt)) { fprintf(stderr, " failed while closing the statement\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); }
If a statement passed to mysql_prepare() is one that produces a result set, mysql_get_metadata() returns the result set metadata in the form of a pointer to a MYSQL_RES structure that can be used to process the meta information such as total number of fields and individual field information. This result set pointer can be passed as an argument to any of the field-based API functions that process result set metadata, such as:
mysql_num_fields()
mysql_fetch_field()
mysql_fetch_field_direct()
mysql_fetch_fields()
mysql_field_count()
mysql_field_seek()
mysql_field_tell()
mysql_free_result()
The result set structure should be freed when you are done with it, which you can do by passing it to mysql_free_result(). This is similar to the way you free a result set obtained from a call to mysql_store_result().
The result set returned by mysql_get_metadata() contains only metadata. It does not contain any row results. The rows are obtained by using the statement handle with mysql_fetch().
A MYSQL_RES result structure. NULL if no meta information exists for the prepared query.
For the usage of mysql_get_metadata(), refer to the Example from mysql_fetch().
For the usage of mysql_param_count(), refer to the Example from mysql_execute().
Prepares the SQL query pointed to by the null-terminated string query, and returns a statement handle to be used for further operations on the statement. The query must consist of a single SQL statement. You should not add a terminating semicolon (;) or \g to the statement.
The application can include one or more parameter markers in the SQL statement by embedding question mark (?) characters into the SQL string at the appropriate positions.
The markers are legal only in certain places in SQL statements. For example, they are allowed in the VALUES() list of an INSERT statement (to specify column values for a row), or in a comparison with a column in a WHERE clause to specify a comparison value. However, they are not allowed for identifiers (such as table or column names), in the select list that names the columns to be returned by a SELECT statement), or to specify both operands of a binary operator such as the = equal sign. The latter restriction is necessary because it would be impossible to determine the parameter type. In general, parameters are legal only in Data Manipulation Languange (DML) statements, and not in Data Defination Language (DDL) statements.
The parameter markers must be bound to application variables using mysql_bind_param() before executing the statement.
A pointer to a MYSQL_STMT structure if the prepare was successful. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query |
CR_UNKNOWN_ERROR | An unknown error occurred. |
If the prepare is not successful (that is, mysql_prepare() returns NULL), the error message can be obtained by calling mysql_error().
For the usage of mysql_prepare(), refer to the Example from mysql_execute().
Allows an application to send parameter data to the server in pieces (or ``chunks''). This function can be called multiple times to send the parts of a character or binary data value for a column, which must be one of the TEXT or BLOB datatypes.
parameter_number indicates which parameter to associate the data with. Parameters are numbered beginning with 0. data is a pointer to a buffer containing data to be sent, and length indicates the number of bytes in the buffer.
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
The following example demonstrates how to send the data for a TEXT column in chunks. It inserts the data value 'MySQL - The most popular open source database' into the text_column column. The mysql variable is assumed to be a valid connection handle.
#define INSERT_QUERY "INSERT INTO test_long_data(text_column) VALUES(?)" MYSQL_BIND bind[1]; long length; if (!mysql_prepare(mysql, INSERT_QUERY, strlen(INSERT_QUERY)) { fprintf(stderr, "\n prepare failed"); fprintf(stderr, "\n %s", mysql_error(mysql)); exit(0); } memset(bind, 0, sizeof(bind)); bind[0].buffer_type= MYSQL_TYPE_STRING; bind[0].length= &length; bind[0].is_null= 0; /* Bind the buffers */ if (mysql_bind_param(stmt, bind)) { fprintf(stderr, "\n param bind failed"); fprintf(stderr, "\n %s", mysql_stmt_error(stmt)); exit(0); } /* Supply data in chunks to server */ if (!mysql_send_long_data(stmt,0,"MySQL",5)) { fprintf(stderr, "\n send_long_data failed"); fprintf(stderr, "\n %s", mysql_stmt_error(stmt)); exit(0); } /* Supply the next piece of data */ if (mysql_send_long_data(stmt,0," - The most popular open source database",40)) { fprintf(stderr, "\n send_long_data failed"); fprintf(stderr, "\n %s", mysql_stmt_error(stmt)); exit(0); } /* Now, execute the query */ if (mysql_execute(stmt)) { fprintf(stderr, "\n mysql_execute failed"); fprintf(stderr, "\n %s", mysql_stmt_error(stmt)); exit(0); }
Returns the total number of rows changed, deleted, or inserted by the last executed statement. May be called immediatlely after mysql_execute() for UPDATE, DELETE, or INSERT statements. For SELECT statements, mysql_stmt_affected_rows() works like mysql_num_rows().
An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records were updated for an UPDATE statement, no rows matched the WHERE clause in the query, or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_stmt_affected_rows() was called prior to calling mysql_stmt_store_result(). Because mysql_stmt_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).
For the usage of mysql_stmt_affected_rows(), refer to the Example from mysql_execute().
Closes the prepared statement. mysql_stmt_close() also deallocates the statement handle pointed to by stmt.
If the current statement has pending or unread results, this function cancels them so that the next query can be executed.
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
For the usage of mysql_stmt_close(), refer to the Example from mysql_execute().
Seeks to an arbitrary row in a statement result set. The offset value is a row number and should be in the range from 0 to mysql_stmt_num_rows(stmt)-1.
This function requires that the statement result set structure contains the entire result of the last executed query, so mysql_stmt_data_seek() may be used only in conjunction with mysql_stmt_store_result().
For the statement specified by stmt, mysql_stmt_errno() returns the error code for the most recently invoked statement API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL errmsg.h header file. Server error message numbers are listed in mysqld_error.h. In the MySQL source distribution you can find a complete list of error messages and error numbers in the file Docs/mysqld_error.txt. The server error codes also are listed at Error-returns.
For the statement specified by stmt, mysql_stmt_error() returns a null-terminated string containing the error message for the most recently invoked statement API function that can succeed or fail. An empty string ("") is returned if no error occurred. This means the following two tests are equivalent:
if (mysql_stmt_errno(stmt)) { // an error occurred } if (mysql_stmt_error(stmt)[0]) { // an error occurred }
The language of the client error messages may be changed by recompiling the MySQL client library. Currently you can choose error messages in several different languages.
Returns the number of rows in the result set.
The use of mysql_stmt_num_rows() depends on whether or not you used mysql_stmt_store_result() to buffer the entire result set in the statement handle.
If you use mysql_stmt_store_result(), mysql_stmt_num_rows() may be called immediately.
Sets the row cursor to an arbitrary row in a statement result set. The offset value is a row offset that should be a value returned from mysql_stmt_row_tell() or from mysql_stmt_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_stmt_data_seek() instead.
This function requires that the result set structure contains the entire result of the query, so mysql_stmt_row_seek() may be used only in conjunction with mysql_stmt_store_result().
The previous value of the row cursor. This value may be passed to a subsequent call to mysql_stmt_row_seek().
Returns the current position of the row cursor for the last mysql_fetch(). This value can be used as an argument to mysql_stmt_row_seek().
You should use mysql_stmt_row_tell() only after mysql_stmt_store_result().
For the statement specified by stmt, mysql_stmt_sqlstate() returns a null-terminated string containing the SQLSTATE error code for the most recently invoked prepared statement API function that can succeed or fail. The error code consists of five characters. "00000" means ``no error''. The values are specified by ANSI SQL and ODBC. For a list of possible values, see Error-returns.
Note that not all MySQL errors are yet mapped to SQLSTATE's. The value "HY000" (general error) is used for unmapped errors.
This function was added to MySQL 4.1.1.
You must call mysql_stmt_store_result() for every query that successfully produces a result set (SELECT, SHOW, DESCRIBE, EXPLAIN), and only if you want to buffer the complete result set by the client, so that the subsequent mysql_fetch() call returns buffered data.
It is unnecessary to call mysql_stmt_store_result() for other queries, but if you do, it will not harm or cause any notable performance in all cases. You can detect whether the query produced a result set by checking if mysql_get_metadata() returns NULL. For more information, refer to mysql_get_metadata().
CR_COMMANDS_OUT_OF_SYNC | Commands were executed in an improper order. |
CR_OUT_OF_MEMORY | Out of memory. |
CR_SERVER_GONE_ERROR | The MySQL server has gone away. |
CR_SERVER_LOST | The connection to the server was lost during the query. |
CR_UNKNOWN_ERROR | An unknown error occurred. |
int mysql_fetch_column(MYSQL_STMT *stmt, MYSQL_BIND *bind, unsigned int column, unsigned long offset)
To be added.
my_bool mysql_send_long_data(MYSQL_STMT *stmt, unsigned int parameter_number, const char *data, unsigned long length)
From version 4.1, MySQL supports the execution of multiple statements specified in a single query string. To use this capability with a given connection, you must specify the CLIENT_MULTI_STATEMENTS option in the flags parameter of mysql_real_connect() when opening the connection. You can also set this for a connection by calling mysql_set_server_option(MYSQL_OPTION_MULTI_STATEMENTS_ON)
By default, mysql_query() and mysql_real_query() return only the first query status and the subsequent queries status can be processed using mysql_more_results() and mysql_next_result().
/* Connect to server with option CLIENT_MULTI_STATEMENTS */ mysql_real_connect(..., CLIENT_MULTI_STATEMENTS); /* Now execute multiple queries */ mysql_query(mysql,"DROP TABLE IF EXISTS test_table;\ CREATE TABLE test_table(id INT);\ INSERT INTO test_table VALUES(10);\ UPDATE test_table SET id=20 WHERE id=10;\ SELECT * FROM test_table;\ DROP TABLE test_table"; do { /* Process all results */ ... printf("total affected rows: %lld", mysql_affected_rows(mysql)); ... if (!(result= mysql_store_result(mysql))) { printf(stderr, "Got fatal error processing query\n"); exit(1); } process_result_set(result); /* client function */ mysql_free_result(result); } while (!mysql_next_result(mysql));
The new binary protocol available in MySQL 4.1 and above allows you to send and receive date and time values (DATE, TIME, DATETIME, and TIMESTAMP), using the MYSQL_TIME structure. The members of this structure are described in C API Prepared statement datatypes.
To send temporal data values, you create a prepared statement with mysql_prepare(). Then, before calling mysql_execute() to execute the statement, use the following procedure to set up each temporal parameter:
In the MYSQL_BIND structure associated with the data value, set the buffer_type member to the type that indicates what kind of temporal value you're sending. For DATE, TIME, DATETIME, or TIMESTAMP values, set buffer_type to MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, respectively.
Set the buffer member of the MYSQL_BIND structure to the address of the MYSQL_TIME structure in which you will pass the temporal value.
Fill in the members of the MYSQL_TIME structure that are appropriate for the type of temporal value you're passing.
Use mysql_bind_param() to bind the parameter data to the statement. Then you can call mysql_execute().
To retrieve temporal values, the procedure is similar, except that you set the buffer_type member to the type of value you expect to receive, and the buffer member to the address of a MYSQL_TIME structure into which the returned value should be placed. Use mysql_bind_results() to bind the buffers to the statement after calling mysql_execute() and before fetching the results.
Here is a simple example that inserts DATE, TIME, and TIMESTAMP data. The mysql variable is assumed to be a valid connection handle.
MYSQL_TIME ts; MYSQL_BIND bind[3]; MYSQL_STMT *stmt; strmov(query, "INSERT INTO test_table(date_field, time_field, timestamp_field) VALUES(?,?,?"); stmt= mysql_prepare(mysql, query, strlen(query))); /* setup input buffers for all 3 parameters */ bind[0].buffer_type= MYSQL_TYPE_DATE; bind[0].buffer= (char *)&ts; bind[0].is_null= 0; bind[0].length= 0; .. bind[1]= bind[2]= bind[0]; .. mysql_bind_param(stmt, bind); /* supply the data to be sent is the ts structure */ ts.year= 2002; ts.month= 02; ts.day= 03; ts.hour= 10; ts.minute= 45; ts.second= 20; mysql_execute(stmt); ..
You need to use the following functions when you want to create a threaded client. See Threaded clients.
This function needs to be called once in the program before calling any MySQL function. This initializes some global variables that MySQL needs. If you are using a thread-safe client library, this will also call mysql_thread_init() for this thread.
This is automatically called by mysql_init(), mysql_server_init() and mysql_connect().
This function needs to be called for each created thread to initialize thread-specific variables.
This is automatically called by my_init() and mysql_connect().
This function needs to be called before calling pthread_exit() to free memory allocated by mysql_thread_init().
Note that this function is not invoked automatically by the client library. It must be called explicitly to avoid a memory leak.
You must use the following functions if you want to allow your application to be linked against the embedded MySQL server library. See libmysqld.
If the program is linked with -lmysqlclient instead of -lmysqld, these functions do nothing. This makes it possible to choose between using the embedded MySQL server and a stand-alone server without modifying any code.
This function must be called once in the program using the embedded server before calling any other MySQL function. It starts the server and initializes any subsystems (mysys, InnoDB, etc.) that the server uses. If this function is not called, the program will crash. If you are using the DBUG package that comes with MySQL, you should call this after you have called MY_INIT().
The argc and argv arguments are analogous to the arguments to main(). The first element of argv is ignored (it typically contains the program name). For convenience, argc may be 0 (zero) if there are no command-line arguments for the server. mysql_server_init() makes a copy of the arguments so it's safe to destroy argv or groups after the call.
The NULL-terminated list of strings in groups selects which groups in the option files will be active. See Option files. For convenience, groups may be NULL, in which case the [server] and [emedded] groups will be active.
#include <mysql.h> #include <stdlib.h> static char *server_args[] = { "this_program", /* this string is not used */ "--datadir=.", "--key_buffer_size=32M" }; static char *server_groups[] = { "embedded", "server", "this_program_SERVER", (char *)NULL }; int main(void) { if (mysql_server_init(sizeof(server_args) / sizeof(char *), server_args, server_groups)) exit(1); /* Use any MySQL API functions here */ mysql_server_end(); return EXIT_SUCCESS; }
This function must be called once in the program after all other MySQL functions. It shuts down the embedded server.
It is possible for mysql_store_result() to return NULL following a successful call to mysql_query(). When this happens, it means one of the following conditions occurred:
There was a malloc() failure (for example, if the result set was too large).
The data couldn't be read (an error occurred on the connection).
The query returned no data (for example, it was an INSERT, UPDATE, or DELETE).
You can always check whether the statement should have produced a non-empty result by calling mysql_field_count(). If mysql_field_count() returns zero, the result is empty and the last query was a statement that does not return values (for example, an INSERT or a DELETE). If mysql_field_count() returns a non-zero value, the statement should have produced a non-empty result. See the description of the mysql_field_count() function for an example.
You can test for an error by calling mysql_error() or mysql_errno().
In addition to the result set returned by a query, you can also get the following information:
mysql_affected_rows() returns the number of rows affected by the last query when doing an INSERT, UPDATE, or DELETE. An exception is that if DELETE is used without a WHERE clause, the table is re-created empty, which is much faster! In this case, mysql_affected_rows() returns zero for the number of records affected.
mysql_num_rows() returns the number of rows in a result set. With mysql_store_result(), mysql_num_rows() may be called as soon as mysql_store_result() returns. With mysql_use_result(), mysql_num_rows() may be called only after you have fetched all the rows with mysql_fetch_row().
mysql_insert_id() returns the ID generated by the last query that inserted a row into a table with an AUTO_INCREMENT index. See mysql_insert_id().
Some queries (LOAD DATA INFILE ..., INSERT INTO ... SELECT ..., UPDATE) return additional information. The result is returned by mysql_info(). See the description for mysql_info() for the format of the string that it returns. mysql_info() returns a NULL pointer if there is no additional information.
If you insert a record into a table that contains an AUTO_INCREMENT column, you can obtain the value stored into that column by calling the mysql_insert_id() function.
You can check if a value was stored into an AUTO_INCREMENT column by executing the following code. This also checks if the query was an INSERT with an AUTO_INCREMENT index:
if (mysql_error(&mysql)[0] == 0 && mysql_num_fields(result) == 0 && mysql_insert_id(&mysql) != 0) { used_id = mysql_insert_id(&mysql); }
For more information, see mysql_insert_id().
When a new AUTO_INCREMENT value has been generated, you can also obtain it by executing a SELECT LAST_INSERT_ID() statement mysql_query() and retrieving the value from the result set returned by the statement.
For LAST_INSERT_ID(), the most recently generated ID is maintained in the server on a per-connection basis. It will not be changed by another client. It will not even be changed if you update another AUTO_INCREMENT column with a non-magic value (that is, a value that is not NULL and not 0).
If you want to use the ID that was generated for one table and insert it into a second table, you can use SQL statements like this:
INSERT INTO foo (auto,text) VALUES(NULL,'text'); # generate ID by inserting NULL INSERT INTO foo2 (id,text) VALUES(LAST_INSERT_ID(),'text'); # use ID in second table
Note that mysql_insert_id() returns the value stored into an AUTO_INCREMENT column, whether that value is automatically generated by storing NULL or 0 or is an explicit value. LAST_INSERT_ID() returns automatically generated AUTO_INCREMENT values. If you store an explicit value other than NULL or 0, it does not affect the value returned by LAST_INSERT_ID().
When linking with the C API, the following errors may occur on some systems:
gcc -g -o client test.o -L/usr/local/lib/mysql -lmysqlclient -lsocket -lnsl Undefined first referenced symbol in file floor /usr/local/lib/mysql/libmysqlclient.a(password.o) ld: fatal: Symbol referencing errors. No output written to client
If this happens on your system, you must include the math library by adding -lm to the end of the compile/link line.
If you compile MySQL clients that you've written yourself or that you obtain from a third-party, they must be linked using the -lmysqlclient -lz option on the link command. You may also need to specify a -L option to tell the linker where to find the library. For example, if the library is installed in /usr/local/mysql/lib, use -L/usr/local/mysql/lib -lmysqlclient -lz on the link command.
For clients that use MySQL header files, you may need to specify a -I option when you compile them (for example, -I/usr/local/mysql/include), so the compiler can find the header files.
To make the above simpler on Unix we have provided the mysql_config script for you. See mysql_config.
You can use this to compile a MySQL client by as follows:
CFG=/usr/local/mysql/bin/mysql_config sh -c "gcc -o progname `$CFG --cflags` progname.c `$CFG --libs`"
The sh -c is need to get the shell to not threat the output from mysql_config as one word.
The client library is almost thread-safe. The biggest problem is that the subroutines in net.c that read from sockets are not interrupt safe. This was done with the thought that you might want to have your own alarm that can break a long read to a server. If you install interrupt handlers for the SIGPIPE interrupt, the socket handling should be thread-safe.
New in 4.0.16: To not abort the program when a connection terminates, MySQL blocks SIGPIPE on the first call to mysql_server_init(), mysql_init() or mysql_connect(). If you want to have your own SIGPIPE handler, you should first call mysql_server_init() and then install your handler. In older versions of MySQL SIGPIPE was blocked, but only in the thread safe client library, for every call to mysql_init().
In the older binaries we distribute on our web site (http://www.mysql.com/), the client libraries are not normally compiled with the thread-safe option (the Windows binaries are by default compiled to be thread-safe). Newer binary distributions should have both a normal and a thread-safe client library.
To get a threaded client where you can interrupt the client from other threads and set timeouts when talking with the MySQL server, you should use the -lmysys, -lmystrings, and -ldbug libraries and the net_serv.o code that the server uses.
If you don't need interrupts or timeouts, you can just compile a thread-safe client library (mysqlclient_r) and use this. See MySQL C API. In this case you don't have to worry about the net_serv.o object file or the other MySQL libraries.
When using a threaded client and you want to use timeouts and interrupts, you can make great use of the routines in the thr_alarm.c file. If you are using routines from the mysys library, the only thing you must remember is to call my_init() first! See C Thread functions.
All functions except mysql_real_connect() are by default thread-safe. The following notes describe how to compile a thread-safe client library and use it in a thread-safe manner. (The notes below for mysql_real_connect() actually apply to mysql_connect() as well, but because mysql_connect() is deprecated, you should be using mysql_real_connect() anyway.)
To make mysql_real_connect() thread-safe, you must recompile the client library with this command:
shell> ./configure --enable-thread-safe-client
This will create a thread-safe client library libmysqlclient_r. (Assuming your OS has a thread-safe gethostbyname_r() function.) This library is thread-safe per connection. You can let two threads share the same connection with the following caveats:
Two threads can't send a query to the MySQL server at the same time on the same connection. In particular, you have to ensure that between a mysql_query() and mysql_store_result() no other thread is using the same connection.
Many threads can access different result sets that are retrieved with mysql_store_result().
If you use mysql_use_result, you have to ensure that no other thread is using the same connection until the result set is closed. However, it really is best for threaded clients that share the same connection to use mysql_store_result().
If you want to use multiple threads on the same connection, you must have a mutex lock around your mysql_query() and mysql_store_result() call combination. Once mysql_store_result() is ready, the lock can be released and other threads may query the same connection.
If you program with POSIX threads, you can use pthread_mutex_lock() and pthread_mutex_unlock() to establish and release a mutex lock.
You need to know the following if you have a thread that is calling MySQL functions which did not create the connection to the MySQL database:
When you call mysql_init() or mysql_connect(), MySQL will create a thread-specific variable for the thread that is used by the debug library (among other things).
If you call a MySQL function, before the thread has called mysql_init() or mysql_connect(), the thread will not have the necessary thread-specific variables in place and you are likely to end up with a core dump sooner or later.
The get things to work smoothly you have to do the following:
Call my_init() at the start of your program if it calls any other MySQL function before calling mysql_real_connect().
Call mysql_thread_init() in the thread handler before calling any MySQL function.
In the thread, call mysql_thread_end() before calling pthread_exit(). This will free the memory used by MySQL thread-specific variables.
You may get some errors because of undefined symbols when linking your client with libmysqlclient_r. In most cases this is because you haven't included the thread libraries on the link/compile line.
The embedded MySQL server library makes it possible to run a full-featured MySQL server inside a client application. The main benefits are increased speed and more simple management for embedded applications.
The embedded server library is based on the client/server version of MySQL, which is written in C/C++. Consequently, the embedded server also is written in C/C++. There is no embedded server available in other languages.
The API is identical for the embedded MySQL version and the client/server version. To change an old threaded application to use the embedded library, you normally only have to add calls to the following functions:
Function | When to call |
mysql_server_init() | Should be called before any other MySQL function is called, preferably early in the main() function. |
mysql_server_end() | Should be called before your program exits. |
mysql_thread_init() | Should be called in each thread you create that will access MySQL. |
mysql_thread_end() | Should be called before calling pthread_exit() |
Then you must link your code with libmysqld.a instead of libmysqlclient.a.
The above mysql_server_xxx functions are also included in libmysqlclient.a to allow you to change between the embedded and the client/server version by just linking your application with the right library. See mysql_server_init().
To get a libmysqld library you should configure MySQL with the --with-embedded-server option.
When you link your program with libmysqld, you must also include the system-specific pthread libraries and some libraries that the MySQL server uses. You can get the full list of libraries by executing mysql_config --libmysqld-libs.
The correct flags for compiling and linking a threaded program must be used, even if you do not directly call any thread functions in your code.
The embedded server has the following limitations:
No support for ISAM tables. (This is mainly done to make the library smaller)
No user-defined functions (UDFs).
No stack trace on core dump.
No internal RAID support. (This is not normally needed as most OS has nowadays support for big files).
You cannot set this up as a master or a slave (no replication).
You can't connect to an embedded server from an outside process with sockets or TCP/IP.
Some of these limitations can be changed by editing the mysql_embed.h include file and recompiling MySQL.
The following is the recommended way to use option files to make it easy to switch between a client/server application and one where MySQL is embedded. See Option files.
Put common options in the [server] section. These will be read by both MySQL versions.
Put client/server-specific options in the [mysqld] section.
Put embedded MySQL-specific options in the [embedded] section.
Put application-specific options in a [ApplicationName_SERVER] section.
We are going to provide options to leave out some parts of MySQL to make the library smaller.
There is still a lot of speed optimization to do.
Errors are written to stderr. We will add an option to specify a filename for these.
We have to change InnoDB to not be so verbose when using in the embedded version.
This example program and makefile should work without any changes on a Linux or FreeBSD system. For other operating systems, minor changes will be needed. This example is designed to give enough details to understand the problem, without the clutter that is a necessary part of a real application.
To try out the example, create an test_libmysqld directory at the same level as the mysql-4.0 source directory. Save the test_libmysqld.c source and the GNUmakefile in the directory, and run GNU make from inside the test_libmysqld directory.
test_libmysqld.c
/* * A simple example client, using the embedded MySQL server library */ #include <mysql.h> #include <stdarg.h> #include <stdio.h> #include <stdlib.h> MYSQL *db_connect(const char *dbname); void db_disconnect(MYSQL *db); void db_do_query(MYSQL *db, const char *query); const char *server_groups[] = { "test_libmysqld_SERVER", "embedded", "server", NULL }; int main(int argc, char **argv) { MYSQL *one, *two; /* mysql_server_init() must be called before any other mysql * functions. * * You can use mysql_server_init(0, NULL, NULL), and it will * initialize the server using groups = { * "server", "embedded", NULL * }. * * In your $HOME/.my.cnf file, you probably want to put: [test_libmysqld_SERVER] language = /path/to/source/of/mysql/sql/share/english * You could, of course, modify argc and argv before passing * them to this function. Or you could create new ones in any * way you like. But all of the arguments in argv (except for * argv[0], which is the program name) should be valid options * for the MySQL server. * * If you link this client against the normal mysqlclient * library, this function is just a stub that does nothing. */ mysql_server_init(argc, argv, (char **)server_groups); one = db_connect("test"); two = db_connect(NULL); db_do_query(one, "SHOW TABLE STATUS"); db_do_query(two, "SHOW DATABASES"); mysql_close(two); mysql_close(one); /* This must be called after all other mysql functions */ mysql_server_end(); exit(EXIT_SUCCESS); } static void die(MYSQL *db, char *fmt, ...) { va_list ap; va_start(ap, fmt); vfprintf(stderr, fmt, ap); va_end(ap); (void)putc('\n', stderr); if (db) db_disconnect(db); exit(EXIT_FAILURE); } MYSQL * db_connect(const char *dbname) { MYSQL *db = mysql_init(NULL); if (!db) die(db, "mysql_init failed: no memory"); /* * Notice that the client and server use separate group names. * This is critical, because the server will not accept the * client's options, and vice versa. */ mysql_options(db, MYSQL_READ_DEFAULT_GROUP, "test_libmysqld_CLIENT"); if (!mysql_real_connect(db, NULL, NULL, NULL, dbname, 0, NULL, 0)) die(db, "mysql_real_connect failed: %s", mysql_error(db)); return db; } void db_disconnect(MYSQL *db) { mysql_close(db); } void db_do_query(MYSQL *db, const char *query) { if (mysql_query(db, query) != 0) goto err; if (mysql_field_count(db) > 0) { MYSQL_RES *res; MYSQL_ROW row, end_row; int num_fields; if (!(res = mysql_store_result(db))) goto err; num_fields = mysql_num_fields(res); while ((row = mysql_fetch_row(res))) { (void)fputs(">> ", stdout); for (end_row = row + num_fields; row < end_row; ++row) (void)printf("%s\t", row ? (char*)*row : "NULL"); (void)fputc('\n', stdout); } (void)fputc('\n', stdout); mysql_free_result(res); } else (void)printf("Affected rows: %lld\n", mysql_affected_rows(db)); return; err: die(db, "db_do_query failed: %s [%s]", mysql_error(db), query); }
GNUmakefile
# This assumes the MySQL software is installed in /usr/local/mysql inc := /usr/local/mysql/include/mysql lib := /usr/local/mysql/lib # If you have not installed the MySQL software yet, try this instead #inc := $(HOME)/mysql-4.0/include #lib := $(HOME)/mysql-4.0/libmysqld CC := gcc CPPFLAGS := -I$(inc) -D_THREAD_SAFE -D_REENTRANT CFLAGS := -g -W -Wall LDFLAGS := -static # You can change -lmysqld to -lmysqlclient to use the # client/server library LDLIBS = -L$(lib) -lmysqld -lz -lm -lcrypt ifneq (,$(shell grep FreeBSD /COPYRIGHT 2>/dev/null)) # FreeBSD LDFLAGS += -pthread else # Assume Linux LDLIBS += -lpthread endif # This works for simple one-file test programs sources := $(wildcard *.c) objects := $(patsubst %c,%o,$(sources)) targets := $(basename $(sources)) all: $(targets) clean: rm -f $(targets) $(objects) *.core
The MySQL source code is covered by the GNU GPL license (see GPL license). One result of this is that any program which includes, by linking with libmysqld, the MySQL source code must be released as free software (under a license compatible with the GPL).
We encourage everyone to promote free software by releasing code under the GPL or a compatible license. For those who are not able to do this, another option is to purchase a commercial license for the MySQL code from MySQL AB. For details, please see MySQL licenses.
Table of Contents
MySQL provides support for ODBC by means of the MyODBC program. This chapter will teach you how to install MyODBC, and how to use it. Here, you will also find a list of common programs that are known to work with MyODBC.
MyODBC 2.50 is a 32-bit ODBC 2.50 specification level 0 (with level 1 and level 2 features) driver for connecting an ODBC-aware application to MySQL. MyODBC works on Windows 9x/Me/NT/2000/XP and most Unix platforms. MyODBC 3.51 is an enhanced version with ODBC 3.5x specification level 1 (complete core API + level 2 features).
MyODBC is Open Source, and you can find the newest version at http://www.mysql.com/downloads/api-myodbc.html. Please note that the 2.50.x versions are LGPL licensed, whereas the 3.51.x versions are GPL licensed.
If you have problem with MyODBC and your program also works with OLEDB, you should try the OLEDB driver.
Normally you only need to install MyODBC on Windows machines. You only need MyODBC for Unix if you have a program like ColdFusion that is running on the Unix machine and uses ODBC to connect to the databases.
If you want to install MyODBC on a Unix box, you will also need an ODBC manager. MyODBC is known to work with most of the Unix ODBC managers.
To install MyODBC on Windows, you should download the appropriate MyODBC .zip file, unpack it with WinZip or some similar program, and execute the SETUP.EXE file.
On Windows/NT/XP you may get the following error when trying to install MyODBC:
An error occurred while copying C:\WINDOWS\SYSTEM\MFC30.DLL. Restart Windows and try installing again (before running any applications which use ODBC)
The problem in this case is that some other program is using ODBC and because of how Windows is designed, you may not in this case be able to install a new ODBC drivers with Microsoft's ODBC setup program. In most cases you can continue by just pressing Ignore to copy the rest of the MyODBC files and the final installation should still work. If this doesn't work, the solution is to reboot your computer in ``safe mode`` (Choose this by pressing F8 just before your machine starts Windows during rebooting), install MyODBC, and reboot to normal mode.
To make a connection to a Unix box from a Windows box, with an ODBC application (one that doesn't support MySQL natively), you must first install MyODBC on the Windows machine.
The user and Windows machine must have the access privileges to the MySQL server on the Unix machine. This is set up with the GRANT command. See GRANT.
You must create an ODBC DSN entry as follows:
Open the Control Panel on the Windows machine.
Double-click the ODBC Data Sources 32-bit icon.
Click the tab User DSN.
Click the button Add.
Select MySQL in the screen Create New Data Source and click the Finish button.
The MySQL Driver default configuration screen is shown. See ODBC administrator.
Now start your application and select the ODBC driver with the DSN you specified in the ODBC administrator.
Notice that there are other configuration options on the screen of MySQL (trace, don't prompt on connect, etc) that you can try if you run into problems.
There are three possibilities for specifying the server name on Windows95:
Use the IP address of the server.
Add a file \windows\lmhosts with the following information:
ip hostname
For example:
194.216.84.21 my_hostname
Configure the PC to use DNS.
Example of how to fill in the ODBC setup:
Windows DSN name: test Description: This is my test database MySQL Database: test Server: 194.216.84.21 User: monty Password: my_password Port:
The value for the Windows DSN name field is any name that is unique in your Windows ODBC setup.
You don't have to specify values for the Server, User, Password, or Port fields in the ODBC setup screen. However, if you do, the values will be used as the defaults later when you attempt to make a connection. You have the option of changing the values at that time.
If the port number is not given, the default port (3306) is used.
If you specify the option Read options from C:\my.cnf, the groups client and odbc will be read from the C:\my.cnf file. You can use all options that are usable by mysql_options(). See mysql_options().
One can specify the following parameters for MyODBC on the [Servername] section of an ODBC.INI file or through the InConnectionString argument in the SQLDriverConnect() call.
Parameter | Default value | Comment |
user | ODBC (on Windows) | The username used to connect to MySQL. |
server | localhost | The hostname of the MySQL server. |
database | The default database. | |
option | 0 | A integer by which you can specify how MyODBC should work. See below. |
port | 3306 | The TCP/IP port to use if server is not localhost. |
stmt | A statement that will be executed when connecting to MySQL. | |
password | The password for the serveruser combination. | |
socket | The socket or Windows pipe to connect to. |
The option argument is used to tell MyODBC that the client isn't 100% ODBC compliant. On Windows, one normally sets the option flag by toggling the different options on the connection screen but one can also set this in the option argument. The following options are listed in the same order as they appear in the MyODBC connect screen:
Bit | Description |
1 | The client can't handle that MyODBC returns the real width of a column. |
2 | The client can't handle that MySQL returns the true value of affected rows. If this flag is set then MySQL returns 'found rows' instead. One must have MySQL 3.21.14 or newer to get this to work. |
4 | Make a debug log in c:\myodbc.log. This is the same as putting MYSQL_DEBUG=d:t:O,c::\myodbc.log in AUTOEXEC.BAT |
8 | Don't set any packet limit for results and parameters. |
16 | Don't prompt for questions even if driver would like to prompt |
32 | Simulate a ODBC 1.0 driver in some context. |
64 | Ignore use of database name in 'database.table.column'. |
128 | Force use of ODBC manager cursors (experimental). |
256 | Disable the use of extended fetch (experimental). |
512 | Pad CHAR fields to full column length. |
1024 | SQLDescribeCol() will return fully qualified column names |
2048 | Use the compressed server/client protocol |
4096 | Tell server to ignore space after function name and before '(' (needed by PowerBuilder). This will make all function names keywords! |
8192 | Connect with named pipes to a mysqld server running on NT. |
16384 | Change LONGLONG columns to INT columns (some applications can't handle LONGLONG). |
32768 | Return 'user' as Table_qualifier and Table_owner from SQLTables (experimental) |
65536 | Read parameters from the client and odbc groups from my.cnf |
131072 | Add some extra safety checks (should not bee needed but...) |
If you want to have many options, you should add the above flags! For example setting option to 12 (4+8) gives you debugging without package limits!
The default MYODBC.DLL is compiled for optimal performance. If you want to debug MyODBC (for example to enable tracing), you should instead use MYODBCD.DLL. To install this file, copy MYODBCD.DLL over the installed MYODBC.DLL file.
MyODBC has been tested with Access, Admndemo.exe, C++-Builder, Borland Builder 4, Centura Team Developer (formerly Gupta SQL/Windows), ColdFusion (on Solaris and NT with svc pack 5), Crystal Reports, DataJunction, Delphi, ERwin, Excel, iHTML, FileMaker Pro, FoxPro, Notes 4.5/4.6, SBSS, Perl DBD-ODBC, Paradox, Powerbuilder, Powerdesigner 32 bit, VC++, and Visual Basic.
If you know of any other applications that work with MyODBC, please send mail to the myodbc mailing list about this! See Mailing-list.
With some programs you may get an error like: Another user has modifies the record that you have modified. In most cases this can be solved by doing one of the following things:
Add a primary key for the table if there isn't one already.
Add a timestamp column if there isn't one already.
Only use double float fields. Some programs may fail when they compare single floats.
If the above doesn't help, you should do a MyODBC trace file and try to figure out why things go wrong.
Most programs should work with MyODBC, but for each of those listed here, we have tested it ourselves or received confirmation from some user that it works:
Program | Comment |
Access |
To make Access work:
|
ADO |
When you are coding with the ADO API and MyODBC you need to put
attention in some default properties that aren't supported by the
MySQL server. For example, using the CursorLocation Property as adUseServer will return for the RecordCount Property a result of -1. To have the right value, you need to set this
property to adUseClient, like is showing in the VB code here:
Dim myconn As New ADODB.Connection Dim myrs As New Recordset Dim mySQL As String Dim myrows As Long myconn.Open "DSN=MyODBCsample" mySQL = "SELECT * from user" myrs.Source = mySQL Set myrs.ActiveConnection = myconn myrs.CursorLocation = adUseClient myrs.Open myrows = myrs.RecordCount myrs.Close myconn.CloseAnother workaround is to use a SELECT COUNT(*) statement for a similar query to get the correct row count. |
Active server pages (ASP) | You should use the option flag Return matching rows. |
BDE applications | To get these to work, you should set the option flags Don't optimize column widths and Return matching rows. |
Borland Builder 4 | When you start a query you can use the property Active or use the method Open. Note that Active will start by automatically issuing a SELECT * FROM ... query that may not be a good thing if your tables are big! |
ColdFusion (On Unix) | The following information is taken from the ColdFusion documentation: Use the following information to configure ColdFusion Server for Linux to use the unixODBC driver with MyODBC for MySQL data sources. Allaire has verified that MyODBC Version 2.50.26 works with MySQL Version 3.22.27 and ColdFusion for Linux. (Any newer version should also work.) You can download MyODBC at http://www.mysql.com/downloads/api-myodbc.html ColdFusion Version 4.5.1 allows you to us the ColdFusion Administrator to add the MySQL data source. However, the driver is not included with ColdFusion Version 4.5.1. Before the MySQL driver will appear in the ODBC datasources drop-down list, you must build and copy the MyODBC driver to /opt/coldfusion/lib/libmyodbc.so. The Contrib directory contains the program mydsn-xxx.zip which allows you to build and remove the DSN registry file for the MyODBC driver on Coldfusion applications. |
DataJunction | You have to change it to output VARCHAR rather than ENUM, as it exports the latter in a manner that causes MySQL grief. |
Excel |
Works. A few tips:
|
Word |
To retrieve data from MySQL to Word/Excel documents, you need to
use the MyODBC driver and the Add-in Microsoft Query help.
For example, create a db with a table containing 2 columns of text:
|
odbcadmin | Test program for ODBC. |
Delphi |
You must use BDE Version 3.2 or newer. Set the Don't optimize column width
option field when connecting to MySQL.
Also, here is some potentially useful Delphi code that sets up both an
ODBC entry and a BDE entry for MyODBC (the BDE entry requires a BDE
Alias Editor that is free at a Delphi Super Page near
you. (Thanks to Bryan Brunton <bryan@flesherfab.com> for this):
fReg:= TRegistry.Create; fReg.OpenKey('\Software\ODBC\ODBC.INI\DocumentsFab', True); fReg.WriteString('Database', 'Documents'); fReg.WriteString('Description', ' '); fReg.WriteString('Driver', 'C:\WINNT\System32\myodbc.dll'); fReg.WriteString('Flag', '1'); fReg.WriteString('Password', ''); fReg.WriteString('Port', ' '); fReg.WriteString('Server', 'xmark'); fReg.WriteString('User', 'winuser'); fReg.OpenKey('\Software\ODBC\ODBC.INI\ODBC Data Sources', True); fReg.WriteString('DocumentsFab', 'MySQL'); fReg.CloseKey; fReg.Free; Memo1.Lines.Add('DATABASE NAME='); Memo1.Lines.Add('USER NAME='); Memo1.Lines.Add('ODBC DSN=DocumentsFab'); Memo1.Lines.Add('OPEN MODE=READ/WRITE'); Memo1.Lines.Add('BATCH COUNT=200'); Memo1.Lines.Add('LANGDRIVER='); Memo1.Lines.Add('MAX ROWS=-1'); Memo1.Lines.Add('SCHEMA CACHE DIR='); Memo1.Lines.Add('SCHEMA CACHE SIZE=8'); Memo1.Lines.Add('SCHEMA CACHE TIME=-1'); Memo1.Lines.Add('SQLPASSTHRU MODE=SHARED AUTOCOMMIT'); Memo1.Lines.Add('SQLQRYMODE='); Memo1.Lines.Add('ENABLE SCHEMA CACHE=FALSE'); Memo1.Lines.Add('ENABLE BCD=FALSE'); Memo1.Lines.Add('ROWSET SIZE=20'); Memo1.Lines.Add('BLOBS TO CACHE=64'); Memo1.Lines.Add('BLOB SIZE=32'); AliasEditor.Add('DocumentsFab','MySQL',Memo1.Lines); |
C++ Builder | Tested with BDE Version 3.0. The only known problem is that when the table schema changes, query fields are not updated. BDE, however, does not seem to recognize primary keys, only the index PRIMARY, though this has not been a problem. |
Vision | You should use the option flag Return matching rows. |
Visual Basic | To be able to update a table, you must define a primary key for the table. Visual Basic with ADO can't handle big integers. This means that some queries like SHOW PROCESSLIST will not work properly. The fix is to set the option OPTION=16384 in the ODBC connect string or to set the Change BIGINT columns to INT option in the MyODBC connect screen. You may also want to set the Return matching rows option. |
VisualInterDev | If you get the error [Microsoft][ODBC Driver Manager] Driver does not support this parameter the reason may be that you have a BIGINT in your result. Try setting the Change BIGINT columns to INT option in the MyODBC connect screen. |
Visual Objects | You should use the option flag Don't optimize column widths. |
A common problem is how to get the value of an automatically generated ID from an INSERT. With ODBC, you can do something like this (assuming that auto is an AUTO_INCREMENT field):
INSERT INTO foo (auto,text) VALUES(NULL,'text'); SELECT LAST_INSERT_ID();
Or, if you are just going to insert the ID into another table, you can do this:
INSERT INTO foo (auto,text) VALUES(NULL,'text'); INSERT INTO foo2 (id,text) VALUES(LAST_INSERT_ID(),'text');
See Getting unique ID.
For the benefit of some ODBC applications (at least Delphi and Access), the following query can be used to find a newly inserted row:
SELECT * FROM tbl_name WHERE auto IS NULL;
If you encounter difficulties with MyODBC, you should start by making a log file from the ODBC manager (the log you get when requesting logs from ODBCADMIN) and a MyODBC log.
To get a MyODBC log, you need to do the following:
Ensure that you are using myodbcd.dll and not myodbc.dll. The easiest way to do this is to get myodbcd.dll from the MyODBC distribution and copy it over the myodbc.dll, which is probably in your C:\windows\system32 or C:\winnt\system32 directory.
Note that you probably want to restore the old myodbc.dll file when you have finished testing, as it is a lot faster than myodbcd.dll.
Select the ``Trace MyODBC'' option in the MyODBC connect/configure screen. The log will be written to the file C:\myodbc.log.
If the trace option is not remembered the next time you visit this screen, it means that you are not using the myodbcd.dll driver. Reread the previous step to verify that you have installed myodbcd.dll.
Start your application and try to get it to fail.
Check the MyODBC trace file, to find out what could be wrong. You should be able to determine what statements were issued by searching for the string >mysql_real_query in the myodbc.log file.
You should also try issuing the statements from the mysql client program or from admndemo. This will help you determine whether the error is in MyODBC or MySQL.
If you find out something is wrong, please only send the relevant rows (max 40 rows) to the myodbc mailing list. See Mailing-list. Please never send the whole MyODBC or ODBC log file!
If you are unable to find out what's wrong, the last option is to make an archive in tar or ZIP format that contains a MyODBC trace file, the ODBC log file, and a README file that explains the problem. You can send this to ftp://support.mysql.com/pub/mysql/secret/. Only we at MySQL AB will have access to the files you upload, and we will be very discreet with the data!
If you can create a program that also demonstrates the problem, please include it in the archive as well.
If the program works with some other SQL server, you should include an ODBC log file where you do exactly the same thing in the other SQL server.
Remember that the more information you can supply to us, the more likely it is that we can fix the problem!
There are 2 supported JDBC drivers for MySQL:
MySQL Connector/J from MySQL AB, implemented in 100% native Java. This product was formerly known as the mm.mysql driver. You can download MySQL Connector/J from http://www.mysql.com/products/connector-j/.
The Resin JDBC driver, which can be found at http://www.caucho.com/projects/jdbc-mysql/index.xtp.
For more information, consult any general JDBC documentation, plus each driver's own documentation for MySQL-specific features.
Documentation for MySQL Connector/J is available online at the MySQL AB web site at http://www.mysql.com/documentation/.
Table of Contents
PHP is a server-side, HTML-embedded scripting language that may be used to create dynamic web pages. It contains support for accessing several databases, including MySQL. PHP may be run as a separate program or compiled as a module for use with the Apache web server.
The distribution and documentation are available at the PHP web site (http://www.php.net/).
Error: "Maximum Execution Time Exceeded" This is a PHP limit; go into the php.ini file and set the maximum execution time up from 30 seconds to something higher, as needed. It is also not a bad idea to double the RAM allowed per script to 16 MB instead of 8 MB.
Error: "Fatal error: Call to unsupported or undefined function mysql_connect() in .." This means that your PHP version isn't compiled with MySQL support. You can either compile a dynamic MySQL module and load it into PHP or recompile PHP with built-in MySQL support. This is described in detail in the PHP manual.
Error: "undefined reference to `uncompress'" This means that the client library is compiled with support for a compressed client/server protocol. The fix is to add -lz last when linking with -lmysqlclient.
The Perl DBI module provides a generic interface for database access. You can write a DBI script that works with many different database engines without change. To use DBI, you must install the DBI module, as well as a DataBase Driver (DBD) module for each type of server you want to access. For MySQL, this driver is the DBD::mysql module.
Perl DBI is now the recommended Perl interface. It replaces an older interface called mysqlperl, which should be considered obsolete.
Installation instructions for Perl DBI support are given in Perl support.
DBI information is available at the command line, online, or in printed form:
Once you have the DBI and DBD::mysql modules installed, you can get information about them at the command line with the perldoc command:
shell> perldoc DBI shell> perldoc DBI::FAQ shell> perldoc DBD::mysql
You can also use pod2man, pod2html, and so forth to translate this information into other formats.
For online information about Perl DBI, visit the DBI web site, http://dbi.perl.org/.
For printed information, the official DBI book is Programming the Perl DBI (Alligator Descartes and Tim Bunce, O'Reilly & Associates, 2000). Information about the book is available at the DBI web site, http://dbi.perl.org/.
For information that focuses specifically on using DBI with MySQL, see MySQL and Perl for the Web (Paul DuBois, New Riders, 2001). This book's web site is http://www.kitebird.com/mysql-perl/.
Table of Contents
MySQL++ is the MySQL API for C++. More information can be found at http://www.mysql.com/products/mysql++/.
You can compile the MySQL Windows source with Borland C++ 5.02. (The Windows source includes only projects for Microsoft VC++, for Borland C++ you have to do the project files yourself.)
One known problem with Borland C++ is that it uses a different structure alignment than VC++. This means that you will run into problems if you try to use the default libmysql.dll libraries (that was compiled with VC++) with Borland C++. You can do one of the following to avoid this problem.
You can use the static MySQL libraries for Borland C++ that you can find on http://www.mysql.com/downloads/os-win32.html.
Only call mysql_init() with NULL as an argument, not a pre-allocated MYSQL structure.
MySQLdb provides MySQL support for Python, compliant with the Python DB API version 2.0. It can be found at http://sourceforge.net/projects/mysql-python/.
MySQLtcl is a simple API for accessing a MySQL database server from the Tcl programming language. It can be found at http://www.xdobry.de/mysqltcl/.
Eiffel MySQL is an interface to the MySQL database server using the Eiffel programming language, written by Michael Ravits. It can be found at http://efsa.sourceforge.net/archive/ravits/mysql.htm.
Table of Contents
This chapter describes how MySQL handles errors.
Following are error codes that may appear when you call MySQL from any host language.
The Name and Error Code columns correspond to definitions in the MySQL source code file: include/mysqld_error.h
The SQLSTATE column corresponds to definitions in the MySQL source code file: include/sql_state.h
The SQLSTATE error code will appear only if you use MySQL version 4.1. SQLSTATE codes were added for compatibility with X/Open / ANSI / ODBC behavior.
A suggested text for each error code can be found in the error-message file: share/english/errmsg.sys
Because updates are frequent, it is possible that the above sources will contain additional error codes.
Name | Error Code | SQLSTATE |
ER_HASHCHK | 1000 | HY000 |
ER_NISAMCHK | 1001 | HY000 |
ER_NO | 1002 | HY000 |
ER_YES | 1003 | HY000 |
ER_CANT_CREATE_FILE | 1004 | HY000 |
ER_CANT_CREATE_TABLE | 1005 | HY000 |
ER_CANT_CREATE_DB | 1006 | HY000 |
ER_DB_CREATE_EXISTS | 1007 | HY000 |
ER_DB_DROP_EXISTS | 1008 | HY000 |
ER_DB_DROP_DELETE | 1009 | HY000 |
ER_DB_DROP_RMDIR | 1010 | HY000 |
ER_CANT_DELETE_FILE | 1011 | HY000 |
ER_CANT_FIND_SYSTEM_REC | 1012 | HY000 |
ER_CANT_GET_STAT | 1013 | HY000 |
ER_CANT_GET_WD | 1014 | HY000 |
ER_CANT_LOCK | 1015 | HY000 |
ER_CANT_OPEN_FILE | 1016 | HY000 |
ER_FILE_NOT_FOUND | 1017 | HY000 |
ER_CANT_READ_DIR | 1018 | HY000 |
ER_CANT_SET_WD | 1019 | HY000 |
ER_CHECKREAD | 1020 | HY000 |
ER_DISK_FULL | 1021 | HY000 |
ER_DUP_KEY | 1022 | 23000 |
ER_ERROR_ON_CLOSE | 1023 | HY000 |
ER_ERROR_ON_READ | 1024 | HY000 |
ER_ERROR_ON_RENAME | 1025 | HY000 |
ER_ERROR_ON_WRITE | 1026 | HY000 |
ER_FILE_USED | 1027 | HY000 |
ER_FILSORT_ABORT | 1028 | HY000 |
ER_FORM_NOT_FOUND | 1029 | HY000 |
ER_GET_ERRNO | 1030 | HY000 |
ER_ILLEGAL_HA | 1031 | HY000 |
ER_KEY_NOT_FOUND | 1032 | HY000 |
ER_NOT_FORM_FILE | 1033 | HY000 |
ER_NOT_KEYFILE | 1034 | HY000 |
ER_OLD_KEYFILE | 1035 | HY000 |
ER_OPEN_AS_READONLY | 1036 | HY000 |
ER_OUTOFMEMORY | 1037 | HY001 |
ER_OUT_OF_SORTMEMORY | 1038 | HY001 |
ER_UNEXPECTED_EOF | 1039 | HY000 |
ER_CON_COUNT_ERROR | 1040 | 08004 |
ER_OUT_OF_RESOURCES | 1041 | 08004 |
ER_BAD_HOST_ERROR | 1042 | 08S01 |
ER_HANDSHAKE_ERROR | 1043 | 08S01 |
ER_DBACCESS_DENIED_ERROR | 1044 | 42000 |
ER_ACCESS_DENIED_ERROR | 1045 | 42000 |
ER_NO_DB_ERROR | 1046 | 42000 |
ER_UNKNOWN_COM_ERROR | 1047 | 08S01 |
ER_BAD_NULL_ERROR | 1048 | 23000 |
ER_BAD_DB_ERROR | 1049 | 42000 |
ER_TABLE_EXISTS_ERROR | 1050 | 42S01 |
ER_BAD_TABLE_ERROR | 1051 | 42S02 |
ER_NON_UNIQ_ERROR | 1052 | 23000 |
ER_SERVER_SHUTDOWN | 1053 | 08S01 |
ER_BAD_FIELD_ERROR | 1054 | 42S22 |
ER_WRONG_FIELD_WITH_GROUP | 1055 | 42000 |
ER_WRONG_GROUP_FIELD | 1056 | 42000 |
ER_WRONG_SUM_SELECT | 1057 | 42000 |
ER_WRONG_VALUE_COUNT | 1058 | 21S01 |
ER_TOO_LONG_IDENT | 1059 | 42000 |
ER_DUP_FIELDNAME | 1060 | 42S21 |
ER_DUP_KEYNAME | 1061 | 42000 |
ER_DUP_ENTRY | 1062 | 23000 |
ER_WRONG_FIELD_SPEC | 1063 | 42000 |
ER_PARSE_ERROR | 1064 | 42000 |
ER_EMPTY_QUERY | 1065 | 42000 |
ER_NONUNIQ_TABLE | 1066 | 42000 |
ER_INVALID_DEFAULT | 1067 | 42000 |
ER_MULTIPLE_PRI_KEY | 1068 | 42000 |
ER_TOO_MANY_KEYS | 1069 | 42000 |
ER_TOO_MANY_KEY_PARTS | 1070 | 42000 |
ER_TOO_LONG_KEY | 1071 | 42000 |
ER_KEY_COLUMN_DOES_NOT_EXITS | 1072 | 42000 |
ER_BLOB_USED_AS_KEY | 1073 | 42000 |
ER_TOO_BIG_FIELDLENGTH | 1074 | 42000 |
ER_WRONG_AUTO_KEY | 1075 | 42000 |
ER_READY | 1076 | 00000 |
ER_NORMAL_SHUTDOWN | 1077 | 00000 |
ER_GOT_SIGNAL | 1078 | 00000 |
ER_SHUTDOWN_COMPLETE | 1079 | 00000 |
ER_FORCING_CLOSE | 1080 | 08S01 |
ER_IPSOCK_ERROR | 1081 | 08S01 |
ER_NO_SUCH_INDEX | 1082 | 42S12 |
ER_WRONG_FIELD_TERMINATORS | 1083 | 42000 |
ER_BLOBS_AND_NO_TERMINATED | 1084 | 42000 |
ER_TEXTFILE_NOT_READABLE | 1085 | HY000 |
ER_FILE_EXISTS_ERROR | 1086 | HY000 |
ER_LOAD_INFO | 1087 | HY000 |
ER_ALTER_INFO | 1088 | HY000 |
ER_WRONG_SUB_KEY | 1089 | HY000 |
ER_CANT_REMOVE_ALL_FIELDS | 1090 | 42000 |
ER_CANT_DROP_FIELD_OR_KEY | 1091 | 42000 |
ER_INSERT_INFO | 1092 | HY000 |
ER_UPDATE_TABLE_USED | 1093 | HY000 |
ER_NO_SUCH_THREAD | 1094 | HY000 |
ER_KILL_DENIED_ERROR | 1095 | HY000 |
ER_NO_TABLES_USED | 1096 | HY000 |
ER_TOO_BIG_SET | 1097 | HY000 |
ER_NO_UNIQUE_LOGFILE | 1098 | HY000 |
ER_TABLE_NOT_LOCKED_FOR_WRITE | 1099 | HY000 |
ER_TABLE_NOT_LOCKED | 1100 | HY000 |
ER_BLOB_CANT_HAVE_DEFAULT | 1101 | 42000 |
ER_WRONG_DB_NAME | 1102 | 42000 |
ER_WRONG_TABLE_NAME | 1103 | 42000 |
ER_TOO_BIG_SELECT | 1104 | 42000 |
ER_UNKNOWN_ERROR | 1105 | HY000 |
ER_UNKNOWN_PROCEDURE | 1106 | 42000 |
ER_WRONG_PARAMCOUNT_TO_PROCEDURE | 1107 | 42000 |
ER_WRONG_PARAMETERS_TO_PROCEDURE | 1108 | HY000 |
ER_UNKNOWN_TABLE | 1109 | 42S02 |
ER_FIELD_SPECIFIED_TWICE | 1110 | 42000 |
ER_INVALID_GROUP_FUNC_USE | 1111 | 42000 |
ER_UNSUPPORTED_EXTENSION | 1112 | 42000 |
ER_TABLE_MUST_HAVE_COLUMNS | 1113 | 42000 |
ER_RECORD_FILE_FULL | 1114 | HY000 |
ER_UNKNOWN_CHARACTER_SET | 1115 | 42000 |
ER_TOO_MANY_TABLES | 1116 | HY000 |
ER_TOO_MANY_FIELDS | 1117 | HY000 |
ER_TOO_BIG_ROWSIZE | 1118 | 42000 |
ER_STACK_OVERRUN | 1119 | HY000 |
ER_WRONG_OUTER_JOIN | 1120 | 42000 |
ER_NULL_COLUMN_IN_INDEX | 1121 | 42000 |
ER_CANT_FIND_UDF | 1122 | HY000 |
ER_CANT_INITIALIZE_UDF | 1123 | HY000 |
ER_UDF_NO_PATHS | 1124 | HY000 |
ER_UDF_EXISTS | 1125 | HY000 |
ER_CANT_OPEN_LIBRARY | 1126 | HY000 |
ER_CANT_FIND_DL_ENTRY | 1127 | HY000 |
ER_FUNCTION_NOT_DEFINED | 1128 | HY000 |
ER_HOST_IS_BLOCKED | 1129 | HY000 |
ER_HOST_NOT_PRIVILEGED | 1130 | HY000 |
ER_PASSWORD_ANONYMOUS_USER | 1131 | 42000 |
ER_PASSWORD_NOT_ALLOWED | 1132 | 42000 |
ER_PASSWORD_NO_MATCH | 1133 | 42000 |
ER_UPDATE_INFO | 1134 | HY000 |
ER_CANT_CREATE_THREAD | 1135 | HY000 |
ER_WRONG_VALUE_COUNT_ON_ROW | 1136 | 21S01 |
ER_CANT_REOPEN_TABLE | 1137 | HY000 |
ER_INVALID_USE_OF_NULL | 1138 | 42000 |
ER_REGEXP_ERROR | 1139 | 42000 |
ER_MIX_OF_GROUP_FUNC_AND_FIELDS | 1140 | 42000 |
ER_NONEXISTING_GRANT | 1141 | 42000 |
ER_TABLEACCESS_DENIED_ERROR | 1142 | 42000 |
ER_COLUMNACCESS_DENIED_ERROR | 1143 | 42000 |
ER_ILLEGAL_GRANT_FOR_TABLE | 1144 | 42000 |
ER_GRANT_WRONG_HOST_OR_USER | 1145 | 42000 |
ER_NO_SUCH_TABLE | 1146 | 42S02 |
ER_NONEXISTING_TABLE_GRANT | 1147 | 42000 |
ER_NOT_ALLOWED_COMMAND | 1148 | 42000 |
ER_SYNTAX_ERROR | 1149 | 42000 |
ER_DELAYED_CANT_CHANGE_LOCK | 1150 | HY000 |
ER_TOO_MANY_DELAYED_THREADS | 1151 | HY000 |
ER_ABORTING_CONNECTION | 1152 | 08S01 |
ER_NET_PACKET_TOO_LARGE | 1153 | 08S01 |
ER_NET_READ_ERROR_FROM_PIPE | 1154 | 08S01 |
ER_NET_FCNTL_ERROR | 1155 | 08S01 |
ER_NET_PACKETS_OUT_OF_ORDER | 1156 | 08S01 |
ER_NET_UNCOMPRESS_ERROR | 1157 | 08S01 |
ER_NET_READ_ERROR | 1158 | 08S01 |
ER_NET_READ_INTERRUPTED | 1159 | 08S01 |
ER_NET_ERROR_ON_WRITE | 1160 | 08S01 |
ER_NET_WRITE_INTERRUPTED | 1161 | 08S01 |
ER_TOO_LONG_STRING | 1162 | 42000 |
ER_TABLE_CANT_HANDLE_BLOB | 1163 | 42000 |
ER_TABLE_CANT_HANDLE_AUTO_INCREMENT | 1164 | 42000 |
ER_DELAYED_INSERT_TABLE_LOCKED | 1165 | HY000 |
ER_WRONG_COLUMN_NAME | 1166 | 42000 |
ER_WRONG_KEY_COLUMN | 1167 | 42000 |
ER_WRONG_MRG_TABLE | 1168 | HY000 |
ER_DUP_UNIQUE | 1169 | 23000 |
ER_BLOB_KEY_WITHOUT_LENGTH | 1170 | 42000 |
ER_PRIMARY_CANT_HAVE_NULL | 1171 | 42000 |
ER_TOO_MANY_ROWS | 1172 | 42000 |
ER_REQUIRES_PRIMARY_KEY | 1173 | 42000 |
ER_NO_RAID_COMPILED | 1174 | HY000 |
ER_UPDATE_WITHOUT_KEY_IN_SAFE_MODE | 1175 | HY000 |
ER_KEY_DOES_NOT_EXITS | 1176 | HY000 |
ER_CHECK_NO_SUCH_TABLE | 1177 | 42000 |
ER_CHECK_NOT_IMPLEMENTED | 1178 | 42000 |
ER_CANT_DO_THIS_DURING_AN_TRANSACTION | 1179 | 25000 |
ER_ERROR_DURING_COMMIT | 1180 | HY000 |
ER_ERROR_DURING_ROLLBACK | 1181 | HY000 |
ER_ERROR_DURING_FLUSH_LOGS | 1182 | HY000 |
ER_ERROR_DURING_CHECKPOINT | 1183 | HY000 |
ER_NEW_ABORTING_CONNECTION | 1184 | 08S01 |
ER_DUMP_NOT_IMPLEMENTED | 1185 | HY000 |
ER_FLUSH_MASTER_BINLOG_CLOSED | 1186 | HY000 |
ER_INDEX_REBUILD | 1187 | HY000 |
ER_MASTER | 1188 | HY000 |
ER_MASTER_NET_READ | 1189 | 08S01 |
ER_MASTER_NET_WRITE | 1190 | 08S01 |
ER_FT_MATCHING_KEY_NOT_FOUND | 1191 | HY000 |
ER_LOCK_OR_ACTIVE_TRANSACTION | 1192 | HY000 |
ER_UNKNOWN_SYSTEM_VARIABLE | 1193 | HY000 |
ER_CRASHED_ON_USAGE | 1194 | HY000 |
ER_CRASHED_ON_REPAIR | 1195 | HY000 |
ER_WARNING_NOT_COMPLETE_ROLLBACK | 1196 | HY000 |
ER_TRANS_CACHE_FULL | 1197 | HY000 |
ER_SLAVE_MUST_STOP | 1198 | HY000 |
ER_SLAVE_NOT_RUNNING | 1199 | HY000 |
ER_BAD_SLAVE | 1200 | HY000 |
ER_MASTER_INFO | 1201 | HY000 |
ER_SLAVE_THREAD | 1202 | HY000 |
ER_TOO_MANY_USER_CONNECTIONS | 1203 | 42000 |
ER_SET_CONSTANTS_ONLY | 1204 | HY000 |
ER_LOCK_WAIT_TIMEOUT | 1205 | HY000 |
ER_LOCK_TABLE_FULL | 1206 | HY000 |
ER_READ_ONLY_TRANSACTION | 1207 | 25000 |
ER_DROP_DB_WITH_READ_LOCK | 1208 | HY000 |
ER_CREATE_DB_WITH_READ_LOCK | 1209 | HY000 |
ER_WRONG_ARGUMENTS | 1210 | HY000 |
ER_NO_PERMISSION_TO_CREATE_USER | 1211 | 42000 |
ER_UNION_TABLES_IN_DIFFERENT_DIR | 1212 | HY000 |
ER_LOCK_DEADLOCK | 1213 | 40001 |
ER_TABLE_CANT_HANDLE_FULLTEXT | 1214 | HY000 |
ER_CANNOT_ADD_FOREIGN | 1215 | HY000 |
ER_NO_REFERENCED_ROW | 1216 | 23000 |
ER_ROW_IS_REFERENCED | 1217 | 23000 |
ER_CONNECT_TO_MASTER | 1218 | 08S01 |
ER_QUERY_ON_MASTER | 1219 | HY000 |
ER_ERROR_WHEN_EXECUTING_COMMAND | 1220 | HY000 |
ER_WRONG_USAGE | 1221 | HY000 |
ER_WRONG_NUMBER_OF_COLUMNS_IN_SELECT | 1222 | 21000 |
ER_CANT_UPDATE_WITH_READLOCK | 1223 | HY000 |
ER_MIXING_NOT_ALLOWED | 1224 | HY000 |
ER_DUP_ARGUMENT | 1225 | HY000 |
ER_USER_LIMIT_REACHED | 1226 | 42000 |
ER_SPECIFIC_ACCESS_DENIED_ERROR | 1227 | HY000 |
ER_LOCAL_VARIABLE | 1228 | HY000 |
ER_GLOBAL_VARIABLE | 1229 | HY000 |
ER_NO_DEFAULT | 1230 | 42000 |
ER_WRONG_VALUE_FOR_VAR | 1231 | 42000 |
ER_WRONG_TYPE_FOR_VAR | 1232 | 42000 |
ER_VAR_CANT_BE_READ | 1233 | HY000 |
ER_CANT_USE_OPTION_HERE | 1234 | 42000 |
ER_NOT_SUPPORTED_YET | 1235 | 42000 |
ER_MASTER_FATAL_ERROR_READING_BINLOG | 1236 | HY000 |
ER_SLAVE_IGNORED_TABLE | 1237 | HY000 |
ER_WRONG_FK_DEF | 1238 | 42000 |
ER_KEY_REF_DO_NOT_MATCH_TABLE_REF | 1239 | HY000 |
ER_CARDINALITY_COL | 1240 | 21000 |
ER_SUBSELECT_NO_1_ROW | 1241 | 21000 |
ER_UNKNOWN_STMT_HANDLER | 1242 | HY000 |
ER_CORRUPT_HELP_DB | 1243 | HY000 |
ER_CYCLIC_REFERENCE | 1244 | HY000 |
ER_AUTO_CONVERT | 1245 | HY000 |
ER_ILLEGAL_REFERENCE | 1246 | 42S22 |
ER_DERIVED_MUST_HAVE_ALIAS | 1247 | 42000 |
ER_SELECT_REDUCED | 1248 | 01000 |
ER_TABLENAME_NOT_ALLOWED_HERE | 1249 | 42000 |
ER_NOT_SUPPORTED_AUTH_MODE | 1250 | 08004 |
ER_SPATIAL_CANT_HAVE_NULL | 1251 | 42000 |
ER_COLLATION_CHARSET_MISMATCH | 1252 | 42000 |
ER_SLAVE_WAS_RUNNING | 1253 | HY000 |
ER_SLAVE_WAS_NOT_RUNNING | 1254 | HY000 |
ER_TOO_BIG_FOR_UNCOMPRESS | 1255 | HY000 |
ER_ZLIB_Z_MEM_ERROR | 1256 | HY000 |
ER_ZLIB_Z_BUF_ERROR | 1257 | HY000 |
ER_ZLIB_Z_DATA_ERROR | 1258 | HY000 |
ER_CUT_VALUE_GROUP_CONCAT | 1259 | HY000 |
ER_WARN_TOO_FEW_RECORDS | 1260 | 01000 |
ER_WARN_TOO_MANY_RECORDS | 1261 | 01000 |
ER_WARN_NULL_TO_NOTNULL | 1262 | 01000 |
ER_WARN_DATA_OUT_OF_RANGE | 1263 | 01000 |
ER_WARN_DATA_TRUNCATED | 1264 | 01000 |
ER_WARN_USING_OTHER_HANDLER | 1265 | 01000 |
ER_CANT_AGGREGATE_COLLATIONS | 1266 | 42000 |
ER_DROP_USER | 1267 | 42000 |
ER_REVOKE_GRANTS | 1268 | 42000 |
ER_CANT_AGGREGATE_3COLLATIONS | 1269 | 42000 |
ER_CANT_AGGREGATE_NCOLLATIONS | 1270 | 42000 |
ER_VARIABLE_IS_NOT_STRUCT | 1271 | HY000 |
ER_UNKNOWN_COLLATION | 1272 | HY000 |
ER_SLAVE_IGNORED_SSL_PARAMS | 1273 | HY000 |
ER_SERVER_IS_IN_SECURE_AUTH_MODE | 1274 | HY000 |
ER_WARN_FIELD_RESOLVED | 1275 | HY000 |
ER_BAD_SLAVE_UNTIL_COND | 1276 | HY000 |
ER_MISSING_SKIP_SLAVE | 1277 | HY000 |
ER_UNTIL_COND_IGNORED | 1278 | HY000 |
Table of Contents
Table of Contents
This chapter describes a lot of things that you need to know when working on the MySQL code. If you plan to contribute to MySQL development, want to have access to the bleeding-edge in-between versions code, or just want to keep track of development, follow the instructions in Installing source tree. If you are interested in MySQL internals, you should also subscribe to our internals mailing list. This list is relatively low traffic. For details on how to subscribe, please see Mailing-list. All developers at MySQL AB are on the internals list and we help other people who are working on the MySQL code. Feel free to use this list both to ask questions about the code and to send patches that you would like to contribute to the MySQL project!
The MySQL server creates the following threads:
The TCP/IP connection thread handles all connection requests and creates a new dedicated thread to handle the authentication and SQL query processing for each connection.
On Windows NT there is a named pipe handler thread that does the same work as the TCP/IP connection thread on named pipe connect requests.
The signal thread handles all signals. This thread also normally handles alarms and calls process_alarm() to force timeouts on connections that have been idle too long.
If mysqld is compiled with -DUSE_ALARM_THREAD, a dedicated thread that handles alarms is created. This is only used on some systems where there are problems with sigwait() or if one wants to use the thr_alarm() code in ones application without a dedicated signal handling thread.
If one uses the --flush_time=# option, a dedicated thread is created to flush all tables at the given interval.
Every connection has its own thread.
Every different table on which one uses INSERT DELAYED gets its own thread.
If you use --master-host, a slave replication thread will be started to read and apply updates from the master.
mysqladmin processlist only shows the connection, INSERT DELAYED, and replication threads.
Until recently, our main full-coverage test suite was based on proprietary customer data and for that reason has not been publicly available. The only publicly available part of our testing process consisted of the crash-me test, a Perl DBI/DBD benchmark found in the sql-bench directory, and miscellaneous tests located in tests directory. The lack of a standardized publicly available test suite has made it difficult for our users, as well developers, to do regression tests on the MySQL code. To address this problem, we have created a new test system that is included in Unix source distributions and binary distributions starting with Version 3.23.29. The tests can be run under Unix, or on Windows in the Cygwin environment if the server has been compiled under Cygwin. They cannot be run in a native Windows environment currently.
The current set of test cases doesn't test everything in MySQL, but it should catch most obvious bugs in the SQL processing code, OS/library issues, and is quite thorough in testing replication. Our eventual goal is to have the tests cover 100% of the code. We welcome contributions to our test suite. You may especially want to contribute tests that examine the functionality critical to your system, as this will ensure that all future MySQL releases will work well with your applications.
The test system consist of a test language interpreter (mysqltest), a shell script to run all tests(mysql-test-run), the actual test cases written in a special test language, and their expected results. To run the test suite on your system after a build, type make test or mysql-test/mysql-test-run from the source root. If you have installed a binary distribution, cd to the install root (eg. /usr/local/mysql), and do scripts/mysql-test-run. All tests should succeed. If not, you should try to find out why and report the problem if this is a bug in MySQL. See Reporting mysqltest bugs.
If you have a copy of mysqld running on the machine where you want to run the test suite you do not have to stop it, as long as it is not using ports 9306 and 9307. If one of those ports is taken, you should edit mysql-test-run and change the values of the master and/or slave port to one that is available.
You can run one individual test case with mysql-test/mysql-test-run test_name.
If one test fails, you should test running mysql-test-run with the --force option to check if any other tests fails.
You can use the mysqltest language to write your own test cases. Unfortunately, we have not yet written full documentation for it. You can, however, look at our current test cases and use them as an example. The following points should help you get started:
The tests are located in mysql-test/t/*.test
A test case consists of ; terminated statements and is similar to the input of mysql command-line client. A statement by default is a query to be sent to MySQL server, unless it is recognized as internal command (eg. sleep).
All queries that produce results---for example, SELECT, SHOW, EXPLAIN, etc., must be preceded with @/path/to/result/file. The file must contain the expected results. An easy way to generate the result file is to run mysqltest -r < t/test-case-name.test from mysql-test directory, and then edit the generated result files, if needed, to adjust them to the expected output. In that case, be very careful about not adding or deleting any invisible characters - make sure to only change the text and/or delete lines. If you have to insert a line, make sure the fields are separated with a hard tab, and there is a hard tab at the end. You may want to use od -c to make sure your text editor has not messed anything up during edit. We hope that you will never have to edit the output of mysqltest -r as you only have to do it when you find a bug.
To be consistent with our setup, you should put your result files in mysql-test/r directory and name them test_name.result. If the test produces more than one result, you should use test_name.a.result, test_name.b.result, etc.
If a statement returns an error, you should on the line before the statement specify with the --error error-number. The error number can be a list of possible error numbers separated with ','.
If you are writing a replication test case, you should on the first line of the test file, put source include/master-slave.inc;. To switch between master and slave, use connection master; and connection slave;. If you need to do something on an alternate connection, you can do connection master1; for the master, and connection slave1; for the slave.
If you need to do something in a loop, you can use something like this:
let $1=1000; while ($1) { # do your queries here dec $1; }
To sleep between queries, use the sleep command. It supports fractions of a second, so you can do sleep 1.3;, for example, to sleep 1.3 seconds.
To run the slave with additional options for your test case, put them in the command-line format in mysql-test/t/test_name-slave.opt. For the master, put them in mysql-test/t/test_name-master.opt.
If you have a question about the test suite, or have a test case to contribute, send an email message to the MySQL internals mailing list. See Mailing-list. As this list does not accept attachments, you should ftp all the relevant files to: ftp://support.mysql.com/pub/mysql/Incoming/
If your MySQL version doesn't pass the test suite you should do the following:
Don't send a bug report before you have found out as much as possible of what when wrong! When you do it, please use the mysqlbug script so that we can get information about your system and MySQL version. See Bug reports.
Make sure to include the output of mysql-test-run, as well as contents of all .reject files in mysql-test/r directory.
If a test in the test suite fails, check if the test fails also when run by its own:
cd mysql-test mysql-test-run --local test-name
If this fails, then you should configure MySQL with --with-debug and run mysql-test-run with the --debug option. If this also fails send the trace file var/tmp/master.trace to ftp://support.mysql.com/pub/mysql/secret so that we can examine it. Please remember to also include a full description of your system, the version of the mysqld binary and how you compiled it.
Try also to run mysql-test-run with the --force option to see if there is any other test that fails.
If you have compiled MySQL yourself, check our manual for how to compile MySQL on your platform or, preferable, use one of the binaries we have compiled for you at http://www.mysql.com/downloads/. All our standard binaries should pass the test suite !
If you get an error, like Result length mismatch or Result content mismatch it means that the output of the test didn't match exactly the expected output. This could be a bug in MySQL or that your mysqld version produces slight different results under some circumstances.
Failed test results are put in a file with the same base name as the result file with the .reject extension. If your test case is failing, you should do a diff on the two files. If you cannot see how they are different, examine both with od -c and also check their lengths.
If a test fails totally, you should check the logs file in the mysql-test/var/log directory for hints of what went wrong.
If you have compiled MySQL with debugging you can try to debug this by running mysql-test-run with the --gdb and/or --debug options. See Making trace files.
If you have not compiled MySQL for debugging you should probably do that. Just specify the --with-debug options to configure! See Installing source.
Table of Contents
There are two ways to add new functions to MySQL:
You can add the function through the user-defined function (UDF) interface. User-defined functions are added and removed dynamically using the CREATE FUNCTION and DROP FUNCTION statements. See CREATE FUNCTION.
You can add the function as a native (built in) MySQL function. Native functions are compiled into the mysqld server and become available on a permanent basis.
Each method has advantages and disadvantages:
If you write a user-defined function, you must install the object file in addition to the server itself. If you compile your function into the server, you don't need to do that.
You can add UDFs to a binary MySQL distribution. Native functions require you to modify a source distribution.
If you upgrade your MySQL distribution, you can continue to use your previously installed UDFs. For native functions, you must repeat your modifications each time you upgrade.
Whichever method you use to add new functions, they may be used just like native functions such as ABS() or SOUNDEX().
CREATE [AGGREGATE] FUNCTION function_name RETURNS {STRING|REAL|INTEGER} SONAME shared_library_name DROP FUNCTION function_name
A user-defined function (UDF) is a way to extend MySQL with a new function that works like native (built in) MySQL function such as ABS() and CONCAT().
AGGREGATE is a new option for MySQL Version 3.23. An AGGREGATE function works exactly like a native MySQL GROUP function like SUM or COUNT().
CREATE FUNCTION saves the function's name, type, and shared library name in the mysql.func system table. You must have the INSERT and DELETE privileges for the mysql database to create and drop functions.
All active functions are reloaded each time the server starts, unless you start mysqld with the --skip-grant-tables option. In this case, UDF initialization is skipped and UDFs are unavailable. (An active function is one that has been loaded with CREATE FUNCTION and not removed with DROP FUNCTION.)
For instructions on writing user-defined functions, see Adding functions. For the UDF mechanism to work, functions must be written in C or C++, your operating system must support dynamic loading and you must have compiled mysqld dynamically (not statically).
Note that to make AGGREGATE work, you must have a mysql.func table that contains the column type. If you do not have this table, you should run the script mysql_fix_privilege_tables to create it.
For the UDF mechanism to work, functions must be written in C or C++ and your operating system must support dynamic loading. The MySQL source distribution includes a file sql/udf_example.cc that defines 5 new functions. Consult this file to see how UDF calling conventions work.
For mysqld to be able to use UDF functions, you should configure MySQL with --with-mysqld-ldflags=-rdynamic The reason is that to on many platforms (including Linux) you can load a dynamic library (with dlopen()) from a static linked program, which you would get if you are using --with-mysqld-ldflags=-all-static If you want to use an UDF that needs to access symbols from mysqld (like the metaphone example in sql/udf_example.cc that uses default_charset_info), you must link the program with -rdynamic (see man dlopen).
If you are using a precompiled version of the server, use MySQL-Max, which supports dynamic loading.
For each function that you want to use in SQL statements, you should define corresponding C (or C++) functions. In the discussion below, the name ``xxx'' is used for an example function name. To distinguish between SQL and C/C++ usage, XXX() (uppercase) indicates an SQL function call, and xxx() (lowercase) indicates a C/C++ function call.
The C/C++ functions that you write to implement the interface for XXX() are:
xxx() (required) | The main function. This is where the function result is computed. The correspondence between the SQL type and return type of your C/C++ function is shown here: |
| ||||||||
xxx_init() (optional) |
The initialization function for xxx(). It can be used to:
| |||||||||
xxx_deinit() (optional) | The deinitialization function for xxx(). It should deallocate any memory allocated by the initialization function. |
When an SQL statement invokes XXX(), MySQL calls the initialization function xxx_init() to let it perform any required setup, such as argument checking or memory allocation. If xxx_init() returns an error, the SQL statement is aborted with an error message and the main and deinitialization functions are not called. Otherwise, the main function xxx() is called once for each row. After all rows have been processed, the deinitialization function xxx_deinit() is called so it can perform any required cleanup.
For aggregate functions (like SUM()), you must also provide the following functions:
xxx_reset() (required) | Reset sum and insert the argument as the initial value for a new group. |
xxx_add() (required) | Add the argument to the old sum. |
When using aggregate UDFs, MySQL works the following way:
Call xxx_init() to let the aggregate function allocate the memory it will need to store results.
Sort the table according to the GROUP BY expression.
For the first row in a new group, call the xxx_reset() function.
For each new row that belongs in the same group, call the xxx_add() function.
When the group changes or after the last row has been processed, call xxx() to get the result for the aggregate.
Repeat 3-5 until all rows has been processed
Call xxx_deinit() to let the UDF free any memory it has allocated.
All functions must be thread-safe (not just the main function, but the initialization and deinitialization functions as well). This means that you are not allowed to allocate any global or static variables that change! If you need memory, you should allocate it in xxx_init() and free it in xxx_deinit().
The main function should be declared as shown here. Note that the return type and parameters differ, depending on whether you will declare the SQL function XXX() to return STRING, INTEGER, or REAL in the CREATE FUNCTION statement:
For STRING functions:
char *xxx(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long *length, char *is_null, char *error);
For INTEGER functions:
long long xxx(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);
For REAL functions:
double xxx(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);
The initialization and deinitialization functions are declared like this:
my_bool xxx_init(UDF_INIT *initid, UDF_ARGS *args, char *message); void xxx_deinit(UDF_INIT *initid);
The initid parameter is passed to all three functions. It points to a UDF_INIT structure that is used to communicate information between functions. The UDF_INIT structure members follow. The initialization function should fill in any members that it wishes to change. (To use the default for a member, leave it unchanged.):
my_bool maybe_null | xxx_init() should set maybe_null to 1 if xxx() can return NULL. The default value is 1 if any of the arguments are declared maybe_null. |
unsigned int decimals | Number of decimals. The default value is the maximum number of decimals in the arguments passed to the main function. (For example, if the function is passed 1.34, 1.345, and 1.3, the default would be 3, because 1.345 has 3 decimals. |
unsigned int max_length | The maximum length of the string result. The default value differs depending on the result type of the function. For string functions, the default is the length of the longest argument. For integer functions, the default is 21 digits. For real functions, the default is 13 plus the number of decimals indicated by initid->decimals. (For numeric functions, the length includes any sign or decimal point characters.) If you want to return a blob, you can set this to 65K or 16M; this memory is not allocated but used to decide which column type to use if there is a need to temporary store the data. |
char *ptr |
A pointer that the function can use for its own purposes. For example,
functions can use initid->ptr to communicate allocated memory
between functions. In xxx_init(), allocate the memory and assign it
to this pointer:
initid->ptr = allocated_memory;In xxx() and xxx_deinit(), refer to initid->ptr to use or deallocate the memory. |
Here follows a description of the different functions you need to define when you want to create an aggregate UDF function.
Note that the following function is NOT needed or used by MySQL 4.1.1. You can keep still have define his function if you want to have your code work with both MySQL 4.0 and MySQL 4.1.1
char *xxx_reset(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);
This function is called when MySQL finds the first row in a new group. In the function you should reset any internal summary variables and then set the given argument as the first argument in the group.
In many cases this is implemented internally by reseting all variables (for example by calling xxx_clear() and then calling xxx_add().
The following function is only required by MySQL 4.1.1 and above:
char *xxx_clear(UDF_INIT *initid, char *is_null, char *error);
This function is called when MySQL needs to reset the summary results. This will be called at the beginning for each new group but can also be called to reset the values for a query where there was no matching rows. is_null will be set to point to CHAR(0) before calling xxx_clear().
You can use the error pointer to store a byte if something went wrong .
char *xxx_add(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);
This function is called for all rows that belongs to the same group, except for the first row. In this you should add the value in UDF_ARGS to your internal summary variable.
The xxx() function should be declared identical as when you define a simple UDF function. See UDF calling.
This function is called when all rows in the group has been processed. You should normally never access the args variable here but return your value based on your internal summary variables.
All argument processing in xxx_reset() and xxx_add() should be done identically as for normal UDFs. See UDF arguments.
The return value handling in xxx() should be done identically as for a normal UDF. See UDF return values.
The pointer argument to is_null and error is the same for all calls to xxx_reset(), xxx_clear(), xxx_add() and xxx(). You can use this to remember that you got an error or if the xxx() function should return NULL. Note that you should not store a string into *error! This is just a 1 byte flag!
is_null is reset for each group (before calling xxx_clear() error is never reset.
If isnull or error are set after xxx() then MySQL will return NULL as the result for the group function.
The args parameter points to a UDF_ARGS structure that has the members listed here:
unsigned int arg_count |
The number of arguments. Check this value in the initialization function
if you want your function to be called with a particular number of arguments.
For example:
if (args->arg_count != 2) { strcpy(message,"XXX() requires two arguments"); return 1; } |
enum Item_result *arg_type |
The types for each argument. The possible type values are
STRING_RESULT, INT_RESULT, and REAL_RESULT.
To make sure that arguments are of a given type and return an
error if they are not, check the arg_type array in the initialization
function. For example:
if (args->arg_type[0] != STRING_RESULT || args->arg_type[1] != INT_RESULT) { strcpy(message,"XXX() requires a string and an integer"); return 1; }As an alternative to requiring your function's arguments to be of particular types, you can use the initialization function to set the arg_type elements to the types you want. This causes MySQL to coerce arguments to those types for each call to xxx(). For example, to specify coercion of the first two arguments to string and integer, do this in xxx_init(): args->arg_type[0] = STRING_RESULT; args->arg_type[1] = INT_RESULT; |
char **args | args->args communicates information to the initialization function
about the general nature of the arguments your function was called with. For a
constant argument i, args->args[i] points to the argument
value. (See below for instructions on how to access the value properly.)
For a non-constant argument, args->args[i] is 0.
A constant argument is an expression that uses only constants, such as
3 or 4*7-2 or SIN(3.14). A non-constant argument is an
expression that refers to values that may change from row to row, such as
column names or functions that are called with non-constant arguments.
For each invocation of the main function, args->args contains the
actual arguments that are passed for the row currently being processed.
Functions can refer to an argument i as follows:
|
unsigned long *lengths | For the initialization function, the lengths array indicates the maximum string length for each argument. You should not change these. For each invocation of the main function, lengths contains the actual lengths of any string arguments that are passed for the row currently being processed. For arguments of types INT_RESULT or REAL_RESULT, lengths still contains the maximum length of the argument (as for the initialization function). |
The initialization function should return 0 if no error occurred and 1 otherwise. If an error occurs, xxx_init() should store a null-terminated error message in the message parameter. The message will be returned to the client. The message buffer is MYSQL_ERRMSG_SIZE characters long, but you should try to keep the message to less than 80 characters so that it fits the width of a standard terminal screen.
The return value of the main function xxx() is the function value, for long long and double functions. A string functions should return a pointer to the result and store the length of the string in the length arguments.
Set these to the contents and length of the return value. For example:
memcpy(result, "result string", 13); *length = 13;
The result buffer that is passed to the calc function is 255 byte big. If your result fits in this, you don't have to worry about memory allocation for results.
If your string function needs to return a string longer than 255 bytes, you must allocate the space for it with malloc() in your xxx_init() function or your xxx() function and free it in your xxx_deinit() function. You can store the allocated memory in the ptr slot in the UDF_INIT structure for reuse by future xxx() calls. See UDF calling.
To indicate a return value of NULL in the main function, set is_null to 1:
*is_null = 1;
To indicate an error return in the main function, set the error parameter to 1:
*error = 1;
If xxx() sets *error to 1 for any row, the function value is NULL for the current row and for any subsequent rows processed by the statement in which XXX() was invoked. (xxx() will not even be called for subsequent rows.) Note: In MySQL versions prior to 3.22.10, you should set both *error and *is_null:
*error = 1; *is_null = 1;
Files implementing UDFs must be compiled and installed on the host where the server runs. This process is described below for the example UDF file udf_example.cc that is included in the MySQL source distribution. This file contains the following functions:
metaphon() returns a metaphon string of the string argument. This is something like a soundex string, but it's more tuned for English.
myfunc_double() returns the sum of the ASCII values of the characters in its arguments, divided by the sum of the length of its arguments.
myfunc_int() returns the sum of the length of its arguments.
sequence([const int]) returns an sequence starting from the given number or 1 if no number has been given.
lookup() returns the IP number for a hostname.
reverse_lookup() returns the hostname for an IP number. The function may be called with a string "xxx.xxx.xxx.xxx" or four numbers.
A dynamically loadable file should be compiled as a sharable object file, using a command something like this:
shell> gcc -shared -o udf_example.so myfunc.cc
You can easily find out the correct compiler options for your system by running this command in the sql directory of your MySQL source tree:
shell> make udf_example.o
You should run a compile command similar to the one that make displays, except that you should remove the -c option near the end of the line and add -o udf_example.so to the end of the line. (On some systems, you may need to leave the -c on the command.)
Once you compile a shared object containing UDFs, you must install it and tell MySQL about it. Compiling a shared object from udf_example.cc produces a file named something like udf_example.so (the exact name may vary from platform to platform). Copy this file to some directory searched by the dynamic linker ld, such as /usr/lib or add the directory in which you placed the shared object to the linker configuration file (for example, /etc/ld.so.conf).
On many systems, you can also set the LD_LIBRARY or LD_LIBRARY_PATH environment variable to point at the directory where you have your UDF function files. The dlopen manual page tells you which variable you should use on your system. You should set this in mysql.server or mysqld_safe startup scripts and restart mysqld.
After the library is installed, notify mysqld about the new functions with these commands:
mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_double RETURNS REAL SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_int RETURNS INTEGER SONAME "udf_example.so"; mysql> CREATE FUNCTION lookup RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION reverse_lookup -> RETURNS STRING SONAME "udf_example.so"; mysql> CREATE AGGREGATE FUNCTION avgcost -> RETURNS REAL SONAME "udf_example.so";
Functions can be deleted using DROP FUNCTION:
mysql> DROP FUNCTION metaphon; mysql> DROP FUNCTION myfunc_double; mysql> DROP FUNCTION myfunc_int; mysql> DROP FUNCTION lookup; mysql> DROP FUNCTION reverse_lookup; mysql> DROP FUNCTION avgcost;
The CREATE FUNCTION and DROP FUNCTION statements update the system table func in the mysql database. The function's name, type and shared library name are saved in the table. You must have the INSERT and DELETE privileges for the mysql database to create and drop functions.
You should not use CREATE FUNCTION to add a function that has already been created. If you need to reinstall a function, you should remove it with DROP FUNCTION and then reinstall it with CREATE FUNCTION. You would need to do this, for example, if you recompile a new version of your function, so that mysqld gets the new version. Otherwise, the server will continue to use the old version.
Active functions are reloaded each time the server starts, unless you start mysqld with the --skip-grant-tables option. In this case, UDF initialization is skipped and UDFs are unavailable. (An active function is one that has been loaded with CREATE FUNCTION and not removed with DROP FUNCTION.)
The procedure for adding a new native function is described here. Note that you cannot add native functions to a binary distribution because the procedure involves modifying MySQL source code. You must compile MySQL yourself from a source distribution. Also note that if you migrate to another version of MySQL (for example, when a new version is released), you will need to repeat the procedure with the new version.
To add a new native MySQL function, follow these steps:
Add one line to lex.h that defines the function name in the sql_functions[] array.
If the function prototype is simple (just takes zero, one, two or three arguments), you should in lex.h specify SYM(FUNC_ARG#) (where # is the number of arguments) as the second argument in the sql_functions[] array and add a function that creates a function object in item_create.cc. Take a look at "ABS" and create_funcs_abs() for an example of this.
If the function prototype is complicated (for example takes a variable number of arguments), you should add two lines to sql_yacc.yy. One indicates the preprocessor symbol that yacc should define (this should be added at the beginning of the file). Then define the function parameters and add an ``item'' with these parameters to the simple_expr parsing rule. For an example, check all occurrences of ATAN in sql_yacc.yy to see how this is done.
In item_func.h, declare a class inheriting from Item_num_func or Item_str_func, depending on whether your function returns a number or a string.
In item_func.cc, add one of the following declarations, depending on whether you are defining a numeric or string function:
double Item_func_newname::val() longlong Item_func_newname::val_int() String *Item_func_newname::Str(String *str)
If you inherit your object from any of the standard items (like Item_num_func), you probably only have to define one of the above functions and let the parent object take care of the other functions. For example, the Item_str_func class defines a val() function that executes atof() on the value returned by ::str().
You should probably also define the following object function:
void Item_func_newname::fix_length_and_dec()
This function should at least calculate max_length based on the given arguments. max_length is the maximum number of characters the function may return. This function should also set maybe_null = 0 if the main function can't return a NULL value. The function can check if any of the function arguments can return NULL by checking the arguments maybe_null variable. You can take a look at Item_func_mod::fix_length_and_dec for a typical example of how to do this.
All functions must be thread-safe (in other words, don't use any global or static variables in the functions without protecting them with mutexes).
If you want to return NULL, from ::val(), ::val_int() or ::str() you should set null_value to 1 and return 0.
For ::str() object functions, there are some additional considerations to be aware of:
The String *str argument provides a string buffer that may be used to hold the result. (For more information about the String type, take a look at the sql_string.h file.)
The ::str() function should return the string that holds the result or (char*) 0 if the result is NULL.
All current string functions try to avoid allocating any memory unless absolutely necessary!
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In MySQL, you can define a procedure in C++ that can access and modify the data in a query before it is sent to the client. The modification can be done on row-by-row or GROUP BY level.
We have created an example procedure in MySQL Version 3.23 to show you what can be done.
Additionally we recommend you to take a look at mylua. With this you can use the LUA language to load a procedure at runtime into mysqld.
analyse([max elements,[max memory]])
This procedure is defined in the sql/sql_analyse.cc. This examines the result from your query and returns an analysis of the results:
max elements (default 256) is the maximum number of distinct values analyse will notice per column. This is used by analyse to check if the optimal column type should be of type ENUM.
max memory (default 8192) is the maximum memory analyse should allocate per column while trying to find all distinct values.
SELECT ... FROM ... WHERE ... PROCEDURE ANALYSE([max elements,[max memory]])
This chapter lists some common problems and error messages that users have run into. You will learn how to figure out what the problem is, and what to do to solve it. You will also find proper solutions to some common problems.
When you run into problems, the first thing you should do is to find out which program / piece of equipment is causing problems:
If you have one of the following symptoms, then it is probably a hardware (like memory, motherboard, CPU, or hard disk) or kernel problem:
The keyboard doesn't work. This can normally be checked by pressing Caps Lock. If the Caps Lock light doesn't change you have to replace your keyboard. (Before doing this, you should try to reboot your computer and check all cables to the keyboard.)
The mouse pointer doesn't move.
The machine doesn't answer to a remote machine's pings.
Different, unrelated programs don't behave correctly.
If your system rebooted unexpectedly (a faulty user level program should never be able to take down your system).
In this case you should start by checking all your cables and run some diagnostic tool to check your hardware! You should also check if there are any patches, updates, or service packs for your operating system that could likely solve your problems. Check also that all your libraries (like glibc) are up to date.
It's always good to use a machine with ECC memory to discover memory problems early!
If your keyboard is locked up, you may be able to fix this by logging into your machine from another machine and execute kbd_mode -a on it.
Please examine your system log file (/var/log/messages or similar) for reasons for your problems. If you think the problem is in MySQL then you should also examine MySQL's log files. See Binary log.
If you don't think you have hardware problems, you should try to find out which program is causing problems.
Try using top, ps, taskmanager, or some similar program, to check which program is taking all CPU or is locking the machine.
Check with top, df, or a similar program if you are out of memory, disk space, open files, or some other critical resource.
If the problem is some runaway process, you can always try to kill it. If it doesn't want to die, there is probably a bug in the operating system.
If after you have examined all other possibilities and you have concluded that it's the MySQL server or a MySQL client that is causing the problem, it's time to do a bug report for our mailing list or our support team. In the bug report, try to give a very detailed description of how the system is behaving and what you think is happening. You should also state why you think it's MySQL that is causing the problems. Take into consideration all the situations in this chapter. State any problems exactly how they appear when you examine your system. Use the 'cut and paste' method for any output and/or error messages from programs and/or log files!
Try to describe in detail which program is not working and all symptoms you see! We have in the past received many bug reports that just state "the system doesn't work". This doesn't provide us with any information about what could be the problem.
If a program fails, it's always useful to know:
Has the program in question made a segmentation fault (core dumped)?
Is the program taking up the whole CPU? Check with top. Let the program run for a while, it may be evaluating something heavy.
If it's the mysqld server that is causing problems, can you do mysqladmin -u root ping or mysqladmin -u root processlist?
What does a client program say (try with mysql, for example) when you try to connect to the MySQL server? Does the client jam? Do you get any output from the program?
When sending a bug report, you should of follow the outlines described in this manual. See Asking questions.
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This section lists some errors that users frequently get. You will find descriptions of the errors, and how to solve the problem here.
This section also covers the related Lost connection to server during query error.
The most common reason for the MySQL server has gone away error is that the server timed out and closed the connection. By default, the server closes the connection after 8 hours if nothing has happened. You can change the time limit by setting the wait_timeout variable when you start mysqld.
Another common reason to receive the MySQL server has gone away error is because you have issued a ``close'' on your MySQL connection and then tried to run a query on the closed connection.
If you have a script, you just have to issue the query again for the client to do an automatic reconnection.
You normally can get the following error codes in this case (which one you get is OS-dependent):
Error code | Description |
CR_SERVER_GONE_ERROR | The client couldn't send a question to the server. |
CR_SERVER_LOST | The client didn't get an error when writing to the server, but it didn't get a full answer (or any answer) to the question. |
You will also get this error if someone has kills the running thread with kill #threadid#.
You can check that the MySQL hasn't died by executing mysqladmin version and examining the uptime. If the problem is that mysqld crashed you should concentrate one finding the reason for the crash. You should in this case start by checking if issuing the query again will kill MySQL again. See Crashing.
You can also get these errors if you send a query to the server that is incorrect or too large. If mysqld gets a packet that is too large or out of order, it assumes that something has gone wrong with the client and closes the connection. If you need big queries (for example, if you are working with big BLOB columns), you can increase the query limit by starting mysqld with the -O max_allowed_packet=# option (default 1M). The extra memory is allocated on demand, so mysqld will allocate more memory only when you issue a big query or when mysqld must return a big result row!
You will also get a lost connection if you are sending a packet >= 16M if your client is older than 4.0.8 and your server is 4.0.8 and above, or the other way around.
If you want to make a bug report regarding this problem, be sure that you include the following information:
Include information if MySQL died or not. (You can find this in the hostname.err file. See Crashing.
If a specific query kills mysqld and the involved tables where checked with CHECK TABLE before you did the query, can you do a test case for this? See Reproduceable test case.
What is the value of the wait_timeout variable in the MySQL server ? mysqladmin variables gives you the value of this
Have you tried to run mysqld with --log and check if the issued query appears in the log ?
See Asking questions.
A MySQL client on Unix can connect to the mysqld server in two different ways: Unix socket files, which connect through a file in the file system (default /tmp/mysqld.sock) or TCP/IP, which connects through a port number. Unix socket files are faster than TCP/IP but can only be used when connecting to a server on the same computer. Unix socket files are used if you don't specify a hostname or if you specify the special hostname localhost.
On Windows, if the mysqld server is running on 9x/Me, you can connect only via TCP/IP. If the server is running on NT/2000/XP and mysqld is started with --enable-named-pipe, you can also connect with named pipes. The name of the named pipe is MySQL. If you don't give a hostname when connecting to mysqld, a MySQL client will first try to connect to the named pipe, and if this doesn't work it will connect to the TCP/IP port. You can force the use of named pipes on Windows by using . as the hostname.
The error (2002) Can't connect to ... normally means that there isn't a MySQL server running on the system or that you are using a wrong socket file or TCP/IP port when trying to connect to the mysqld server.
Start by checking (using ps or the task manager on Windows) that there is a process running named mysqld on your server! If there isn't any mysqld process, you should start one. See Starting server.
If a mysqld process is running, you can check the server by trying these different connections (the port number and socket pathname might be different in your setup):
shell> mysqladmin version shell> mysqladmin variables shell> mysqladmin -h `hostname` version variables shell> mysqladmin -h `hostname` --port=3306 version shell> mysqladmin -h 'ip for your host' version shell> mysqladmin --protocol=socket --socket=/tmp/mysql.sock version
Note the use of backquotes rather than forward quotes with the hostname command; these cause the output of hostname (that is, the current hostname) to be substituted into the mysqladmin command.
Here are some reasons the Can't connect to local MySQL server error might occur:
mysqld is not running.
You are running on a system that uses MIT-pthreads. If you are running on a system that doesn't have native threads, mysqld uses the MIT-pthreads package. See Which OS. However, not all MIT-pthreads versions support Unix socket files. On a system without sockets support you must always specify the hostname explicitly when connecting to the server. Try using this command to check the connection to the server:
shell> mysqladmin -h `hostname` version
Someone has removed the Unix socket that mysqld uses (default /tmp/mysqld.sock). You might have a cron job that removes the MySQL socket (for example, a job that removes old files from the /tmp directory). You can always run mysqladmin version and check that the socket mysqladmin is trying to use really exists. The fix in this case is to change the cron job to not remove mysqld.sock or to place the socket somewhere else. See Problems with mysql.sock.
You have started the mysqld server with the --socket=/path/to/socket option. If you change the socket pathname for the server, you must also notify the MySQL clients about the new path. You can do this by providing the socket path as an argument to the client. See Problems with mysql.sock.
You are using Linux and one thread has died (core dumped). In this case you must kill the other mysqld threads (for example, with the mysql_zap script before you can start a new MySQL server. See Crashing.
You may not have read and write privilege to either the directory that holds the socket file or privilege to the socket file itself. In this case you have to either change the privilege for the directory / file or restart mysqld so that it uses a directory that you can access.
If you get the error message Can't connect to MySQL server on some_hostname, you can try the following things to find out what the problem is:
Check if the server is up by doing telnet your-host-name tcp-ip-port-number and press Enter a couple of times. If there is a MySQL server running on this port you should get a responses that includes the version number of the running MySQL server. If you get an error like telnet: Unable to connect to remote host: Connection refused, then there is no server running on the given port.
Try connecting to the mysqld daemon on the local machine and check the TCP/IP port that mysqld it's configured to use (variable port) with mysqladmin variables.
Check that your mysqld server is not started with the --skip-networking option.
MySQL 4.1 uses an authentication protocal based on a password hashing algorithm that is incompatible with that used by older clients. If you upgrade the server to 4.1, attempts to connect to a it with an older client may fail with the following message:
shell> mysql Client does not support authentication protocol requested by server; consider upgrading MySQL client
To solve this problem you should do one of the following:
Upgrade all client programs to use the 4.1.1 or newer client library.
Use a user account with an old password when connecting from a pre 4.1 client.
Reset the user that needs a pre-4.1 client to use an old password:
mysql> UPDATE user SET Password = OLD_PASSWORD('mypass') -> WHERE Host = 'some_host' AND User = 'some_user'; mysql> FLUSH PRIVILEGES;
Tell the server to use the older password hashing algorithm:
Start mysqld with --old-passwords.
Set the password for all users that has a long password. You can find these users with:
SELECT * FROM mysql.user WHERE LENGTH(password) > 16;
For background on password hashing and authentication, see Password hashing.
If you get an error like this:
Host 'hostname' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts'
This means that mysqld has gotten a lot (max_connect_errors) of connect requests from the host 'hostname' that have been interrupted in the middle. After max_connect_errors failed requests, mysqld assumes that something is wrong (like an attack from a cracker), and blocks the site from further connections until you execute a mysqladmin flush-hosts command or issue a FLUSH HOSTS statement.
By default, mysqld blocks a host after 10 connection errors. You can easily adjust this by starting the server like this:
shell> mysqld_safe -O max_connect_errors=10000 &
Note that if you get this error message for a given host, you should first check that there isn't anything wrong with TCP/IP connections from that host. If your TCP/IP connections aren't working, it won't do you any good to increase the value of the max_connect_errors variable!
If you get the error Too many connections when you try to connect to MySQL, this means that there is already max_connections clients connected to the mysqld server.
If you need more connections than the default (100), then you should restart mysqld with a bigger value for the max_connections variable.
Note that mysqld actually allows (max_connections+1) clients to connect. The last connection is reserved for a user with the SUPER privilege. By not giving this privilege to normal users (they shouldn't need this), an administrator with this privilege can log in and use SHOW PROCESSLIST to find out what could be wrong. See SHOW PROCESSLIST.
The maximum number of connects MySQL is depending on how good the thread library is on a given platform. Linux or Solaris should be able to support 500-1000 simultaneous connections, depending on how much RAM you have and what your clients are doing.
If you get the error/warning: Warning: Some non-transactional changed tables couldn't be rolled back when trying to do a ROLLBACK, this means that some of the tables you used in the transaction didn't support transactions. These non-transactional tables will not be affected by the ROLLBACK statement.
The most typical case when this happens is when you have tried to create a table of a type that is not supported by your mysqld binary. If mysqld doesn't support a table type (or if the table type is disabled by a startup option) , it will instead create the table type with the table type that is most resembles to the one you requested, probably MyISAM.
You can check the table type for a table by doing:
SHOW TABLE STATUS LIKE 'table_name'. See SHOW TABLE STATUS.
You can check the extensions your mysqld binary supports by doing:
show variables like 'have_%'. See SHOW VARIABLES.
If you issue a query and get something like the following error:
mysql: Out of memory at line 42, 'malloc.c' mysql: needed 8136 byte (8k), memory in use: 12481367 bytes (12189k) ERROR 2008: MySQL client ran out of memory
note that the error refers to the MySQL client mysql. The reason for this error is simply that the client does not have enough memory to store the whole result.
To remedy the problem, first check that your query is correct. Is it reasonable that it should return so many rows? If so, you can use mysql --quick, which uses mysql_use_result() to retrieve the result set. This places less of a load on the client (but more on the server).
When a MySQL client or the mysqld server gets a packet bigger than max_allowed_packet bytes, it issues a Packet too large error and closes the connection.
In MySQL 3.23 the biggest possible packet is 16M (due to limits in the client/server protocol). In MySQL 4.0.1 and up, this is only limited by the amount on memory you have on your server (up to a theoretical maximum of 2G).
A communication packet is a single SQL statement sent to the MySQL server or a single row that is sent to the client.
When a MySQL client or the mysqld server gets a packet bigger than max_allowed_packet bytes, it issues a Packet too large error and closes the connection. With some clients, you may also get Lost connection to MySQL server during query error if the communication packet is too big.
Note that both the client and the server has it's own max_allowed_packet variable. If you want to handle big packets, you have to increase this variable both in the client and in the server.
It's safe to increase this variable as memory is only allocated when needed; this variable is more a precaution to catch wrong packets between the client/server and also to ensure that you don't accidentally use big packets so that you run out of memory.
If you are using the mysql client, you may specify a bigger buffer by starting the client with mysql --set-variable=max_allowed_packet=8M. Other clients have different methods to set this variable. Please note that --set-variable is deprecated since MySQL 4.0, just use --max-allowed-packet=8M instead.
You can use the option file to set max_allowed_packet to a larger size in mysqld. For example, if you are expecting to store the full length of a MEDIUMBLOB into a table, you'll need to start the server with the set-variable=max_allowed_packet=16M option.
You can also get strange problems with large packets if you are using big blobs, but you haven't given mysqld access to enough memory to handle the query. If you suspect this is the case, try adding ulimit -d 256000 to the beginning of the mysqld_safe script and restart mysqld.
Starting with MySQL 3.23.40 you only get the Aborted connection error of you start mysqld with --warnings.
If you find errors like the following in your error log.
010301 14:38:23 Aborted connection 854 to db: 'users' user: 'josh'
See Error log.
This means that something of the following has happened:
The client program did not call mysql_close() before exit.
The client had been sleeping more than wait_timeout or interactive_timeout without doing any requests. See wait_timeout. See interactive_timeout.
The client program ended abruptly in the middle of the transfer.
When the above happens, the server variable Aborted_clients is incremented.
The server variable Aborted_connects is incremented when:
When a connection packet doesn't contain the right information.
When the user didn't have privileges to connect to a database.
When a user uses a wrong password.
When it takes more than connect_timeout seconds to get a connect package. See connect_timeout.
Note that the above could indicate that someone is trying to break into your database!
Other reasons for problems with Aborted clients / Aborted connections.
Usage of Ethernet protocol with Linux, both half and full duplex. Many Linux Ethernet drivers have this bug. You should test for this bug by transferring a huge file via ftp between these two machines. If a transfer goes in burst-pause-burst-pause ... mode then you are experiencing a Linux duplex syndrome. The only solution is switching duplex mode for both your network card and Hub/Switch to either full duplex or to half duplex and testing the results to decide on the best setting.
Some problem with the thread library that causes interrupts on reads.
Badly configured TCP/IP.
Faulty Ethernets or hubs or switches, cables ... This can be diagnosed properly only by replacing hardware.
max_allowed_packet is too small or queries require more memory than you have allocated for mysqld. See Packet too large.
There are a couple of different cases when you can get this error:
You are using an older MySQL version (before 3.23.0) when an in-memory temporary table becomes larger than tmp_table_size bytes. To avoid this problem, you can use the -O tmp_table_size=# option to make mysqld increase the temporary table size or use the SQL option SQL_BIG_TABLES before you issue the problematic query. See SET.
You can also start mysqld with the --big-tables option. This is exactly the same as using SQL_BIG_TABLES for all queries.
In MySQL Version 3.23, if an in-memory temporary table becomes larger than tmp_table_size, the server automatically converted it to a disk-based MyISAM table.
You are using InnoDB tables and run out of room in the InnoDB tablespace. In this case the solution is to extend the InnoDB tablespace.
You are using ISAM or MyISAM tables on an OS that only supports files of 2G in size and you have hit this limit for the datafile or index file.
You are using MyISAM tables and the needed data or index size is bigger than what MySQL has allocated pointers for. (If you don't specify MAX_ROWS to CREATE TABLE MySQL will only allocate pointers to hold 4G of data).
You can check the maximum data/index sizes by doing
SHOW TABLE STATUS FROM database LIKE 'table_name';
or using myisamchk -dv database/table_name.
If this is the problem, you can fix it by doing something like:
ALTER TABLE table_name MAX_ROWS=1000000000 AVG_ROW_LENGTH=nnn;
You only have to specify AVG_ROW_LENGTH for tables with BLOB/TEXT fields as in this case MySQL can't optimize the space required based only on the number of rows.
If you get an error for some queries of type:
Can't create/write to file '\\sqla3fe_0.ism'.
this means that MySQL can't create a temporary file for the result set in the given temporary directory. (The above error is a typical error message on Windows, and the Unix error message is similar.) The fix is to start mysqld with --tmpdir=path or to add to your option file:
[mysqld] tmpdir=C:/temp
assuming that the c:\\temp directory exists. See Option files.
Check also the error code that you get with perror. One reason may also be a disk full error;
shell> perror 28 Error code 28: No space left on device
If you get Commands out of sync; you can't run this command now in your client code, you are calling client functions in the wrong order!
This can happen, for example, if you are using mysql_use_result() and try to execute a new query before you have called mysql_free_result(). It can also happen if you try to execute two queries that return data without a mysql_use_result() or mysql_store_result() in between.
If you get the following error:
Found wrong password for user: 'some_user@some_host'; ignoring user
this means that when mysqld was started or when it reloaded the permissions tables, it found an entry in the user table with an invalid password. As a result, the entry is simply ignored by the permission system.
Possible causes of and fixes for this problem:
You may be running a new version of mysqld with an old user table. You can check this by executing mysqlshow mysql user to see whether the password field is shorter than 16 characters. If so, you can correct this condition by running the scripts/add_long_password script.
The user has an old password (8 characters long) and you didn't start mysqld with the --old-protocol option. Update the user in the user table with a new password or restart mysqld with --old-protocol.
You have specified a password in the user table without using the PASSWORD() function. Use mysql to update the user in the user table with a new password. Make sure to use the PASSWORD() function:
mysql> UPDATE user SET password=PASSWORD('your password') -> WHERE user='XXX';
If you get the error Table 'xxx' doesn't exist or Can't find file: 'xxx' (errno: 2), this means that no table exists in the current database with the name xxx.
Note that as MySQL uses directories and files to store databases and tables, the database and table names are case sensitive! (On Windows the databases and tables names are not case sensitive, but all references to a given table within a query must use the same case!)
You can check which tables you have in the current database with SHOW TABLES. See SHOW.
If you get an error like:
MySQL Connection Failed: Can't initialize character set xxx
This means one of the following things:
The character set is a multi-byte character set and you have no support for the character set in the client.
In this case you need to recompile the client with --with-charset=xxx or with --with-extra-charsets=xxx. See configure options.
All standard MySQL binaries are compiled with --with-extra-character-sets=complex which will enable support for all multi-byte character sets. See Character sets.
The character set is a simple character set which is not compiled into mysqld and the character set definition files are not in the place where the client expects to find them.
In this case you need to:
Recompile the client with support for the character set. See configure options.
Specify to the client where the character set definition files are. For many clients you can do this with the --character-sets-dir=path-to-charset-dir option.
Copy the character definition files to the path where the client expects them to be.
If you get ERROR '...' not found (errno: 23), Can't open file: ... (errno: 24), or any other error with errno 23 or errno 24 from MySQL, it means that you haven't allocated enough file descriptors for MySQL. You can use the perror utility to get a description of what the error number means:
shell> perror 23 File table overflow shell> perror 24 Too many open files shell> perror 11 Resource temporarily unavailable
The problem here is that mysqld is trying to keep open too many files simultaneously. You can either tell mysqld not to open so many files at once or increase the number of file descriptors available to mysqld.
To tell mysqld to keep open fewer files at a time, you can make the table cache smaller by using the -O table_cache=32 option to mysqld_safe (the default value is 64). Reducing the value of max_connections will also reduce the number of open files (the default value is 90).
To change the number of file descriptors available to mysqld, you can use the option --open-files-limit=# to mysqld_safe or -O open_files_limit=# to mysqld. See open_files_limit. The easiest way to do that is to add the option to your option file. See Option files. If you have an old mysqld version that doesn't support this, you can edit the mysqld_safe script. There is a commented-out line ulimit -n 256 in the script. You can remove the '#' character to uncomment this line, and change the number 256 to affect the number of file descriptors available to mysqld.
ulimit (and open-files-limit) can increase the number of file descriptors, but only up to the limit imposed by the operating system. There is also a 'hard' limit that can only be overridden if you start mysqld_safe or mysqld as root (just remember that you need to also use the --user=... option in this case). If you need to increase the OS limit on the number of file descriptors available to each process, consult the documentation for your operating system.
Note that if you run the tcsh shell, ulimit will not work! tcsh will also report incorrect values when you ask for the current limits! In this case you should start mysqld_safe with sh!
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If you are linking your program and you get errors for unreferenced symbols that start with mysql_, like the following:
/tmp/ccFKsdPa.o: In function `main': /tmp/ccFKsdPa.o(.text+0xb): undefined reference to `mysql_init' /tmp/ccFKsdPa.o(.text+0x31): undefined reference to `mysql_real_connect' /tmp/ccFKsdPa.o(.text+0x57): undefined reference to `mysql_real_connect' /tmp/ccFKsdPa.o(.text+0x69): undefined reference to `mysql_error' /tmp/ccFKsdPa.o(.text+0x9a): undefined reference to `mysql_close'
you should be able to solve this by adding -Lpath-to-the-mysql-library -lmysqlclient last on your link line.
If you get undefined reference errors for the uncompress or compress function, add -lz last on your link line and try again!
If you get undefined reference errors for functions that should exist on your system, like connect, check the man page for the function in question, for which libraries you should add to the link line!
If you get undefined reference errors for functions that don't exist on your system, like the following:
mf_format.o(.text+0x201): undefined reference to `__lxstat'
it usually means that your library is compiled on a system that is not 100% compatible with yours. In this case you should download the latest MySQL source distribution and compile this yourself. See Installing source.
If you are trying to run a program and you then get errors for unreferenced symbols that start with mysql_ or that the mysqlclient library can't be found, this means that your system can't find the share libmysqlclient.so library.
The fix for this is to tell your system to search after shared libraries where the library is located by one of the following methods:
Add the path to the directory where you have libmysqlclient.so the LD_LIBRARY_PATH environment variable.
Add the path to the directory where you have libmysqlclient.so the LD_LIBRARY environment variable.
Copy libmysqlclient.so to some place that is searched by your system, like /lib, and update the shared library information by executing ldconfig.
Another way to solve this problem is to link your program statically, with -static, or by removing the dynamic MySQL libraries before linking your code. In the second case you should be sure that no other programs are using the dynamic libraries!
The MySQL server mysqld can be started and run by any user. In order to change mysqld to run as a Unix user user_name, you must do the following:
Stop the server if it's running (use mysqladmin shutdown).
Change the database directories and files so that user_name has privileges to read and write files in them (you may need to do this as the Unix root user):
shell> chown -R user_name /path/to/mysql/datadir
If directories or files within the MySQL data directory are symlinks, you'll also need to follow those links and change the directories and files they point to. chown -R may not follow symlinks for you.
Start the server as user user_name, or, if you are using MySQL Version 3.22 or later, start mysqld as the Unix root user and use the --user=user_name option. mysqld will switch to run as the Unix user user_name before accepting any connections.
To start the server as the given username automatically at system startup time, add a user line that specifies the username to the [mysqld] group of the /etc/my.cnf option file or the my.cnf option file in the server's data directory. For example:
[mysqld] user=user_name
At this point, your mysqld process should be running fine and dandy as the Unix user user_name. One thing hasn't changed, though: the contents of the permissions tables. By default (right after running the permissions table install script mysql_install_db), the MySQL user root is the only user with permission to access the mysql database or to create or drop databases. Unless you have changed those permissions, they still hold. This shouldn't stop you from accessing MySQL as the MySQL root user when you're logged in as a Unix user other than root; just specify the -u root option to the client program.
Note that accessing MySQL as root, by supplying -u root on the command-line, has nothing to do with MySQL running as the Unix root user, or, indeed, as another Unix user. The access permissions and usernames of MySQL are completely separate from Unix usernames. The only connection with Unix usernames is that if you don't provide a -u option when you invoke a client program, the client will try to connect using your Unix login name as your MySQL user name.
If your Unix box itself isn't secured, you should probably at least put a password on the MySQL root users in the access tables. Otherwise, any user with an account on that machine can run mysql -u root db_name and do whatever he likes.
On Windows, you can install MySQL 4.0.17 and MySQL 4.1.2 as services as a normal user. (Older MySQL versions required you to have administrator rights; This was a bug introduced in MySQL 3.23.54).
If you have problems with file permissions, for example, if mysql issues the following error message when you create a table:
ERROR: Can't find file: 'path/with/filename.frm' (Errcode: 13)
then the environment variable UMASK might be set incorrectly when mysqld starts. The default umask value is 0660. You can change this behavior by starting mysqld_safe as follows:
shell> UMASK=384 # = 600 in octal shell> export UMASK shell> /path/to/mysqld_safe &
By default MySQL will create database and RAID directories with permission type 0700. You can modify this behavior by setting the UMASK_DIR variable. If you set this, new directories are created with the combined UMASK and UMASK_DIR. For example, if you want to give group access to all new directories, you can do:
shell> UMASK_DIR=504 # = 770 in octal shell> export UMASK_DIR shell> /path/to/mysqld_safe &
In MySQL Version 3.23.25 and above, MySQL assumes that the value for UMASK and UMASK_DIR is in octal if it starts with a zero.
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All MySQL versions are tested on many platforms before they are released. This doesn't mean that there aren't any bugs in MySQL, but it means if there are bugs, they are very few and can be hard to find. If you have a problem, it will always help if you try to find out exactly what crashes your system, as you will have a much better chance of getting this fixed quickly.
First, you should try to find out whether the problem is that the mysqld daemon dies or whether your problem has to do with your client. You can check how long your mysqld server has been up by executing mysqladmin version. If mysqld has died, you may find the reason for this in the file mysql-data-directory/`hostname`.err. See Error log.
On some systems you can find in this file a stack trace of where mysqld died that you can resolve with resolve_back_stack. See Using stack trace. Note that the variable values written in the .err file may not always be 100 percent correct.
Many crashes of MySQL are caused by corrupted index files or datafiles. MySQL will update the data on disk, with the write() system call, after every SQL statement and before the client is notified about the result. (This is not true if you are running with delay_key_write, in which case only the data is written.) This means that the data is safe even if mysqld crashes, as the OS will ensure that the not flushed data is written to disk. You can force MySQL to sync everything to disk after every SQL command by starting mysqld with --flush.
The above means that normally you shouldn't get corrupted tables unless:
Someone/something killed mysqld or the machine in the middle of an update.
You have found a bug in mysqld that caused it to die in the middle of an update.
Someone is manipulating the data/index files outside of mysqld without locking the table properly.
If you are running many mysqld servers on the same data on a system that doesn't support good filesystem locks (normally handled by the lockd daemon ) or if you are running multiple servers with --skip-external-locking
You have a crashed index/datafile that contains very wrong data that got mysqld confused.
You have found a bug in the data storage code. This isn't that likely, but it's at least possible. In this case you can try to change the file type to another storage engine by using ALTER TABLE on a repaired copy of the table!
Because it is very difficult to know why something is crashing, first try to check whether things that work for others crash for you. Please try the following things:
Take down the mysqld daemon with mysqladmin shutdown, run myisamchk --silent --force */*.MYI on all tables, and restart the mysqld daemon. This will ensure that you are running from a clean state. See MySQL Database Administration.
Use mysqld --log and try to determine from the information in the log whether some specific query kills the server. About 95% of all bugs are related to a particular query! Normally this is one of the last queries in the log file just before MySQL restarted. See Query log. If you can repeatedly kill MySQL with one of the queries, even when you have checked all tables just before doing the query, then you have been able to locate the bug and should do a bug report for this! See Bug reports.
Try to make a test case that we can use to reproduce the problem. See Reproduceable test case.
Try running the included mysql-test test and the MySQL benchmarks. See MySQL test suite. They should test MySQL rather well. You can also add code to the benchmarks that simulates your application! The benchmarks can be found in the bench directory in the source distribution or, for a binary distribution, in the sql-bench directory under your MySQL installation directory.
Try fork_test.pl and fork2_test.pl.
If you configure MySQL for debugging, it will be much easier to gather information about possible errors if something goes wrong. Reconfigure MySQL with the --with-debug option or --with-debug=full to configure and then recompile. See Debugging server.
Configuring MySQL for debugging causes a safe memory allocator to be included that can find some errors. It also provides a lot of output about what is happening.
Have you applied the latest patches for your operating system?
Use the --skip-external-locking option to mysqld. On some systems, the lockd lock manager does not work properly; the --skip-external-locking option tells mysqld not to use external locking. (This means that you cannot run 2 mysqld servers on the same data and that you must be careful if you use myisamchk, but it may be instructive to try the option as a test.)
Have you tried mysqladmin -u root processlist when mysqld appears to be running but not responding? Sometimes mysqld is not comatose even though you might think so. The problem may be that all connections are in use, or there may be some internal lock problem. mysqladmin processlist will usually be able to make a connection even in these cases, and can provide useful information about the current number of connections and their status.
Run the command mysqladmin -i 5 status or mysqladmin -i 5 -r status or in a separate window to produce statistics while you run your other queries.
Try the following:
Start mysqld from gdb (or in another debugger). See Using gdb on mysqld.
Run your test scripts.
Print the backtrace and the local variables at the 3 lowest levels. In gdb you can do this with the following commands when mysqld has crashed inside gdb:
backtrace info local up info local up info local
With gdb you can also examine which threads exist with info threads and switch to a specific thread with thread #, where # is the thread ID.
Try to simulate your application with a Perl script to force MySQL to crash or misbehave.
Send a normal bug report. See Bug reports. Be even more detailed than usual. Because MySQL works for many people, it may be that the crash results from something that exists only on your computer (for example, an error that is related to your particular system libraries).
If you have a problem with tables with dynamic-length rows and you are not using BLOB/TEXT columns (but only VARCHAR columns), you can try to change all VARCHAR to CHAR with ALTER TABLE. This will force MySQL to use fixed-size rows. Fixed-size rows take a little extra space, but are much more tolerant to corruption!
The current dynamic row code has been in use at MySQL AB for at least 3 years without any problems, but by nature dynamic-length rows are more prone to errors, so it may be a good idea to try the above to see whether it helps!
If you never set a root password for MySQL, then the server will not require a password at all for connecting as root. It is recommended to always set a password for each user. See Security guidelines.
If you have set a root password, but forgot what it was, you can set a new password with the following procedure:
Take down the mysqld server by sending a kill (not kill -9) to the mysqld server. The pid is stored in a .pid file, which is normally in the MySQL database directory:
shell> kill `cat /mysql-data-directory/hostname.pid`
You must be either the Unix root user or the same user mysqld runs as to do this.
Restart mysqld with the --skip-grant-tables option.
Set a new password with the mysqladmin password command:
shell> mysqladmin -u root password "mynewpassword"
Now you can either stop mysqld and restart it normally, or just load the privilege tables with:
shell> mysqladmin -h hostname flush-privileges
After this, you should be able to connect using the new password.
Alternatively, you can set the new password using the mysql client:
Take down and restart mysqld with the --skip-grant-tables option as described above.
Connect to the mysqld server with:
shell> mysql -u root mysql
Issue the following commands in the mysql client:
mysql> UPDATE user SET Password=PASSWORD('mynewpassword') -> WHERE User='root'; mysql> FLUSH PRIVILEGES;
After this, you should be able to connect using the new password.
You can now stop mysqld and restart it normally.
When a disk-full condition occurs, MySQL does the following:
It checks once every minute to see whether there is enough space to write the current row. If there is enough space, it continues as if nothing had happened.
Every 6 minutes it writes an entry to the log file warning about the disk full condition.
To alleviate the problem, you can take the following actions:
To continue, you only have to free enough disk space to insert all records.
To abort the thread, you must send a mysqladmin kill to the thread. The thread will be aborted the next time it checks the disk (in 1 minute).
Note that other threads may be waiting for the table that caused the disk full condition. If you have several ``locked'' threads, killing the one thread that is waiting on the disk-full condition will allow the other threads to continue.
Exceptions to the above behavior is when you use REPAIR or OPTIMIZE or when the indexes are created in a batch after an LOAD DATA INFILE or after an ALTER TABLE statement.
All of the above commands may use big temporary files that left to themself would cause big problems for the rest of the system. If MySQL gets disk full while doing any of the above operations, it will remove the big temporary files and mark the table as crashed (except for ALTER TABLE, in which the old table will be left unchanged).
MySQL uses the value of the TMPDIR environment variable as the pathname of the directory in which to store temporary files. If you don't have TMPDIR set, MySQL uses the system default, which is normally /tmp or /usr/tmp. If the filesystem containing your temporary file directory is too small, you should edit mysqld_safe to set TMPDIR to point to a directory in a filesystem where you have enough space! You can also set the temporary directory using the --tmpdir option to mysqld.
MySQL creates all temporary files as hidden files. This ensures that the temporary files will be removed if mysqld is terminated. The disadvantage of using hidden files is that you will not see a big temporary file that fills up the filesystem in which the temporary file directory is located.
When sorting (ORDER BY or GROUP BY), MySQL normally uses one or two temporary files. The maximum disk-space needed is:
(length of what is sorted + sizeof(database pointer)) * number of matched rows * 2
sizeof(database pointer) is usually 4, but may grow in the future for really big tables.
For some SELECT queries, MySQL also creates temporary SQL tables. These are not hidden and have names of the form SQL_*.
ALTER TABLE creates a temporary table in the same directory as the original table.
If you use MySQL 4.1 or later you can spread load between several physical disks by setting --tmpdir to a list of paths separated by colon : (semicolon ; on Windows). They will be used in round-robin fashion. Note: These paths should end up on different physical disks, not different partitions of the same disk.
It is possible to set tmpdir to point to a memory-based filesystem, except if the MySQL server is a slave. If it is a slave, it needs some of its temporary files (for replication of temporary tables or of LOAD DATA INFILE) to survive a machine's reboot, so a memory-based tmpdir which is cleared when the machine reboots is not suitable; a disk-based tmpdir is necessary.
If you have problems with the fact that anyone can delete the MySQL communication socket /tmp/mysql.sock, you can, on most versions of Unix, protect your /tmp filesystem by setting the sticky bit on it. Log in as root and do the following:
shell> chmod +t /tmp
This will protect your /tmp filesystem so that files can be deleted only by their owners or the superuser (root).
You can check if the sticky bit is set by executing ls -ld /tmp. If the last permission bit is t, the bit is set.
You can change the place where MySQL uses / puts the socket file the following ways:
Specify the path in a global or local option file. For example, put in /etc/my.cnf:
[client] socket=path-for-socket-file [mysqld] socket=path-for-socket-file
See Option files.
Specifying this on the command-line to mysqld_safe and most clients with the --socket=path-for-socket-file option.
Specify the path to the socket in the MYSQL_UNIX_PORT environment variable.
Defining the path with the configure option --with-unix-socket-path=path-for-socket-file. See configure options.
You can test that the socket works with this command:
shell> mysqladmin --socket=/path/to/socket version
If you have a problem with SELECT NOW() returning values in GMT and not your local time, you have to set the TZ environment variable to your current time zone. This should be done for the environment in which the server runs, for example, in mysqld_safe or mysql.server. See Environment variables.
The same applies if UNIX_TIMESTAMP() returns the wrong value.
You can set the time zone for the server by setting the TZ environment variable before you start mysqld. You can also set it with the --timezone=timezone_name argument to mysqld_safe.
The allowable TZ values are system-dependent. Consult your operating system documentation to see what values are acceptable.
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By default, MySQL searches are not case sensitive (although there are some character sets that are never case-insensitive, such as czech). That means that if you search with col_name LIKE 'a%', you will get all column values that start with A or a. If you want to make this search case sensitive, use something like INSTR(col_name, "A")=1 to check a prefix. Or use STRCMP(col_name, "A") = 0 if the column value must be exactly "A".
Simple comparison operations (>=, >, = , < , <=, sorting and grouping) are based on each character's ``sort value''. Characters with the same sort value (like E, e and é) are treated as the same character!
In older MySQL versions LIKE comparisons were done on the uppercase value of each character (E == e but E <> é). In newer MySQL versions LIKE works just like the other comparison operators.
If you want a column always to be treated in case-sensitive fashion, declare it as BINARY. See CREATE TABLE.
If you are using Chinese data in the so-called big5 encoding, you want to make all character columns BINARY. This works because the sorting order of big5 encoding characters is based on the order of ASCII codes.
The format of a DATE value is 'YYYY-MM-DD'. According to standard SQL, no other format is allowed. You should use this format in UPDATE expressions and in the WHERE clause of SELECT statements. For example:
mysql> SELECT * FROM tbl_name WHERE date >= '1997-05-05';
As a convenience, MySQL automatically converts a date to a number if the date is used in a numeric context (and vice versa). It is also smart enough to allow a ``relaxed'' string form when updating and in a WHERE clause that compares a date to a TIMESTAMP, DATE, or a DATETIME column. (Relaxed form means that any punctuation character may be used as the separator between parts. For example, '1998-08-15' and '1998#08#15' are equivalent.) MySQL can also convert a string containing no separators (such as '19980815'), provided it makes sense as a date.
The special date '0000-00-00' can be stored and retrieved as '0000-00-00'. When using a '0000-00-00' date through MyODBC, it will automatically be converted to NULL in MyODBC Version 2.50.12 and above, because ODBC can't handle this kind of date.
Because MySQL performs the conversions described above, the following statements work:
mysql> INSERT INTO tbl_name (idate) VALUES (19970505); mysql> INSERT INTO tbl_name (idate) VALUES ('19970505'); mysql> INSERT INTO tbl_name (idate) VALUES ('97-05-05'); mysql> INSERT INTO tbl_name (idate) VALUES ('1997.05.05'); mysql> INSERT INTO tbl_name (idate) VALUES ('1997 05 05'); mysql> INSERT INTO tbl_name (idate) VALUES ('0000-00-00'); mysql> SELECT idate FROM tbl_name WHERE idate >= '1997-05-05'; mysql> SELECT idate FROM tbl_name WHERE idate >= 19970505; mysql> SELECT MOD(idate,100) FROM tbl_name WHERE idate >= 19970505; mysql> SELECT idate FROM tbl_name WHERE idate >= '19970505';
However, the following will not work:
mysql> SELECT idate FROM tbl_name WHERE STRCMP(idate,'19970505')=0;
STRCMP() is a string function, so it converts idate to a string and performs a string comparison. It does not convert '19970505' to a date and perform a date comparison.
Note that MySQL does very limited checking whether the date is correct. If you store an incorrect date, such as '1998-2-31', the wrong date will be stored.
Because MySQL packs dates for storage, it can't store any given date as it would not fit onto the result buffer. The rules for accepting a date are:
If MySQL can store and retrieve a given date, the wrong date is accepted for DATE and DATETIME columns.
All days values between 0-31 are accepted for any date. This makes it very convenient for web applications where you ask year, month and day in 3 different fields.
The day or month field may be zero. This is convenient if you want to store a birthdate in a DATE column and you only know part of the date.
If the date cannot be converted to any reasonable value, a 0 is stored in the DATE field, which will be retrieved as 0000-00-00. This is both a speed and convenience issue as we believe that the database's responsibility is to retrieve the same date you stored (even if the data was not logically correct in all cases). We think it is up to the application to check the dates, and not the server.
The concept of the NULL value is a common source of confusion for newcomers to SQL, who often think that NULL is the same thing as an empty string "". This is not the case! For example, the following statements are completely different:
mysql> INSERT INTO my_table (phone) VALUES (NULL); mysql> INSERT INTO my_table (phone) VALUES ("");
Both statements insert a value into the phone column, but the first inserts a NULL value and the second inserts an empty string. The meaning of the first can be regarded as ``phone number is not known'' and the meaning of the second can be regarded as ``she has no phone''.
In SQL, the NULL value is always false in comparison to any other value, even NULL. An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for the operators and functions involved in the expression. All columns in the following example return NULL:
mysql> SELECT NULL,1+NULL,CONCAT('Invisible',NULL);
If you want to search for column values that are NULL, you cannot use the =NULL test. The following statement returns no rows, because expr = NULL is FALSE, for any expression:
mysql> SELECT * FROM my_table WHERE phone = NULL;
To look for NULL values, you must use the IS NULL test. The following shows how to find the NULL phone number and the empty phone number:
mysql> SELECT * FROM my_table WHERE phone IS NULL; mysql> SELECT * FROM my_table WHERE phone = "";
Note that you can add an index on a column that can have NULL values only if you are using MySQL Version 3.23.2 or newer and are using the MyISAM, InnoDB, or BDB table type. In earlier versions and with other table types, you must declare such columns NOT NULL. This also means you cannot then insert NULL into an indexed column.
When reading data with LOAD DATA INFILE, empty columns are updated with ''. If you want a NULL value in a column, you should use \N in the text file. The literal word 'NULL' may also be used under some circumstances. See LOAD DATA.
When using ORDER BY, NULL values are presented first, or last if you specify DESC to sort in descending order. Exception: In MySQL versions 4.0.2 through 4.0.10, NULL values sort first regardless of sort order.
When using GROUP BY, all NULL values are regarded as equal.
Aggregate (summary) functions such as COUNT(), MIN(), and SUM() ignore NULL values. The exception to this is COUNT(*), which counts rows and not individual column values. For example, the following statement would produce two counts. The first is a count of the number of rows in the table, and the second is a count of the number of non-NULL values in the age column:
mysql> SELECT COUNT(*), COUNT(age) FROM person;
To help with NULL handling, you can use the IS NULL and IS NOT NULL operators and the IFNULL() function.
For some column types, NULL values are handled specially. If you insert NULL into the first TIMESTAMP column of a table, the current date and time is inserted. If you insert NULL into an AUTO_INCREMENT column, the next number in the sequence is inserted.
You can use an alias to refer to a column in the GROUP BY, ORDER BY, or in the HAVING part. Aliases can also be used to give columns better names:
SELECT SQRT(a*b) as rt FROM table_name GROUP BY rt HAVING rt > 0; SELECT id,COUNT(*) AS cnt FROM table_name GROUP BY id HAVING cnt > 0; SELECT id AS "Customer identity" FROM table_name;
Note that standard SQL doesn't allow you to refer to an alias in a WHERE clause. This is because when the WHERE code is executed the column value may not yet be determined. For example, the following query is illegal:
SELECT id,COUNT(*) AS cnt FROM table_name WHERE cnt > 0 GROUP BY id;
The WHERE statement is executed to determine which rows should be included in the GROUP BY part while HAVING is used to decide which rows from the result set should be used.
As MySQL doesn't support subqueries (prior to Version 4.1), nor the use of more than one table in the DELETE statement (prior to Version 4.0), you should use the following approach to delete rows from 2 related tables:
SELECT the rows based on some WHERE condition in the main table.
DELETE the rows in the main table based on the same condition.
DELETE FROM related_table WHERE related_column IN (selected_rows).
If the total number of characters in the query with related_column is more than 1,048,576 (the default value of max_allowed_packet, you should split it into smaller parts and execute multiple DELETE statements. You will probably get the fastest DELETE by only deleting 100-1000 related_column ids per query if the related_column is an index. If the related_column isn't an index, the speed is independent of the number of arguments in the IN clause.
If you have a complicated query that has many tables and that doesn't return any rows, you should use the following procedure to find out what is wrong with your query:
Test the query with EXPLAIN and check if you can find something that is obviously wrong. See EXPLAIN.
Select only those fields that are used in the WHERE clause.
Remove one table at a time from the query until it returns some rows. If the tables are big, it's a good idea to use LIMIT 10 with the query.
Do a SELECT for the column that should have matched a row against the table that was last removed from the query.
If you are comparing FLOAT or DOUBLE columns with numbers that have decimals, you can't use '='. This problem is common in most computer languages because floating-point values are not exact values. In most cases, changing the FLOAT to a DOUBLE will fix this. See Problems with float.
If you still can't figure out what's wrong, create a minimal test that can be run with mysql test < query.sql that shows your problems. You can create a test file with mysqldump --quick database tables > query.sql. Open the file in an editor, remove some insert lines (if there are too many of these), and add your select statement at the end of the file.
Test that you still have your problem by doing:
shell> mysqladmin create test2 shell> mysql test2 < query.sql
Post the test file using mysqlbug to the general MySQL mailing list. See Mailing-list.
floating-point numbers cause confusion sometimes, because these numbers are not stored as exact values inside computer architecture. What one can see on the screen usually is not the exact value of the number.
Field types FLOAT, DOUBLE and DECIMAL are such.
CREATE TABLE t1 (i INT, d1 DECIMAL(9,2), d2 DECIMAL(9,2)); INSERT INTO t1 VALUES (1, 101.40, 21.40), (1, -80.00, 0.00), (2, 0.00, 0.00), (2, -13.20, 0.00), (2, 59.60, 46.40), (2, 30.40, 30.40), (3, 37.00, 7.40), (3, -29.60, 0.00), (4, 60.00, 15.40), (4, -10.60, 0.00), (4, -34.00, 0.00), (5, 33.00, 0.00), (5, -25.80, 0.00), (5, 0.00, 7.20), (6, 0.00, 0.00), (6, -51.40, 0.00); mysql> SELECT i, SUM(d1) AS a, SUM(d2) AS b -> FROM t1 GROUP BY i HAVING a <> b; +------+--------+-------+ | i | a | b | +------+--------+-------+ | 1 | 21.40 | 21.40 | | 2 | 76.80 | 76.80 | | 3 | 7.40 | 7.40 | | 4 | 15.40 | 15.40 | | 5 | 7.20 | 7.20 | | 6 | -51.40 | 0.00 | +------+--------+-------+
The result is correct. Although the first five records look like they shouldn't pass the comparison test, they may do so because the difference between the numbers show up around tenth decimal, or so depending on computer architecture.
The problem cannot be solved by using ROUND() (or similar function), because the result is still a floating-point number. Example:
mysql> SELECT i, ROUND(SUM(d1), 2) AS a, ROUND(SUM(d2), 2) AS b -> FROM t1 GROUP BY i HAVING a <> b; +------+--------+-------+ | i | a | b | +------+--------+-------+ | 1 | 21.40 | 21.40 | | 2 | 76.80 | 76.80 | | 3 | 7.40 | 7.40 | | 4 | 15.40 | 15.40 | | 5 | 7.20 | 7.20 | | 6 | -51.40 | 0.00 | +------+--------+-------+
This is what the numbers in column 'a' look like:
mysql> SELECT i, ROUND(SUM(d1), 2)*1.0000000000000000 AS a, -> ROUND(SUM(d2), 2) AS b FROM t1 GROUP BY i HAVING a <> b; +------+----------------------+-------+ | i | a | b | +------+----------------------+-------+ | 1 | 21.3999999999999986 | 21.40 | | 2 | 76.7999999999999972 | 76.80 | | 3 | 7.4000000000000004 | 7.40 | | 4 | 15.4000000000000004 | 15.40 | | 5 | 7.2000000000000002 | 7.20 | | 6 | -51.3999999999999986 | 0.00 | +------+----------------------+-------+
Depending on the computer architecture you may or may not see similar results. Each CPU may evaluate floating-point numbers differently. For example in some machines you may get 'right' results by multiplying both arguments with 1, an example follows.
WARNING: NEVER TRUST THIS METHOD IN YOUR APPLICATION, THIS IS AN EXAMPLE OF A WRONG METHOD!!!
mysql> SELECT i, ROUND(SUM(d1), 2)*1 AS a, ROUND(SUM(d2), 2)*1 AS b -> FROM t1 GROUP BY i HAVING a <> b; +------+--------+------+ | i | a | b | +------+--------+------+ | 6 | -51.40 | 0.00 | +------+--------+------+
The reason why the above example seems to be working is that on the particular machine where the test was done, the CPU floating-point arithmetics happens to round the numbers to same, but there is no rule that any CPU should do so, so it cannot be trusted.
The correct way to do floating-point number comparison is to first decide on what is the wanted tolerance between the numbers and then do the comparison against the tolerance number. For example, if we agree on that floating-point numbers should be regarded the same, if they are same with precision of one of ten thousand (0.0001), the comparison should be done like this:
mysql> SELECT i, SUM(d1) AS a, SUM(d2) AS b FROM t1 -> GROUP BY i HAVING ABS(a - b) > 0.0001; +------+--------+------+ | i | a | b | +------+--------+------+ | 6 | -51.40 | 0.00 | +------+--------+------+ 1 row in set (0.00 sec)
And vice versa, if we wanted to get rows where the numbers are the same, the test would be:
mysql> SELECT i, SUM(d1) AS a, SUM(d2) AS b FROM t1 -> GROUP BY i HAVING ABS(a - b) < 0.0001; +------+-------+-------+ | i | a | b | +------+-------+-------+ | 1 | 21.40 | 21.40 | | 2 | 76.80 | 76.80 | | 3 | 7.40 | 7.40 | | 4 | 15.40 | 15.40 | | 5 | 7.20 | 7.20 | +------+-------+-------+
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MySQL uses a cost based optimizer to find out the best way to resolve a query. In many cases MySQL can calculate the best possible query plan but in some cases MySQL doesn't have enough information about the data at hand and have to do some 'educated' guesses about the data.
This manual section is intended for the cases when MySQL doesn't get it right.
The tools one has available to help MySQL do the 'right' things are:
EXPLAIN. See EXPLAIN.
ANALYZE TABLE. See ANALYZE TABLE.
USE INDEX, FORCE INDEX and IGNORE INDEX. See SELECT.
Global and table level STRAIGHT JOIN. See SELECT.
Setting thread specific variables. See SHOW VARIABLES.
EXPLAIN will show ALL in the type column when MySQL uses a table scan to resolve a query. This happens usually when:
The table is so small that it's faster to do a table scan than a key lookup. This is a common case for tables with < 10 rows and a short row length.
There is no usable restrictions in the ON or WHERE clause for indexed columns.
You are comparing indexed columns with constants and MySQL has calculated (based on the index tree) that the constants covers a too big part of the table and a table scan would be faster. See Where optimisations.
You are using a key with low cardinality (= many matching rows) through another column. MySQL will in this case assume that by using the key it will probably do a lot of key lookups and in this case the table scan would be faster.
What you can do to avoid a 'wrong' table scan for big tables are:
Use ANALYZE TABLE for the scanned table to update key distributions. See ANALYZE TABLE.
Use FORCE INDEX for the scanned table to tell MySQL that table scans are very expensive compared to use one of the given index. See SELECT.
SELECT * FROM t1,t2 force index(index_for_column) WHERE t1.column=t2.column;
Start mysqld with --max-seeks-for-key=1000 or do SET MAX_SEEKS_FOR_KEY=1000 to tell the optimizer that for no key scan will cause more than 1000 key seeks.
Table of Contents
ALTER TABLE changes a table to the current character set. If you get a duplicate key error during ALTER TABLE, then the cause is either that the new character sets maps two keys to the same value or that the table is corrupted, in which case you should run REPAIR TABLE on the table.
If ALTER TABLE dies with an error like this:
Error on rename of './database/name.frm' to './database/B-a.frm' (Errcode: 17)
the problem may be that MySQL has crashed in a previous ALTER TABLE and there is an old table named A-something or B-something lying around. In this case, go to the MySQL data directory and delete all files that have names starting with A- or B-. (You may want to move them elsewhere instead of deleting them.)
ALTER TABLE works the following way:
Create a new table named A-xxx with the requested changes.
All rows from the old table are copied to A-xxx.
The old table is renamed B-xxx.
A-xxx is renamed to your old table name.
B-xxx is deleted.
If something goes wrong with the renaming operation, MySQL tries to undo the changes. If something goes seriously wrong (this shouldn't happen), MySQL may leave the old table as B-xxx, but a simple rename on the system level should get your data back.
The whole point of SQL is to abstract the application from the data storage format. You should always specify the order in which you wish to retrieve your data. For example:
SELECT col_name1, col_name2, col_name3 FROM tbl_name;
will return columns in the order col_name1, col_name2, col_name3, whereas:
SELECT col_name1, col_name3, col_name2 FROM tbl_name;
will return columns in the order col_name1, col_name3, col_name2.
If you want to change the order of columns anyway, you can do it as follows:
Create a new table with the columns in the right order.
Execute INSERT INTO new_table SELECT fields-in-new_table-order FROM old_table.
Drop or rename old_table.
ALTER TABLE new_table RENAME old_table.
In an application, you should never use SELECT * and retrieve the columns based on their position, because the order and position in which columns are returned will not remain the same if you add, move, or delete columns. A simple change to your database structure would then cause your application to fail. SELECT * is quite suitable for testing queries.
The following are a list of the limitations with TEMPORARY TABLES.
A temporary table can only be of type HEAP, ISAM, MyISAM, MERGE, or InnoDB.
You can't use temporary tables more than once in the same query. For example, the following doesn't work.
mysql> SELECT * FROM temporary_table, temporary_table AS t2;
You can't use RENAME on a TEMPORARY table. Note that ALTER TABLE org_name RENAME new_name works!
This appendix lists the developers, contributors, and supporters that have helped to make MySQL what it is today.
These are the developers that are or have been employed by MySQL AB to work on the MySQL database software, roughly in the order they started to work with us. Following each developer is a small list of the tasks that the developer is responsible for, or the accomplishments they have made. All developers are involved in support.
Michael (Monty) Widenius
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David Axmark
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Jani Tolonen
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Sinisa Milivojevic
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Tonu Samuel (past developer)
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Sasha Pachev
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Matt Wagner
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Miguel Solorzano
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Timothy Smith (past developer)
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Sergei Golubchik
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Jeremy Cole
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Indrek Siitan
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Jorge del Conde
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Venu Anuganti
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Arjen Lentz
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Alexander (Bar) Barkov, Alexey (Holyfoot) Botchkov, and Ramil Kalimullin
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Oleksandr (Sanja) Byelkin
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Aleksey (Walrus) Kishkin and Alexey (Ranger) Stroganov
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Zak Greant
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Carsten Pedersen
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Lenz Grimmer
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Peter Zaitsev
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Alexander (Salle) Keremidarski
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Per-Erik Martin
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Jim Winstead
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Mark Matthews
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Peter Gulutzan
SQL-99, SQL:2003 standards compliance.
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Guilhem Bichot
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Antony T. Curtis
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While MySQL AB owns all copyrights in the MySQL server and the MySQL manual, we wish to recognize those who have made contributions of one kind or another to the MySQL distribution. Contributors are listed here, in somewhat random order:
Gianmassimo Vigazzola <qwerg@mbox.vol.it> or <qwerg@tin.it> | The initial port to Win32/NT. |
Per Eric Olsson | For more or less constructive criticism and real testing of the dynamic record format. |
Irena Pancirov <irena@mail.yacc.it> | Win32 port with Borland compiler. mysqlshutdown.exe and mysqlwatch.exe |
David J. Hughes | For the effort to make a shareware SQL database. At TcX, the predecessor of MySQL AB, we started with mSQL, but found that it couldn't satisfy our purposes so instead we wrote an SQL interface to our application builder Unireg. mysqladmin and mysql client are programs that were largely influenced by their mSQL counterparts. We have put a lot of effort into making the MySQL syntax a superset of mSQL. Many of the API's ideas are borrowed from mSQL to make it easy to port free mSQL programs to the MySQL API. The MySQL software doesn't contain any code from mSQL. Two files in the distribution (client/insert_test.c and client/select_test.c) are based on the corresponding (non-copyrighted) files in the mSQL distribution, but are modified as examples showing the changes necessary to convert code from mSQL to MySQL Server. (mSQL is copyrighted David J. Hughes.) |
Patrick Lynch | For helping us acquire http://www.mysql.com/. |
Fred Lindberg | For setting up qmail to handle the MySQL mailing list and for the incredible help we got in managing the MySQL mailing lists. |
Igor Romanenko <igor@frog.kiev.ua> | mysqldump (previously msqldump, but ported and enhanced by Monty). |
Yuri Dario | For keeping up and extending the MySQL OS/2 port. |
Tim Bunce | Author of mysqlhotcopy. |
Zarko Mocnik <zarko.mocnik@dem.si> | Sorting for Slovenian language. |
"TAMITO" <tommy@valley.ne.jp> | The _MB character set macros and the ujis and sjis character sets. |
Joshua Chamas <joshua@chamas.com> | Base for concurrent insert, extended date syntax, debugging on NT, and answering on the MySQL mailing list. |
Yves Carlier <Yves.Carlier@rug.ac.be> | mysqlaccess, a program to show the access rights for a user. |
Rhys Jones <rhys@wales.com> (And GWE Technologies Limited) | For one of the early JDBC drivers. |
Dr Xiaokun Kelvin ZHU <X.Zhu@brad.ac.uk> | Further development of one of the early JDBC drivers and other MySQL-related Java tools. |
James Cooper <pixel@organic.com> | For setting up a searchable mailing list archive at his site. |
Rick Mehalick <Rick_Mehalick@i-o.com> | For xmysql, a graphical X client for MySQL Server. |
Doug Sisk <sisk@wix.com> | For providing RPM packages of MySQL for Red Hat Linux. |
Diemand Alexander V. <axeld@vial.ethz.ch> | For providing RPM packages of MySQL for Red Hat Linux-Alpha. |
Antoni Pamies Olive <toni@readysoft.es> | For providing RPM versions of a lot of MySQL clients for Intel and SPARC. |
Jay Bloodworth <jay@pathways.sde.state.sc.us> | For providing RPM versions for MySQL Version 3.21. |
David Sacerdote <davids@secnet.com> | Ideas for secure checking of DNS hostnames. |
Wei-Jou Chen <jou@nematic.ieo.nctu.edu.tw> | Some support for Chinese(BIG5) characters. |
Wei He <hewei@mail.ied.ac.cn> | A lot of functionality for the Chinese(GBK) character set. |
Jan Pazdziora <adelton@fi.muni.cz> | Czech sorting order. |
Zeev Suraski <bourbon@netvision.net.il> | FROM_UNIXTIME() time formatting, ENCRYPT() functions, and bison advisor. Active mailing list member. |
Luuk de Boer <luuk@wxs.nl> | Ported (and extended) the benchmark suite to DBI/DBD. Have been of great help with crash-me and running benchmarks. Some new date functions. The mysql_setpermissions script. |
Alexis Mikhailov <root@medinf.chuvashia.su> | User-defined functions (UDFs); CREATE FUNCTION and DROP FUNCTION. |
Andreas F. Bobak <bobak@relog.ch> | The AGGREGATE extension to UDF functions. |
Ross Wakelin <R.Wakelin@march.co.uk> | Help to set up InstallShield for MySQL-Win32. |
Jethro Wright III <jetman@li.net> | The libmysql.dll library. |
James Pereria <jpereira@iafrica.com> | Mysqlmanager, a Win32 GUI tool for administering MySQL Servers. |
Curt Sampson <cjs@portal.ca> | Porting of MIT-pthreads to NetBSD/Alpha and NetBSD 1.3/i386. |
Martin Ramsch <m.ramsch@computer.org> | Examples in the MySQL Tutorial. |
Steve Harvey | For making mysqlaccess more secure. |
Konark IA-64 Centre of Persistent Systems Private Limited | http://www.pspl.co.in/konark/. Help with the Win64 port of the MySQL server. |
Albert Chin-A-Young. | Configure updates for Tru64, large file support and better TCP wrappers support. |
John Birrell | Emulation of pthread_mutex() for OS/2. |
Benjamin Pflugmann | Extended MERGE tables to handle INSERTS. Active member on the MySQL mailing lists. |
Jocelyn Fournier | Excellent spotting and reporting innumerable bugs (especially in the MySQL 4.1 subquery code). |
Marc Liyanage | Maintaining the Mac OS X packages and providing invaluable feedback on how to create Mac OS X PKGs. |
Robert Rutherford | Providing invaluable information and feedback about the QNX port. |
Other contributors, bugfinders, and testers: James H. Thompson, Maurizio Menghini, Wojciech Tryc, Luca Berra, Zarko Mocnik, Wim Bonis, Elmar Haneke, <jehamby@lightside>, <psmith@BayNetworks.com>, <duane@connect.com.au>, Ted Deppner <ted@psyber.com>, Mike Simons, Jaakko Hyvatti.
And lots of bug report/patches from the folks on the mailing list.
A big tribute goes to those that help us answer questions on the MySQL mailing lists:
Daniel Koch <dkoch@amcity.com> | Irix setup. |
Luuk de Boer <luuk@wxs.nl> | Benchmark questions. |
Tim Sailer <tps@users.buoy.com> | DBD::mysql questions. |
Boyd Lynn Gerber <gerberb@zenez.com> | SCO-related questions. |
Richard Mehalick <RM186061@shellus.com> | xmysql-related questions and basic installation questions. |
Zeev Suraski <bourbon@netvision.net.il> | Apache module configuration questions (log & auth), PHP-related questions, SQL syntax-related questions and other general questions. |
Francesc Guasch <frankie@citel.upc.es> | General questions. |
Jonathan J Smith <jsmith@wtp.net> | Questions pertaining to OS-specifics with Linux, SQL syntax, and other things that might need some work. |
David Sklar <sklar@student.net> | Using MySQL from PHP and Perl. |
Alistair MacDonald <A.MacDonald@uel.ac.uk> | Not yet specified, but is flexible and can handle Linux and maybe HP-UX. Will try to get user to use mysqlbug. |
John Lyon <jlyon@imag.net> | Questions about installing MySQL on Linux systems, using either .rpm files or compiling from source. |
Lorvid Ltd. <lorvid@WOLFENET.com> | Simple billing/license/support/copyright issues. |
Patrick Sherrill <patrick@coconet.com> | ODBC and VisualC++ interface questions. |
Randy Harmon <rjharmon@uptimecomputers.com> | DBD, Linux, some SQL syntax questions. |
The following people has helped us with writing the MySQL documentation and translating the documentation or error messages in MySQL.
Paul DuBois | Ongoing help with making this manual correct and understandable. That includes rewriting Monty's and David's attempts at English into English as other people know it. |
Kim Aldale | Helped to rewrite Monty's and David's early attempts at English into English. |
Michael J. Miller Jr. <mke@terrapin.turbolift.com> | For the first MySQL manual. And a lot of spelling/language fixes for the FAQ (that turned into the MySQL manual a long time ago). |
Yan Cailin | First translator of the MySQL Reference Manual into simplified Chinese in early 2000 on which the Big5 and HK coded (http://mysql.hitstar.com/) versions were based. Personal home page at linuxdb.yeah.net. |
Jay Flaherty <fty@mediapulse.com> | Big parts of the Perl DBI/DBD section in the manual. |
Paul Southworth <pauls@etext.org>, Ray Loyzaga <yar@cs.su.oz.au> | Proof-reading of the Reference Manual. |
Therrien Gilbert <gilbert@ican.net>, Jean-Marc Pouyot <jmp@scalaire.fr> | French error messages. |
Petr Snajdr, <snajdr@pvt.net> | Czech error messages. |
Jaroslaw Lewandowski <jotel@itnet.com.pl> | Polish error messages. |
Miguel Angel Fernandez Roiz | Spanish error messages. |
Roy-Magne Mo <rmo@www.hivolda.no> | Norwegian error messages and testing of Version 3.21.#. |
Timur I. Bakeyev <root@timur.tatarstan.ru> | Russian error messages. |
<brenno@dewinter.com> & Filippo Grassilli <phil@hyppo.com> | Italian error messages. |
Dirk Munzinger <dirk@trinity.saar.de> | German error messages. |
Billik Stefan <billik@sun.uniag.sk> | Slovak error messages. |
Stefan Saroiu <tzoompy@cs.washington.edu> | Romanian error messages. |
Peter Feher | Hungarian error messages. |
Roberto M. Serqueira | Portuguese error messages. |
Carsten H. Pedersen | Danish error messages. |
Arjen G. Lentz | Dutch error messages, completing earlier partial translation (also work on consistency and spelling). |
The following is a list of the creators of the libraries we have included with the MySQL server source to make it easy to compile and install MySQL. We are very thankfully to all individuals that have created these and it has made our life much easier.
Fred Fish | For his excellent C debugging and trace library. Monty has made a number of smaller improvements to the library (speed and additional options). |
Richard A. O'Keefe | For his public domain string library. |
Henry Spencer | For his regex library, used in WHERE column REGEXP regexp. |
Chris Provenzano | Portable user level pthreads. From the copyright: This product includes software developed by Chris Provenzano, the University of California, Berkeley, and contributors. We are currently using version 1_60_beta6 patched by Monty (see mit-pthreads/Changes-mysql). |
Jean-loup Gailly and Mark Adler | For the zlib library (used on MySQL on Windows). |
Bjorn Benson | For his safe_malloc (memory checker) package which is used in when you configure MySQL with --debug. |
Free Software Foundation | The readline library (used by the mysql command line client). |
The NetBSD foundation | The libedit package (optionally used by the mysql command line client). |
The following is a list of creators/maintainers of some of the most important API/packages/applications that a lot of people use with MySQL.
We can't list every possible package here becasue the list would then be way to hard to maintain. For other packages, please refer to the software portal at http://www.mysql.com/portal/software.
Tim Bunce, Alligator Descartes | For the DBD (Perl) interface. |
Andreas Koenig <a.koenig@mind.de> | For the Perl interface for MySQL Server. |
Jochen Wiedmann <wiedmann@neckar-alb.de> | For maintaining the Perl DBD::mysql module. |
Eugene Chan <eugene@acenet.com.sg> | For porting PHP for MySQL Server. |
Georg Richter | MySQL 4.1 testing and bug hunting. New PHP 5.0 mysqli extension (API) for use with MySQL 4.1 and up. |
Giovanni Maruzzelli <maruzz@matrice.it> | For porting iODBC (Unix ODBC). |
Xavier Leroy <Xavier.Leroy@inria.fr> | The author of LinuxThreads (used by the MySQL Server on Linux). |
The following is a list of some of the tools we have used to create MySQL. We use this to express our thanks to those that has created them as without these we could not have made MySQL what is is today.
Free Software Foundation | From whom we got an excellent compiler (gcc), an excellent debugger (gdb and the libc library (from which we have borrowed strto.c to get some code working in Linux). |
Free Software Foundation & The XEmacs development team | For a really great editor/environment used by almost everybody at MySQL AB. |
Julian Seward | Author of valgrind, an excellent memory checker tool that has helped us find a lot of otherwise hard to find bugs in MySQL. |
Dorothea Lütkehaus and Andreas Zeller | For DDD (The Data Display Debugger) which is an excellent graphical frontend to gdb). |
While MySQL AB owns all copyrights in the MySQL server and the MySQL manual, we wish to recognize the following companies, which helped us finance the development of the MySQL server, such as by paying us for developing a new feature or giving us hardware for development of the MySQL server.
VA Linux / Andover.net | Funded replication. |
NuSphere | Editing of the MySQL manual. |
Stork Design studio | The MySQL web site in use between 1998-2000. |
Intel | Contributed to development on Windows and Linux platforms. |
Compaq | Contributed to Development on Linux/Alpha. |
SWSoft | Development on the embedded mysqld version. |
FutureQuest | --skip-show-database |
This appendix lists the changes from version to version in the MySQL source code.
We are now working actively on MySQL 4.1 and 5.0, and will provide only critical bug fixes for MySQL 4.0 and MySQL 3.23. We update this section as we add new features, so that everybody can follow the development.
Our TODO section contains what further plans we have for 4.1 & 5.0. See TODO.
Note that we tend to update the manual at the same time we make changes to MySQL. If you find a version listed here that you can't find on the MySQL download page (http://www.mysql.com/downloads/), this means that the version has not yet been released!
The date mentioned with a release version is the date of the last BitKeeper ChangeSet that this particular release has been based on, not the date when the packages have been made available. The binaries are usually made available a few days after the date of the tagged ChangeSet - building and testing all packages takes some time.
Table of Contents
The following changelog shows what has already been done in the 5.0 tree:
Basic support for stored procedures (SQL:2003 style). See Stored Procedures.
Added SELECT INTO list_of_vars, which can be of mixed, that is, global and local type. See SELECT INTO Statement.
Removed the update log. It is fully replaced by the binary log. If the MySQL server is started with --log-update, it will be translated to --log-bin (or ignored if the server is explicitly started with --log-bin), and a warning message will be written to the error log. Setting SQL_LOG_UPDATE will silently set SQL_LOG_BIN instead (or do nothing if the server is explicitly started with --log-bin).
User variable names are now case insensitive: if you do SET @a=10; then SELECT @A; will now return 10. Case sensitivity of a variable's value depends on the collation of the value.
For a full list of changes, please refer to the changelog sections for each individual 5.0.x release.
Functionality added or changed:
For replication of HEAP tables: Made the master automatically write a DELETE FROM statement to its binary log when a HEAP table is opened for the first time since master's startup. This is for the case where the slave has replicated a non-empty HEAP table, then the master is shut down and restarted: the table is now empty on master; the DELETE FROM empties it on slave too. Note that even with this fix, between the master's restart and the first use of the table on master, the slave still has out-of-date data in the table. But if you use the init-file option to populate the HEAP table on the master at startup, it ensures that the failing time interval is zero. (Bug #2477)
Bugs fixed:
ALTER DATABASE caused the client to hang if the database did not exist. (Bug #2333)
SLAVE START (which is a deprecated syntax, START SLAVE should be used instead) could crash the slave. (Bug #2516)
Multiple-table DELETE statements were never replicated by the slave if there were any replicate-*-table options. (Bug #2527)
The MySQL server did not report any error if the query (submitted through mysql_real_query() or mysql_prepare()) was terminated by garbage characters (which can happen if you pass a wrong length parameter to mysql_real_query() or mysql_prepare()); the result was that the garbage characters were written into the binary log. (Bug #2703)
Functionality added or changed:
The KILL statement now takes CONNECTION and QUERY variants. The first is the same as KILL with no modifier (it kills a given connection thread). The second kills only the statement currently being executed by the connection.
Added TIMESTAMPADD() and TIMESTAMPDIFF() functions.
Added WEEK and QUARTER values as INTERVAL arguments for DATE_ADD() and DATE_SUB() functions.
New binary log format which enables replication of those session variables: SQL_MODE, SQL_AUTO_IS_NULL, FOREIGN_KEY_CHECKS (that one was already replicated since 4.0.14 but here it's done more efficiently: takes less space in the binary logs), UNIQUE_CHECKS. Other variables (like character sets, SQL_SELECT_LIMIT...) will be replicated in next 5.0.x releases.
Merge Index optimization for OR clauses. See OR optimizations.
Basic support for stored procedures (SQL:2003 style). See Stored Procedures.
Added SELECT INTO list_of_vars, which can be of mixed, that is, global and local type. See SELECT INTO Statement.
Easier replication upgrade (5.0.0 masters can read older binary logs, 5.0.0 slaves can read older relay logs; see Replication Upgrade for more details). The format of the binary log and relay log is changed compared to the one of MySQL 4.1 and older.
IMPORTANT NOTE: If you upgrade to InnoDB-4.1.1 or higher, you cannot downgrade to a version lower than 4.1.1 any more! That is because earlier versions of InnoDB are not aware of multiple tablespaces.
Bugs fixed:
Table of Contents
Version 4.1 of the MySQL server includes many enhancements and new features. Binaries for this version are available for download at http://www.mysql.com/downloads/mysql-4.1.html.
Subqueries and derived tables (unnamed views). See Subqueries.
INSERT ... ON DUPLICATE KEY UPDATE ... syntax. This allows you to UPDATE an existing row if the insert would cause a duplicate value in a PRIMARY or UNIQUE key. (REPLACE allows you to overwrite an existing row, which is something entirely different.) See INSERT.
A newly designed GROUP_CONCAT() aggregate function. See Group by functions and modifiers.
Extensive Unicode (UTF8) support.
Character sets can be defined per column, table, and database.
New key cache for MyISAM tables with many tunable parameters. You can have multiple key caches, preload index into caches for batches...
BTREE index on HEAP tables.
Support for OpenGIS spatial types (geographical data). See Spatial extensions in MySQL.
SHOW WARNINGS shows warnings for the last command. See SHOW WARNINGS.
Faster binary protocol with prepared statements and parameter binding. See C API Prepared statements.
You can now issue multiple statements with a single C API call and then read the results in one go. See C API multiple queries.
Create Table: CREATE [TEMPORARY] TABLE [IF NOT EXISTS] table2 LIKE table1.
Server based HELP command that can be used in the mysql command line client (and other clients) to get help for SQL statements.
For a full list of changes, please refer to the changelog sections for each individual 4.1.x release.
Functionality added or changed:
ft_boolean_syntax variable is now changeable. See ft_boolean_syntax.
REVOKE ALL PRIVILEGES, GRANT FROM user_list is changed to a more consistent REVOKE ALL PRIVILEGES, GRANT OPTION FROM user_list. (Bug #2642)
Internal string-to-number conversion now support only SQL:2003 compatible syntax for numbers. In particular "0x10"+0 will not work anymore (actually even before it worked only on some systems, e.g. on Linux, and did not work on others, like FreeBSD, or Solaris. Making these queries OS-independent was the goal of this change). Use CONV() to convert hexadecimal numbers to decimal. E.g. CONV(MID("0x10",3),16,10)+0.
mysqlhotcopy now works on NetWare.
ALTER TABLE DROP PRIMARY KEY no longer drops the first UNIQUE index if there is no primary index. (Bug #2361)
Added latin1_spanish_ci (Modern Spanish) collation for the latin1 character set.
ENGINE is now a synonym for the TYPE option for CREATE TABLE and ALTER TABLE.
Added init_connect and init_slave server variables. The values should be SQL statements to be executed when each client connects or each time a slave's SQL thread starts, respectively.
C API enhancement: SERVER_QUERY_NO_INDEX_USED and SERVER_QUERY_NO_GOOD_INDEX_USED flags are now set in server_status field of MYSQL structure. It is these flags that make the query to be logged as slow if mysqld was started with --log-slow-queries --log-queries-not-using-indexes.
For replication of HEAP tables: Made the master automatically write a DELETE FROM statement to its binary log when a HEAP table is opened for the first time since master's startup. This is for the case where the slave has replicated a non-empty HEAP table, then the master is shut down and restarted: the table is now empty on master; the DELETE FROM empties it on slave too. Note that even with this fix, between the master's restart and the first use of the table on master, the slave still has out-of-date data in the table. But if you use the init-file option to populate the HEAP table on the master at startup, it ensures that the failing time interval is zero. (Bug #2477)
Bugs fixed:
Crash in MATCH ... AGAINST() on a phrase search operator with a missing closing double quote fixed. (Bug #2708)
For now SQL_SELECT_LIMIT variable have not influence on subqueries. (Bug #2600)
Fixed output of mysqldump --tab (Bug #2705)
Fix for a bug in UNION's which prevented proper handling of NULL columns. This is happening only if a column in the first SELECT node was NOT NULL. (Bug #2508)
Fix for a bug in UNION's with INNODB storage engine, when some columns from one table where used in one SELECT node and some were used in another node. (Bug #2552)
Fixed bug in range optimizer which caused segmentation fault. (Bug #2698)
Fixed bug with SHOW CREATE TABLE ... which didn't properly double quotes. (Bug #2593)
Queries with subqueries in FROM clause locks all tables at once for now. This also fixed bugs in EXPLAIN of subqueries in FROM output. (Bug #2120)
Fixed bug when mysqldump didn't quote "tricky" names correctly (Bug #2592)
Fix for a bug in 4.1.2 that prevented table / column privileges from being loaded on startup. (Bug #2546)
Fixed bug in replication with CREATE TABLE .. LIKE .. that resulted in a statement not being written to the binary log. (Bug #2557)
Fixed memory leak in INSERT ... ON DUPLICATE KEY UPDATE .... (Bug #2438)
Fixed bug in the parser, making the syntax CONVERT(expression,type) legal again.
Fixed parsing of short-form IP addresses in INET_ATON(). (Bug #2310)
Fixed a bug in CREATE ... SELECT that sometimes caused a string column with a multi-byte character set (such as utf8) to have insufficient length to hold the data.
Fixed a rare table corruption on adding data (INSERT, REPLACE, UPDATE, etc. but not DELETE) to a FULLTEXT index. (Bug #2417)
Compile the MySQL-client RPM package against libreadline instead of libedit. (Bug #2289)
Fix for a crashing bug that was caused by not setting vio_timeout() virtual function for all protocols. This bug occurred on Windows. (Bug #2025)
Fix for a bug that caused mysql client program to erroneously cache the value of the current database. (Bug #2025)
Fix for a bug that caused client/server communication to be broken when mysql_set_server_option() or mysql_get_server_option() were invoked. (Bug #2207)
Fix for a bug that caused wong results when CAST() was applied on NULL to signed or unsigned integer column. (Bug #2219)
Fix for a crashing bug that occurred in the mysql client program when database name was longer then expected. (Bug #2221)
Fixed a bug in CHECK TABLE that occasionally resulted in spurious "Found key at page ... that points to record outside datafile" error on a table with a FULLTEXT index. (Bug #2190)
Fixed bug in GRANT with table-level privilege handling. (Bug #2178)
Fixed bug in ORDER BY on a small column. (Bug #2147)
Fixed a bug with the INTERVAL() function when 8 or more comparison arguments are provided. (Bug #1561)
Packaging: Fixed a bug in the Mac OS PKG postinstall script (mysql_install_db was called with an obsolete argument).
Packaging: Added missing file mysql_create_system_tables to the server RPM package. This bug was fixed for the 4.1.1 RPMs by updating the MySQL-server RPM from MySQL-server-4.1.1-0 to MySQL-server-4.1.1-1. The other RPMs were not affected by this change.
Fixed a bug in myisamchk and CHECK TABLE that sometimes resulted in a spurious error Found key at page ..... that points to record outside datafile for a table with a FULLTEXT index. (Bug #1977)
Fixed a hang in full-text indexing of strings in multi-byte (all besides utf8) charsets. (Bug #2065)
Fixed a crash in full-text indexing of UTF8 data. (Bug #2033)
Replication: a rare race condition in the slave SQL thread that could lead to an incorrect complaint that the relay log is corrupted. (Bug #2011)
Replication: if an administrative command on a table (OPTIMIZE TABLE, REPAIR TABLE etc) was run on the slave, this could sometimes stop the slave SQL thread (this did not lead to any corruption; one just had to type START SLAVE to get replication going again). (Bug #1858)
Replication: in the slave SQL thread, a multi-table UPDATE could produce an incorrect complaint that some record was not found in one table, if the UPDATE was preceded by a INSERT ... SELECT. (Bug #1701)
Replication: sometimes the master gets a non-fatal error during the execution of a statement but finally the statements succeeds (for example, a write to a MyISAM table first receives "no space left on device" but is able to finally complete, see Full disk); the bug was that the master forgot to reset the error code to 0 after success, so the error code got into its binary log, thus making the slave giving false alarms like "did not get the same error as on master". (Bug #2083)
Removed a misleading "check permissions on master.info" from a replication error message, because the cause of the problem could be different from permissions. (Bug #2121)
Fixed a crash when the replication slave was unable to create the first relay log. (Bug #2145)
ALTER DATABASE caused the client to hang if the database did not exist. (Bug #2333)
Multi-table DELETE statements were never replicated by the slave if there were any replicate-*-table options. (Bug #2527)
Fixed bug in ALTER TABLE RENAME, when rename to the table with the same name in another database silently dropped destination table if it existed. (Bug #2628)
The MySQL server did not report any error if the query (submitted through mysql_real_query() or mysql_prepare()) was terminated by garbage characters (which can happen if you pass a wrong length parameter to mysql_real_query() or mysql_prepare()); the result was that the garbage characters were written into the binary log. (Bug #2703)
Fixed bug in client library which caused mysql_fetch and mysql_stmt_store_result() to hang if they were called without prior call of mysql_execute(). Now they give an error instead. (Bug #2248)
This release includes all fixes in MySQL 4.0.16 and most of the fixes in MySQL 4.0.17.
Functionality added or changed:
It is now possible to create multiple key caches, assign table indexes to particular caches, and to preload indexes into caches. See CACHE INDEX. See LOAD INDEX. Structured system variables are introduced as a means of grouping related key cache parameters. See Structured System Variables.
New COERCIBILITY() function to return the collation coercibility of a string.
mysqldump now includes a statement in the dump output to set FOREIGN_KEY_CHECKS to 0 to avoid problems with tables having to be reloaded in a particular order when the dump is reloaded. The existing FOREIGN_KEY_CHECKS value is saved and restored.
IMPORTANT NOTE: if you upgrade to InnoDB-4.1.1 or higher, you cannot downgrade to a version lower than 4.1.1 any more! That is because earlier versions of InnoDB are not aware of multiple tablespaces.
One can revoke all privileges from a user with REVOKE ALL PRIVILEGES, GRANT FROM user_list.
Added IGNORE option for DELETE statement.
The MySQL source distribution now also includes the MySQL Internals Manual internals.texi.
Added mysql_set_server_option() C API client function to allow multiple statement handling in the server to be enabled or disabled.
The mysql_next_result() C API function now returns -1 if there are no more result sets.
Renamed CLIENT_MULTI_QUERIES connect option flag to CLIENT_MULTI_STATEMENTS. To allow for a transition period, the old option will continue to be recognized for a while.
Require DEFAULT before table and database default character set. This enables us to use ALTER TABLE table_name ... CHARACTER SET=... to change the character set for all CHAR, VARCHAR, and TEXT columns in a table.
Added MATCH ... AGAINST( ... WITH QUERY EXPANSION) and the ft_query_expansion_limit server variable.
Removed unused ft_max_word_len_for_sort server variable.
Full-text search now supports multi-byte character sets and the Unicode utf8 character set. (The Unicode ucs2 character set is not yet supported.)
Phrase search in MATCH ... AGAINST ( ... IN BOOLEAN MODE) no longer matches partial words.
Added aggregate function BIT_XOR() for bitwise XOR operations.
Replication over SSL now works.
The START SLAVE statement now supports an UNTIL clause for specifying that the slave SQL thread should be started but run only until it reaches a given position in the master's binary logs or in the slave's relay logs.
Produce warnings even for single-row INSERT statements, not just for multiple-row INSERT statements. Previously, it was necessary to set SQL_WARNINGS=1 to generate warnings for single-row statements.
Added delimiter (\d) command to the mysql command-line client for changing the statement delimiter (terminator). The default delimiter is semicolon.
CHAR, VARCHAR, and TEXT columns now have lengths measured in characters rather than in bytes. The character size depends on the column's character set. This means, for example, that a CHAR(n) column for a multi-byte character set will take more storage than before. Similarly, index values on such columns are measured in characters, not bytes.
LIMIT no longer accepts negative arguments (they used to be treated as very big positive numbers before).
The DATABASE() function now returns NULL rather than the empty string if there is no database selected.
Added --sql-mode=NO_AUTO_VALUE_ON_ZERO option to suppress the usual behavior of generating the next sequence number when zero is stored in an AUTO_INCREMENT column. With this mode enabled, zero is stored as zero; only storing NULL generates a sequence number.
Warning: Incompatible change! Client authentication now is based on 41-byte passwords in the user table, not 45-byte passwords as in 4.1.0. Any 45-byte passwords created for 4.1.0 must be reset after running the mysql_fix_privilege_tables script.
Added MySQL Server option and global variable 'secure-auth' that disallows authentication for accounts that have old (pre-4.1.1) passwords.
Added MySQL command line client option 'secure-auth'. If this option is set, client will refuse to send password in old (pre-4.1.1) format.
Warning: Incompatible change! Renamed the C API mysql_prepare_result() function to mysql_get_metadata() as the old name was confusing.
Added DROP USER 'username'@'hostname' statement to drop an account that has no privileges.
The interface to aggregated UDF functions has changed a bit. You must now declare a xxx_clear() function for each aggregate function XXX().
Added new ADDTIME(), DATE(), DATEDIFF(), LAST_DAY(), MAKEDATE(), MAKETIME(), MICROSECOND(), SUBTIME(), TIME(), TIMEDIFF(), TIMESTAMP(), UTC_DATE(), UTC_TIME(), UTC_TIMESTAMP(), and WEEKOFYEAR() functions.
Added new syntax for ADDDATE() and SUBDATE(). The second argument now may be a number representing the number of days to be added to or subtracted from the first date argument.
Added new type values DAY_MICROSECOND, HOUR_MICROSECOND, MINUTE_MICROSECOND, SECOND_MICROSECOND, and MICROSECOND for DATE_ADD(), DATE_SUB(), and EXTRACT().
Added new %f microseconds format specifier for DATE_FORMAT() and TIME_FORMAT().
All queries in which at least one SELECT does not use indexes properly now are written to the slow query log when long log format is used.
It is now possible to create a MERGE table from MyISAM tables in different databases. Formerly, all the MyISAM tables had to be in the same database, and the MERGE table had to be created in that database as well.
Added new COMPRESS(), UNCOMPRESS(), and UNCOMPRESSED_LENGTH() functions.
When doing SET sql_mode="mode" for a complex mode (like ANSI), we now update the sql_mode variable to include all the individual options implied by the complex mode.
Added the OLAP (On-Line Analytical Processing) function ROLLUP, which provides summary rows for each GROUP BY level.
Added SQLSTATE codes for all server errors.
Added mysql_sqlstate() and mysql_stmt_sqlstate() C API client functions that return the SQLSTATE error code for the last error.
TIME columns with hour values greater than 24 were returned incorrectly to the client.
ANALYZE, OPTIMIZE, REPAIR, and FLUSH statements are now stored in the binary log and thus replicated to slaves. This logging does not occur if the optional NO_WRITE_TO_BINLOG keyword (or its alias LOCAL) is given. Exceptions are that FLUSH LOGS, FLUSH MASTER, FLUSH SLAVE, and FLUSH TABLES WITH READ LOCK are not logged in any case. For a syntax example, see FLUSH.
New global variable RELAY_LOG_PURGE to enable or disable automatic relay log purging.
LOAD DATA now produces warnings that can be fetched with SHOW WARNINGS.
Added support for syntax CREATE TABLE table2 (LIKE table1) that creates an empty table table2 with a definition that is exactly the same as table1, including any indexes.
CREATE TABLE table_name (...) TYPE=storage_engine now generates a warning if the named storage engine is not available. The table is still created as a MyISAM table, as before.
Most subqueries are now much faster than before.
Added PURGE BINARY LOGS as an alias for PURGE MASTER LOGS.
Disabled the PURGE LOGS statement that was added in in version 4.1.0. The statement now should be issued as PURGE MASTER LOGS or PURGE BINARY LOGS.
Added SHOW BDB LOGS as an alias for SHOW LOGS.
Added SHOW MASTER LOGS (which had been deleted in version 4.1.0) as an alias for SHOW BINARY LOGS.
Added Slave_IO_State and Seconds_Behind_Master columns to the output of SHOW SLAVE STATUS. Slave_IO_State indicates the state of the slave I/O thread, and Seconds_Behind_Master indicates the number of seconds by which the slave is late compared to the master.
--lower-case-table-names=1 now also makes aliases case insensitive. (Bug #534)
Bugs fixed:
Fixed mysql parser not to erroneously interpret ; character within /* ... */ comment as statement terminator.
Fixed merging types and length of result set columns for UNION operations. The types and lengths now are determined taking into account values for all SELECT statements in the UNION, not just the first SELECT.
Fixed a bug in privilege handling that caused connections from certain IP addresses to be assigned incorrect database-level privileges. A connection could be assigned the database privileges of the previous successful authentication from one of those IP addresses, even if the IP address username and database name were different. (Bug #1636)
Error-handling functions were not called properly when an error resulted from [CREATE | REPLACE| INSERT] ... SELECT statements.
HASH, BTREE, RTREE, ERRORS, and WARNINGS no longer are reserved words. (Bug #724)
Fix for bug in ROLLUP when all tables were const tables. (Bug #714)
Fixed a bug in UNION that prohibited NULL values from being inserted into result set columns where the first SELECT of the UNION retrieved NOT NULL columns. The type and max_length of the result column is now defined based on all UNION parts.
Fixed name resolution of columns of reduced subqueries in unions. (Bug #745)
Fixed memory overrun in subqueries in select list with WHERE clause bigger than outer query WHERE clause. (Bug #726)
Fixed a bug that caused MyISAM tables with FULLTEXT indexes created in 4.0.x to be unreadable in 4.1.x.
Fixed a data loss bug in REPAIR TABLE ... USE_FRM when used with tables that contained TIMESTAMP columns and were created in 4.0.x.
Fixed reduced subquery processing in ORDER BY/GROUP BY clauses. (Bug #442)
Fixed name resolution of outer columns of subquery in INSERT/REPLACE statements. (Bug #446)
Fixed bug in marking columns of reduced subqueries. (Bug #679)
Fixed a bug that made CREATE FULLTEXT INDEX syntax illegal.
Fixed a crash when a SELECT that required a temporary table (marked by Using temporary in EXPLAIN output) was used as a derived table in EXPLAIN command. (Bug #251)
Fixed a rare table corruption bug in DELETE from a big table with a new (created by MySQL-4.1) full-text index.
LAST_INSERT_ID() now returns 0 if the last INSERT statement didn't insert any rows.
Fixed missing last character in function output. (Bug #447)
Fixed a rare replication bug when a transaction spanned two or more relay logs, and the slave was stopped while executing the part of the transaction that was in the second or later relay log. Then replication would resume at the beginning of the second or later relay log, which was incorrect. (It should resume at BEGIN, in the first relay log.) (Bug #53)
CONNECTION_ID() now is properly replicated. (Bug #177)
The new PASSWORD() function in 4.1 is now properly replicated. (Bug #344)
Fixed a bug with double freed memory.
Fixed a crashing bug in UNION operations that involved temporary tables.
Fixed a crashing bug in DERIVED TABLES when EXPLAIN is used on a DERIVED TABLES with a join.
Fixed a crashing bug in DELETE with ORDER BY and LIMIT caused by an uninitialized array of reference pointers.
Fixed a bug in the USER() function caused by an error in the size of the allocated string.
Fixed a crashing bug when attempting to create a table containing a spatial (GIS) column with a storage engine that does not support spatial types.
Fixed a crashing bug in UNION caused by the empty select list and a non-existent column being used in some of the individual SELECT statements.
Fixed a replication bug with a 3.23 master and a 4.0 slave: The slave lost the replicated temporary tables if FLUSH LOGS was issued on the master. (Bug #254)
Fixed a security bug: A server compiled without SSL support still allowed connections by users that had the REQUIRE SSL option specified for their accounts.
When an undefined user variable was used in a updating query on the master (such as INSERT INTO t VALUES(@a), where @a had never been set by this connection before), the slave could replicate the query incorrectly if a previous transaction on the master used a user variable of the same name. (Bug #1331)
Fixed bug with prepared statements: Using the ? prepared statement parameter as the argument to certain functions or statement clauses caused a server crash when mysql_prepare() was invoked. (Bug #1500)
Fixed bug with prepared statements: after call to mysql_stmt_prepare placeholders became allowed in all consequent statements, even if they are not prepared (Bug #1946)
SLAVE START (which is a deprecated syntax, START SLAVE should be used instead) could crash the slave. (Bug #2516)
Fixed bug in ALTER TABLE RENAME, when rename to the table with the same name in another database silently dropped destination table if it existed. (Bug #2628)
Functionality added or changed:
New CHARSET() and COLLATION() functions to return the character set and collation of a string.
Allow index type to be specified explicitly for some storage engines via USING type_name syntax in index definition.
New function IS_USED_LOCK() for determining the connection identifier of the client that holds a given advisory lock.
New more secure client authentication based on 45-byte passwords in the user table.
New CRC32() function to compute cyclic redundancy check value.
On Windows, we are now using shared memory to communicate between server and client when they are running on the same machine and you are connecting to localhost.
REPAIR of MyISAM tables now uses less temporary disk space when sorting char columns.
DATE/DATETIME checking is now a bit stricter to support the ability to automatically distinguish between date, datetime, and time with microseconds. For example, dates of type YYYYMMDD HHMMDD are no longer supported; you must either have separators between each DATE/TIME part or not at all.
Server side help for all MySQL functions. One can now type help week in the mysql client and get help for the week() function.
Added new mysql_get_server_version() C API client function.
Fixed bug in libmysqlclient that fetched column defaults.
Fixed bug in mysql.cc client when skipping comments
Added record_in_range() method to MERGE tables to be able to choose the right index when there are many to choose from.
Replication now works with RAND() and user variables @var.
Allow one to change mode for ANSI_QUOTES on the fly.
EXPLAIN SELECT now can be killed. See KILL.
REPAIR TABLE now can be killed. See KILL.
Allow empty index lists to be specified for USE INDEX, IGNORE INDEX, and FORCE INDEX.
DROP TEMPORARY TABLE now drops only temporary tables and doesn't end transactions.
Added support for UNION in derived tables.
Warning: Incompatible change! TIMESTAMP is now returned as a string of type 'YYYY-MM-DD HH:MM:SS' and different timestamp lengths are not supported.
This change was necessary for SQL standards compliance. In a future version, a further change will be made (backward compatible with this change), allowing the timestamp length to indicate the desired number of digits of fractions of a second.
New faster client/server protocol that supports prepared statements, bound parameters, and bound result columns, binary transfer of data, warnings.
Added database and real table name (in case of alias) to the MYSQL_FIELD structure.
Multi-line queries: You can now issue several queries at once and then read the results in one go.
In CREATE TABLE foo (a INT not null primary key) the PRIMARY word is now optional.
In CREATE TABLE the attribute SERIAL is now an alias for BIGINT NOT NULL AUTO_INCREMENT UNIQUE.
SELECT ... FROM DUAL is an alias for SELECT .... (To be compatible with some other databases).
If one creates a too long CHAR/VARCHAR it's now automatically changed to TEXT or BLOB; One will get a warning in this case.
One can specify the different BLOB/TEXT types with the syntax BLOB(length) and TEXT(length). MySQL will automatically change it to one of the internal BLOB/TEXT types.
CHAR BYTE is an alias for CHAR BINARY.
VARCHARACTER is an alias for VARCHAR.
New operators integer MOD integer and integer DIV integer.
SERIAL DEFAULT VALUE added as an alias for AUTO_INCREMENT.
TRUE and FALSE added as alias for 1 and 0, respectively.
Aliases are now forced in derived tables, as per SQL-99.
Fixed SELECT .. LIMIT 0 to return proper row count for SQL_CALC_FOUND_ROWS.
One can specify many temporary directories to be used in a round-robin fashion with: --tmpdir=dirname1:dirname2:dirname3.
Subqueries: SELECT * from t1 where t1.a=(SELECT t2.b FROM t2).
Derived tables:
SELECT a.col1, b.col2 FROM (SELECT MAX(col1) AS col1 FROM root_table) a, other_table b WHERE a.col1=b.col1;
Character sets to be defined per column, table and database.
Unicode (UTF8) support.
New CONVERT(... USING ...) syntax for converting string values between character sets.
BTREE index on HEAP tables.
Faster embedded server (new internal communication protocol).
One can add a comment per column in CREATE TABLE.
SHOW FULL COLUMNS FROM table_name shows column comments.
ALTER DATABASE.
Support for GIS (Geometrical data). See Spatial extensions in MySQL.
SHOW [COUNT(*)] WARNINGS shows warnings from the last command.
One can specify a column type for a colum in CREATE TABLE ... SELECT by defining the column in the CREATE part.
CREATE TABLE foo (a tinyint not null) SELECT b+1 AS 'a' FROM bar;
expr SOUNDS LIKE expr same as SOUNDEX(expr)=SOUNDEX(expr).
Added new VARIANCE(expr) function returns the variance of expr
One can create a table from the existing table using CREATE [TEMPORARY] TABLE [IF NOT EXISTS] table (LIKE table). The table can be either normal or temporary.
New options --reconnect and --disable-reconnect for the mysql client, to reconnect automatically or not if the connection is lost.
START SLAVE (STOP SLAVE) no longer returns an error if the slave is already started (stopped); it returns a warning instead.
SLAVE START and SLAVE STOP are no longer accepted by the query parser; use START SLAVE and STOP SLAVE instead.
Table of Contents
Version 4.0 of the MySQL server includes many enhancements and new features:
The InnoDB storage engine is now included in the standard binaries, adding transactions, row-level locking, and foreign keys. See InnoDB.
A query cache, offering vastly increased performance for many applications. By caching complete result sets, later identical queries can return instantly. See Query Cache.
Improved full-text indexing with boolean mode, truncation, and phrase searching. See Fulltext Search.
Enhanced MERGE tables, now supporting INSERT statements and AUTO_INCREMENT. See MERGE.
UNION syntax in SELECT. See UNION.
Multiple-table DELETE statements. See DELETE.
libmysqld, the embedded server library. See libmysqld.
Additional GRANT privilege options for even tighter control and security. See GRANT.
Management of user resources in the GRANT system, particularly useful for ISPs and other hosting providers. See User resources.
Dynamic server variables, allowing configuration changes to be made without having to stop and restart the server. See SET OPTION.
Improved replication code and features. See Replication.
Numerous new functions and options.
Changes to existing code for enhanced performance and reliability.
For a full list of changes, please refer to the changelog sections for each individual 4.0.x release.
Functionality added or changed:
Bugs fixed:
Fixed bug in range optimizer which caused segmentation fault. (Bug #2698)
Functionality added or changed:
Fixed processing of LOAD DATA by mysqlbinlog in remote mode. (Bug #1378)
New utility program myisam_ftdump was added to binary distributions.
mysqlhotcopy now works on NetWare.
ENGINE is now a synonym for the TYPE option for CREATE TABLE and ALTER TABLE.
lower_case_table_names system variable now can take a value of 2, to store table names in mixed case on case-insensitive filesystems.
For replication of HEAP tables: Made the master automatically write a DELETE FROM statement to its binary log when a HEAP table is opened for the first time since master's startup. This is for the case where the slave has replicated a non-empty HEAP table, then the master is shut down and restarted: the table is now empty on master; the DELETE FROM empties it on slave too. Note that even with this fix, between the master's restart and the first use of the table on master, the slave still has out-of-date data in the table. But if you use the init-file option to populate the HEAP table on the master at startup, it ensures that the failing time interval is zero. (Bug #2477)
Optimizer is now better tuned for the case where the first used key part (of many) is a constant. (Bug #1679)
Removed old non-working --old-rpl-compat server option, which was a holdover from the very first 4.0.x versions. (Bug #2428)
Bugs fixed:
Fixed bug when --init-file crashes MySQL if it contains a large SELECT. (Bug #2526)
SHOW KEYS now shows NULL in the Sub_part column for FULLTEXT indexes.
The signal thread's stack size was increased to enable mysqld to run on Debian/IA-64 with a TLS-enabled glibc. (Bug #2599)
Now only the SELECT privilege is needed for tables that are only read in multiple-table UPDATE statements. (Bug #2377)
Give proper error message if one uses LOCK TABLES ... ; INSERT ... SELECT and one used the same table in the INSERT and SELECT part. (Bug #2296)
SELECT INTO ... DUMPFILE now deletes the generated file on error.
Fixed foreign key reference handling to allow references to column names that contain spaces. (Bug #1725)
Fixed problem with index reads on character fields with BDB tables. The symptom was that data could be returned in wrong lettercase. (Bug #2509)
Fixed a spurious table corruption problem that could sometimes appear on tables with indexed TEXT columns if these columns happened to contain values having trailing spaces. This bug was introduced in 4.0.17.
Fixed a problem where some queries could hang if a condition like indexed_TEXT_column = expr was present and the column contained values having trailing spaces. This bug was introduced in 4.0.17.
Fixed a bug that could cause incorrect results from a query that involved range conditions on indexed TEXT columns that happened to contain values having trailing spaces. This bug was introduced in 4.0.17. (Bug #2295)
Fixed incorrect path names in some of the manual pages. (Bug #2270)
Fixed spurious ``table corrupted'' errors in parallel repair operations. See myisam_repair_threads.
Fixed a crashing bug in parallel repair operations. See myisam_repair_threads.
Fixed bug in updating MyISAM tables for BLOB values longer than 16M. (Bug #2159)
Fixed bug in mysqld_safe when running multiple instances of MySQL. (Bug #2114)
Fixed a bug in using HANDLER statement with tables not from a current database. (Bug #2304)
Fixed a crashing bug that occurred due to the fact that multiple-table UPDATE statements did not check that there was only one table to be updated. (Bug #2103)
Fixed a crashing bug that occurred due to BLOB column type index size being calculated incorrectly in MIN() and MAX() optimizations. (Bug #2189)
Fixed a bug with incorrect syntax for LOCK TABLES in mysqldump. (Bug #2242)
Fixed a bug in mysqld_safe that caused mysqld to generate a warning about duplicate user=xxx options if this option was specified in the [mysqld] or [server] sections of my.cnf. (Bug #2163)
INSERT DELAYED ... SELECT ... could cause table corruption because tables were not locked properly. This is now fixed by ignoring DELAYED in this context. (Bug #1983)
Replication: Sometimes the master gets a non-fatal error during the execution of a statement that does not immediately succeed. (For example, a write to a MyISAM table may first receive ``no space left on device,'' but later complete when disk space becomes available. See Full disk.) The bug was that the master forgot to reset the error code to 0 after success, so the error code got into its binary log, thus causing the slave to issue false alarms such as ``did not get the same error as on master.'' (Bug #2083)
Removed a misleading ``check permissions on master.info'' from a replication error message, because the cause of the problem could be something other than permissions. (Bug #2121)
Fixed a crash when the replication slave was unable to create the first relay log. (Bug #2145)
Replication of LOAD DATA INFILE for an empty file from a 3.23 master to a 4.0 slave caused the slave to print an error. (Bug #2452)
When automatically forcing lower_case_table_names to 1 if the file system was case insensitive, mysqld could crash. This bug existed only in MySQL 4.0.17. (Bug #2481)
Restored ability to specify default values for TIMESTAMP columns that was erroneously disabled in previous release. (Bug #2539) Fixed SHOW CREATE TABLE to reflect these values. (Bug #1885) Note that because of the auto-update feature for the first TIMESTAMP column in a table, it makes no sense to specify a default value for the column. Any such default will be silently ignored (unless another TIMESTAMP column is added before this one). Also fixed the meaning of the DEFAULT keyword when it is used to specify the value to be inserted into a TIMESTAMP column other than the first. (Bug #2464)
Fixed bug for out-of-range arguments on QNX platform that caused UNIX_TIMESTAMP() to produce incorrect results or that caused non-zero values to be inserted into TIMESTAMP columns. (Bug #2523) Also, current time zone now is taken into account when checking if datetime values satisfy both range boundaries for TIMESTAMP columns. The range allowed for a TIMESTAMP column is time zone-dependant and equivalent to a range of 1970-01-01 00:00:01 UTC to 2037-12-31 23:59:59 UTC.
Multi-table DELETE statements were never replicated by the slave if there were any replicate-*-table options. (Bug #2527)
Changes to session counterparts of variables query_prealloc_size, query_alloc_block_size, trans_prealloc_size, trans_alloc_block_size now have effect (Bug #1948)
Fixed bug in ALTER TABLE RENAME, when rename to the table with the same name in another database silently dropped destination table if it existed. (Bug #2628)
Functionality added or changed:
mysqldump no longer dumps data for MERGE tables. (Bug #1846)
lower_case_table_names is now forced to 1 if the database directory is located on a case-insensitive file system. (Bug #1812)
Symlink creation is now disabled on systems where realpath() doesn't work. (Before one could use CREATE TABLE .. DATA DIRECTORY=.. even if HAVE_BROKEN_REALPATH was defined. This is now disabled to avoid problems when running ALTER TABLE).
Inserting a negative AUTO_INCREMENT value in a MyISAM table no longer updates the AUTO_INCREMENT counter to a big unsigned value. (Bug #1366)
Added four new modes to WEEK(..., mode) function. See WEEK(date: (mode)). (Bug #1178)
Allow UNION DISTINCT syntax.
mysql_server_init() now returns 1 if it can't initialize the environment. (Previously mysql_server_init() called exit(1) if it could not create a key with pthread_key_create(). (Bug #2062)
Allow spaces in Windows service names.
Changed the default Windows service name for mysqld from MySql to MySQL. This should not affect usage, because service names are not case sensitive.
When you install mysqld as a service on Windows systems, mysqld will read startup options in option files from the option group with the same name as the service name. (Except when the service name is MySQL).
Bugs fixed:
Sending SIGHUP to mysqld crashed server if it was running with --log-bin. (Bug #2045)
One can now configure MySQL as a Windows service as a normal user. (Bug #1802). Thanks to Richard Hansen for fixing this.
Database names are now compared in lowercase in ON clauses when lower_case_table_names is set. (Bug #1736)
IGNORE ... LINES option to LOAD DATA INFILE didn't work when used with fixed length rows. (Bug #1704)
Fixed problem with UNIX_TIMESTAMP() for timestamps close to 0. (Bug #1998)
Fixed problem with character values greater than 128 in the QUOTE() function. (Bug #1868)
Fixed searching of TEXT with end space. (Bug #1651)
Fixed caching bug in multiple-table updates where same table was used twice. (Bug #1711)
Fixed directory permissions for the MySQL-server RPM documentation directory. (Bug #1672)
Fixed server crash when updating an ENUM column that is set to the empty string (for example, with REPLACE()). (Bug #2023)
mysql client program now correctly prints connection identifier returned by mysql_thread_id() as unsigned integer rather than as signed integer. (Bug #1951)
FOUND_ROWS() could return incorrect number of rows after a query with an impossible WHERE condition. (Bug #1468)
SHOW DATABASES no longer shows .sym files (on Windows) that do not point to a valid directory. (Bug #1385)
Fixed a possible memory leak on Mac OS X when using the shared libmysql.so library. (from pthread_key_create()). (Bug #2061)
Fixed bug in UNION statement with alias *. (Bug #1249)
Fixed a bug in DELETE ... ORDER BY ... LIMIT where the rows where not deleted in the proper order. (Bug #1024, Bug #1697).
Fixed serious problem with multi-threaded programs on Windows that used the embedded MySQL libraries. (Locks of tables were not handled correctly between different threads).
Code cleanup: Fixed a few code defects (potential memory leaks, null pointer dereferences, uninitialized variables). Thanks to Reasoning Inc. for informing us about these findings.
Fixed a buffer overflow error that occurred with prepended 0 characters in some columns of type DECIMAL. (Bug #2128)
Filesort was never shown in EXPLAIN if query contained an ORDER BY NULL clause. (Bug #1335)
Fixed invalidation of whole query cache on DROP DATABASE. (Bug #1898)
Fixed bug in range optimizer that caused wrong results for some unlikely AND/OR queries. (Bug #1828)
Fixed a crash in ORDER BY when ordering by expression and identifier. (Bug #1945)
Fixed a crash in an open HANDLER when an ALTER TABLE was executed in a different connection. (Bug #1826)
Fixed a bug in trunc* operator of full-text search which sometimes caused MySQL not to find all matched rows.
Fixed bug in prepending 0 characters to DECIMAL column values.
Fixed optimizer bug, introduced in 4.0.16, when REF access plan was preferred to more efficient RANGE on another column.
Fixed problem when installing a MySQL server as a Windows service using a command of the form mysqld --install mysql --defaults-file=path-to-file. (Bug #1643)
Fixed an incorrect result from a query that uses only const tables (such as one-row tables) and non-constant expression (such as RAND()). (Bug #1271)
Fixed bug when the optimizer did not take SQL_CALC_FOUND_ROWS into account if LIMIT clause was present. (Bug #1274)
mysqlbinlog now asks for a password at the console when the -p or --password option is used with no argument. This is consistent with the way that other clients such mysqladmin and mysqldump already behave. Note: A consequence of this change is that it is no longer possible to invoke mysqlbinlog as mysqlbinlog -p pass_val (with a space between the -p option and the following password value). (Bug #1595)
Fixed bug accidentally introduced in 4.0.16 where the slave SQL thread deleted its replicated temporary tables when STOP SLAVE was issued.
In a ``chain'' replication setup A->B->C, if 2 sessions on A updated temporary tables of the same name at the same time, the binary log of B became incorrect, resulting in C becoming confused. (Bug #1686)
In a ``chain'' replication setup A->B->C, if STOP SLAVE was issued on B while it was replicating a temporary table from A, then when START SLAVE was issued on B, the binary log of B became incorrect, resulting in C becoming confused. (Bug #1240)
When MASTER_LOG_FILE and MASTER_LOG_POS were not specified, CHANGE MASTER used the coordinates of the slave I/O thread to set up replication, which broke replication if the slave SQL thread lagged behind the slave I/O thread. This caused the slave SQL thread to lose some events. The new behavior is to use the coordinates of the slave SQL thread instead. See CHANGE MASTER TO. (Bug #1870)
Now if integer is stored or converted to TIMESTAMP or DATETIME value checks of year, month, day, hour, minute and second ranges are performed and numbers representing illegal timestamps are converted to 0 value. This behavior is consistent with manual and with behavior of string to TIMESTAMP/DATETIME conversion. (Bug #1448)
Fixed bug when BIT_AND() and BIT_OR() group functions returned incorrect value if SELECT used a temporary table and no rows were found. (Bug #1790).
BIT_AND() is now unsigned in all contexts. This means that it will now return 18446744073709551615 (= 0xffffffffffffffff) instead of -1 if there were no rows in the result.
Fixed bug with BIT_AND() still returning signed value for an empty set in some cases. (Bug #1972)
Fixed bug with ^ (XOR) and >> (bit shift) still returning signed value in some cases. (Bug #1993)
Replication: a rare race condition in the slave SQL thread, which could lead to a wrong complain that the relay log is corrupted. (Bug #2011)
Replication: if an administrative command on a table (OPTIMIZE TABLE, REPAIR TABLE etc) was run on the slave, this could sometimes stop the slave SQL thread (this did not led to any corruption; one just had to type START SLAVE to get replication going again). (Bug #1858)
Replication: in the slave SQL thread, a multi-table UPDATE could produce a wrong complain that some record was not found in one table, if the UPDATE was preceded by a INSERT ... SELECT. (Bug #1701)
Fixed deficiency in MySQL code which is responsible for scanning directories. This deficiency caused SHOW TABLE STATUS to be very slow when a database contained a large number of tables, even if a single particular table were specified. (Bug #1952)
Functionality added or changed:
Option values in option files now may be quoted. This is useful for values that contain whitespace or comment characters.
Write memory allocation information to error log when doing mysqladmin debug. This works only on systems that support the mallinfo() call (like newer Linux systems).
Added the following new server variables to allow more precise memory allocation: range_alloc_block_size, query_alloc_block_size, query_prealloc_size, transaction_alloc_block_size, and transaction_prealloc_size.
mysqlbinlog now reads option files. To make this work one must now specify --read-from-remote-server when reading binary logs from a MySQL server. (Note that using a remote server is deprecated and may disappear in future mysqlbinlog versions).
Block SIGPIPE signals also for non-threaded programs. The blocking is moved from mysql_init() to mysql_server_init(), which is automatically called on the first call to mysql_init().
Added --libs_r and --include options to mysql_config.
New `> prompt for mysql. This prompt is similar to the '> and "> prompts, but indicates that an identifier quoted with backticks was begun on an earlier line and the closing backtick has not yet been seen.
Updated mysql_install_db to be able to use the local machine's IP address instead of the hostname when building the initial grant tables if skip-name-resolve has been specified. This option can be helpful on FreeBSD to avoid thread-safety problems with the FreeBSD resolver libraries. (Thanks to Jeremy Zawodny for the patch.)
A documentation change: Added a note that when backing up a slave, it is necessary also to back up the master.info and relay-log.info files, as well as any SQL_LOAD-* files located in the directory specified by the --slave-load-tmpdir option. All these files are needed when the slave resumes replication after you restore the slave's data.
Bugs fixed:
Fixed a spurious error ERROR 14: Can't change size of file (Errcode: 2) on Windows in DELETE FROM table_name without a WHERE clause or TRUNCATE TABLE table_name, when table_name is a MyISAM table. (Bug #1397)
Fixed a bug that resulted in thr_alarm queue is full warnings after increasing the max_connections variable with SET GLOBAL. (Bug #1435)
Made LOCK TABLES to work when Lock_tables_priv is granted on the database level and Select_priv is granted on the table level.
Fixed crash of FLUSH QUERY CACHE on queries that use same table several times (Bug #988).
Fixed core dump bug when setting an enum system variable (such as SQL_WARNINGS) to NULL.
Extended the default timeout value for Windows clients from 30 seconds to 1 year. (The timeout that was added in MySQL 4.0.15 was way too short). This fixes a bug that caused ERROR 2013: Lost connection to MySQL server during query for queries that lasted longer than 30 seconds, if the client didn't specify a limit with mysql_options(). Users of 4.0.15 on Windows should upgrade to avoid this problem.
More ``out of memory'' checking in range optimizer.
Fixed and documented a problem when setting and using a user variable within the same SELECT statement. (Bug #1194).
Fixed bug in overrun check for BLOB values with compressed tables. This was a bug introduced in 4.0.14. It caused MySQL to regard some correct tables containing BLOB values as corrupted. (Bug #770, Bug #1304, and maybe Bug #1295)
SHOW GRANTS showed USAGE instead of the real column-level privileges when no table-level privileges were given.
When copying a database from the master, LOAD DATA FROM MASTER dropped the corresponding database on the slave, thus erroneously dropping tables that had no counterpart on the master and tables that may have been excluded from replication using replicate-*-table rules. Now LOAD DATA FROM MASTER no longer drops the database. Instead, it drops only the tables that have a counterpart on the master and that match the replicate-*-table rules. replicate-*-db rules can still be used to include or exclude a database as a whole from LOAD DATA FROM MASTER. A database will also be included or excluded as a whole if there are some rules like replicate-wild-do-table=db1.% or replicate-wild-ignore-table=db1.%, as is already the case for CREATE DATABASE and DROP DATABASE in replication. (Bug #1248)
Fixed a bug where mysqlbinlog crashed with a segmentation fault when used with the -h or --host option. (Bug #1258)
Fixed a bug where mysqlbinlog crashed with a segmentation fault when used on a binary log containing only final events for LOAD DATA. (Bug #1340)
mysqlbinlog will not reuse temporary file names from previous runs. Previously mysqlbinlog failed if was used several times on the same binary log file that contained a LOAD DATA command.
Fixed compilation problem when compiling with OpenSSL 0.9.7 with disabled old DES support (If OPENSSL_DISABLE_OLD_DES_SUPPORT option was enabled).
Fixed a bug when two (or more) MySQL servers were running on the same machine, and they were both slaves, and at least one of them was replicating some LOAD DATA INFILE command from its master. The bug was that one slave MySQL server sometimes deleted the SQL_LOAD-* files (used for replication of LOAD DATA INFILE and located in the slave-load-tmpdir directory, which defaults to tmpdir) belonging to the other slave MySQL server of this machine, if these slaves had the same slave-load-tmpdir directory. When that happened, the other slave could not replicate LOAD DATA INFILE and complained about not being able to open some SQL_LOAD-* file. (Bug #1357)
If LOAD DATA INFILE failed for a small file, the master forgot to write a marker (a Delete_file event) in its binary log, so the slave could not delete 2 files (SQL_LOAD-*.info and SQL_LOAD-*.data from its tmpdir. (Bug #1391)
On Windows, the slave forgot to delete a SQL_LOAD-*.info file from tmpdir after successfully replicating a LOAD DATA INFILE command. (Bug #1392)
When a connection terminates, MySQL writes DROP TEMPORARY TABLE statements to the binary log for all temporary tables which the connection had not explicitly dropped. MySQL forgot to backquote the database and table names in the statement. (Bug #1345)
On some 64-bit machines (some HP-UX and Solaris machines), a slave installed with the 64-bit MySQL binary could not connect to its master (it connected to itself instead). (Bug #1256, Bug #1381)
Code was introduced in MySQL 4.0.15 for the slave to detect that the master had died while writing a transaction to its binary log. This code reported an error in a legal situation: When the slave I/O thread was stopped while copying a transaction to the relay log, the slave SQL thread would later pretend that it found an unfinished transaction. (Bug #1475)
IMPORTANT:
If you are using this release on Windows, you should upgrade at least your clients (any program that uses libmysql.lib) to 4.0.16 or above. This is because the 4.0.15 release had a bug in the Windows client library that causes Windows clients using the library to die with a Lost connection to MySQL server during query error for queries that take more than 30 seconds. This problem is specific to Windows; clients on other platforms are unaffected.
Functionality added or changed:
mysqldump now correctly quotes all identifiers when communicating with the server. This assures that during the dump process, mysqldump will never send queries to the server that result in a syntax error. This problem is not related to the mysqldump program's output, which was not changed. (Bug #1148)
Change result set metadata information so that MIN() and MAX() report that they can return NULL (this is true because an empty set will return NULL). (Bug #324)
Produce an error message on Windows if a second mysqld server is started on the same TCP/IP port as an already running mysqld server.
The mysqld server variables wait_timeout, net_read_timeout, and net_write_timeout now work on Windows. One can now also set timeouts for read and writes in Windows clients with mysql_options().
Added option --sql-mode=NO_DIR_IN_CREATE to make it possible for slaves to ignore INDEX DIRECTORY and DATA DIRECTORY options given to CREATE TABLE. When this is mode is on, SHOW CREATE TABLE will not show the given directories.
SHOW CREATE TABLE now shows the INDEX DIRECTORY and DATA DIRECTORY options, if they were specified when the table was created.
The open_files_limit server variable now shows the real open files limit.
MATCH ... AGAINST() in natural language mode now treats words that are present in more than 2,000,000 rows as stopwords.
The Mac OS X installation disk images now include an additional MySQLStartupItem.pkg package that enables the automatic startup of MySQL on system bootup. See Mac OS X installation.
Most of the documentation included in the binary tarball distributions (.tar.gz) has been moved into a subdirectory docs. See Installation layouts.
The manual is now included as an additional info file in the binary distributions. (Bug #1019)
The binary distributions now include the embedded server library (libmysqld.a) by default. Due to a linking problem with non-gcc compilers, it was not included in all packages of the initial 4.0.15 release. The affected packages were rebuilt and released as 4.0.15a. See Nutshell Embedded MySQL.
MySQL can now use range optimization for BETWEEN with non-constant limits. (Bug #991)
Replication error messages now include the default database, so that users can check which database the failing query was run for.
A documentation change: Added a paragraph about how the binlog-do-db and binlog-ignore-db options are tested against the database on the master (see Binary log), and a paragraph about how replicate-do-db, replicate-do-table and analogous options are tested against the database and tables on the slave (see Replication Options).
Now the slave does not replicate SET PASSWORD if it is configured to exclude the mysql database from replication (using for example replicate-wild-ignore-table=mysql.%). This was already the case for GRANT and REVOKE since version 4.0.13 (though there was Bug #980 in 4.0.13 & 4.0.14, which has been fixed in 4.0.15).
Rewrote the information shown in the State column of SHOW PROCESSLIST for replication threads and for MASTER_POS_WAIT() and added the most common states for these threads to the documentation, see Replication Implementation Details.
Added a test in replication to detect the case where the master died in the middle of writing a transaction to the binlog; such unfinished transactions now trigger an error message on the slave.
A GRANT command that creates an anonymous user (that is, an account with an empty username) no longer requires FLUSH PRIVILEGES for the account to be recognized by the server. (Bug #473)
CHANGE MASTER now flushes relay-log.info. Previously this was deferred to the next run of START SLAVE, so if mysqld was shutdown on the slave after CHANGE MASTER without having run START SLAVE, the relay log's name and position were lost. At restart they were reloaded from relay-log.info, thus reverting to their old (incorrect) values from before CHANGE MASTER and leading to error messages (as the old relay log did not exist any more) and the slave threads refusing to start. (Bug #858)
Bugs fixed:
Fixed buffer overflow in password handling which could potentially be exploited by MySQL users with ALTER privilege on the mysql.user table to execute random code or to gain shell access with the UID of the mysqld process (thanks to Jedi/Sector One for spotting and reporting this bug).
Fixed server crash on FORCE INDEX in a query that contained "Range checked for each record" in the EXPLAIN output. (Bug #1172)
Fixed table/column grant handling - proper sort order (from most specific to less specific, see Request access) was not honored. (Bug #928)
Fixed rare bug in MYISAM introduced in 4.0.3 where the index file header was not updated directly after an UPDATE of split dynamic rows. The symptom was that the table had a corrupted delete-link if mysqld was shut down or the table was checked directly after the update.
Fixed Can't unlock file error when running myisamchk --sort-index on Windows. (Bug #1119)
Fixed possible deadlock when changing key_buffer_size while the key cache was actively used. (Bug #1088)
Fixed overflow bug in MyISAM and ISAM when a row is updated in a table with a large number of columns and at least one BLOB/TEXT column.
Fixed incorrect result when doing UNION and LIMIT #,# when one didn't use braces around the SELECT parts.
Fixed incorrect result when doing UNION and ORDER BY .. LIMIT # when one didn't use braces around the SELECT parts.
Fixed problem with SELECT SQL_CALC_FOUND_ROWS ... UNION ALL ... LIMIT # where FOUND_ROWS() returned incorrect number of rows.
Fixed unlikely stack bug when having a BIG expression of type 1+1-1+1-1... in certain combinations. (Bug #871)
Fixed the bug that sometimes prevented a table with a FULLTEXT index from being marked as "analyzed".
Fixed MySQL so that the column length (in C API) for the second column in SHOW CREATE TABLE is always larger than the data length. The only known application that was affected by the old behavior was Borland dbExpress, which truncated the output from the command. (Bug #1064)
Fixed crash in comparisons of strings using the tis620 character set. (Bug #1116)
Fixed ISAM bug in MAX() optimization.
myisamchk --sort-records=N no longer marks table as crashed if sorting failed because of an inappropriate key. (Bug #892)
Fixed a minor bug in MyISAM compressed table handling that sometimes made it impossible to repair compressed table in "Repair by sort" mode. "Repair with keycache" (myisamchk --safe-recover) worked, though. (Bug #1015)
Fixed bug in propagating the version number to the manual included in the distribution files. (Bug #1020)
Fixed key sorting problem (a PRIMARY key declared for a column that is not explicitly marked NOT NULL was sorted after a UNIQUE key for a NOT NULL column).
Fixed the result of INTERVAL when applied to a DATE value. (Bug #792)
Fixed compiling of the embedded server library in the RPM spec file. (Bug #959)
Added some missing files to the RPM spec file and fixed some RPM building errors that occurred on Red Hat Linux 9. (Bug #998)
Fixed incorrect XOR evaluation in WHERE clause. (Bug #992)
Fixed bug with processing in query cache merged tables constructed from more then 255 tables. (Bug #930)
Fixed incorrect results from outer join query (e.g. LEFT JOIN) when ON condition is always false, and range search in used. (Bug #926)
Fixed a bug causing incorrect results from MATCH ... AGAINST() in some joins. (Bug #942)
MERGE tables do not ignore "Using index" (from EXPLAIN output) anymore.
Fixed a bug that prevented an empty table from being marked as "analyzed". (Bug #937)
Fixed myisamchk --sort-records crash when used on compressed table.
Fixed slow (as compared to 3.23) ALTER TABLE and related commands such as CREATE INDEX. (Bug #712)
Fixed segmentation fault resulting from LOAD DATA FROM MASTER when the master was running without the --log-bin option. (Bug #934)
Fixed a security bug: A server compiled without SSL support still allowed connections by users that had the REQUIRE SSL option specified for their accounts.
Fixed a random bug: Sometimes the slave would replicate GRANT or REVOKE queries even if it was configured to exclude the mysql database from replication (for example, using replicate-wild-ignore-table=mysql.%). (Bug #980)
The Last_Errno and Last_Error fields in the output of SHOW SLAVE STATUS are now cleared by CHANGE MASTER and when the slave SQL thread starts. (Bug #986)
A documentation mistake: It said that RESET SLAVE does not change connection information (master host, port, user, and password), whereas it does. The statement resets these to the startup options (master-host etc) if there were some. (Bug #985)
SHOW SLAVE STATUS now shows correct information (master host, port, user, and password) after RESET SLAVE (that is, it shows the new values, which are copied from the startup options if there were some). (Bug #985)
Disabled propagation of the original master's log position for events because this caused unexpected values for Exec_Master_Log_Pos and problems with MASTER_POS_WAIT() in A->B->C replication setup. (Bug #1086)
Fixed a segfault in mysqlbinlog when --position=x was used with x being between a Create_file event and its fellow Append_block, Exec_load or Delete_file events. (Bug #1091)
mysqlbinlog printed superfluous warnings when using --database, which caused syntax errors when piped to mysql. (Bug #1092)
Made mysqlbinlog --database filter LOAD DATA INFILE too (previously, it filtered all queries except LOAD DATA INFILE). (Bug #1093)
mysqlbinlog in some cases forgot to put a leading '#' in front of the original LOAD DATA INFILE (this command is displayed only for information, not to be run; it is later reworked to LOAD DATA LOCAL with a different filename, for execution by mysql). (Bug #1096)
binlog-do-db and binlog-ignore-db incorrectly filtered LOAD DATA INFILE (it was half-written to the binary log). This resulted in a corrupted binary log, which could cause the slave to stop with an error. (Bug #1100)
When, in a transaction, a transactional table (such as an InnoDB table) was updated, and later in the same transaction a non-transactional table (such as a MyISAM table) was updated using the updated content of the transactional table (with INSERT ... SELECT for example), the queries were written to the binary log in an incorrect order. (Bug #873)
When, in a transaction, INSERT ... SELECT updated a non-transactional table, and ROLLBACK was issued, no error was returned to the client. Now the client is warned that some changes could not be rolled back, as this was already the case for normal INSERT. (Bug #1113)
Fixed a potential bug: When STOP SLAVE was run while the slave SQL thread was in the middle of a transaction, and then CHANGE MASTER was used to point the slave to some non-transactional statement, the slave SQL thread could get confused (because it would still think, from the past, that it was in a transaction).
Functionality added or changed:
mysqld now reads an additional option file group having a name corresponding to the server's release series: [mysqld-4.0] for 4.0.x servers, [mysqld-4.1] for 4.1.x servers, and so forth. This allows options to be specified on a series-specific basis.
The CONCAT_WS() function no longer skips empty strings. (Bug #586).
InnoDB now supports indexing a prefix of a column. This means, in particular, that BLOB and TEXT columns can be indexed in InnoDB tables, which was not possible before.
A documentation change: Function INTERVAL(NULL, ...) returns -1.
Enabled INSERT from SELECT when the table into which the records are inserted is also a table listed in the SELECT.
Allow CREATE TABLE and INSERT from any UNION.
The SQL_CALC_FOUND_ROWS option now always returns the total number of rows for any UNION.
Removed --table option from mysqlbinlog to avoid repeating mysqldump functionality.
Comment lines in option files can now start from the middle of a line, too (like basedir=c:\mysql # installation directory).
Changed optimizer slightly to prefer index lookups over full table scans in some boundary cases.
Added thread-specific max_seeks_for_key variable that can be used to force the optimizer to use keys instead of table scans even if the cardinality of the index is low.
Added optimization that converts LEFT JOIN to normal join in some cases.
A documentation change: added a paragraph about failover in replication (how to use a surviving slave as the new master, how to resume to the original setup). See Replication FAQ.
A documentation change: added warning notes about safe use of the CHANGE MASTER command. See CHANGE MASTER TO.
MySQL now issues a warning (not an error, as in 4.0.13) when it opens a table that was created with MySQL 4.1.
Added --nice option to mysqld_safe to allow setting the niceness of the mysqld process. (Thanks to Christian Hammers for providing the initial patch.) (Bug #627)
Added --read-only option to cause mysqld to allow no updates except from slave threads or from users with the SUPER privilege. (Original patch from Markus Benning).
SHOW BINLOG EVENTS FROM x where x is less than 4 now silently converts x to 4 instead of printing an error. The same change was done for CHANGE MASTER TO MASTER_LOG_POS=x and CHANGE MASTER TO RELAY_LOG_POS=x.
mysqld now only adds an interrupt handler for the SIGINT signal if you start it with the new --gdb option. This is because some MySQL users encountered strange problems when they accidentally sent SIGINT to mysqld threads.
RESET SLAVE now clears the Last_Errno and Last_Error fields in the output of SHOW SLAVE STATUS.
Added max_relay_log_size variable; the relay log will be rotated automatically when its size exceeds max_relay_log_size. But if max_relay_log_size is 0 (the default), max_binlog_size will be used (as in older versions). max_binlog_size still applies to binary logs in any case.
FLUSH LOGS now rotates relay logs in addition to the other types of logs it already rotated.
Bugs fixed:
Comparison/sorting for latin1_de character set was rewritten. The old algorithm could not handle cases like "sä" > "ßa". See German character set. In rare cases it resulted in table corruption.
Fixed a problem with the password prompt on Windows. (Bug #683)
ALTER TABLE ... UNION=(...) for MERGE table is now allowed even if some underlying MyISAM tables are read-only. (Bug #702)
Fixed a problem with CREATE TABLE t1 SELECT x'41'. (Bug #801)
Removed some incorrect lock warnings from the error log.
Fixed memory overrun when doing REPAIR on a table with a multi-part auto_increment key where one part was a packed CHAR.
Fixed a probable race condition in the replication code that could potentially lead to INSERT statements not being replicated in the event of a FLUSH LOGS command or when the binary log exceeds max_binlog_size. (Bug #791)
Fixed a crashing bug in INTERVAL and GROUP BY or DISTINCT. (Bug #807)
Fixed bug in mysqlhotcopy so it actually aborts for unsuccessful table copying operations. Fixed another bug so that it succeeds when there are thousands of tables to copy. (Bug #812)
Fixed problem with mysqlhotcopy failing to read options from option files. (Bug #808)
Fixed bugs in optimizer that sometimes prevented MySQL from using FULLTEXT indexes even though it was possible (for example, in SELECT * FROM t1 WHERE MATCH a,b AGAINST("index") > 0).
Fixed a bug with ``table is full'' in UNION operations.
Fixed a security problem that enabled users with no privileges to obtain information on the list of existing databases by using SHOW TABLES and similar commands.
Fixed a stack problem on UnixWare/OpenUnix.
Fixed a configuration problem on UnixWare/OpenUNIX and OpenServer.
Fixed a stack overflow problem in password verification.
Fixed a problem with max_user_connections.
HANDLER without an index now works properly when a table has deleted rows. (Bug #787)
Fixed a bug with LOAD DATA in mysqlbinlog. (Bug #670)
Fixed that SET CHARACTER SET DEFAULT works. (Bug #462)
Fixed MERGE table behavior in ORDER BY ... DESC queries. (Bug #515)
Fixed server crash on PURGE MASTER LOGS or SHOW MASTER LOGS when the binary log is off. (Bug #733)
Fixed password-checking problem on Windows. (Bug #464)
Fixed the bug in comparison of a DATETIME column and an integer constant. (Bug #504)
Fixed remote mode of mysqlbinlog. (Bug #672)
Fixed ERROR 1105: Unknown error that occurred for some SELECT queries, where a column that was declared as NOT NULL was compared with an expression that took NULL value.
Changed timeout in mysql_real_connect() to use poll() instead of select() to work around problem with many open files in the client.
Fixed incorrect results from MATCH ... AGAINST used with a LEFT JOIN query.
Fixed a bug that limited the maximum value for mysqld variables to 4294967295 when they are specified on the command line.
Fixed a bug that sometimes caused spurious ``Access denied'' errors in HANDLER ... READ statements, when a table is referenced via an alias.
Fixed portability problem with safe_malloc, which caused MySQL to give "Freeing wrong aligned pointer" errors on SCO 3.2.
ALTER TABLE ... ENABLE/DISABLE KEYS could cause a core dump when done after an INSERT DELAYED statement on the same table.
Fixed problem with conversion of localtime to GMT where some times resulted in different (but correct) timestamps. Now MySQL should use the smallest possible timestamp value in this case. (Bug #316)
Very small query cache sizes could crash mysqld. (Bug #549)
Fixed a bug (accidentally introduced by us but present only in version 4.0.13) that made INSERT ... SELECT into an AUTO_INCREMENT column not replicate well. This bug is in the master, not in the slave. (Bug #490)
Fixed a bug: When an INSERT ... SELECT statement inserted rows into a non-transactional table, but failed at some point (for example, due to a ``Duplicate key'' error), the query was not written to the binlog. Now it is written to the binlog, with its error code, as all other queries are. About the slave-skip-errors option for how to handle partially completed queries in the slave, see Replication Options. (Bug #491)
SET FOREIGN_KEY_CHECKS=0 was not replicated properly. The fix probably will not be backported to 3.23.
On a slave, LOAD DATA INFILE which had no IGNORE or REPLACE clause on the master, was replicated with IGNORE. While this is not a problem if the master and slave data are identical (a LOAD that produces no duplicate conflicts on the master will produce none on the slave anyway), which is true in normal operation, it is better for debugging not to silently add the IGNORE. That way, you can get an error message on the slave and discover that for some reason, the data on master and slave are different and investigate why. (Bug #571)
On a slave, LOAD DATA INFILE printed an incomplete ``Duplicate entry '%-.64s' for key %d''' message (the key name and value were not mentioned) in case of duplicate conflict (which does not happen in normal operation). (Bug #573)
When using a slave compiled with --debug, CHANGE MASTER TO RELAY_LOG_POS could cause a debug assertion failure. (Bug #576)
When doing a LOCK TABLES WRITE on an InnoDB table, commit could not happen, if the query was not written to the binary log (for example, if --log-bin was not used, or binlog-ignore-db was used). (Bug #578)
If a 3.23 master had open temporary tables that had been replicated to a 4.0 slave, and the binlog got rotated, these temporary tables were immediately dropped by the slave (which caused problems if the master used them subsequently). This bug had been fixed in 4.0.13, but in a manner which caused an unlikely inconvenience: if the 3.23 master died brutally (power failure), without having enough time to automatically write DROP TABLE statements to its binlog, then the 4.0.13 slave would not notice the temporary tables have to be dropped, until the slave mysqld server is restarted. This minor inconvenience is fixed in 3.23.57 and 4.0.14 (meaning the master must be upgraded to 3.23.57 and the slave to 4.0.14 to remove the inconvenience). (Bug #254)
If MASTER_POS_WAIT() was waiting, and the slave was idle, and the slave SQL thread terminated, MASTER_POS_WAIT() would wait forever. Now when the slave SQL thread terminates, MASTER_POS_WAIT() immediately returns NULL (``slave stopped''). (Bug #651)
After RESET SLAVE; START SLAVE;, the Relay_Log_Space value displayed by SHOW SLAVE STATUS was too big by four bytes. (Bug #763)
If a query was ignored on the slave (because of replicate-ignore-table and other similar rules), the slave still checked if the query got the same error code (0, no error) as on the master. So if the master had an error on the query (for example, ``Duplicate entry'' in a multiple-row insert), then the slave stopped and warned that the error codes didn't match. (Bug #797)
Functionality added or changed:
PRIMARY KEY now implies NOT NULL. (Bug #390)
The Windows binary packages are now compiled with --enable-local-infile to match the Unix build configuration.
Removed timing of tests from mysql-test-run. time does not accept all required parameters on many platforms (for example, QNX) and timing the tests is not really required (it's not a benchmark anyway).
SHOW MASTER STATUS and SHOW SLAVE STATUS required the SUPER privilege; now they accept REPLICATION CLIENT as well. (Bug #343)
Added multi-threaded MyISAM repair optimization and myisam_repair_threads variable to enable it. See myisam_repair_threads.
Added innodb_max_dirty_pages_pct variable which controls amount of dirty pages allowed in InnoDB buffer pool.
CURRENT_USER() and Access denied error messages now report the hostname exactly as it was specified in the GRANT command.
Removed benchmark results from the source and binary distributions. They are still available in the BK source tree, though.
InnoDB tables now support ANALYZE TABLE.
MySQL now issues an error when it opens a table that was created with MySQL 4.1.
Option --new now changes binary items (0xFFDF) to be treated as binary strings instead of numbers by default. This fixes some problems with character sets where it's convenient to input the string as a binary item. After this change you have to convert the binary string to INTEGER with a CAST if you want to compare two binary items with each other and know which one is bigger than the other. SELECT CAST(0xfeff AS UNSIGNED) < CAST(0xff AS UNSIGNED). This will be the default behavior in MySQL 4.1. (Bug #152)
Enabled delayed_insert_timeout on Linux (most modern glibc libraries have a fixed pthread_cond_timedwait()). (Bug #211)
Don't create more insert delayed threads than given by max_insert_delayed_threads. (Bug #211)
Changed UPDATE ... LIMIT to apply the limit to rows that were matched, whether or not they actually were changed. Previously the limit was applied as a restriction on the number of rows changed.
Tuned optimizer to favor clustered index over table scan.
BIT_AND() and BIT_OR() now return an unsigned 64-bit value.
Added warnings to error log of why a secure connection failed (when running with --log-warnings).
Deprecated options --skip-symlink and --use-symbolic-links and replaced these with --symbolic-links.
The default option for innodb_flush_log_at_trx_commit was changed from 0 to 1 to make InnoDB tables ACID by default. See InnoDB start.
Added a feature to SHOW KEYS to display keys that are disabled by ALTER TABLE DISABLE KEYS command.
When using a non-existing table type with CREATE TABLE, first try if the default table type exists before falling back to MyISAM.
Added MEMORY as an alias for HEAP.
Renamed function rnd to my_rnd as the name was too generic and is an exported symbol in libmysqlclient (thanks to Dennis Haney for the initial patch).
Portability fix: renamed include/dbug.h to include/my_debug.h.
mysqldump no longer silently deletes the binlogs when called with --master-data or --first-slave; while this behavior was convenient for some users, others may suffer from it. Now one has to explicitly ask for this deletion with the new --delete-master-logs option.
If the slave is configured (using for example replicate-wild-ignore-table=mysql.%) to exclude mysql.user, mysql.host, mysql.db, mysql.tables_priv and mysql.columns_priv from replication, then GRANT and REVOKE will not be replicated.
Bugs fixed:
Logged Access denied error message had incorrect Using password value. (Bug #398)
Fixed bug with NATURAL LEFT JOIN, NATURAL RIGHT JOIN and RIGHT JOIN when using many joined tables. The problem was that the JOIN method was not always associated with the tables surrounding the JOIN method. If you have a query that uses many RIGHT JOIN or NATURAL ... JOINS you should check that they work as you expected after upgrading MySQL to this version. (Bug #291)
Fixed mysql parser not to erroneously interpret ' or " characters within /* ... */ comment as beginning a quoted string.
mysql command line client no longer looks for \* commands inside backtick-quoted strings.
Fixed Unknown error when using UPDATE ... LIMIT. (Bug #373)
Fixed problem with ANSI mode and GROUP BY with constants. (Bug #387)
Fixed bug with UNION and OUTER JOIN. (Bug #386)
Fixed bug if one used a multiple-table UPDATE and the query required a temporary table bigger than tmp_table_size. (Bug #286)
Run mysql_install_db with the -IN-RPM option for the Mac OS X installation to not fail on systems with improperly configured hostname configurations.
LOAD DATA INFILE will now read 000000 as a zero date instead as "2000-00-00".
Fixed bug that caused DELETE FROM table WHERE const_expression always to delete the whole table (even if expression result was false). (Bug #355)
Fixed core dump bug when using FORMAT('nan',#). (Bug #284)
Fixed name resolution bug with HAVING ... COUNT(DISTINCT ...).
Fixed incorrect result from truncation operator (*) in MATCH ... AGAINST() in some complex joins.
Fixed a crash in REPAIR ... USE_FRM command, when used on read-only, nonexisting table or a table with a crashed index file.
Fixed a crashing bug in mysql monitor program. It occurred if program was started with --no-defaults, with a prompt that contained hostname and connection to non-existing db was requested
Fixed problem when comparing a key for a multi-byte-character set. (Bug #152)
Fixed bug in LEFT, RIGHT and MID when used with multi-byte character sets and some GROUP BY queries. (Bug #314)
Fix problem with ORDER BY being discarded for some DISTINCT queries. (Bug #275)
Fixed that SET SQL_BIG_SELECTS=1 works as documented (This corrects a new bug introduced in 4.0)
Fixed some serious bugs in UPDATE ... ORDER BY. (Bug #241)
Fixed unlikely problem in optimizing WHERE clause with constant expression like in WHERE 1 AND (a=1 AND b=1).
Fixed that SET SQL_BIG_SELECTS=1 works again.
Introduced proper backtick quoting for db.table in SHOW GRANTS.
FULLTEXT index stopped working after ALTER TABLE that converts TEXT column to CHAR. (Bug #283)
Fixed a security problem with SELECT and wildcarded select list, when user only had partial column SELECT privileges on the table.
Mark a MyISAM table as "analyzed" only when all the keys are indeed analyzed.
Only ignore world-writable my.cnf files that are regular files (and not, for example, named pipes or character devices).
Fixed few smaller issues with SET PASSWORD.
Fixed error message which contained deprecated text.
Fixed a bug with two NATURAL JOINs in the query.
SUM() didn't return NULL when there was no rows in result or when all values was NULL.
On Unix symbolic links handling was not enabled by default and there was no way to turn this on.
Added missing dashes to parameter --open-files-limit in mysqld_safe. (Bug #264)
Fixed incorrect hostname for TCP/IP connections displayed in SHOW PROCESSLIST.
Fixed a bug with NAN in FORMAT(...) function ...
Fixed a bug with improperly cached database privileges.
Fixed a bug in ALTER TABLE ENABLE / DISABLE KEYS which failed to force a refresh of table data in the cache.
Fixed bugs in replication of LOAD DATA INFILE for custom parameters (ENCLOSED, TERMINATED and so on) and temporary tables. (Bug #183, Bug #222)
Fixed a replication bug when the master is 3.23 and the slave 4.0: the slave lost the replicated temporary tables if FLUSH LOGS was issued on the master. (Bug #254)
Fixed a bug when doing LOAD DATA INFILE IGNORE: When reading the binary log, mysqlbinlog and the replication code read REPLACE instead of IGNORE. This could make the slave's table become different from the master's table. (Bug #218)
Fixed a deadlock when relay_log_space_limit was set to a too small value. (Bug #79)
Fixed a bug in HAVING clause when an alias is used from the select list.
Fixed overflow bug in MyISAM when a row is inserted into a table with a large number of columns and at least one BLOB/TEXT column. Bug was caused by incorrect calculation of the needed buffer to pack data.
Fixed a bug when SELECT @nonexistent_variable caused the error in client - server protocol due to net_printf() being sent to the client twice.
Fixed a bug in setting SQL_BIG_SELECTS option.
Fixed a bug in SHOW PROCESSLIST which only displayed a localhost in the "Host" column. This was caused by a glitch that used only current thread information instead of information from the linked list of threads.
Removed unnecessary Mac OS X helper files from server RPM. (Bug #144)
Allow optimization of multiple-table update for InnoDB tables as well.
Fixed a bug in multiple-table updates that caused some rows to be updated several times.
Fixed a bug in mysqldump when it was called with --master-data: the CHANGE MASTER TO commands appended to the SQL dump had incorrect coordinates. (Bug #159)
Fixed a bug when an updating query using USER() was replicated on the slave; this caused segfault on the slave. (Bug #178). USER() is still badly replicated on the slave (it is replicated to "").
Functionality added or changed:
mysqld no longer reads options from world-writable config files.
Integer values between 9223372036854775807 and 9999999999999999999 are now regarded as unsigned longlongs, not as floats. This makes these values work similar to values between 10000000000000000000 and 18446744073709551615.
SHOW PROCESSLIST will now include the client TCP port after the hostname to make it easier to know from which client the request originated.
Bugs fixed:
Fixed mysqld crash on extremely small values of sort_buffer variable.
INSERT INTO u SELECT ... FROM t was written too late to the binary log if t was very frequently updated during the execution of this query. This could cause a problem with mysqlbinlog or replication. The master must be upgraded, not the slave. (Bug #136)
Fixed checking of random part of WHERE clause. (Bug #142)
Fixed a bug with multiple-table updates with InnoDB tables. This bug occurred as, in many cases, InnoDB tables cannot be updated ``on the fly,'' but offsets to the records have to be stored in a temporary table.
Added missing file mysql_secure_installation to the server RPM subpackage. (Bug #141)
Fixed MySQL (and myisamchk) crash on artificially corrupted .MYI files.
Don't allow BACKUP TABLE to overwrite existing files.
Fixed a bug with multiple-table UPDATE statements when user had all privileges on the database where tables are located and there were any entries in tables_priv table, that is, grant_option was true.
Fixed a bug that allowed a user with table or column grants on some table, TRUNCATE any table in the same database.
Fixed deadlock when doing LOCK TABLE followed by DROP TABLE in the same thread. In this case one could still kill the thread with KILL.
LOAD DATA LOCAL INFILE was not properly written to the binary log (hence not properly replicated). (Bug #82)
RAND() entries were not read correctly by mysqlbinlog from the binary log which caused problems when restoring a table that was inserted with RAND(). INSERT INTO t1 VALUES(RAND()). In replication this worked ok.
SET SQL_LOG_BIN=0 was ignored for INSERT DELAYED queries. (Bug #104)
SHOW SLAVE STATUS reported too old positions (columns Relay_Master_Log_File and Exec_Master_Log_Pos) for the last executed statement from the master, if this statement was the COMMIT of a transaction. The master must be upgraded for that, not the slave. (Bug #52)
LOAD DATA INFILE was not replicated by the slave if replicate_*_table was set on the slave. (Bug #86)
After RESET SLAVE, the coordinates displayed by SHOW SLAVE STATUS looked un-reset (though they were, but only internally). (Bug #70)
Fixed query cache invalidation on LOAD DATA.
Fixed memory leak on ANALYZE procedure with error.
Fixed a bug in handling CHAR(0) columns that could cause incorrect results from the query.
Fixed rare bug with incorrect initialization of AUTO_INCREMENT column, as a secondary column in a multi-column key (see AUTO_INCREMENT on secondary column in a multi-column key), when data was inserted with INSERT ... SELECT or LOAD DATA into an empty table.
On Windows, STOP SLAVE didn't stop the slave until the slave got one new command from the master (this bug has been fixed for MySQL 4.0.11 by releasing updated 4.0.11a Windows packages, which include this individual fix on top of the 4.0.11 sources). (Bug #69)
Fixed a crash when no database was selected and LOAD DATA command was issued with full table name specified, including database prefix.
Fixed a crash when shutting down replication on some platforms (for example, Mac OS X).
Fixed a portability bug with pthread_attr_getstacksize on HP-UX 10.20 (Patch was also included in 4.0.11a sources).
Fixed the bigint test to not fail on some platforms (for example, HP-UX and Tru64) due to different return values of the atof() function.
Fixed the rpl_rotate_logs test to not fail on certain platforms (e.g. Mac OS X) due to a too long file name (changed slave-master-info.opt to .slave-mi).
Functionality added or changed:
NULL is now sorted LAST if you use ORDER BY ... DESC (as it was before MySQL 4.0.2). This change was required to comply with the SQL-99 standard. (The original change was made because we thought that SQL-99 required NULL to be always sorted at the same position, but this was incorrect).
Added START TRANSACTION (SQL-99 syntax) as alias for BEGIN. This is recommended to use instead of BEGIN to start a transaction.
Added OLD_PASSWORD() as a synonym for PASSWORD().
Allow keyword ALL in group functions.
Added support for some new INNER JOIN and JOIN syntaxes. For example, SELECT * FROM t1 INNER JOIN t2 didn't work before.
Novell NetWare 6.0 porting effort completed, Novell patches merged into the main source tree.
Bugs fixed:
Fixed problem with multiple-table delete and InnoDB tables.
Fixed a problem with BLOB NOT NULL columns used with IS NULL.
Re-added missing pre- and post(un)install scripts to the Linux RPM packages (they were missing after the renaming of the server subpackage).
Fixed that table locks are not released with multiple-table updates and deletes with InnoDB storage engine.
Fixed bug in updating BLOB columns with long strings.
Fixed integer-wraparound when giving big integer (>= 10 digits) to function that requires an unsigned argument, like CREATE TABLE (...) AUTO_INCREMENT=#.
MIN(key_column) could in some cases return NULL on a column with NULL and other values.
MIN(key_column) and MAX(key_column) could in some cases return incorrect values when used in OUTER JOIN.
MIN(key_column) and MAX(key_column) could return incorrect values if one of the tables was empty.
Fixed rare crash in compressed MyISAM tables with blobs.
Fixed bug in using aggregate functions as argument for INTERVAL, CASE, FIELD, CONCAT_WS, ELT and MAKE_SET functions.
When running with --lower-case-table-names (default on Windows) and you had tables or databases with mixed case on disk, then executing SHOW TABLE STATUS followed with DROP DATABASE or DROP TABLE could fail with Errcode 13.
Functionality added or changed:
Added option --log-error[=file_name] to mysqld_safe and mysqld. This option will force all error messages to be put in a log file if the option --console is not given. On Windows --log-error is enabled as default, with a default name of host_name.err if the name is not specified.
Changed some things from Warning: to Note: in the log files.
The mysqld server should now compile on NetWare.
Added optimization that if one does GROUP BY ... ORDER BY NULL then result is not sorted.
New --ft-stopword-file command-line option for mysqld to replace/disable the built-in stopword list that is used in full-text searches. See ft_stopword_file.
Changed default stack size from 64K to 192K; This fixes a core dump problem on Red Hat 8.0 and other systems with a glibc that requires a stack size larger than 128K for gethostbyaddr() to resolve a hostname. You can fix this for earlier MySQL versions by starting mysqld with --thread-stack=192K.
Added mysql_waitpid to the binary distribution and the MySQL-client RPM subpackage (required for mysql-test-run).
Renamed the main MySQL RPM package to MySQL-server. When updating from an older version, MySQL-server.rpm will simply replace MySQL.rpm.
If a slave is configured with replicate_wild_do_table=db.% or replicate_wild_ignore_table=db.%, these rules will be applied to CREATE/DROP DATABASE, too.
Added timeout value for MASTER_POS_WAIT().
Bugs fixed:
Fixed initialization of the random seed for newly created threads to give a better rand() distribution from the first call.
Fixed a bug that caused mysqld to hang when a table was opened with the HANDLER command and then dropped without being closed.
Fixed bug in logging to binary log (which affects replication) a query that inserts a NULL in an AUTO_INCREMENT column and also uses LAST_INSERT_ID().
Fixed an unlikely bug that could cause a memory overrun when using ORDER BY constant_expression.
Fixed a table corruption in myisamchk's parallel repair mode.
Fixed bug in query cache invalidation on simple table renaming.
Fixed bug in mysqladmin --relative.
On some 64-bit systems, show status reported a strange number for Open_files and Open_streams.
Fixed incorrect number of columns in EXPLAIN on empty table.
Fixed bug in LEFT JOIN that caused zero rows to be returned in the case the WHERE condition was evaluated as FALSE after reading const tables. (Unlikely condition).
FLUSH PRIVILEGES didn't correctly flush table/column privileges when mysql.tables_priv is empty.
Fixed bug in replication when using LOAD DATA INFILE one a file that updated an AUTO_INCREMENT column with NULL or 0. This bug only affected MySQL 4.0 masters (not slaves or MySQL 3.23 masters). Note: If you have a slave that has replicated a file with generated AUTO_INCREMENT columns then the slave data is corrupted and you should reinitialize the affected tables from the master.
Fixed possible memory overrun when sending a BLOB value larger than 16M to the client.
Fixed incorrect error message when setting a NOT NULL column to an expression that returned NULL.
Fixed core dump bug in str LIKE "%other_str%" where str or other_str contained characters >= 128.
Fixed bug: When executing on master LOAD DATA and InnoDB failed with table full error the binary log was corrupted.
Functionality added or changed:
OPTIMIZE TABLE will for MyISAM tables treat all NULL values as different when calculating cardinality. This helps in optimizing joins between tables where one of the tables has a lot of NULL values in a indexed column:
SELECT * from t1,t2 where t1.a=t2.key_with_a_lot_of_null;
Added join operator FORCE INDEX (key_list). This acts likes USE INDEX (key_list) but with the addition that a table scan is assumed to be VERY expensive. One bad thing with this is that it makes FORCE a reserved word.
Reset internal row buffer in MyISAM after each query. This will reduce memory in the case you have a lot of big blobs in a table.
Bugs fixed:
A security patch in 4.0.8 causes the mysqld server to die if the remote hostname can't be resolved. This is now fixed.
Fixed crash when replication big LOAD DATA INFILE statement that caused log rotation.
Functionality added or changed:
Default max_packet_length for libmysqld.c is now 1024*1024*1024.
One can now specify max_allowed_packet in a file ready by mysql_options(MYSQL_READ_DEFAULT_FILE). for clients.
When sending a too big packet to the server with the not compressed protocol, the client now gets an error message instead of a lost connection.
We now send big queries/result rows in bigger hunks, which should give a small speed improvement.
Fixed some bugs with the compressed protocol for rows > 16M.
InnoDB tables now also support ON UPDATE CASCADE in FOREIGN KEY constraints. See the InnoDB section in the manual for the InnoDB changelog.
Bugs fixed:
Fixed bug in ALTER TABLE with BDB tables.
Fixed core dump bug in QUOTE() function.
Fixed a bug in handling communication packets bigger than 16M. Unfortunately this required a protocol change; If you upgrade the server to 4.0.8 and above and have clients that uses packets >= 255*255*255 bytes (=16581375) you must also upgrade your clients to at least 4.0.8. If you don't upgrade, the clients will hang when sending a big packet.
Fixed bug when sending blobs longer than 16M to client.
Fixed bug in GROUP BY when used on BLOB column with NULL values.
Fixed a bug in handling NULL values in CASE ... WHEN ...
Functionality added or changed:
mysqlbug now also reports the compiler version used for building the binaries (if the compiler supports the option --version).
Bugs fixed:
Fixed compilation problems on OpenUnix and HPUX 10.20.
Fixed some optimization problems when compiling MySQL with -DBIG_TABLES on a 32-bit system.
mysql_drop_db() didn't check permissions properly so anyone could drop another users database. DROP DATABASE is checked properly.
Functionality added or changed:
Added syntax support for CHARACTER SET xxx and CHARSET=xxx table options (to be able to read table dumps from 4.1).
Fixed replication bug that caused the slave to loose its position in some cases when the replication log was rotated.
Fixed that a slave will restart from the start of a transaction if it's killed in the middle of one.
Moved the manual pages from man to man/man1 in the binary distributions.
The default type returned by IFNULL(A,B) is now set to be the more 'general' of the types of A and B. (The order is STRING, REAL or INTEGER).
Moved the mysql.server startup script in the RPM packages from /etc/rc.d/init.d/mysql to /etc/init.d/mysql (which almost all current Linux distributions support for LSB compliance).
Added Qcache_lowmem_prunes status variable (number of queries that were deleted from cache because of low memory).
Fixed mysqlcheck so it can deal with table names containing dashes.
Bulk insert optimization (see bulk_insert_buffer_size) is no longer used when inserting small (less than 100) number of rows.
Optimization added for queries like SELECT ... FROM merge_table WHERE indexed_column=constant_expr.
Added functions LOCALTIME and LOCALTIMESTAMP as synonyms for NOW().
CEIL is now an alias for CEILING.
The CURRENT_USER() function can be used to get a user@host value as it was matched in the GRANT system. See CURRENT_USER().
Fixed CHECK constraints to be compatible with SQL-99. This made CHECK a reserved word. (Checking of CHECK constraints is still not implemented).
Added CAST(... as CHAR).
Added PostgreSQL compatible LIMIT syntax: SELECT ... LIMIT row_count OFFSET offset
mysql_change_user() will now reset the connection to the state of a fresh connect (Ie, ROLLBACK any active transaction, close all temporary tables, reset all user variables etc..)
CHANGE MASTER and RESET SLAVE now require that slave threads be both already stopped; these commands will return an error if at least one of these two threads is running.
Bugs fixed:
Fixed number of found rows returned in multi table updates
Make --lower-case-table-names default on Mac OS X as the default file system (HFS+) is case insensitive. See Name case sensitivity.
Transactions in AUTOCOMMIT=0 mode didn't rotate binary log.
A fix for the bug in a SELECT with joined tables with ORDER BY and LIMIT clause when filesort had to be used. In that case LIMIT was applied to filesort of one of the tables, although it could not be. This fix also solved problems with LEFT JOIN.
mysql_server_init() now makes a copy of all arguments. This fixes a problem when using the embedded server in C# program.
Fixed buffer overrun in libmysqlclient library that allowed a malicious MySQL server to crash the client application.
Fixed security-related bug in mysql_change_user() handling. All users are strongly recommended to upgrade to version 4.0.6.
Fixed bug that prevented --chroot command-line option of mysqld from working.
Fixed bug in phrase operator "..." in boolean full-text search.
Fixed bug that caused OPTIMIZE TABLE to corrupt the table under some rare circumstances.
Part rewrite of multiple-table-update to optimize it, make it safer and more bug free.
LOCK TABLES now works together with multiple-table-update and multiple-table-delete.
--replicate-do=xxx didn't work for UPDATE commands. (Bug introduced in 4.0.0)
Fixed shutdown problem on Mac OS X.
Major InnoDB bugs in REPLACE, AUTO_INCREMENT, INSERT INTO ... SELECT ... were fixed. See the InnoDB changelog in the InnoDB section of the manual.
RESET SLAVE caused a crash if the slave threads were running.
Functionality added or changed:
Port number was added to hostname (if it is known) in SHOW PROCESSLIST command
Changed handling of last argument in WEEK() so that one can get week number according to the ISO 8601 specification. (Old code should still work).
Fixed that INSERT DELAYED threads don't hang on Waiting for INSERT when one sends a SIGHUP to mysqld.
Change that AND works according to SQL-99 when it comes to NULL handling. In practice, this only affects queries where you do something like WHERE ... NOT (NULL AND 0).
mysqld will now resolve basedir to its full path (with realpath()). This enables one to use relative symlinks to the MySQL installation directory. This will however cause show variables to report different directories on systems where there is a symbolic link in the path.
Fixed that MySQL will not use index scan on index disabled with IGNORE INDEX or USE INDEX. to be ignored.
Added --use-frm option to mysqlcheck. When used with REPAIR, it gets the table structure from the .frm file, so the table can be repaired even if the .MYI header is corrupted.
Fixed bug in MAX() optimization when used with JOIN and ON expressions.
Added support for reading of MySQL 4.1 table definition files.
BETWEEN behavior changed (see Comparison Operators). Now datetime_col BETWEEN timestamp AND timestamp should work as expected.
One can create TEMPORARY MERGE tables now.
DELETE FROM myisam_table now shrinks not only the .MYD file but also the .MYI file.
When one uses the --open-files-limit=# option to mysqld_safe it's now passed on to mysqld.
Changed output from EXPLAIN from 'where used' to 'Using where' to make it more in line with other output.
Removed variable safe_show_database as it was no longer used.
Updated source tree to be built using automake 1.5 and libtool 1.4.
Fixed an inadvertently changed option (--ignore-space) back to the original --ignore-spaces in mysqlclient. (Both syntaxes will work).
Don't require UPDATE privilege when using REPLACE.
Added support for DROP TEMPORARY TABLE ..., to be used to make replication safer.
When transactions are enabled, all commands that update temporary tables inside a BEGIN/COMMIT are now stored in the binary log on COMMIT and not stored if one does ROLLBACK. This fixes some problems with non-transactional temporary tables used inside transactions.
Allow braces in joins in all positions. Formerly, things like SELECT * FROM (t2 LEFT JOIN t3 USING (a)), t1 worked, but not SELECT * FROM t1, (t2 LEFT JOIN t3 USING (a)). Note that braces are simply removed, they do not change the way the join is executed.
InnoDB now supports also isolation levels READ UNCOMMITTED and READ COMMITTED. For a detailed InnoDB changelog, see InnoDB change history in this manual.
Bugs fixed:
Fixed bug in MAX() optimization when used with JOIN and ON expressions.
Fixed that INSERT DELAY threads don't hang on Waiting for INSERT when one sends a SIGHUP to mysqld.
Fixed that MySQL will not use an index scan on an index that has been disabled with IGNORE INDEX or USE INDEX.
Corrected test for root user in mysqld_safe.
Fixed error message issued when storage engine cannot do CHECK or REPAIR.
Fixed rare core dump problem in complicated GROUP BY queries that didn't return any result.
Fixed mysqlshow to work properly with wildcarded database names and with database names that contain underscores.
Portability fixes to get MySQL to compile cleanly with Sun Forte 5.0.
Fixed MyISAM crash when using dynamic-row tables with huge numbers of packed fields.
Fixed query cache behavior with BDB transactions.
Fixed possible floating point exception in MATCH relevance calculations.
Fixed bug in full-text search IN BOOLEAN MODE that made MATCH to return incorrect relevance value in some complex joins.
Fixed a bug that limited MyISAM key length to a value slightly less that 500. It is exactly 500 now.
Fixed that GROUP BY on columns that may have a NULL value doesn't always use disk based temporary tables.
The filename argument for the --des-key-file argument to mysqld is interpreted relative to the data directory if given as a relative pathname.
Removed a condition that temp table with index on column that can be NULL has to be MyISAM. This was okay for 3.23, but not needed in 4.*. This resulted in slowdown in many queries since 4.0.2.
Small code improvement in multiple-table updates.
Fixed a newly introduced bug that caused ORDER BY ... LIMIT row_count to not return all rows.
Fixed a bug in multiple-table deletes when outer join is used on an empty table, which gets first to be deleted.
Fixed a bug in multiple-table updates when a single table is updated.
Fixed bug that caused REPAIR TABLE and myisamchk to corrupt FULLTEXT indexes.
Fixed bug with caching the mysql grant table database. Now queries in this database are not cached in the query cache.
Small fix in mysqld_safe for some shells.
Give error if a MyISAM MERGE table has more than 2 ^ 32 rows and MySQL was not compiled with -DBIG_TABLES.
Fixed some ORDER BY ... DESC problems with InnoDB tables.
Fixed bug where GRANT/REVOKE failed if hostname was given in non-matching case.
Don't give warning in LOAD DATA INFILE when setting a timestamp to a string value of '0'.
Fixed bug in myisamchk -R mode.
Fixed bug that caused mysqld to crash on REVOKE.
Fixed bug in ORDER BY when there is a constant in the SELECT statement.
One didn't get an error message if mysqld couldn't open the privilege tables.
SET PASSWORD FOR ... closed the connection in case of errors (bug from 4.0.3).
Increased max possible max_allowed_packet in mysqld to 1 GB.
Fixed bug when doing a multi-line INSERT on a table with an AUTO_INCREMENT key which was not in the first part of the key.
Changed LOAD DATA INFILE to not re-create index if the table had rows from before.
Fixed overrun bug when calling AES_DECRYPT() with incorrect arguments.
--skip-ssl can now be used to disable SSL in the MySQL clients, even if one is using other SSL options in an option file or previously on the command line.
Fixed bug in MATCH ... AGAINST( ... IN BOOLEAN MODE) used with ORDER BY.
Added LOCK TABLES and CREATE TEMPORARY TABLES privilege on the database level. One must run the mysql_fix_privilege_tables script on old installations to activate these.
In SHOW TABLE ... STATUS, compressed tables sometimes showed up as dynamic.
SELECT @@[global|session].var_name didn't report global | session in the result column name.
Fixed problem in replication that FLUSH LOGS in a circular replication setup created an infinite number of binary log files. Now a rotate-binary-log command in the binary log will not cause slaves to rotate logs.
Removed STOP EVENT from binary log when doing FLUSH LOGS.
Disable the use of SHOW NEW MASTER FOR SLAVE as this needs to be completely reworked in a future release.
Fixed a bug with constant expression (for example, field of a one-row table, or field from a table, referenced by a UNIQUE key) appeared in ORDER BY part of SELECT DISTINCT.
--log-binary=a.b.c now properly strips off .b.c.
FLUSH LOGS removed numerical extension for all future update logs.
GRANT ... REQUIRE didn't store the SSL information in the mysql.user table if SSL was not enabled in the server.
GRANT ... REQUIRE NONE can now be used to remove SSL information.
AND is now optional between REQUIRE options.
REQUIRE option was not properly saved, which could cause strange output in SHOW GRANTS.
Fixed that mysqld --help reports correct values for --datadir and --bind-address.
Fixed that one can drop UDFs that didn't exist when mysqld was started.
Fixed core dump problem with SHOW VARIABLES on some 64-bit systems (like Solaris SPARC).
Fixed a bug in my_getopt(); --set-variable syntax didn't work for those options that didn't have a valid variable in the my_option struct. This affected at least the default-table-type option.
Fixed a bug from 4.0.2 that caused REPAIR TABLE and myisamchk --recover to fail on tables with duplicates in a unique key.
Fixed a bug from 4.0.3 in calculating the default datatype for some functions. This affected queries of type CREATE TABLE table_name SELECT expression(),...
Fixed bug in queries of type SELECT * FROM table-list GROUP BY ... and SELECT DISTINCT * FROM ....
Fixed bug with the --slow-log when logging an administrator command (like FLUSH TABLES).
Fixed a bug that OPTIMIZE of locked and modified table, reported table corruption.
Fixed a bug in my_getopt() in handling of special prefixes (--skip-, --enable-). --skip-external-locking didn't work and the bug may have affected other similar options.
Fixed bug in checking for output file name of the tee option.
Added some more optimization to use index for SELECT ... FROM many_tables .. ORDER BY key limit #
Fixed problem in SHOW OPEN TABLES when a user didn't have access permissions to one of the opened tables.
Fixed problem with types of user variables. (Bug #551)
Fixed problem with configure ... --localstatedir=....
Cleaned up mysql.server script.
Fixed a bug in mysqladmin shutdown when pid file was modified while mysqladmin was still waiting for the previous one to disappear. This could happen during a very quick restart and caused mysqladmin to hang until shutdown_timeout seconds had passed.
Don't increment warnings when setting AUTO_INCREMENT columns to NULL in LOAD DATA INFILE.
Fixed all boolean type variables/options to work with the old syntax, for example, all of these work: --lower-case-table-names, --lower-case-table-names=1, -O lower-case-table-names=1, --set-variable=lower-case-table-names=1
Fixed shutdown problem (SIGTERM signal handling) on Solaris. (Bug from 4.0.2).
SHOW MASTER STATUS now returns an empty set if binary log is not enabled.
SHOW SLAVE STATUS now returns an empty set if slave is not initialized.
Don't update MyISAM index file on update if not strictly necessary.
Fixed bug in SELECT DISTINCT ... FROM many_tables ORDER BY not-used-column.
Fixed a bug with BIGINT values and quoted strings.
Added QUOTE() function that performs SQL quoting to produce values that can be used as data values in queries.
Changed variable DELAY_KEY_WRITE to an enum to allow one set DELAY_KEY_WRITE for all tables without taking down the server.
Changed behavior of IF(condition,column,NULL) so that it returns the value of the column type.
Made safe_mysqld a symlink to mysqld_safe in binary distribution.
Fixed security bug when having an empty database name in the user.db table.
Fixed some problems with CREATE TABLE ... SELECT function().
mysqld now has the option --temp-pool enabled by default as this gives better performance with some operating systems.
Fixed problem with too many allocated alarms on slave when connecting to master many times (normally not a very critical error).
Fixed hang in CHANGE MASTER TO if the slave thread died very quickly.
Big cleanup in replication code (less logging, better error messages, etc..)
If the --code-file option is specified, the server calls setrlimit() to set the maximum allowed core file size to unlimited, so core files can be generated.
Fixed bug in query cache after temporary table creation.
Added --count=N (-c) option to mysqladmin, to make the program do only N iterations. To be used with --sleep (-i). Useful in scripts.
Fixed bug in multiple-table UPDATE: when updating a table, do_select() became confused about reading records from a cache.
Fixed bug in multiple-table UPDATE when several fields were referenced from a single table
Fixed bug in truncating nonexisting table.
Fixed bug in REVOKE that caused user resources to be randomly set.
Fixed bug in GRANT for the new CREATE TEMPORARY TABLE privilege.
Fixed bug in multiple-table DELETE when tables are re-ordered in the table initialization method and ref_lengths are of different sizes.
Fixed two bugs in SELECT DISTINCT with large tables.
Fixed bug in query cache initialization with very small query cache size.
Allow DEFAULT with INSERT statement.
The startup parameters myisam_max_sort_file_size and myisam_max_extra_sort_file_size are now given in bytes, not megabytes.
External system locking of MyISAM/ISAM files is now turned off by default. One can turn this on with --external-locking. (For most users this is never needed).
Fixed core dump bug with INSERT ... SET db_name.table_name.colname="".
Fixed client hangup bug when using some SQL commands with incorrect syntax.
Fixed a timing bug in DROP DATABASE
New SET [GLOBAL | SESSION] syntax to change thread-specific and global server variables at runtime.
Added variable slave_compressed_protocol.
Renamed variable query_cache_startup_type to query_cache_type, myisam_bulk_insert_tree_size to bulk_insert_buffer_size, record_buffer to read_buffer_size and record_rnd_buffer to read_rnd_buffer_size.
Renamed some SQL variables, but old names will still work until 5.0. See Upgrading-from-3.23.
Renamed --skip-locking to --skip-external-locking.
Removed unused variable query_buffer_size.
Fixed a bug that made the pager option in the mysql client non-functional.
Added full AUTO_INCREMENT support to MERGE tables.
Extended LOG() function to accept an optional arbitrary base parameter. See Mathematical functions.
Added LOG2() function (useful for finding out how many bits a number would require for storage).
Added LN() natural logarithm function for compatibility with other databases. It is synonymous with LOG(X).
Cleaned up NULL handling for default values in DESCRIBE table_name.
Fixed truncate() to round up negative values to the nearest integer.
Changed --chroot=path option to execute chroot() immediately after all options have been parsed.
Don't allow database names that contain \.
lower_case_table_names now also affects database names.
Added XOR operator (logical and bitwise XOR) with ^ as a synonym for bitwise XOR.
Added function IS_FREE_LOCK("lock_name"). Based on code contributed by Hartmut Holzgraefe <hartmut@six.de>.
Removed mysql_ssl_clear() from C API, as it was not needed.
DECIMAL and NUMERIC types can now read exponential numbers.
Added SHA1() function to calculate 160 bit hash value as described in RFC 3174 (Secure Hash Algorithm). This function can be considered a cryptographically more secure equivalent of MD5(). See Encryption functions.
Added AES_ENCRYPT() and AES_DECRYPT() functions to perform encryption according to AES standard (Rijndael). See Encryption functions.
Added --single-transaction option to mysqldump, allowing a consistent dump of InnoDB tables. See mysqldump, Dumping Table Structure and Data.
Fixed bug in innodb_log_group_home_dir in SHOW VARIABLES.
Fixed a bug in optimizer with merge tables when non-unique values are used in summing up (causing crashes).
Fixed a bug in optimizer when a range specified makes index grouping impossible (causing crashes).
Fixed a rare bug when FULLTEXT index is present and no tables are used.
Added privileges CREATE TEMPORARY TABLES, EXECUTE, LOCK TABLES, REPLICATION CLIENT, REPLICATION SLAVE, SHOW DATABASES and SUPER. To use these, you must have run the mysql_fix_privilege_tables script after upgrading.
Fixed query cache align data bug.
Fixed mutex bug in replication when reading from master fails.
Added missing mutex in TRUNCATE TABLE; This fixes some core dump/hangup problems when using TRUNCATE TABLE.
Fixed bug in multiple-table DELETE when optimizer uses only indexes.
Fixed that ALTER TABLE table_name RENAME new_table_name is as fast as RENAME TABLE.
Fixed bug in GROUP BY with two or more fields, where at least one field can contain NULL values.
Use Turbo Boyer-Moore algorithm to speed up LIKE "%keyword%" searches.
Fixed bug in DROP DATABASE with symlink.
Fixed crash in REPAIR ... USE_FRM.
Fixed bug in EXPLAIN with LIMIT offset != 0.
Fixed bug in phrase operator "..." in boolean full-text search.
Fixed bug that caused duplicated rows when using truncation operator * in boolean full-text search.
Fixed bug in truncation operator of boolean full-text search (incorrect results when there are only +word*s in the query).
Fixed bug in boolean full-text search that caused a crash when an identical MATCH expression that did not use an index appeared twice.
Query cache is now automatically disabled in mysqldump.
Fixed problem on Windows 98 that made sending of results very slow.
Boolean full-text search weighting scheme changed to something more reasonable.
Fixed bug in boolean full-text search that caused MySQL to ignore queries of ft_min_word_len characters.
Boolean full-text search now supports ``phrase searches''.
New configure option --without-query-cache.
Memory allocation strategy for ``root memory'' changed. Block size now grows with number of allocated blocks.
INET_NTOA() now returns NULL if you give it an argument that is too large (greater than the value corresponding to 255.255.255.255).
Fix SQL_CALC_FOUND_ROWS to work with UNION. It will work only if the first SELECT has this option and if there is global LIMIT for the entire statement. For the moment, this requires using parentheses for individual SELECT queries within the statement.
Fixed bug in SQL_CALC_FOUND_ROWS and LIMIT.
Don't give an error for CREATE TABLE ...(... VARCHAR(0)).
Fixed SIGINT and SIGQUIT problems in mysql.cc on Linux with some glibc versions.
Fixed bug in convert.cc, which is caused by having an incorrect net_store_length() linked in the CONVERT::store() method.
DOUBLE and FLOAT columns now honor the UNSIGNED flag on storage.
InnoDB now retains foreign key constraints through ALTER TABLE and CREATE/DROP INDEX.
InnoDB now allows foreign key constraints to be added through the ALTER TABLE syntax.
InnoDB tables can now be set to automatically grow in size (autoextend).
Added --ignore-lines=n option to mysqlimport. This has the same effect as the IGNORE n LINES clause for LOAD DATA.
Fixed bug in UNION with last offset being transposed to total result set.
REPAIR ... USE_FRM added.
Fixed that DEFAULT_SELECT_LIMIT is always imposed on UNION result set.
Fixed that some SELECT options can appear only in the first SELECT.
Fixed bug with LIMIT with UNION, where last select is in the braces.
Fixed that full-text works fine with UNION operations.
Fixed bug with indexless boolean full-text search.
Fixed bug that sometimes appeared when full-text search was used with const tables.
Fixed incorrect error value when doing a SELECT with an empty HEAP table.
Use ORDER BY column DESC now sorts NULL values first. (In other words, NULL values sort first in all cases, whether or not DESC is specified.) This is changed back in 4.0.10.
Fixed bug in WHERE key_name="constant" ORDER BY key_name DESC.
Fixed bug in SELECT DISTINCT ... ORDER BY DESC optimization.
Fixed bug in ... HAVING 'GROUP_FUNCTION'(xxx) IS [NOT] NULL.
Fixed bug in truncation operator for boolean full-text search.
Allow value of --user=# option for mysqld to be specified as a numeric user ID.
Fixed a bug where SQL_CALC_ROWS returned an incorrect value when used with one table and ORDER BY and with InnoDB tables.
Fixed that SELECT 0 LIMIT 0 doesn't hang thread.
Fixed some problems with USE/IGNORE INDEX when using many keys with the same start column.
Don't use table scan with BerkeleyDB and InnoDB tables when we can use an index that covers the whole row.
Optimized InnoDB sort-buffer handling to take less memory.
Fixed bug in multiple-table DELETE and InnoDB tables.
Fixed problem with TRUNCATE and InnoDB tables that produced the error Can't execute the given command because you have active locked tables or an active transaction.
Added NO_UNSIGNED_SUBTRACTION to the set of flags that may be specified with the --sql-mode option for mysqld. It disables unsigned arithmetic rules when it comes to subtraction. (This will make MySQL 4.0 behave more like 3.23 with UNSIGNED columns).
The result returned for all bit functions (|, <<, ...) is now of type unsigned integer.
Added detection of nan values in MyISAM to make it possible to repair tables with nan in float or double columns.
Fixed new bug in myisamchk where it didn't correctly update number of ``parts'' in the MyISAM index file.
Changed to use autoconf 2.52 (from autoconf 2.13).
Fixed optimization problem where the MySQL Server was in ``preparing'' state for a long time when selecting from an empty table which had contained a lot of rows.
Fixed bug in complicated join with const tables. This fix also improves performance a bit when referring to another table from a const table.
First pre-version of multiple-table UPDATE statement.
Fixed bug in multiple-table DELETE.
Fixed bug in SELECT CONCAT(argument_list) ... GROUP BY 1.
INSERT ... SELECT did a full rollback in case of an error. Fixed so that we only roll back the last statement in the current transaction.
Fixed bug with empty expression for boolean full-text search.
Fixed core dump bug in updating full-text key from/to NULL.
ODBC compatibility: Added BIT_LENGTH() function.
Fixed core dump bug in GROUP BY BINARY column.
Added support for NULL keys in HEAP tables.
Use index for ORDER BY in queries of type: SELECT * FROM t WHERE key_part1=1 ORDER BY key_part1 DESC,key_part2 DESC
Fixed bug in FLUSH QUERY CACHE.
Added CAST() and CONVERT() functions. The CAST and CONVERT functions are nearly identical and mainly useful when you want to create a column with a specific type in a CREATE ... SELECT statement. For more information, read Cast Functions.
CREATE ... SELECT on DATE and TIME functions now create columns of the expected type.
Changed order in which keys are created in tables.
Added new columns Null and Index_type to SHOW INDEX output.
Added --no-beep and --prompt options to mysql command-line client.
New feature: management of user resources.
GRANT ... WITH MAX_QUERIES_PER_HOUR N1 MAX_UPDATES_PER_HOUR N2 MAX_CONNECTIONS_PER_HOUR N3;
See User resources.
Added mysql_secure_installation to the scripts/ directory.
Added system command to mysql.
Fixed bug when HANDLER was used with some unsupported table type.
mysqldump now puts ALTER TABLE tbl_name DISABLE KEYS and ALTER TABLE tbl_name ENABLE KEYS in the sql dump.
Added mysql_fix_extensions script.
Fixed stack overrun problem with LOAD DATA FROM MASTER on OSF/1.
Fixed shutdown problem on HP-UX.
Added DES_ENCRYPT() and DES_DECRYPT() functions.
Added FLUSH DES_KEY_FILE statement.
Added --des-key-file option to mysqld.
HEX(string) now returns the characters in string converted to hexadecimal.
Fixed problem with GRANT when using lower_case_table_names=1.
Changed SELECT ... IN SHARE MODE to SELECT ... LOCK IN SHARE MODE (as in MySQL 3.23).
A new query cache to cache results from identical SELECT queries.
Fixed core dump bug on 64-bit machines when it got an incorrect communication packet.
MATCH ... AGAINST(... IN BOOLEAN MODE) can now work without FULLTEXT index.
Fixed slave to replicate from 3.23 master.
Miscellaneous replication fixes/cleanup.
Got shutdown to work on Mac OS X.
Added myisam/ft_dump utility for low-level inspection of FULLTEXT indexes.
Fixed bug in DELETE ... WHERE ... MATCH ....
Added support for MATCH ... AGAINST(... IN BOOLEAN MODE). Note: You must rebuild your tables with ALTER TABLE tablename TYPE=MyISAM to be able to use boolean full-text search.
LOCATE() and INSTR() are now case sensitive if either argument is a binary string.
Changed RAND() initialization so that RAND(N) and RAND(N+1) are more distinct.
Fixed core dump bug in UPDATE ... ORDER BY.
In 3.23, INSERT INTO ... SELECT always had IGNORE enabled. Now MySQL will stop (and possibly roll back) by default in case of an error unless you specify IGNORE.
Ignore DATA DIRECTORY and INDEX DIRECTORY directives on Windows.
Added boolean full-text search code. It should be considered early alpha.
Extended MODIFY and CHANGE in ALTER TABLE to accept the FIRST and AFTER keywords.
Indexes are now used with ORDER BY on a whole InnoDB table.
Added --xml option to mysql for producing XML output.
Added full-text variables ft_min_word_len, ft_max_word_len, and ft_max_word_len_for_sort.
Added documentation for libmysqld, the embedded MySQL server library. Also added example programs (a mysql client and mysqltest test program) which use libmysqld.
Removed all Gemini hooks from MySQL server.
Removed my_thread_init() and my_thread_end() from mysql_com.h, and added mysql_thread_init() and mysql_thread_end() to mysql.h.
Support for communication packets > 16M. In 4.0.1 we will extend MyISAM to be able to handle these.
Secure connections (with SSL).
Unsigned BIGINT constants now work. MIN() and MAX() now handle signed and unsigned BIGINT numbers correctly.
New character set latin1_de which provides correct German sorting.
STRCMP() now uses the current character set when doing comparisons, which means that the default comparison behavior now is case insensitive.
TRUNCATE TABLE and DELETE FROM tbl_name are now separate functions. One bonus is that DELETE FROM tbl_name now returns the number of deleted rows, rather than zero.
DROP DATABASE now executes a DROP TABLE on all tables in the database, which fixes a problem with InnoDB tables.
Added support for UNION.
Added support for multiple-table DELETE operations.
A new HANDLER interface to MyISAM tables.
Added support for INSERT on MERGE tables. Patch from Benjamin Pflugmann.
Changed WEEK(date,0) to match the calendar in the USA.
COUNT(DISTINCT) is about 30% faster.
Speed up all internal list handling.
Speed up IS NULL, ISNULL() and some other internal primitives.
Full-text index creation now is much faster.
Tree-like cache to speed up bulk inserts and myisam_bulk_insert_tree_size variable.
Searching on packed (CHAR/VARCHAR) keys is now much faster.
Optimized queries of type: SELECT DISTINCT * from tbl_name ORDER by key_part1 LIMIT row_count.
SHOW CREATE TABLE now shows all table attributes.
ORDER BY ... DESC can now use keys.
LOAD DATA FROM MASTER ``automatically'' sets up a slave.
Renamed safe_mysqld to mysqld_safe to make this name more in line with other MySQL scripts/commands.
Added support for symbolic links to MyISAM tables. Symlink handling is now enabled by default for Windows.
Added SQL_CALC_FOUND_ROWS and FOUND_ROWS(). This makes it possible to know how many rows a query would have returned without a LIMIT clause.
Changed output format of SHOW OPEN TABLES.
Allow SELECT expression LIMIT ....
Added ORDER BY syntax to UPDATE and DELETE.
SHOW INDEXES is now a synonym for SHOW INDEX.
Added ALTER TABLE tbl_name DISABLE KEYS and ALTER TABLE tbl_name ENABLE KEYS commands.
Allow use of IN as a synonym for FROM in SHOW commands.
Implemented ``repair by sort'' for FULLTEXT indexes. REPAIR TABLE, ALTER TABLE, and OPTIMIZE TABLE for tables with FULLTEXT indexes are now up to 100 times faster.
Allow SQL-99 syntax X'hexadecimal-number'.
Cleaned up global lock handling for FLUSH TABLES WITH READ LOCK.
Fixed problem with DATETIME = constant in WHERE optimization.
Added --master-data and --no-autocommit options to mysqldump. (Thanks to Brian Aker for this.)
Added script mysql_explain_log.sh to distribution. (Thanks to mobile.de).
Table of Contents
Please note that since release 4.0 is now production level, only critical fixes are done in the 3.23 release series. You are recommended to upgrade when possible, to take advantage of all speed and feature improvements in 4.0. See Upgrading-from-3.23.
The 3.23 release has several major features that are not present in previous versions. We have added three new table types:
MyISAM | A new ISAM library which is tuned for SQL and supports large files. |
InnoDB | A transaction-safe storage engine that supports row level locking, and many Oracle-like features. |
BerkeleyDB or BDB | Uses the Berkeley DB library from Sleepycat Software to implement transaction-safe tables. |
Note that only MyISAM is available in the standard binary distribution.
The 3.23 release also includes support for database replication between a master and many slaves, full-text indexing, and much more.
All new features are being developed in the 4.x version. Only bug fixes and minor enhancements to existing features will be added to 3.23.
The replication code and BerkeleyDB code is still not as tested and as the rest of the code, so we will probably need to do a couple of future releases of 3.23 with small fixes for this part of the code. As long as you don't use these features, you should be quite safe with MySQL 3.23!
Note that the above doesn't mean that replication or Berkeley DB don't work. We have done a lot of testing of all code, including replication and BDB without finding any problems. It only means that not as many users use this code as the rest of the code and because of this we are not yet 100% confident in this code.
Fixed bug in ACOS(), ASIN(). (Bug #2338) The cause of the problem is an overly strong optimization done by gcc in this case.
Fixed bug in INSERT ... SELECT statements where, if a NOT NULL column is assigned a value of NULL, the following columns in the row might be assigned a value of zero. (Bug #2012)
If a query was ignored on the slave (because of replicate-ignore-table and other similar rules), the slave still checked if the query got the same error code (0, no error) as on the master. So if the master had an error on the query (for example, ``Duplicate entry'' in a multiple-row insert), then the slave stopped and warned that the error codes didn't match. This is a backport of the fix for MySQL 4.0. (Bug #797)
mysqlbinlog now asks for a password at console when the -p/--password option is used with no argument. This is how the other clients (mysqladmin, mysqldump..) already behave. Note that one now has to use mysqlbinlog -p<my_password>; mysqlbinlog -p <my_password> will not work anymore (in other words, put no space after -p). (Bug #1595)
On some 64-bit machines (some HP-UX and Solaris machines), a slave installed with the 64-bit MySQL binary could not connect to its master (it connected to itself instead). (Bug #1256, #1381)
Fixed a Windows-specific bug present since MySQL version 3.23.57 and 3.23.58, which caused Windows slaves to crash when they started replication if a master.info file existed. (Bug #1720)
Fixed bug in ALTER TABLE RENAME, when rename to the table with the same name in another database silently dropped destination table if it existed. (Bug #2628)
Fixed buffer overflow in password handling which could potentially be exploited by MySQL users with ALTER privilege on the mysql.user table to execute random code or to gain shell access with the UID of the mysqld process (thanks to Jedi/Sector One for spotting and reporting this bug).
mysqldump now correctly quotes all identifiers when communicating with the server. This assures that during the dump process, mysqldump will never send queries to the server that result in a syntax error. This problem is not related to the mysqldump program's output, which was not changed. (Bug #1148)
Fixed table/column grant handling - proper sort order (from most specific to less specific, see Request access) was not honored. (Bug #928)
Fixed overflow bug in MyISAM and ISAM when a row is updated in a table with a large number of columns and at least one BLOB/TEXT column.
Fixed MySQL so that field length (in C API) for the second column in SHOW CREATE TABLE is always larger than the data length. The only known application that was affected by the old behavior was Borland dbExpress, which truncated the output from the command. (Bug #1064)
Fixed ISAM bug in MAX() optimization.
Fixed Unknown error when doing ORDER BY on reference table which was used with NULL value on NOT NULL column. (Bug #479)
Fixed problem in alarm handling that could cause problems when getting a packet that is too large.
Fixed problem when installing MySQL as a service on Windows when one gave two arguments (option file group name and service name) to mysqld.
Fixed kill pid-of-mysqld to work on Mac OS X.
SHOW TABLE STATUS displayed incorrect Row_format value for tables that have been compressed with myisampack. (Bug #427)
SHOW VARIABLES LIKE 'innodb_data_file_path' displayed only the name of the first datafile. (Bug #468)
Fixed security problem where mysqld didn't allow one to UPDATE rows in a table even if one had a global UPDATE privilege and a database SELECT privilege.
Fixed a security problem with SELECT and wildcarded select list, when user only had partial column SELECT privileges on the table.
Fixed unlikely problem in optimizing WHERE clause with a constant expression such as in WHERE 1 AND (a=1 AND b=1).
Fixed problem on IA-64 with timestamps that caused mysqlbinlog to fail.
The default option for innodb_flush_log_at_trx_commit was changed from 0 to 1 to make InnoDB tables ACID by default. See InnoDB start.
Fixed problem with too many allocated alarms on slave when connecting to master many times (normally not a very critical error).
Fixed a bug in replication of temporary tables. (Bug #183)
Fixed 64-bit bug that affected at least AMD hammer systems.
Fixed a bug when doing LOAD DATA INFILE IGNORE: When reading the binary log, mysqlbinlog and the replication code read REPLACE instead of IGNORE. This could make the slave's table become different from the master's table. (Bug #218)
Fixed overflow bug in MyISAM when a row is inserted into a table with a large number of columns and at least one BLOB/TEXT column. Bug was caused by incorrect calculation of the needed buffer to pack data.
The binary log was not locked during TRUNCATE table_name or DELETE FROM table_name statements, which could cause an INSERT to table_name to be written to the log before the TRUNCATE or DELETE statements.
Fixed rare bug in UPDATE of InnoDB tables where one row could be updated multiple times.
Produce an error for empty table and column names.
Changed PROCEDURE ANALYSE() to report DATE instead of NEWDATE.
Changed PROCEDURE ANALYSE(#) to restrict the number of values in an ENUM column to # also for string values.
mysqldump no longer silently deletes the binary logs when invoked with the --master-data or --first-slave option; while this behavior was convenient for some users, others may suffer from it. Now one has to explicitly ask for binary logs to be deleted by using the new --delete-master-logs option.
Fixed a bug in mysqldump when it was invoked with the --master-data option: The CHANGE MASTER TO statements that were appended to the SQL dump had incorrect coordinates. (Bug #159)
Fixed mysqld crash on extremely small values of sort_buffer variable.
Fixed a bug in privilege system for GRANT UPDATE on the column level.
Fixed a rare bug when using a date in HAVING with GROUP BY.
Fixed checking of random part of WHERE clause. (Bug #142)
Fixed MySQL (and myisamchk) crash on artificially corrupted .MYI files.
Security enhancement: mysqld no longer reads options from world-writable config files.
Security enhancement: mysqld and safe_mysqld now use only the first --user option specified on the command line. (Normally this comes from /etc/my.cnf)
Security enhancement: Don't allow BACKUP TABLE to overwrite existing files.
Fixed unlikely deadlock bug when one thread did a LOCK TABLE and another thread did a DROP TABLE. In this case one could do a KILL on one of the threads to resolve the deadlock.
LOAD DATA INFILE was not replicated by slave if replicate_*_table was set on the slave.
Fixed a bug in handling CHAR(0) columns that could cause incorrect results from the query.
Fixed a bug in SHOW VARIABLES on 64-bit platforms. The bug was caused by incorrect declaration of variable server_id.
The Comment column in SHOW TABLE STATUS now reports that it can contain NULL values (which is the case for a crashed .frm file).
Fixed the rpl_rotate_logs test to not fail on certain platforms (e.g. Mac OS X) due to a too long file name (changed slave-master-info.opt to .slave-mi).
Fixed a problem with BLOB NOT NULL columns used with IS NULL.
Fixed bug in MAX() optimization in MERGE tables.
Better RAND() initialization for new connections.
Fixed bug with connect timeout. This bug was manifested on OS's with poll() system call, which resulted in timeout the value specified as it was executed in both select() and poll().
Fixed bug in SELECT * FROM table WHERE datetime1 IS NULL OR datetime2 IS NULL.
Fixed bug in using aggregate functions as argument for INTERVAL, CASE, FIELD, CONCAT_WS, ELT and MAKE_SET functions.
When running with --lower-case-table-names=1 (default on Windows) and you had tables or databases with mixed case on disk, then executing SHOW TABLE STATUS followed with DROP DATABASE or DROP TABLE could fail with Errcode 13.
Fixed bug in logging to binary log (which affects replication) a query that inserts a NULL in an auto_increment field and also uses LAST_INSERT_ID().
Fixed bug in mysqladmin --relative.
On some 64-bit systems, show status reported a strange number for Open_files and Open_streams.
Fixed double free'd pointer bug in mysql_change_user() handling, that enabled a specially hacked version of MySQL client to crash mysqld. Note, that you must log in to the server by using a valid user account to be able to exploit this bug.
Fixed bug with the --slow-log when logging an administrator command (like FLUSH TABLES).
Fixed bug in GROUP BY when used on BLOB column with NULL values.
Fixed a bug in handling NULL values in CASE ... WHEN ....
Bugfix for --chroot (see --chroot) is reverted. Unfortunately, there is no way to make it to work, without introducing backward-incompatible changes in my.cnf. Those who need --chroot functionality, should upgrade to MySQL 4.0. (The fix in the 4.0 branch did not break backward-compatibility).
Make --lower-case-table-names default on Mac OS X as the default file system (HFS+) is case insensitive.
Fixed a bug in scripts/mysqld_safe.sh in NOHUP_NICENESS testing.
Transactions in AUTOCOMMIT=0 mode didn't rotate binary log.
Fixed a bug in scripts/make_binary_distribution that resulted in a remaining @HOSTNAME@ variable instead of replacing it with the correct path to the hostname binary.
Fixed a very unlikely bug that could cause SHOW PROCESSLIST to core dump in pthread_mutex_unlock() if a new thread was connecting.
Forbid SLAVE STOP if the thread executing the query has locked tables. This removes a possible deadlock situation.
Fixed a bug, that allowed to crash mysqld with a specially crafted packet.
Fixed a rare crash (double free'd pointer) when altering a temporary table.
Fixed buffer overrun in libmysqlclient library that allowed malicious MySQL server to crash the client application.
Fixed security-related bug in mysql_change_user() handling. All users are strongly recommended to upgrade to the version 3.23.54.
Fixed bug that prevented --chroot command-line option of mysqld from working.
Fixed bug that made OPTIMIZE TABLE to corrupt the table under some rare circumstances.
Fixed mysqlcheck so it can deal with table names containing dashes.
Fixed shutdown problem on Mac OS X.
Fixed bug with comparing an indexed NULL field with <=> NULL.
Fixed bug that caused IGNORE INDEX and USE INDEX sometimes to be ignored.
Fixed rare core dump problem in complicated GROUP BY queries that didn't return any result.
Fixed a bug where MATCH ... AGAINST () >=0 was treated as if it was >.
Fixed core dump in SHOW PROCESSLIST when running with an active slave (unlikely timing bug).
Make it possible to use multiple MySQL servers on Windows (code backported from 4.0.2).
One can create TEMPORARY MERGE tables now.
Fixed that --core-file works on Linux (at least on kernel 2.4.18).
Fixed a problem with BDB and ALTER TABLE.
Fixed reference to freed memory when doing complicated GROUP BY ... ORDER BY queries. Symptom was that mysqld died in function send_fields.
Allocate heap rows in smaller blocks to get better memory usage.
Fixed memory allocation bug when storing BLOB values in internal temporary tables used for some (unlikely) GROUP BY queries.
Fixed a bug in key optimizing handling where the expression WHERE column_name = key_column_name was calculated as true for NULL values.
Fixed core dump bug when doing LEFT JOIN ... WHERE key_column=NULL.
Fixed MyISAM crash when using dynamic-row tables with huge numbers of packed fields.
Updated source tree to be built using automake 1.5 and libtool 1.4.
Fixed crash when SHOW INNODB STATUS was used and skip-innodb was defined.
Fixed possible memory corruption bug in binary log file handling when slave rotated the logs (only affected 3.23, not 4.0).
Fixed problem in LOCK TABLES on Windows when one connects to a database that contains uppercase letters.
Fixed that --skip-show-databases doesn't reset the --port option.
Small fix in safe_mysqld for some shells.
Fixed that FLUSH STATUS doesn't reset delayed_insert_threads.
Fixed core dump bug when using the BINARY cast on a NULL value.
Fixed race condition when someone did a GRANT at the same time a new user logged in or did a USE database.
Fixed bug in ALTER TABLE and RENAME TABLE when running with -O lower_case_table_names=1 (typically on Windows) when giving the table name in uppercase.
Fixed that -O lower_case_table_names=1 also converts database names to lowercase.
Fixed unlikely core dump with SELECT ... ORDER BY ... LIMIT.
Changed AND/OR to report that they can return NULL. This fixes a bug in GROUP BY on AND/OR expressions that return NULL.
Fixed a bug that OPTIMIZE of locked and modified MyISAM table, reported table corruption.
Fixed a BDB-related ALTER TABLE bug with dropping a column and shutting down immediately thereafter.
Fixed problem with configure ... --localstatedir=....
Fixed problem with UNSIGNED BIGINT on AIX (again).
Fixed bug in pthread_mutex_trylock() on HPUX 11.0.
Multi-threaded stress tests for InnoDB.
Wrap BEGIN/COMMIT around transaction in the binary log. This makes replication honor transactions.
Fixed security bug when having an empty database name in the user.db table.
Changed initialization of RND() to make it less predicatable.
Fixed problem with GROUP BY on result with expression that created a BLOB field.
Fixed problem with GROUP BY on columns that have NULL values. To solve this we now create an MyISAM temporary table when doing a GROUP BY on a possible NULL item. From MySQL 4.0.5 we can use in memory HEAP tables for this case.
Fixed problem with privilege tables when downgrading from 4.0.2 to 3.23.
Fixed thread bug in SLAVE START, SLAVE STOP and automatic repair of MyISAM tables that could cause table cache to be corrupted.
Fixed possible thread related key-cache-corruption problem with OPTIMIZE TABLE and REPAIR TABLE.
Added name of 'administrator command' logs.
Fixed bug with creating an auto-increment value on second part of a UNIQUE() key where first part could contain NULL values.
Don't write slave-timeout reconnects to the error log.
Fixed bug with slave net read timeouting
Fixed a core-dump bug with MERGE tables and MAX() function.
Fixed bug in ALTER TABLE with BDB tables.
Fixed bug when logging LOAD DATA INFILE to binary log with no active database.
Fixed a bug in range optimizer (causing crashes).
Fixed possible problem in replication when doing DROP DATABASE on a database with InnoDB tables.
Fixed mysql_info() to return 0 for Duplicates value when using INSERT DELAYED IGNORE.
Added -DHAVE_BROKEN_REALPATH to the Mac OS X (darwin) compile options in configure.in to fix a failure under high load.
Fix bug with closing tags missing slash for mysqldump XML output.
Remove end space from ENUM values. (This fixed a problem with SHOW CREATE TABLE.)
Fixed bug in CONCAT_WS() that cut the result.
Changed name of server variables Com_show_master_stat to Com_show_master_status and Com_show_slave_stat to Com_show_slave_status.
Changed handling of gethostbyname() to make the client library thread-safe even if gethostbyname_r doesn't exist.
Fixed core-dump problem when giving a wrong password string to GRANT.
Fixed bug in DROP DATABASE with symlinked directory.
Fixed optimization problem with DATETIME and value outside DATETIME range.
Removed Sleepycat's BDB doc files from the source tree, as they're not needed (MySQL covers BDB in its own documentation).
Fixed MIT-pthreads to compile with glibc 2.2 (needed for make dist).
Fixed the FLOAT(X+1,X) is not converted to FLOAT(X+2,X). (This also affected DECIMAL, DOUBLE and REAL types)
Fixed the result from IF() is case in-sensitive if the second and third arguments are case sensitive.
Fixed core dump problem on OSF/1 in gethostbyname_r.
Fixed that underflowed decimal fields are not zero filled.
If we get an overflow when inserting '+11111' for DECIMAL(5,0) UNSIGNED columns, we will just drop the sign.
Fixed optimization bug with ISNULL(expression_which_cannot_be_null) and ISNULL(constant_expression).
Fixed host lookup bug in the glibc library that we used with the 3.23.50 Linux-x86 binaries.
Fixed buffer overflow problem if someone specified a too long datadir parameter to mysqld
Add missing <row> tags for mysqldump XML output.
Fixed problem with crash-me and gcc 3.0.4.
Fixed that @@unknown_variable doesn't hang server.
Added @@VERSION as a synonym for VERSION().
SHOW VARIABLES LIKE 'xxx' is now case-insensitive.
Fixed timeout for GET_LOCK() on HP-UX with DCE threads.
Fixed memory allocation bug in the glibc library used to build Linux binaries, which caused mysqld to die in 'free()'.
Fixed SIGINT and SIGQUIT problems in mysql.
Fixed bug in character table converts when used with big ( > 64K) strings.
InnoDB now retains foreign key constraints through ALTER TABLE and CREATE/DROP INDEX.
InnoDB now allows foreign key constraints to be added through the ALTER TABLE syntax.
InnoDB tables can now be set to automatically grow in size (autoextend).
Our Linux RPMS and binaries are now compiled with gcc 3.0.4, which should make them a bit faster.
Fixed some buffer overflow problems when reading startup parameters.
Because of problems on shutdown we have now disabled named pipes on Windows by default. One can enable named pipes by starting mysqld with --enable-named-pipe.
Fixed bug when using WHERE key_column = 'J' or key_column="j".
Fixed core-dump bug when using --log-bin with LOAD DATA INFILE without an active database.
Fixed bug in RENAME TABLE when used with lower_case_table_names=1 (default on Windows).
Fixed unlikely core-dump bug when using DROP TABLE on a table that was in use by a thread that also used queries on only temporary tables.
Fixed problem with SHOW CREATE TABLE and PRIMARY KEY when using 32 indexes.
Fixed that one can use SET PASSWORD for the anonymous user.
Fixed core dump bug when reading client groups from option files using mysql_options().
Memory leak (16 bytes per every corrupted table) closed.
Fixed binary builds to use --enable-local-infile.
Update source to work with new version of bison.
Updated shell scripts to now agree with new POSIX standard.
Fixed bug where DATE_FORMAT() returned empty string when used with GROUP BY.
Don't give warning for a statement that is only a comment; this is needed for mysqldump --disable-keys to work.
Fixed unlikely caching bug when doing a join without keys. In this case the last used field for a table always returned NULL.
Added options to make LOAD DATA LOCAL INFILE more secure.
MySQL binary release 3.23.48 for Linux contained a new glibc library, which has serious problems under high load and Red Hat 7.2. The 3.23.49 binary release doesn't have this problem.
Fixed shutdown problem on NT.
Added --xml option to mysqldump for producing XML output.
Changed to use autoconf 2.52 (from autoconf 2.13)
Fixed bug in complicated join with const tables.
Added internal safety checks for InnoDB.
Some InnoDB variables were always shown in SHOW VARIABLES as OFF on high-byte-first systems (like SPARC).
Fixed problem with one thread using an InnoDB table and another thread doing an ALTER TABLE on the same table. Before that, mysqld could crash with an assertion failure in row0row.c, line 474.
Tuned the InnoDB SQL optimizer to favor index searches more often over table scans.
Fixed a performance problem with InnoDB tables when several large SELECT queries are run concurrently on a multiprocessor Linux computer. Large CPU-bound SELECT queries will now also generally run faster on all platforms.
If MySQL binlogging is used, InnoDB now prints after crash recovery the latest MySQL binlog name and the offset InnoDB was able to recover to. This is useful, for example, when resynchronizing a master and a slave database in replication.
Added better error messages to help in installation problems of InnoDB tables.
It is now possible to recover MySQL temporary tables that have become orphaned inside the InnoDB tablespace.
InnoDB now prevents a FOREIGN KEY declaration where the signedness is not the same in the referencing and referenced integer columns.
Calling SHOW CREATE TABLE or SHOW TABLE STATUS could cause memory corruption and make mysqld crash. Especially at risk was mysqldump, because it frequently calls SHOW CREATE TABLE.
If inserts to several tables containing an AUTO_INCREMENT column were wrapped inside one LOCK TABLES, InnoDB asserted in lock0lock.c.
In 3.23.47 we allowed several NULL values in a UNIQUE secondary index for an InnoDB table. But CHECK TABLE was not relaxed: it reports the table as corrupt. CHECK TABLE no longer complains in this situation.
SHOW GRANTS now shows REFERENCES instead of REFERENCE.
Fixed bug when using the following construct: SELECT ... WHERE key=@var_name OR key=@var_name2
Restrict InnoDB keys to 500 bytes.
InnoDB now supports NULL in keys.
Fixed shutdown problem on HP-UX. (Introduced in 3.23.46)
Fixed core dump bug in replication when using SELECT RELEASE_LOCK().
Added new command: DO expression,[expression]
Added slave-skip-errors option.
Added statistics variables for all MySQL commands. (SHOW STATUS is now much longer.)
Fixed default values for InnoDB tables.
Fixed that GROUP BY expr DESC works.
Fixed bug when using t1 LEFT JOIN t2 ON t2.key=constant.
mysql_config now also works with binary (relocated) distributions.
Fixed problem with aliased temporary table replication.
InnoDB and BDB tables will now use index when doing an ORDER BY on the whole table.
Fixed bug where one got an empty set instead of a DEADLOCK error when using BDB tables.
One can now kill ANALYZE, REPAIR, and OPTIMIZE TABLE when the thread is waiting to get a lock on the table.
Fixed race condition in ANALYZE TABLE.
Fixed bug when joining with caching (unlikely to happen).
Fixed race condition when using the binary log and INSERT DELAYED which could cause the binary log to have rows that were not yet written to MyISAM tables.
Changed caching of binary log to make replication slightly faster.
Fixed bug in replication on Mac OS X.
(UPDATE|DELETE) ...WHERE MATCH bugfix.
shutdown should now work on Darwin (Mac OS X).
Fixed core dump when repairing corrupted packed MyISAM files.
--core-file now works on Solaris.
Fix a bug which could cause InnoDB to complain if it cannot find free blocks from the buffer cache during recovery.
Fixed bug in InnoDB insert buffer B-tree handling that could cause crashes.
Fixed bug in InnoDB lock timeout handling.
Fixed core dump bug in ALTER TABLE on a TEMPORARY InnoDB table.
Fixed bug in OPTIMIZE TABLE that reset index cardinality if it was up to date.
Fixed problem with t1 LEFT_JOIN t2 ... WHERE t2.date_column IS NULL when date_column was declared as NOT NULL.
Fixed bug with BDB tables and keys on BLOB columns.
Fixed bug in MERGE tables on OS with 32-bit file pointers.
Fixed bug in TIME_TO_SEC() when using negative values.
Fixed Rows_examined count in slow query log.
Fixed bug when using a reference to an AVG() column in HAVING.
Fixed that date functions that require correct dates, like DAYOFYEAR(column), will return NULL for 0000-00-00 dates.
Fixed bug in const-propagation when comparing columns of different types. (SELECT * FROM date_col="2001-01-01" and date_col=time_col)
Fixed bug that caused error message Can't write, because of unique constraint with some GROUP BY queries.
Fixed problem with sjis character strings used within quoted table names.
Fixed core dump when using CREATE ... FULLTEXT keys with other storage engines than MyISAM.
Don't use signal() on Windows because this appears to not be 100% reliable.
Fixed bug when doing WHERE col_name=NULL on an indexed column that had NULL values.
Fixed bug when doing LEFT JOIN ... ON (col_name = constant) WHERE col_name = constant.
When using replications, aborted queries that contained % could cause a core dump.
TCP_NODELAY was not used on some systems. (Speed problem.)
Applied portability fixes for OS/2. (Patch by Yuri Dario.)
The following changes are for InnoDB tables:
Add missing InnoDB variables to SHOW VARIABLES.
Foreign keys checking is now done for InnoDB tables.
DROP DATABASE now works also for InnoDB tables.
InnoDB now supports datafiles and raw disk partitions bigger than 4 GB on those operating systems that have big files.
InnoDB calculates better table cardinality estimates for the MySQL optimizer.
Accent characters in the default character set latin1 are ordered according to the MySQL ordering.
Note: If you are using latin1 and have inserted characters whose code is greater than 127 into an indexed CHAR column, you should run CHECK TABLE on your table when you upgrade to 3.23.44, and drop and reimport the table if CHECK TABLE reports an error!
A new my.cnf parameter, innodb_thread_concurrency, helps in performance tuning in heavily concurrent environments.
A new my.cnf parameter, innodb_fast_shutdown, speeds up server shutdown.
A new my.cnf parameter, innodb_force_recovery, helps to save your data in case the disk image of the database becomes corrupt.
innodb_monitor has been improved and a new innodb_table_monitor added.
Increased maximum key length from 500 to 7000 bytes.
Fixed a bug in replication of AUTO_INCREMENT columns with multiple-line inserts.
Fixed a bug when the case of letters changes in an update of an indexed secondary column.
Fixed a hang when there are > 24 datafiles.
Fixed a crash when MAX(col) is selected from an empty table, and col is not the first column in a multi-column index.
Fixed a bug in purge which could cause crashes.
Fixed a bug in INSERT DELAYED and FLUSH TABLES introduced in 3.23.42.
Fixed unlikely bug, which returned non-matching rows, in SELECT with many tables and multi-column indexes and 'range' type.
Fixed an unlikely core dump bug when doing EXPLAIN SELECT when using many tables and ORDER BY.
Fixed bug in LOAD DATA FROM MASTER when using table with CHECKSUM=1.
Added unique error message when one gets a DEADLOCK during a transaction with BDB tables.
Fixed problem with BDB tables and UNIQUE columns defined as NULL.
Fixed problem with myisampack when using pre-space filled CHAR columns.
Applied patch from Yuri Dario for OS/2.
Fixed bug in --safe-user-create.
Fixed problem when using LOCK TABLES and BDB tables.
Fixed problem with REPAIR TABLE on MyISAM tables with row lengths in the range from 65517 to 65520 bytes.
Fixed rare hang when doing mysqladmin shutdown when there was a lot of activity in other threads.
Fixed problem with INSERT DELAYED where delayed thread could be hanging on upgrading locks for no apparent reason.
Fixed problem with myisampack and BLOB.
Fixed problem when one edited .MRG tables by hand. (Patch from Benjamin Pflugmann).
Enforce that all tables in a MERGE table come from the same database.
Fixed bug with LOAD DATA INFILE and transactional tables.
Fix bug when using INSERT DELAYED with wrong column definition.
Fixed core dump during REPAIR of some particularly broken tables.
Fixed bug in InnoDB and AUTO_INCREMENT columns.
Fixed bug in InnoDB and RENAME TABLE columns.
Fixed critical bug in InnoDB and BLOB columns. If you have used BLOB columns larger than 8000 bytes in an InnoDB table, it is necessary to dump the table with mysqldump, drop it and restore it from the dump.
Applied large patch for OS/2 from Yuri Dario.
Fixed problem with InnoDB when one could get the error Can't execute the given command... even when no transaction was active.
Applied some minor fixes that concern Gemini.
Use real arithmetic operations even in integer context if not all arguments are integers. (Fixes uncommon bug in some integer contexts).
Don't force everything to lowercase on Windows. (To fix problem with Windows and ALTER TABLE). Now --lower_case_table_names also works on Unix.
Fixed that automatic rollback is done when thread end doesn't lock other threads.
Added --sql-mode=value[,value[,value]] option to mysqld. See Server options.
Fixed possible problem with shutdown on Solaris where the .pid file wasn't deleted.
InnoDB now supports < 4 GB rows. The former limit was 8000 bytes.
The doublewrite file flush method is used in InnoDB. It reduces the need for Unix fsync() calls to a fraction and improves performance on most Unix flavors.
You can now use the InnoDB Monitor to print a lot of InnoDB state information, including locks, to the standard output. This is useful in performance tuning.
Several bugs which could cause hangs in InnoDB have been fixed.
Split record_buffer to record_buffer and record_rnd_buffer. To make things compatible to previous MySQL versions, if record_rnd_buffer is not set, then it takes the value of record_buffer.
Fixed optimizing bug in ORDER BY where some ORDER BY parts where wrongly removed.
Fixed overflow bug with ALTER TABLE and MERGE tables.
Added prototypes for my_thread_init() and my_thread_end() to mysql_com.h
Added --safe-user-create option to mysqld.
Fixed bug in SELECT DISTINCT ... HAVING that caused error message Can't find record in #...
Fixed problem with --low-priority-updates and INSERT statements.
Fixed bug in slave thread when under some rare circumstances it could get 22 bytes ahead on the offset in the master.
Added slave_net_timeout for replication.
Fixed problem with UPDATE and BDB tables.
Fixed hard bug in BDB tables when using key parts.
Fixed problem when using GRANT FILE ON database.* ...; previously we added the DROP privilege for the database.
Fixed DELETE FROM tbl_name ... LIMIT 0 and UPDATE FROM tbl_name ... LIMIT 0, which acted as though the LIMIT clause was not present (they deleted or updated all selected rows).
CHECK TABLE now checks if an AUTO_INCREMENT column contains the value 0.
Sending a SIGHUP to mysqld will now only flush the logs, not reset the replication.
Fixed parser to allow floats of type 1.0e1 (no sign after e).
Option --force to myisamchk now also updates states.
Added option --warnings to mysqld. Now mysqld prints the error Aborted connection only if this option is used.
Fixed problem with SHOW CREATE TABLE when you didn't have a PRIMARY KEY.
Properly fixed the rename of innodb_unix_file_flush_method variable to innodb_flush_method.
Fixed bug when converting BIGINT UNSIGNED to DOUBLE. This caused a problem when doing comparisons with BIGINT values outside of the signed range.
Fixed bug in BDB tables when querying empty tables.
Fixed a bug when using COUNT(DISTINCT) with LEFT JOIN and there weren't any matching rows.
Removed all documentation referring to the GEMINI table type. GEMINI is not released under an Open Source license.
The AUTO_INCREMENT sequence wasn't reset when dropping and adding an AUTO_INCREMENT column.
CREATE ... SELECT now creates non-unique indexes delayed.
Fixed problem where LOCK TABLES tbl_name READ followed by FLUSH TABLES put an exclusive lock on the table.
REAL @variable values were represented with only 2 digits when converted to strings.
Fixed problem that client ``hung'' when LOAD TABLE FROM MASTER failed.
myisamchk --fast --force will no longer repair tables that only had the open count wrong.
Added functions to handle symbolic links to make life easier in 4.0.
We are now using the -lcma thread library on HP-UX 10.20 so that MySQL will be more stable on HP-UX.
Fixed problem with IF() and number of decimals in the result.
Fixed date-part extraction functions to work with dates where day and/or month is 0.
Extended argument length in option files from 256 to 512 chars.
Fixed problem with shutdown when INSERT DELAYED was waiting for a LOCK TABLE.
Fixed core dump bug in InnoDB when tablespace was full.
Fixed problem with MERGE tables and big tables (> 4G) when using ORDER BY.
Fixed a bug when SELECT from MERGE table sometimes results in incorrectly ordered rows.
Fixed a bug in REPLACE() when using the ujis character set.
Applied Sleepycat BDB patches 3.2.9.1 and 3.2.9.2.
Added --skip-stack-trace option to mysqld.
CREATE TEMPORARY now works with InnoDB tables.
InnoDB now promotes sub keys to whole keys.
Added option CONCURRENT to LOAD DATA.
Better error message when slave max_allowed_packet is too low to read a very long log event from the master.
Fixed bug when too many rows where removed when using SELECT DISTINCT ... HAVING.
SHOW CREATE TABLE now returns TEMPORARY for temporary tables.
Added Rows_examined to slow query log.
Fixed problems with function returning empty string when used together with a group function and a WHERE that didn't match any rows.
New program mysqlcheck.
Added database name to output for administrative commands like CHECK, REPAIR, OPTIMIZE.
Lots of portability fixes for InnoDB.
Changed optimizer so that queries like SELECT * FROM tbl_name,tbl_name2 ... ORDER BY key_part1 LIMIT row_count will use index on key_part1 instead of filesort.
Fixed bug when doing LOCK TABLE to_table WRITE,...; INSERT INTO to_table... SELECT ... when to_table was empty.
Fixed bug with LOCK TABLE and BDB tables.
Fixed a bug when using MATCH() in HAVING clause.
Fixed a bug when using HEAP tables with LIKE.
Added --mysql-version option to safe_mysqld
Changed INNOBASE to InnoDB (because the INNOBASE name was already used). All configure options and mysqld start options now use innodb instead of innobase. This means that before upgrading to this version, you have to change any configuration files where you have used innobase options!
Fixed bug when using indexes on CHAR(255) NULL columns.
Slave thread will now be started even if master-host is not set, as long as server-id is set and valid master.info is present.
Partial updates (terminated with kill) are now logged with a special error code to the binary log. Slave will refuse to execute them if the error code indicates the update was terminated abnormally, and will have to be recovered with SET SQL_SLAVE_SKIP_COUNTER=1; SLAVE START after a manual sanity check/correction of data integrity.
Fixed bug that erroneously logged a drop of internal temporary table on thread termination to the binary log --- this bug affected replication.
Fixed a bug in REGEXP on 64-bit machines.
UPDATE and DELETE with WHERE unique_key_part IS NULL didn't update/delete all rows.
Disabled INSERT DELAYED for tables that support transactions.
Fixed bug when using date functions on TEXT/BLOB column with wrong date format.
UDFs now also work on Windows. (Patch by Ralph Mason.)
Fixed bug in ALTER TABLE and LOAD DATA INFILE that disabled key-sorting. These commands should now be faster in most cases.
Fixed performance bug where reopened tables (tables that had been waiting for FLUSH or REPAIR) would not use indexes for the next query.
Fixed problem with ALTER TABLE to InnoDB tables on FreeBSD.
Added mysqld variables myisam_max_sort_file_size and myisam_max_extra_sort_file_size.
Initialize signals early to avoid problem with signals in InnoDB.
Applied patch for the tis620 character set to make comparisons case-independent and to fix a bug in LIKE for this character set. Note: All tables that uses the tis620 character set must be fixed with myisamchk -r or REPAIR TABLE !
Added --skip-safemalloc option to mysqld.
Fixed a bug that allowed use of database names containing a . character. This fixes a serious security issue when mysqld is run as root.
Fixed bug when thread creation failed (could happen when doing a lot of connections in a short time).
Fixed some problems with FLUSH TABLES and TEMPORARY tables. (Problem with freeing the key cache and error Can't reopen table....)
Fixed a problem in InnoDB with other character sets than latin1 and another problem when using many columns.
Fixed bug that caused a core dump when using a very complex query involving DISTINCT and summary functions.
Added SET TRANSACTION ISOLATION LEVEL ...
Added SELECT ... FOR UPDATE.
Fixed bug where the number of affected rows was not returned when MySQL was compiled without transaction support.
Fixed a bug in UPDATE where keys weren't always used to find the rows to be updated.
Fixed a bug in CONCAT_WS() where it returned incorrect results.
Changed CREATE ... SELECT and INSERT ... SELECT to not allow concurrent inserts as this could make the binary log hard to repeat. (Concurrent inserts are enabled if you are not using the binary or update log.)
Changed some macros to be able to use fast mutex with glibc 2.2.
Fixed newly introduced bug in ORDER BY.
Fixed wrong define CLIENT_TRANSACTIONS.
Fixed bug in SHOW VARIABLES when using INNOBASE tables.
Setting and using user variables in SELECT DISTINCT didn't work.
Tuned SHOW ANALYZE for small tables.
Fixed handling of arguments in the benchmark script run-all-tests.
Added extra files to the distribution to allow INNOBASE support to be compiled.
Added the INNOBASE storage engine and the BDB storage engine to the MySQL source distribution.
Updated the documentation about GEMINI tables.
Fixed a bug in INSERT DELAYED that caused threads to hang when inserting NULL into an AUTO_INCREMENT column.
Fixed a bug in CHECK TABLE / REPAIR TABLE that could cause a thread to hang.
REPLACE will not replace a row that conflicts with an AUTO_INCREMENT generated key.
mysqld now only sets CLIENT_TRANSACTIONS in mysql->server_capabilities if the server supports a transaction-safe storage engine.
Fixed LOAD DATA INFILE to allow numeric values to be read into ENUM and SET columns.
Improved error diagnostic for slave thread exit.
Fixed bug in ALTER TABLE ... ORDER BY.
Added max_user_connections variable to mysqld.
Limit query length for replication by max_allowed_packet, not the arbitrary limit of 4 MB.
Allow space around = in argument to --set-variable.
Fixed problem in automatic repair that could leave some threads in state Waiting for table.
SHOW CREATE TABLE now displays the UNION=() for MERGE tables.
ALTER TABLE now remembers the old UNION=() definition.
Fixed bug when replicating timestamps.
Fixed bug in bidirectional replication.
Fixed bug in the BDB storage engine that occurred when using an index on multi-part key where a key part may be NULL.
Fixed MAX() optimization on sub-key for BDB tables.
Fixed problem where garbage results were returned when using BDB tables and BLOB or TEXT fields when joining many tables.
Fixed a problem with BDB tables and TEXT columns.
Fixed bug when using a BLOB key where a const row wasn't found.
Fixed that mysqlbinlog writes the timestamp value for each query. This ensures that one gets same values for date functions like NOW() when using mysqlbinlog to pipe the queries to another server.
Allow --skip-gemini, --skip-bdb, and --skip-innodb options to be specified when invoking mysqld, even if these storage engines are not compiled in to mysqld.
One can now do GROUP BY ... DESC.
Fixed a deadlock in the SET code, when one ran SET @foo=bar, where bar is a column reference, an error was not properly generated.
Fixed DNS lookups not to use the same mutex as the hostname cache. This will enable known hosts to be quickly resolved even if a DNS lookup takes a long time.
Added --character-sets-dir option to myisampack.
Removed warnings when running REPAIR TABLE ... EXTENDED.
Fixed a bug that caused a core dump when using GROUP BY on an alias, where the alias was the same as an existing column name.
Added SEQUENCE() as an example UDF function.
Changed mysql_install_db to use BINARY for CHAR columns in the privilege tables.
Changed TRUNCATE tbl_name to TRUNCATE TABLE tbl_name to use the same syntax as Oracle. Until 4.0 we will also allow TRUNCATE tbl_name to not crash old code.
Fixed ``no found rows'' bug in MyISAM tables when a BLOB was first part of a multi-part key.
Fixed bug where CASE didn't work with GROUP BY.
Added --sort-recover option to myisamchk.
myisamchk -S and OPTIMIZE TABLE now work on Windows.
Fixed bug when using DISTINCT on results from functions that referred to a group function, like:
SELECT a, DISTINCT SEC_TO_TIME(SUM(a)) FROM tbl_name GROUP BY a, b;
Fixed buffer overrun in libmysqlclient library. Fixed bug in handling STOP event after ROTATE event in replication.
Fixed another buffer overrun in DROP DATABASE.
Added Table_locks_immediate and Table_locks_waited status variables.
Fixed bug in replication that broke slave server start with existing master.info. This fixes a bug introduced in 3.23.32.
Added SET SQL_SLAVE_SKIP_COUNTER=n command to recover from replication glitches without a full database copy.
Added max_binlog_size variable; the binary log will be rotated automatically when the size crosses the limit.
Added Last_Error, Last_Errno, and Slave_skip_counter variables to SHOW SLAVE STATUS.
Fixed bug in MASTER_POS_WAIT() function.
Execute core dump handler on SIGILL, and SIGBUS in addition to SIGSEGV.
On x86 Linux, print the current query and thread (connection) id, if available, in the core dump handler.
Fixed several timing bugs in the test suite.
Extended mysqltest to take care of the timing issues in the test suite.
ALTER TABLE can now be used to change the definition for a MERGE table.
Fixed creation of MERGE tables on Windows.
Portability fixes for OpenBSD and OS/2.
Added --temp-pool option to mysqld. Using this option will cause most temporary files created to use a small set of names, rather than a unique name for each new file. This is to work around a problem in the Linux kernel dealing with creating a bunch of new files with different names. With the old behavior, Linux seems to "leak" memory, as it's being allocated to the directory entry cache instead of the disk cache.
Changed code to get around compiler bug in Compaq C++ on OSF/1, that broke BACKUP, RESTORE, CHECK, REPAIR, and ANALYZE TABLE.
Added option FULL to SHOW COLUMNS. Now we show the privilege list for the columns only if this option is given.
Fixed bug in SHOW LOGS when there weren't any BDB logs.
Fixed a timing problem in replication that could delay sending an update to the client until a new update was done.
Don't convert field names when using mysql_list_fields(). This is to keep this code compatible with SHOW FIELDS.
MERGE tables didn't work on Windows.
Fixed problem with SET PASSWORD=... on Windows.
Added missing my_config.h to RPM distribution.
TRIM("foo" from "foo") didn't return an empty string.
Added --with-version-suffix option to configure.
Fixed core dump when client aborted connection without mysql_close().
Fixed a bug in RESTORE TABLE when trying to restore from a non-existent directory.
Fixed a bug which caused a core dump on the slave when replicating SET PASSWORD.
Added MASTER_POS_WAIT().
The test suite now tests all reachable BDB interface code. During testing we found and fixed many errors in the interface code.
Using HAVING on an empty table could produce one result row when it shouldn't.
Fixed the MySQL RPM so it no longer depends on Perl5.
Fixed some problems with HEAP tables on Windows.
SHOW TABLE STATUS didn't show correct average row length for tables larger than 4G.
CHECK TABLE ... EXTENDED didn't check row links for fixed size tables.
Added option MEDIUM to CHECK TABLE.
Fixed problem when using DECIMAL() keys on negative numbers.
HOUR() (and some other TIME functions) on a CHAR column always returned NULL.
Fixed security bug in something (please upgrade if you are using an earlier MySQL 3.23 version).
Fixed buffer overflow bug when writing a certain error message.
Added usage of setrlimit() on Linux to get -O --open_files_limit=# to work on Linux.
Added bdb_version variable to mysqld.
Fixed bug when using expression of type:
SELECT ... FROM t1 LEFT JOIN t2 ON (t1.a=t2.a) WHERE t1.a=t2.a
In this case the test in the WHERE clause was wrongly optimized away.
Fixed bug in MyISAM when deleting keys with possible NULL values, but the first key-column was not a prefix-compressed text column.
Fixed mysql.server to read the [mysql.server] option file group rather than the [mysql_server] group.
Fixed safe_mysqld and mysql.server to also read the server option section.
Added Threads_created status variable to mysqld.
Added SHOW OPEN TABLES command.
Fixed that myisamdump works against old mysqld servers.
Fixed myisamchk -k# so that it works again.
Fixed a problem with replication when the binary log file went over 2G on 32-bit systems.
LOCK TABLES will now automatically start a new transaction.
Changed BDB tables to not use internal subtransactions and reuse open files to get more speed.
Added --mysqld=# option to safe_mysqld.
Allow hex constants in the --fields-*-by and --lines-terminated-by options to mysqldump and mysqlimport. By Paul DuBois.
Added --safe-show-database option to mysqld.
Added have_bdb, have_gemini, have_innobase, have_raid and have_openssl to SHOW VARIABLES to make it easy to test for supported extensions.
Added --open-files-limit option to mysqld.
Changed --open-files option to --open-files-limit in safe_mysqld.
Fixed a bug where some rows were not found with HEAP tables that had many keys.
Fixed that --bdb-no-sync works.
Changed --bdb-recover to --bdb-no-recover as recover should be on by default.
Changed the default number of BDB locks to 10000.
Fixed a bug from 3.23.29 when allocating the shared structure needed for BDB tables.
Changed mysqld_multi.sh to use configure variables. Patch by Christopher McCrory.
Added fixing of include files for Solaris 2.8.
Fixed bug with --skip-networking on Debian Linux.
Fixed problem that some temporary files where reported as having the name UNOPENED in error messages.
Fixed bug when running two simultaneous SHOW LOGS queries.
Configure updates for Tru64, large file support, and better TCP wrapper support. By Albert Chin-A-Young.
Fixed bug in <=> operator.
Fixed bug in REPLACE with BDB tables.
LPAD() and RPAD() will shorten the result string if it's longer than the length argument.
Added SHOW LOGS command.
Remove unused BDB logs on shutdown.
When creating a table, put PRIMARY keys first, followed by UNIQUE keys.
Fixed a bug in UPDATE involving multi-part keys where one specified all key parts both in the update and the WHERE part. In this case MySQL could try to update a record that didn't match the whole WHERE part.
Changed drop table to first drop the tables and then the .frm file.
Fixed a bug in the hostname cache which caused mysqld to report the hostname as '' in some error messages.
Fixed a bug with HEAP type tables; the variable max_heap_table_size wasn't used. Now either MAX_ROWS or max_heap_table_size can be used to limit the size of a HEAP type table.
Changed the default server-id to 1 for masters and 2 for slaves to make it easier to use the binary log.
Renamed bdb_lock_max variable to bdb_max_lock.
Added support for AUTO_INCREMENT on sub-fields for BDB tables.
Added ANALYZE of BDB tables.
In BDB tables, we now store the number of rows; this helps to optimize queries when we need an approximation of the number of rows.
If we get an error in a multi-row statement, we now only roll back the last statement, not the entire transaction.
If you do a ROLLBACK when you have updated a non-transactional table you will get an error as a warning.
Added --bdb-shared-data option to mysqld.
Added Slave_open_temp_tables status variable to mysqld
Added binlog_cache_size and max_binlog_cache_size variables to mysqld.
DROP TABLE, RENAME TABLE, CREATE INDEX and DROP INDEX are now transaction endpoints.
If you do a DROP DATABASE on a symbolically linked database, both the link and the original database are deleted.
Fixed DROP DATABASE to work on OS/2.
Fixed bug when doing a SELECT DISTINCT ... table1 LEFT JOIN table2 ... when table2 was empty.
Added --abort-slave-event-count and --disconnect-slave-event-count options to mysqld for debugging and testing of replication.
Fixed replication of temporary tables. Handles everything except slave server restart.
SHOW KEYS now shows whether key is FULLTEXT.
New script mysqld_multi. See mysqld_multi.
Added new script, mysql-multi.server.sh. Thanks to Tim Bunce <Tim.Bunce@ig.co.uk> for modifying mysql.server to easily handle hosts running many mysqld processes.
safe_mysqld, mysql.server, and mysql_install_db have been modified to use mysql_print_defaults instead of various hacks to read the my.cnf files. In addition, the handling of various paths has been made more consistent with how mysqld handles them by default.
Automatically remove Berkeley DB transaction logs that no longer are in use.
Fixed bug with several FULLTEXT indexes in one table.
Added a warning if number of rows changes on REPAIR/OPTIMIZE.
Applied patches for OS/2 by Yuri Dario.
FLUSH TABLES tbl_name didn't always flush the index tree to disk properly.
--bootstrap is now run in a separate thread. This fixes a problem that caused mysql_install_db to core dump on some Linux machines.
Changed mi_create() to use less stack space.
Fixed bug with optimizer trying to over-optimize MATCH() when used with UNIQUE key.
Changed crash-me and the MySQL benchmarks to also work with FrontBase.
Allow RESTRICT and CASCADE after DROP TABLE to make porting easier.
Reset status variable which could cause problem if one used --slow-log.
Added connect_timeout variable to mysql and mysqladmin.
Added connect-timeout as an alias for timeout for option files read by mysql_options().
Added new options --pager[=...], --no-pager, --tee=... and --no-tee to the mysql client. The new corresponding interactive commands are pager, nopager, tee and notee. See mysql, mysql --help and the interactive help for more information.
Fixed crash when automatic repair of MyISAM table failed.
Fixed a major performance bug in the table locking code when one constantly had a lot of SELECT, UPDATE and INSERT statements running. The symptom was that the UPDATE and INSERT queries were locked for a long time while new SELECT statements were executed before the updates.
When reading options_files with mysql_options() the return-found-rows option was ignored.
One can now specify interactive-timeout in the option file that is read by mysql_options(). This makes it possible to force programs that run for a long time (like mysqlhotcopy) to use the interactive_timeout time instead of the wait_timeout time.
Added to the slow query log the time and the username for each logged query. If you are using --log-long-format then also queries that do not use an index are logged, even if the query takes less than long_query_time seconds.
Fixed a problem in LEFT JOIN which caused all columns in a reference table to be NULL.
Fixed a problem when using NATURAL JOIN without keys.
Fixed a bug when using a multi-part keys where the first part was of type TEXT or BLOB.
DROP of temporary tables wasn't stored in the update/binary log.
Fixed a bug where SELECT DISTINCT * ... LIMIT row_count only returned one row.
Fixed a bug in the assembler code in strstr() for SPARC and cleaned up the global.h header file to avoid a problem with bad aliasing with the compiler submitted with Red Hat 7.0. (Reported by Trond Eivind Glomsrød)
The --skip-networking option now works properly on NT.
Fixed a long outstanding bug in the ISAM tables when a row with a length of more than 65K was shortened by a single byte.
Fixed a bug in MyISAM when running multiple updating processes on the same table.
Allow one to use FLUSH TABLE tbl_name.
Added --replicate-ignore-table, --replicate-do-table, --replicate-wild-ignore-table, and --replicate-wild-do-table options to mysqld.
Changed all log files to use our own IO_CACHE mechanism instead of FILE to avoid OS problems when there are many files open.
Added --open-files and --timezone options to safe_mysqld.
Fixed a fatal bug in CREATE TEMPORARY TABLE ... SELECT ....
Fixed a problem with CREATE TABLE ... SELECT NULL.
Added variables large_file_support,net_read_timeout, net_write_timeout and query_buffer_size to SHOW VARIABLES.
Added status variables created_tmp_files and sort_merge_passes to SHOW STATUS.
Fixed a bug where we didn't allow an index name after the FOREIGN KEY definition.
Added TRUNCATE table_name as a synonym for DELETE FROM table_name.
Fixed a bug in a BDB key compare function when comparing part keys.
Added bdb_lock_max variable to mysqld.
Added more tests to the benchmark suite.
Fixed an overflow bug in the client code when using overly long database names.
mysql_connect() now aborts on Linux if the server doesn't answer in timeout seconds.
SLAVE START did not work if you started with --skip-slave-start and had not explicitly run CHANGE MASTER TO.
Fixed the output of SHOW MASTER STATUS to be consistent with SHOW SLAVE STATUS. (It now has no directory in the log name.)
Added PURGE MASTER LOGS TO.
Added SHOW MASTER LOGS.
Added --safemalloc-mem-limit option to mysqld to simulate memory shortage when compiled with the --with-debug=full option.
Fixed several core dumps in out-of-memory conditions.
SHOW SLAVE STATUS was using an uninitialized mutex if the slave had not been started yet.
Fixed bug in ELT() and MAKE_SET() when the query used a temporary table.
CHANGE MASTER TO without specifying MASTER_LOG_POS would set it to 0 instead of 4 and hit the magic number in the master binlog.
ALTER TABLE ... ORDER BY ... syntax added. This will create the new table with the rows in a specific order.
Fixed a bug where the automatic repair of MyISAM tables sometimes failed when the datafile was corrupt.
Fixed a bug in SHOW CREATE when using AUTO_INCREMENT columns.
Changed BDB tables to use new compare function in Berkeley DB 3.2.3.
You can now use Unix socket files with MIT-pthreads.
Added the latin5 (turkish) character set.
Small portability fixes.
Renamed FLUSH MASTER and FLUSH SLAVE to RESET MASTER and RESET SLAVE.
Fixed <> to work properly with NULL.
Fixed a problem with SUBSTRING_INDEX() and REPLACE(). (Patch by Alexander Igonitchev)
Fix CREATE TEMPORARY TABLE IF NOT EXISTS not to produce an error if the table exists.
If you don't create a PRIMARY KEY in a BDB table, a hidden PRIMARY KEY will be created.
Added read-only-key optimization to BDB tables.
LEFT JOIN in some cases preferred a full table scan when there was no WHERE clause.
When using --log-slow-queries, don't count the time waiting for a lock.
Fixed bug in lock code on Windows which could cause the key cache to report that the key file was crashed even if it was okay.
Automatic repair of MyISAM tables if you start mysqld with --myisam-recover.
Removed the TYPE= keyword from CHECK and REPAIR. Allow CHECK options to be combined. (You can still use TYPE=, but this usage is deprecated.)
Fixed mutex bug in the binary replication log --- long update queries could be read only in part by the slave if it did it at the wrong time, which was not fatal, but resulted in a performance-degrading reconnect and a scary message in the error log.
Changed the format of the binary log --- added magic number, server version, binlog version. Added the server ID and query error code for each query event.
Replication thread from the slave now will kill all the stale threads from the same server.
Long replication usernames were not being handled properly.
Added --replicate-rewrite-db option to mysqld.
Added --skip-slave-start option to mysqld.
Updates that generated an error code (such as INSERT INTO foo(some_key) values (1),(1)) erroneously terminated the slave thread.
Added optimization of queries where DISTINCT is used only on columns from some of the tables.
Allow floating-point numbers where there is no sign after the exponent (like 1e1).
SHOW GRANTS didn't always show all column grants.
Added --default-extra-file=# option to all MySQL clients.
Columns referenced in INSERT statements now are initialized properly.
UPDATE didn't always work when used with a range on a timestamp that was part of the key that was used to find rows.
Fixed a bug in FULLTEXT index when inserting a NULL column.
Changed to use mkstemp() instead of tempnam(). Based on a patch from John Jones.
Fixed that databasename works as second argument to mysqlhotcopy.
The values for the UMASK and UMASK_DIR environment variables now can be specified in octal by beginning the value with a zero.
Added RIGHT JOIN. This makes RIGHT a reserved word.
Added @@IDENTITY as a synonym for LAST_INSERT_ID(). (This is for MSSQL compatibility.)
Fixed a bug in myisamchk and REPAIR when using FULLTEXT index.
LOAD DATA INFILE now works with FIFOs. (Patch by Toni L. Harbaugh-Blackford.)
FLUSH LOGS broke replication if you specified a log name with an explicit extension as the value of the log-bin option.
Fixed a bug in MyISAM with packed multi-part keys.
Fixed crash when using CHECK TABLE on Windows.
Fixed a bug where FULLTEXT index always used the koi8_ukr character set.
Fixed privilege checking for CHECK TABLE.
The MyISAM repair/reindex code didn't use the --tmpdir option for its temporary files.
Added BACKUP TABLE and RESTORE TABLE.
Fixed core dump on CHANGE MASTER TO when the slave did not have the master to start with.
Fixed incorrect Time in the processlist for Connect of the slave thread.
The slave now logs when it connects to the master.
Fixed a core dump bug when doing FLUSH MASTER if you didn't specify a filename argument to --log-bin.
Added missing ha_berkeley.x files to the MySQL Windows distribution.
Fixed some mutex bugs in the log code that could cause thread blocks if new log files couldn't be created.
Added lock time and number of selected processed rows to slow query log.
Added --memlock option to mysqld to lock mysqld in memory on systems with the mlockall() call (as in Solaris).
HEAP tables didn't use keys properly. (Bug from 3.23.23.)
Added better support for MERGE tables (keys, mapping, creation, documentation...). See MERGE.
Fixed bug in mysqldump from 3.23 which caused some CHAR columns not to be quoted.
Merged analyze, check, optimize and repair code.
OPTIMIZE TABLE is now mapped to REPAIR with statistics and sorting of the index tree. This means that for the moment it only works on MyISAM tables.
Added a pre-alloced block to root_malloc to get fewer mallocs.
Added a lot of new statistics variables.
Fixed ORDER BY bug with BDB tables.
Removed warning that mysqld couldn't remove the .pid file under Windows.
Changed --log-isam to log MyISAM tables instead of isam tables.
Fixed CHECK TABLE to work on Windows.
Added file mutexes to make pwrite() safe on Windows.
Added created_tmp_disk_tables variable to mysqld.
To make it possible to reliably dump and restore tables with TIMESTAMP(X) columns, MySQL now reports columns with X other than 14 or 8 to be strings.
Changed sort order for latin1 as it was before MySQL Version 3.23.23. Any table that was created or modified with 3.23.22 must be repaired if it has CHAR columns that may contain characters with ASCII values greater than 128!
Fixed small memory leak introduced from 3.23.22 when creating a temporary table.
Fixed problem with BDB tables and reading on a unique (not primary) key.
Restored the win1251 character set (it's now only marked deprecated).
Changed sort order for 'German'; all tables created with 'German' sortorder must be repaired with REPAIR TABLE or myisamchk before use!
Added --core-file option to mysqld to get a core file on Linux if mysqld dies on the SIGSEGV signal.
MySQL client mysql now starts with option --no-named-commands (-g) by default. This option can be disabled with --enable-named-commands (-G). This may cause incompatibility problems in some cases, for example, in SQL scripts that use named commands without a semicolon, etc.! Long format commands still work from the first line.
Fixed a problem when using many pending DROP TABLE statements at the same time.
Optimizer didn't use keys properly when using LEFT JOIN on an empty table.
Added shorter help text when invoking mysqld with incorrect options.
Fixed non-fatal free() bug in mysqlimport.
Fixed bug in MyISAM index handling of DECIMAL/NUMERIC keys.
Fixed a bug in concurrent insert in MyISAM tables. In some contexts, usage of MIN(key_part) or MAX(key_part) returned an empty set.
Updated mysqlhotcopy to use the new FLUSH TABLES table_list syntax. Only tables which are being backed up are flushed now.
Changed behavior of --enable-thread-safe-client so that both non-threaded (-lmysqlclient) and threaded (-lmysqlclient_r) libraries are built. Users who linked against a threaded -lmysqlclient will need to link against -lmysqlclient_r now.
Added atomic RENAME TABLE command.
Don't count NULL values in COUNT(DISTINCT ...).
Changed ALTER TABLE, LOAD DATA INFILE on empty tables and INSERT ... SELECT ... on empty tables to create non-unique indexes in a separate batch with sorting. This will make the above calls much faster when you have many indexes.
ALTER TABLE now logs the first used insert_id correctly.
Fixed crash when adding a default value to a BLOB column.
Fixed a bug with DATE_ADD/DATE_SUB where it returned a datetime instead of a date.
Fixed a problem with the thread cache which made some threads show up as ***DEAD*** in SHOW PROCESSLIST.
Fixed a lock in our thr_rwlock code, which could make selects that run at the same time as concurrent inserts crash. This only affects systems that don't have the pthread_rwlock_rdlock code.
When deleting rows with a non-unique key in a HEAP table, all rows weren't always deleted.
Fixed bug in range optimizer for HEAP tables for searches on a part index.
Fixed SELECT on part keys to work with BDB tables.
Fixed INSERT INTO bdb_table ... SELECT to work with BDB tables.
CHECK TABLE now updates key statistics for the table.
ANALYZE TABLE will now only update tables that have been changed since the last ANALYZE. Note that this is a new feature and tables will not be marked to be analysed until they are updated in any way with 3.23.23 or newer. For older tables, you have to do CHECK TABLE to update the key distribution.
Fixed some minor privilege problems with CHECK, ANALYZE, REPAIR and SHOW CREATE commands.
Added CHANGE MASTER TO statement.
Added FAST, QUICK EXTENDED check types to CHECK TABLES.
Changed myisamchk so that --fast and --check-only-changed are also honored with --sort-index and --analyze.
Fixed fatal bug in LOAD TABLE FROM MASTER that did not lock the table during index re-build.
LOAD DATA INFILE broke replication if the database was excluded from replication.
More variables in SHOW SLAVE STATUS and SHOW MASTER STATUS.
SLAVE STOP now will not return until the slave thread actually exits.
Full-text search via the MATCH() function and FULLTEXT index type (for MyISAM files). This makes FULLTEXT a reserved word.
Fixed that lex_hash.h is created properly for each MySQL distribution.
Fixed that MASTER and COLLECTION are not reserved words.
The log generated by --slow-query-log didn't contain the whole queries.
Fixed that open transactions in BDB tables are rolled back if the connection is closed unexpectedly.
Added workaround for a bug in gcc 2.96 (intel) and gcc 2.9 (IA-64) in gen_lex_hash.c.
Fixed memory leak in the client library when using host= in the my.cnf file.
Optimized functions that manipulate the hours/minutes/seconds.
Fixed bug when comparing the result of DATE_ADD()/DATE_SUB() against a number.
Changed the meaning of -F, --fast for myisamchk. Added -C, --check-only-changed option to myisamchk.
Added ANALYZE tbl_name to update key statistics for tables.
Changed binary items 0x... to be regarded as integers by default.
Fix for SCO and SHOW PROCESSLIST.
Added auto-rehash on reconnect for the mysql client.
Fixed a newly introduced bug in MyISAM, where the index file couldn't get bigger than 64M.
Added SHOW MASTER STATUS and SHOW SLAVE STATUS.
Added mysql_character_set_name() function to the MySQL C API.
Made the update log ASCII 0 safe.
Added the mysql_config script.
Fixed problem when using < or > with a char column that was only partly indexed.
One would get a core dump if the log file was not readable by the MySQL user.
Changed mysqladmin to use CREATE DATABASE and DROP DATABASE statements instead of the old deprecated API calls.
Fixed chown warning in safe_mysqld.
Fixed a bug in ORDER BY that was introduced in 3.23.19.
Only optimize the DELETE FROM tbl_name to do a drop+create of the table if we are in AUTOCOMMIT mode (needed for BDB tables).
Added extra checks to avoid index corruption when the ISAM/MyISAM index files get full during an INSERT/UPDATE.
myisamchk didn't correctly update row checksum when used with -ro (this only gave a warning in subsequent runs).
Fixed bug in REPAIR TABLE so that it works with tables without indexes.
Fixed buffer overrun in DROP DATABASE.
LOAD TABLE FROM MASTER is sufficiently bug-free to announce it as a feature.
MATCH and AGAINST are now reserved words.
Fixed bug in 3.23.19; DELETE FROM tbl_name removed the .frm file.
Added SHOW CREATE TABLE.
Changed copyright for all files to GPL for the server code and utilities and to LGPL for the client libraries. See http://www.fsf.org/licenses/.
Fixed bug where all rows matching weren't updated on a MyISAM table when doing update based on key on a table with many keys and some key changed values.
The Linux MySQL RPMs and binaries are now statically linked with a linuxthread version that has faster mutex handling when used with MySQL.
ORDER BY can now use REF keys to find subsets of the rows that need to be sorted.
Changed name of print_defaults program to my_print_defaults to avoid name confusion.
Fixed NULLIF() to work as required by SQL-99.
Added net_read_timeout and net_write_timeout as startup parameters to mysqld.
Fixed bug that destroyed index when doing myisamchk --sort-records on a table with prefix compressed index.
Added pack_isam and myisampack to the standard MySQL distribution.
Added the syntax BEGIN WORK (the same as BEGIN).
Fixed core dump bug when using ORDER BY on a CONV() expression.
Added LOAD TABLE FROM MASTER.
Added FLUSH MASTER and FLUSH SLAVE.
Fixed big/little endian problem in the replication.
Fixed a problem from 3.23.17 when choosing character set on the client side.
Added FLUSH TABLES WITH READ LOCK to make a global lock suitable for making a copy of MySQL datafiles.
CREATE TABLE ... SELECT ... PROCEDURE now works.
Internal temporary tables will now use compressed index when using GROUP BY on VARCHAR/CHAR columns.
Fixed a problem when locking the same table with both a READ and a WRITE lock.
Fixed problem with myisamchk and RAID tables.
Fixed a bug in FIND_IN_SET() when the first argument was NULL.
Added table locks to Berkeley DB.
Fixed a bug with LEFT JOIN and ORDER BY where the first table had only one matching row.
Added 4 sample my.cnf example files in the support-files directory.
Fixed duplicated key problem when doing big GROUP BY operations. (This bug was probably introduced in 3.23.15.)
Changed syntax for INNER JOIN to match SQL-99.
Added NATURAL JOIN syntax.
A lot of fixes in the BDB interface.
Added handling of --no-defaults and --defaults-file to safe_mysqld.sh and mysql_install_db.sh.
Fixed bug in reading compressed tables with many threads.
Fixed that USE INDEX works with PRIMARY keys.
Added BEGIN statement to start a transaction in AUTOCOMMIT mode.
Added support for symbolic links for Windows.
Changed protocol to let client know if the server is in AUTOCOMMIT mode and if there is a pending transaction. If there is a pending transaction, the client library will give an error before reconnecting to the server to let the client know that the server did a rollback. The protocol is still backward-compatible with old clients.
KILL now works on a thread that is locked on a 'write' to a dead client.
Fixed memory leak in the replication slave thread.
Added new log-slave-updates option to mysqld, to allow daisy-chaining the slaves.
Fixed compile error on FreeBSD and other systems where pthread_t is not the same as int.
Fixed master shutdown aborting the slave thread.
Fixed a race condition in INSERT DELAYED code when doing ALTER TABLE.
Added deadlock detection sanity checks to INSERT DELAYED.
Added SLAVE START and SLAVE STOP statements.
Added TYPE=QUICK option to CHECK and to REPAIR.
Fixed bug in REPAIR TABLE when the table was in use by other threads.
Added a thread cache to make it possible to debug MySQL with gdb when one does a lot of reconnects. This will also improve systems where you can't use persistent connections.
Lots of fixes in the Berkeley DB interface.
UPDATE IGNORE will not abort if an update results in a DUPLICATE_KEY error.
Put CREATE TEMPORARY TABLE commands in the update log.
Fixed bug in handling of masked IP numbers in the privilege tables.
Fixed bug with delay_key_write tables and CHECK TABLE.
Added replicate-do-db and replicate-ignore-db options to mysqld, to restrict which databases get replicated.
Added SQL_LOG_BIN option.
To start mysqld as root, you must now use the --user=root option.
Added interface to Berkeley DB. (This is not yet functional; play with it at your own risk!)
Replication between master and slaves.
Fixed bug that other threads could steal a lock when a thread had a lock on a table and did a FLUSH TABLES command.
Added the slow_launch_time variable and the Slow_launch_threads status variable to mysqld. These can be examined with mysqladmin variables and mysqladmin extended-status.
Added functions INET_NTOA() and INET_ATON().
The default type of IF() now depends on the second and third arguments and not only on the second argument.
Fixed case when myisamchk could go into a loop when trying to repair a crashed table.
Don't write INSERT DELAYED to update log if SQL_LOG_UPDATE=0.
Fixed problem with REPLACE on HEAP tables.
Added possible character sets and time zone to SHOW VARIABLES output.
Fixed bug in locking code that could result in locking problems with concurrent inserts under high load.
Fixed a problem with DELETE of many rows on a table with compressed keys where MySQL scanned the index to find the rows.
Fixed problem with CHECK on table with deleted keyblocks.
Fixed a bug in reconnect (at the client side) where it didn't free memory properly in some contexts.
Fixed problems in update log when using LAST_INSERT_ID() to update a table with an AUTO_INCREMENT key.
Added NULLIF() function.
Fixed bug when using LOAD DATA INFILE on a table with BLOB/TEXT columns.
Optimized MyISAM to be faster when inserting keys in sorted order.
EXPLAIN SELECT ... now also prints out whether MySQL needs to create a temporary table or use file sorting when resolving the SELECT.
Added optimization to skip ORDER BY parts where the part is a constant expression in the WHERE part. Indexes can now be used even if the ORDER BY doesn't match the index exactly, as long as all the unused index parts and all the extra ORDER BY columns are constants in the WHERE clause. See MySQL indexes.
UPDATE and DELETE on a whole unique key in the WHERE part are now faster than before.
Changed RAID_CHUNKSIZE to be in 1024-byte increments.
Fixed core dump in LOAD_FILE(NULL).
Added mysql_real_escape_string() function to the MySQL C API.
Fixed a bug in CONCAT() where one of the arguments was a function that returned a modified argument.
Fixed a critical bug in myisamchk, where it updated the header in the index file when one only checked the table. This confused the mysqld daemon if it updated the same table at the same time. Now the status in the index file is only updated if one uses --update-state. With older myisamchk versions you should use --read-only when only checking tables, if there is the slightest chance that the mysqld server is working on the table at the same time!
Fixed that DROP TABLE is logged in the update log.
Fixed problem when searching on DECIMAL() key field where the column data contained leading zeros.
Fix bug in myisamchk when the AUTO_INCREMENT column isn't the first key.
Allow DATETIME in ISO8601 format: 2000-03-12T12:00:00
Dynamic character sets. A mysqld binary can now handle many different character sets (you can choose which when starting mysqld).
Added command REPAIR TABLE.
Added mysql_thread_safe() function to the MySQL C API.
Added the UMASK_DIR environment variable.
Added CONNECTION_ID() function to return the client connection thread ID.
When using = on BLOB or VARCHAR BINARY keys, where only a part of the column was indexed, the whole column of the result row wasn't compared.
Fix for sjis character set and ORDER BY.
When running in ANSI mode, don't allow columns to be used that aren't in the GROUP BY part.
Fixed problem when doing locks on the same table more than 2 times in the same LOCK TABLE command; this fixed the problem one got when running the test-ATIS test with --fast or --check-only-changed.
Added SQL_BUFFER_RESULT option to SELECT.
Removed end space from double/float numbers in results from temporary tables.
Added CHECK TABLE command.
Added changes for MyISAM in 3.23.12 that didn't get into the source distribution because of CVS problems.
Fixed bug so that mysqladmin shutdown will wait for the local server to close down.
Fixed a possible endless loop when calculating timestamp.
Added print_defaults program to the .rpm files. Removed mysqlbug from the client .rpm file.
Fixed bug in MyISAM involving REPLACE ... SELECT ... which could give a corrupted table.
Fixed bug in myisamchk where it incorrectly reset the AUTO_INCREMENT value.
LOTS of patches for Linux Alpha. MySQL now appears to be relatively stable on Alpha.
Changed DISTINCT on HEAP temporary tables to use hashed keys to quickly find duplicated rows. This mostly concerns queries of type SELECT DISTINCT ... GROUP BY .... This fixes a problem where not all duplicates were removed in queries of the above type. In addition, the new code is MUCH faster.
Added patches to make MySQL compile on Mac OS X.
Added IF NOT EXISTS clause to CREATE DATABASE.
Added --all-databases and --databases options to mysqldump to allow dumping of many databases at the same time.
Fixed bug in compressed DECIMAL() index in MyISAM tables.
Fixed bug when storing 0 into a timestamp.
When doing mysqladmin shutdown on a local connection, mysqladmin now waits until the PID file is gone before terminating.
Fixed core dump with some COUNT(DISTINCT ...) queries.
Fixed that myisamchk works properly with RAID tables.
Fixed problem with LEFT JOIN and key_field IS NULL.
Fixed bug in net_clear() which could give the error Aborted connection in the MySQL clients.
Added options USE INDEX (key_list) and IGNORE INDEX (key_list) as parameters in SELECT.
DELETE and RENAME should now work on RAID tables.
Allow the ALTER TABLE tbl_name ADD (field_list) syntax.
Fixed problem with optimizer that could sometimes use incorrect keys.
Fixed that GRANT/REVOKE ALL PRIVILEGES doesn't affect GRANT OPTION.
Removed extra ) from the output of SHOW GRANTS.
Fixed problem when storing numbers in timestamps.
Fix problem with time zones that have half hour offsets.
Allow the syntax UNIQUE INDEX in CREATE statements.
mysqlhotcopy - fast online hot-backup utility for local MySQL databases. By Tim Bunce.
New more secure mysqlaccess. Thanks to Steve Harvey for this.
Added --i-am-a-dummy and --safe-updates options to mysql.
Added select_limit and max_join_size variables to mysql.
Added SQL_MAX_JOIN_SIZE and SQL_SAFE_UPDATES options.
Added READ LOCAL lock that doesn't lock the table for concurrent inserts. (This is used by mysqldump.)
Changed that LOCK TABLES ... READ no longer allows concurrent inserts.
Added --skip-delay-key-write option to mysqld.
Fixed security problem in the protocol regarding password checking.
_rowid can now be used as an alias for an integer type unique indexed column.
Added back blocking of SIGPIPE when compiling with --thread-safe-clients to make things safe for old clients.
Fixed bug in 3.23.9 where memory wasn't properly freed when using LOCK TABLES.
Fixed problem that affected queries that did arithmetic on group functions.
Fixed problem with timestamps and INSERT DELAYED.
Fixed that date_col BETWEEN const_date AND const_date works.
Fixed problem when only changing a 0 to NULL in a table with BLOB/TEXT columns.
Fixed bug in range optimizer when using many key parts and or on the middle key parts: WHERE K1=1 and K3=2 and (K2=2 and K4=4 or K2=3 and K4=5)
Added source command to mysql to allow reading of batch files inside the mysql client. Original patch by Matthew Vanecek.
Fixed critical problem with the WITH GRANT OPTION option.
Don't give an unnecessary GRANT error when using tables from many databases in the same query.
Added VIO wrapper (needed for SSL support; by Andrei Errapart and Tõnu Samuel).
Fixed optimizer problem on SELECT when using many overlapping indexes. MySQL should now be able to choose keys even better when there are many keys to choose from.
Changed optimizer to prefer a range key instead of a ref key when the range key can uses more columns than the ref key (which only can use columns with =). For example, the following type of queries should now be faster: SELECT * from key_part_1=const and key_part_2 > const2
Fixed bug that a change of all VARCHAR columns to CHAR columns didn't change row type from dynamic to fixed.
Disabled floating-point exceptions for FreeBSD to fix core dump when doing SELECT FLOOR(POW(2,63)).
Renamed mysqld startup option from --delay-key-write to --delay-key-write-for-all-tables.
Added read-next-on-key to HEAP tables. This should fix all problems with HEAP tables when using non-UNIQUE keys.
Added option to print default arguments to all clients.
Added --log-slow-queries option to mysqld to log all queries that take a long time to a separate log file with a time indicating how long the query took.
Fixed core dump when doing WHERE key_col=RAND(...).
Fixed optimization bug in SELECT ... LEFT JOIN ... key_col IS NULL, when key_col could contain NULL values.
Fixed problem with 8-bit characters as separators in LOAD DATA INFILE.
Fixed problem when handling indexfiles larger than 8G.
Added latest patches to MIT-pthreads for NetBSD.
Fixed problem with time zones that are < GMT - 11.
Fixed a bug when deleting packed keys in NISAM.
Fixed problem with ISAM when doing some ORDER BY ... DESC queries.
Fixed bug when doing a join on a text key which didn't cover the whole key.
Option --delay-key-write didn't enable delayed key writing.
Fixed update of TEXT column which involved only case changes.
Fixed that INSERT DELAYED doesn't update timestamps that are given.
Added function YEARWEEK() and options x, X, v and V to DATE_FORMAT().
Fixed problem with MAX(indexed_column) and HEAP tables.
Fixed problem with BLOB NULL keys and LIKE "prefix%".
Fixed problem with MyISAM and fixed-length rows < 5 bytes.
Fixed problem that could cause MySQL to touch freed memory when doing very complicated GROUP BY queries.
Fixed core dump if you got a crashed table where an ENUM field value was too big.
Fixed workaround under Linux to avoid problems with pthread_mutex_timedwait(), which is used with INSERT DELAYED. See Linux.
Fixed that one will get a 'disk full' error message if one gets disk full when doing sorting (instead of waiting until we got more disk space).
Fixed a bug in MyISAM with keys > 250 characters.
In MyISAM one can now do an INSERT at the same time as other threads are reading from the table.
Added max_write_lock_count variable to mysqld to force a READ lock after a certain number of WRITE locks.
Inverted flag delay_key_write on show variables.
Renamed concurrency variable to thread_concurrency.
The following functions are now multi-byte-safe: LOCATE(substr,str), POSITION(substr IN str), LOCATE(substr,str,pos), INSTR(str,substr), LEFT(str,len), RIGHT(str,len), SUBSTRING(str,pos,len), SUBSTRING(str FROM pos FOR len), MID(str,pos,len), SUBSTRING(str,pos), SUBSTRING(str FROM pos), SUBSTRING_INDEX(str,delim,count), RTRIM(str), TRIM([[BOTH | TRAILING] [remstr] FROM] str), REPLACE(str,from_str,to_str), REVERSE(str), INSERT(str,pos,len,newstr), LCASE(str), LOWER(str), UCASE(str) and UPPER(str); patch by Wei He.
Fix core dump when releasing a lock from a non-existent table.
Remove locks on tables before starting to remove duplicates.
Added option FULL to SHOW PROCESSLIST.
Added option --verbose to mysqladmin.
Fixed problem when automatically converting HEAP to MyISAM.
Fixed bug in HEAP tables when doing insert + delete + insert + scan the table.
Fixed bugs on Alpha with REPLACE() and LOAD DATA INFILE.
Added interactive_timeout variable to mysqld.
Changed the argument to mysql_data_seek() from ulong to ulonglong.
Added -O lower_case_table_names={0|1} option to mysqld to allow users to force table names to lowercase.
Added SELECT ... INTO DUMPFILE.
Added --ansi option to mysqld to make some functions SQL-99 compatible.
Temporary table names now start with #sql.
Added quoting of identifiers with ` (" in --ansi mode).
Changed to use snprintf() when printing floats to avoid some buffer overflows on FreeBSD.
Made FLOOR() overflow safe on FreeBSD.
Added --quote-names option to mysqldump.
Fixed bug that one could make a part of a PRIMARY KEY NOT NULL.
Fixed encrypt() to be thread-safe and not reuse buffer.
Added mysql_odbc_escape_string() function to support big5 characters in MyODBC.
Rewrote the storage engine to use classes. This introduces a lot of new code, but will make table handling faster and better.
Added patch by Sasha for user-defined variables.
Changed that FLOAT and DOUBLE (without any length modifiers) no longer are fixed decimal point numbers.
Changed the meaning of FLOAT(X): Now this is the same as FLOAT if X <= 24 and a DOUBLE if 24 < X <= 53.
DECIMAL(X) is now an alias for DECIMAL(X,0) and DECIMAL is now an alias for DECIMAL(10,0). The same goes for NUMERIC.
Added option ROW_FORMAT={DEFAULT | DYNAMIC | FIXED | COMPRESSED} to CREATE_TABLE.
DELETE FROM table_name didn't work on temporary tables.
Changed function CHAR_LENGTH() to be multi-byte character safe.
Added function ORD(string).
Fixed some Y2K problems in the new date handling in 3.23.
Fixed problem with SELECT DISTINCT ... ORDER BY RAND().
Added patches by Sergei A. Golubchik for text searching on the MyISAM level.
Fixed cache overflow problem when using full joins without keys.
Fixed some configure issues.
Some small changes to make parsing faster.
Adding a column after the last field with ALTER TABLE didn't work.
Fixed problem when using an AUTO_INCREMENT column in two keys
With MyISAM, you now can have an AUTO_INCREMENT column as a key sub part: CREATE TABLE foo (a INT NOT NULL AUTO_INCREMENT, b CHAR(5), PRIMARY KEY (b,a))
Fixed bug in MyISAM with packed char keys that could be NULL.
AS on field name with CREATE TABLE table_name SELECT ... didn't work.
Allow use of NATIONAL and NCHAR when defining character columns. This is the same as not using BINARY.
Don't allow NULL columns in a PRIMARY KEY (only in UNIQUE keys).
Clear LAST_INSERT_ID() if one uses this in ODBC: WHERE auto_increment_column IS NULL. This seems to fix some problems with Access.
SET SQL_AUTO_IS_NULL=0|1 now turns on/off the handling of searching after the last inserted row with WHERE auto_increment_column IS NULL.
Added new variable concurrency to mysqld for Solaris.
Added --relative option to mysqladmin to make extended-status more useful to monitor changes.
Fixed bug when using COUNT(DISTINCT ...) on an empty table.
Added support for the Chinese character set GBK.
Fixed problem with LOAD DATA INFILE and BLOB columns.
Added bit operator ~ (negation).
Fixed problem with UDF functions.
Inserting a DATETIME into a TIME column no longer will try to store 'days' in it.
Fixed problem with storage of float/double on little endian machines. (This affected SUM().)
Added connect timeout on TCP/IP connections.
Fixed problem with LIKE "%" on an index that may have NULL values.
REVOKE ALL PRIVILEGES didn't revoke all privileges.
Allow creation of temporary tables with same name as the original table.
When granting a user a GRANT option for a database, he couldn't grant privileges to other users.
New command: SHOW GRANTS FOR user (by Sinisa).
New date_add syntax: date/datetime + INTERVAL # interval_type. By Joshua Chamas.
Fixed privilege check for LOAD DATA REPLACE.
Automatic fixing of broken include files on Solaris 2.7
Some configure issues to fix problems with big filesystem detection.
REGEXP is now case-insensitive if you use non-binary strings.
Added patches for MIT-pthreads on NetBSD.
Fixed range bug in MyISAM.
ASC is now the default again for ORDER BY.
Added LIMIT to UPDATE.
Added mysql_change_user() function to the MySQL C API.
Added character set to SHOW VARIABLES.
Added support of --[whitespace] comments.
Allow INSERT into tbl_name VALUES (), that is, you may now specify an empty value list to insert a row in which each column is set to its default value.
Changed SUBSTRING(text FROM pos) to conform to SQL-99. (Before this construct returned the rightmost pos characters.)
SUM() with GROUP BY returned 0 on some systems.
Changed output for SHOW TABLE STATUS.
Added DELAY_KEY_WRITE option to CREATE TABLE.
Allow AUTO_INCREMENT on any key part.
Fixed problem with YEAR(NOW()) and YEAR(CURDATE()).
Added CASE construct.
New function COALESCE().
Fixed range optimizer bug: SELECT * FROM table_name WHERE key_part1 >= const AND (key_part2 = const OR key_part2 = const). The bug was that some rows could be duplicated in the result.
Running myisamchk without -a updated the index distribution incorrectly.
SET SQL_LOW_PRIORITY_UPDATES=1 was causing a parse error.
You can now update index columns that are used in the WHERE clause. UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100
Date handling should now be a bit faster.
Added handling of fuzzy dates (dates where day or month is 0), such as '1999-01-00'.
Fixed optimization of SELECT ... WHERE key_part1=const1 AND key_part_2=const2 AND key_part1=const4 AND key_part2=const4; indextype should be range instead of ref.
Fixed egcs 1.1.2 optimizer bug (when using BLOB values) on Linux Alpha.
Fixed problem with LOCK TABLES combined with DELETE FROM table.
MyISAM tables now allow keys on NULL and BLOB/TEXT columns.
The following join is now much faster: SELECT ... FROM t1 LEFT JOIN t2 ON ... WHERE t2.not_null_column IS NULL.
ORDER BY and GROUP BY can be done on functions.
Changed handling of 'const_item' to allow handling of ORDER BY RAND().
Indexes are now used for WHERE key_column = function.
Indexes are now used for WHERE key_column = col_name even if the columns are not identically packed.
Indexes are now used for WHERE col_name IS NULL.
Changed heap tables to be stored in low_byte_first order (to make it easy to convert to MyISAM tables)
Automatic change of HEAP temporary tables to MyISAM tables in case of ``table is full'' errors.
Added --init-file=file_name option to mysqld.
Added COUNT(DISTINCT value, [value, ...]).
CREATE TEMPORARY TABLE now creates a temporary table, in its own namespace, that is automatically deleted if connection is dropped.
New reserved words (required for CASE): CASE, THEN, WHEN, ELSE and END.
New functions EXPORT_SET() and MD5().
Support for the GB2312 Chinese character set.
A new storage engine library (MyISAM) with a lot of new features. See MyISAM.
You can create in-memory HEAP tables which are extremely fast for lookups.
Support for big files (63-bit) on OSs that support big files.
New function LOAD_FILE(filename) to get the contents of a file as a string value.
New operator <=> which will act as = but will return TRUE if both arguments are NULL. This is useful for comparing changes between tables.
Added the ODBC 3.0 EXTRACT(interval FROM datetime) function.
Columns defined as FLOAT(X) are not rounded on storage and may be in scientific notation (1.0 E+10) when retrieved.
REPLACE is now faster than before.
Changed LIKE character comparison to behave as =; This means that 'e' LIKE 'é' is now true. (If the line doesn't display correctly, the latter 'e' is a French 'e' with a dot above.)
SHOW TABLE STATUS returns a lot of information about the tables.
Added LIKE to the SHOW STATUS command.
Added Privileges column to SHOW COLUMNS.
Added Packed and Comment columns to SHOW INDEX.
Added comments to tables (with CREATE TABLE ... COMMENT "xxx").
Added UNIQUE, as in CREATE TABLE table_name (col INT not null UNIQUE)
New create syntax: CREATE TABLE table_name SELECT ...
New create syntax: CREATE TABLE IF NOT EXISTS ...
Allow creation of CHAR(0) columns.
DATE_FORMAT() now requires % before any format character.
DELAYED is now a reserved word (sorry about that :( ).
An example procedure is added: analyse, file: sql_analyse.c. This will describe the data in your query. Try the following:
SELECT ... FROM ... WHERE ... PROCEDURE ANALYSE([max elements,[max memory]])
This procedure is extremely useful when you want to check the data in your table!
BINARY cast to force a string to be compared in case-sensitive fashion.
Added --skip-show-database option to mysqld.
Check whether a row has changed in an UPDATE now also works with BLOB/TEXT columns.
Added the INNER join syntax. NOTE: This made INNER a reserved word!
Added support for netmasks to the hostname in the MySQL grant tables. You can specify a netmask using the IP/NETMASK syntax.
If you compare a NOT NULL DATE/DATETIME column with IS NULL, this is changed to a compare against 0 to satisfy some ODBC applications. (By <shreeve@uci.edu>.)
NULL IN (...) now returns NULL instead of 0. This will ensure that null_column NOT IN (...) doesn't match NULL values.
Fix storage of floating-point values in TIME columns.
Changed parsing of TIME strings to be more strict. Now the fractional second part is detected (and currently skipped). The following formats are supported:
[[DAYS] [H]H:]MM:]SS[.fraction]
[[[[[H]H]H]H]MM]SS[.fraction]
Detect (and ignore) fractional second part from DATETIME.
Added the LOW_PRIORITY attribute to LOAD DATA INFILE.
The default index name now uses the same case as the column name on which the index name is based.
Changed default number of connections to 100.
Use bigger buffers when using LOAD DATA INFILE.
DECIMAL(x,y) now works according to SQL-99.
Added aggregate UDF functions. Thanks to Andreas F. Bobak (<bobak@relog.ch>) for this!
LAST_INSERT_ID() is now updated for INSERT INTO ... SELECT.
Some small changes to the join table optimizer to make some joins faster.
SELECT DISTINCT is much faster; it uses the new UNIQUE functionality in MyISAM. One difference compared to MySQL Version 3.22 is that the output of DISTINCT is no longer sorted.
All C client API macros are now functions to make shared libraries more reliable. Because of this, you can no longer call mysql_num_fields() on a MYSQL object, you must use mysql_field_count() instead.
Added use of LIBWRAP; patch by Henning P. Schmiedehausen.
Don't allow AUTO_INCREMENT for other than numerical columns.
Using AUTO_INCREMENT will now automatically make the column NOT NULL.
Show NULL as the default value for AUTO_INCREMENT columns.
Added SQL_BIG_RESULT; SQL_SMALL_RESULT is now default.
Added a shared library RPM. This enhancement was contributed by David Fox (<dsfox@cogsci.ucsd.edu>).
Added --enable-large-files and --disable-large-files switches to configure. See configure.in for some systems where this is automatically turned off because of broken implementations.
Upgraded readline to 4.0.
New CREATE TABLE options: PACK_KEYS and CHECKSUM.
Added --default-table-type option to mysqld.
Table of Contents
The 3.22 version has faster and safer connect code than version 3.21, as well as a lot of new nice enhancements. As there aren't really any major changes, upgrading from 3.21 to 3.22 should be very easy and painless. See Upgrading-from-3.21.
Fixed problem with STD().
Merged changes from the newest ISAM library from 3.23.
Fixed problem with INSERT DELAYED.
Fixed a bug core dump when using a LEFT JOIN/STRAIGHT_JOIN on a table with only one row.
Fixed problem with GROUP BY on TINYBLOB columns; this caused bugzilla to not show rows in some queries.
Had to do total recompile of the Windows binary version as VC++ didn't compile all relevant files for 3.22.33 :(
Fixed problems in Windows when locking tables with LOCK TABLE.
Quicker kill of SELECT DISTINCT queries.
Fixed problem when storing numbers in timestamps.
Fix problem with time zones that have half hour offsets.
Added mysqlhotcopy, a fast online hot-backup utility for local MySQL databases. By Tim Bunce.
New more secure mysqlaccess. Thanks to Steve Harvey for this.
Fixed security problem in the protocol regarding password checking.
Fixed problem that affected queries that did arithmetic on GROUP functions.
Fixed a bug in the ISAM code when deleting rows on tables with packed indexes.
Fixed optimizer problem on SELECT when using many overlapping indexes.
Disabled floating-point exceptions for FreeBSD to fix core dump when doing SELECT FLOOR(POW(2,63)).
Added print of default arguments options to all clients.
Fixed critical problem with the WITH GRANT OPTION option.
Fixed non-critical Y2K problem when writing short date to log files.
Upgraded the configure and include files to match the latest 3.23 version. This should increase portability and make it easier to build shared libraries.
Added latest patches to MIT-pthreads for NetBSD.
Fixed problem with time zones that are < GMT -11.
Fixed a bug when deleting packed keys in NISAM.
Fixed problem that could cause MySQL to touch freed memory when doing very complicated GROUP BY queries.
Fixed core dump if you got a crashed table where an ENUM field value was too big.
Added mysqlshutdown.exe and mysqlwatch.exe to the Windows distribution.
Fixed problem when doing ORDER BY on a reference key.
Fixed that INSERT DELAYED doesn't update timestamps that are given.
Fixed problem with LEFT JOIN and COUNT() on a column which was declared NULL + and it had a DEFAULT value.
Fixed core dump problem when using CONCAT() in a WHERE clause.
Fixed problem with AVG() and STD() with NULL values.
Fixed prototype in my_ctype.h when using other character sets.
Some configure issues to fix problems with big filesystem detection.
Fixed problem when sorting on big BLOB columns.
ROUND() will now work on Windows.
Fixed core dump with empty BLOB/TEXT column argument to REVERSE().
Extended /*! */ with version numbers.
Changed SUBSTRING(text FROM pos) to conform to SQL-99. (Before this construct returned the rightmost 'pos' characters.)
Fixed problem with LOCK TABLES combined with DELETE FROM table
Fixed problem that INSERT ... SELECT didn't use BIG_TABLES.
SET SQL_LOW_PRIORITY_UPDATES=# didn't work.
Password wasn't updated correctly if privileges didn't change on: GRANT ... IDENTIFIED BY
Fixed range optimizer bug in SELECT * FROM table_name WHERE key_part1 >= const AND (key_part2 = const OR key_part2 = const).
Fixed bug in compression key handling in ISAM.
DATA is no longer a reserved word.
Fixed optimizer bug with tables with only one row.
Fixed bug when using LOCK TABLES table_name READ; FLUSH TABLES;
Applied some patches for HP-UX.
isamchk should now work on Windows.
Changed configure to not use big file handling on Linux as this crashes some Red Hat 6.0 systems
Upgraded to use Autoconf 2.13, Automake 1.4 and libtool 1.3.2.
Better support for SCO in configure.
Added option --defaults-file=file_name to option file handling to force use of only one specific option file.
Extended CREATE syntax to ignore MySQL Version 3.23 keywords.
Fixed deadlock problem when using INSERT DELAYED on a table locked with LOCK TABLES.
Fixed deadlock problem when using DROP TABLE on a table that was locked by another thread.
Add logging of GRANT/REVOKE commands in the update log.
Fixed isamchk to detect a new error condition.
Fixed bug in NATURAL LEFT JOIN.
Fixed problem in the C API when you called mysql_close() directly after mysql_init().
Better client error message when you can't open socket.
Fixed delayed_insert_thread counting when you couldn't create a new delayed_insert thread.
Fixed bug in CONCAT() with many arguments.
Added patches for DEC 3.2 and SCO.
Fixed path-bug when installing MySQL as a service on NT.
MySQL on Windows is now compiled with VC++ 6.0 instead of with VC++ 5.0.
New installation setup for MySQL on Windows.
Fixed problem with DELETE FROM TABLE when table was locked by another thread.
Fixed bug in LEFT JOIN involving empty tables.
Changed the mysql.db column from CHAR(32) to CHAR(60).
MODIFY and DELAYED are no longer reserved words.
Fixed a bug when storing days in a TIME column.
Fixed a problem with Host '...' is not allowed to connect to this MySQL server after one had inserted a new MySQL user with a GRANT command.
Changed to use TCP_NODELAY also on Linux (should give faster TCP/IP connections).
Fixed STD() for big tables when result should be 0.
The update log didn't have newlines on some operating systems.
INSERT DELAYED had some garbage at end in the update log.
Fixed bug in mysql_install_db (from 3.22.17).
Changed default key cache size to 8M.
Fixed problem with queries that needed temporary tables with BLOB columns.
Fixes a fatal problem in 3.22.17 on Linux; after shutdown not all threads died properly.
Added option -O flush_time=# to mysqld. This is mostly useful on Windows and tells how often MySQL should close all unused tables and flush all updated tables to disk.
Fixed problem that a VARCHAR column compared with CHAR column didn't use keys efficiently.
Fixed a core dump problem when using --log-update and connecting without a default database.
Fixed some configure and portability problems.
Using LEFT JOIN on tables that had circular dependencies caused mysqld to hang forever.
mysqladmin processlist could kill the server if a new user logged in.
DELETE FROM tbl_name WHERE key_column=col_name didn't find any matching rows. Fixed.
DATE_ADD(column, ...) didn't work.
INSERT DELAYED could deadlock with status upgrading lock.
Extended ENCRYPT() to take longer salt strings than 2 characters.
longlong2str is now much faster than before. For Intel x86 platforms, this function is written in optimized assembler.
Added the MODIFY keyword to ALTER TABLE.
GRANT used with IDENTIFIED BY didn't take effect until privileges were flushed.
Name change of some variables in SHOW STATUS.
Fixed problem with ORDER BY with 'only index' optimization when there were multiple key definitions for a used column.
DATE and DATETIME columns are now up to 5 times faster than before.
INSERT DELAYED can be used to let the client do other things while the server inserts rows into a table.
LEFT JOIN USING (col1,col2) didn't work if one used it with tables from 2 different databases.
LOAD DATA LOCAL INFILE didn't work in the Unix version because of a missing file.
Fixed problems with VARCHAR/BLOB on very short rows (< 4 bytes); error 127 could occur when deleting rows.
Updating BLOB/TEXT through formulas didn't work for short (< 256 char) strings.
When you did a GRANT on a new host, mysqld could die on the first connect from this host.
Fixed bug when one used ORDER BY on column name that was the same name as an alias.
Added BENCHMARK(loop_count,expression) function to time expressions.
Allow empty arguments to mysqld to make it easier to start from shell scripts.
Setting a TIMESTAMP column to NULL didn't record the timestamp value in the update log.
Fixed lock handler bug when one did INSERT INTO TABLE ... SELECT ... GROUP BY.
Added a patch for localtime_r() on Windows so that it will no lonher crash if your date is > 2039, but instead will return a time of all zero.
Names for user-defined functions are no longer case-sensitive.
Added escape of ^Z (ASCII 26) to \Z as ^Z doesn't work with pipes on Windows.
mysql_fix_privileges adds a new column to the mysql.func to support aggregate UDF functions in future MySQL releases.
Saving NOW(), CURDATE() or CURTIME() directly in a column didn't work.
SELECT COUNT(*) ... LEFT JOIN ... didn't work with no WHERE part.
Updated config.guess to allow MySQL to configure on UnixWare 7.1.x.
Changed the implementation of pthread_cond() on the Windows version. get_lock() now correctly times out on Windows!
Fixed problem when using DATE_ADD() and DATE_SUB() in a WHERE clause.
You can now set the password for a user with the GRANT ... TO user IDENTIFIED BY 'password' syntax.
Fixed bug in GRANT checking with SELECT on many tables.
Added missing file mysql_fix_privilege_tables to the RPM distribution. This is not run by default because it relies on the client package.
Added option SQL_SMALL_RESULT to SELECT to force use of fast temporary tables when you know that the result set will be small.
Allow use of negative real numbers without a decimal point.
Day number is now adjusted to maximum days in month if the resulting month after DATE_ADD/DATE_SUB() doesn't have enough days.
Fix that GRANT compares columns in case-insensitive fashion.
Fixed a bug in sql_list.h that made ALTER TABLE dump core in some contexts.
The hostname in user@hostname can now include . and - without quotes in the context of the GRANT, REVOKE and SET PASSWORD FOR ... statements.
Fix for isamchk for tables which need big temporary files.
Important: You must run the mysql_fix_privilege_tables script when you upgrade to this version! This is needed because of the new GRANT system. If you don't do this, you will get Access denied when you try to use ALTER TABLE, CREATE INDEX, or DROP INDEX.
GRANT to allow/deny users table and column access.
Changed USER() to return a value in user@host format. Formerly it returned only user.
Changed the syntax for how to set PASSWORD for another user.
New command FLUSH STATUS that resets most status variables to zero.
New status variables: aborted_threads, aborted_connects.
New option variable: connection_timeout.
Added support for Thai sorting (by Pruet Boonma <pruet@ds90.intanon.nectec.or.th>).
Slovak and Japanese error messages.
Configuration and portability fixes.
Added option SET SQL_WARNINGS=1 to get a warning count also for simple (single-row) inserts.
MySQL now uses SIGTERM instead of SIGQUIT with shutdown to work better on FreeBSD.
Added option \G (print vertically) to mysql.
SELECT HIGH_PRIORITY ... killed mysqld.
IS NULL on a AUTO_INCREMENT column in a LEFT JOIN didn't work as expected.
New function MAKE_SET().
mysql_install_db no longer starts the MySQL server! You should start mysqld with safe_mysqld after installing it! The MySQL RPM will, however, start the server as before.
Added --bootstrap option to mysqld and recoded mysql_install_db to use it. This will make it easier to install MySQL with RPMs.
Changed +, - (sign and minus), *, /, %, ABS() and MOD() to be BIGINT aware (64-bit safe).
Fixed a bug in ALTER TABLE that caused mysqld to crash.
MySQL now always reports the conflicting key values when a duplicate key entry occurs. (Before this was only reported for INSERT.)
New syntax: INSERT INTO tbl_name SET col_name=value, col_name=value, ...
Most errors in the .err log are now prefixed with a time stamp.
Added option MYSQL_INIT_COMMAND to mysql_options() to make a query on connect or reconnect.
Added option MYSQL_READ_DEFAULT_FILE and MYSQL_READ_DEFAULT_GROUP to mysql_options() to read the following parameters from the MySQL option files: port, socket, compress, password, pipe, timeout, user, init-command, host and database.
Added maybe_null to the UDF structure.
Added option IGNORE to INSERT statements with many rows.
Fixed some problems with sorting of the koi8 character sets; users of koi8 must run isamchk -rq on each table that has an index on a CHAR or VARCHAR column.
New script mysql_setpermission, by Luuk de Boer. It allows easy creation of new users with permissions for specific databases.
Allow use of hexadecimal strings (0x...) when specifying a constant string (like in the column separators with LOAD DATA INFILE).
Ported to OS/2 (thanks to Antony T. Curtis <antony.curtis@olcs.net>).
Added more variables to SHOW STATUS and changed format of output to be like SHOW VARIABLES.
Added extended-status command to mysqladmin which will show the new status variables.
SET SQL_LOG_UPDATE=0 caused a lockup of the server.
New SQL command: FLUSH [ TABLES | HOSTS | LOGS | PRIVILEGES ] [, ...]
New SQL command: KILL thread_id.
Added casts and changed include files to make MySQL easier to compile on AIX and DEC OSF/1 4.x
Fixed conversion problem when using ALTER TABLE from a INT to a short CHAR() column.
Added SELECT HIGH_PRIORITY; this will get a lock for the SELECT even if there is a thread waiting for another SELECT to get a WRITE LOCK.
Moved wild_compare() to string class to be able to use LIKE on BLOB/TEXT columns with \0.
Added ESCAPE option to LIKE.
Added a lot more output to mysqladmin debug.
You can now start mysqld on Windows with the --flush option. This will flush all tables to disk after each update. This makes things much safer on the Windows platforms but also much slower.
Czech character sets should now work much better.
DATE_ADD() and DATE_SUB() didn't work with group functions.
mysql will now also try to reconnect on USE database commands.
Fix problem with ORDER BY and LEFT JOIN and const tables.
Fixed problem with ORDER BY if the first ORDER BY column was a key and the rest of the ORDER BY columns wasn't part of the key.
Fixed a big problem with OPTIMIZE TABLE.
MySQL clients on NT will now by default first try to connect with named pipes and after this with TCP/IP.
Fixed a problem with DROP TABLE and mysqladmin shutdown on Windows (a fatal bug from 3.22.6).
Fixed problems with TIME columns and negative strings.
Added an extra thread signal loop on shutdown to avoid some error messages from the client.
MySQL now uses the next available number as extension for the update log file.
Added patches for UNIXWARE 7.
Added LIMIT clause for the DELETE statement.
You can now use the /*! ... */ syntax to hide MySQL-specific keywords when you write portable code. MySQL will parse the code inside the comments as if the surrounding /*! and */ comment characters didn't exist.
OPTIMIZE TABLE tbl_name can now be used to reclaim disk space after many deletes. Currently, this uses ALTER TABLE to regenerate the table, but in the future it will use an integrated isamchk for more speed.
Upgraded libtool to get the configure more portable.
Fixed slow UPDATE and DELETE operations when using DATETIME or DATE keys.
Changed optimizer to make it better at deciding when to do a full join and when using keys.
You can now use mysqladmin proc to display information about your own threads. Only users with the PROCESS privilege can get information about all threads. (In 4.0.2, you need the SUPER privilege for this.)
Added handling of formats YYMMDD, YYYYMMDD, YYMMDDHHMMSS for numbers when using DATETIME and TIMESTAMP types. (Formerly these formats only worked with strings.)
Added connect option CLIENT_IGNORE_SPACE to allow use of spaces after function names and before ( (Powerbuilder requires this). This will make all function names reserved words.
Added the --log-long-format option to mysqld to enable timestamps and INSERT_IDs in the update log.
Added --where option to mysqldump (patch by Jim Faucette).
The lexical analyzer now uses ``perfect hashing'' for faster parsing of SQL statements.
Faster mysqldump.
For the LOAD DATA INFILE statement, you can now use the new LOCAL keyword to read the file from the client. mysqlimport will automatically use LOCAL when importing with the TCP/IP protocol.
Fixed small optimize problem when updating keys.
Changed makefiles to support shared libraries.
MySQL-NT can now use named pipes, which means that you can now use MySQL-NT without having to install TCP/IP.
All table lock handing is changed to avoid some very subtle deadlocks when using DROP TABLE, ALTER TABLE, DELETE FROM TABLE and mysqladmin flush-tables under heavy usage. Changed locking code to get better handling of locks of different types.
Updated DBI to 1.00 and DBD to 1.2.0.
Added a check that the error message file contains error messages suitable for the current version of mysqld. (To avoid errors if you accidentally try to use an old error message file.)
All count structures in the client (affected_rows(), insert_id(), ...) are now of type BIGINT to allow 64-bit values to be used. This required a minor change in the MySQL protocol which should affect only old clients when using tables with AUTO_INCREMENT values > 16M.
The return type of mysql_fetch_lengths() has changed from uint * to ulong *. This may give a warning for old clients but should work on most machines.
Change mysys and dbug libraries to allocate all thread variables in one struct. This makes it easier to make a threaded libmysql.dll library.
Use the result from gethostname() (instead of uname()) when constructing .pid file names.
New better compressed server/client protocol.
COUNT(), STD() and AVG() are extended to handle more than 4G rows.
You can now store values in the range -838:59:59 <= x <= 838:59:59 in a TIME column.
Warning: Incompatible change!! If you set a TIME column to too short a value, MySQL now assumes the value is given as: [[[D ]HH:]MM:]SS instead of HH[:MM[:SS]].
TIME_TO_SEC() and SEC_TO_TIME() can now handle negative times and hours up to 32767.
Added new option SET SQL_LOG_UPDATE={0|1} to allow users with the PROCESS privilege to bypass the update log. (Modified patch from Sergey A Mukhin <violet@rosnet.net>.)
Fixed fatal bug in LPAD().
Initialize line buffer in mysql.cc to make BLOB reading from pipes safer.
Added -O max_connect_errors=# option to mysqld. Connect errors are now reset for each correct connection.
Increased the default value of max_allowed_packet to 1M in mysqld.
Added --low-priority-updates option to mysqld, to give table-modifying operations (INSERT, REPLACE, UPDATE, DELETE) lower priority than retrievals. You can now use {INSERT | REPLACE | UPDATE | DELETE} LOW_PRIORITY ... You can also use SET SQL_LOW_PRIORITY_UPDATES={0|1} to change the priority for one thread. One side effect is that LOW_PRIORITY is now a reserved word. :(
Add support for INSERT INTO table ... VALUES(...),(...),(...), to allow inserting multiple rows with a single statement.
INSERT INTO tbl_name is now also cached when used with LOCK TABLES. (Previously only INSERT ... SELECT and LOAD DATA INFILE were cached.)
Allow GROUP BY functions with HAVING:
mysql> SELECT col FROM table GROUP BY col HAVING COUNT(*)>0;
mysqld will now ignore trailing ; characters in queries. This is to make it easier to migrate from some other SQL servers that require the trailing ;.
Fix for corrupted fixed-format output generated by SELECT INTO OUTFILE.
Warning: Incompatible change! Added Oracle GREATEST() and LEAST() functions. You must now use these instead of the MAX() and MIN() functions to get the largest/smallest value from a list of values. These can now handle REAL, BIGINT and string (CHAR or VARCHAR) values.
Warning: Incompatible change! DAYOFWEEK() had offset 0 for Sunday. Changed the offset to 1.
Give an error for queries that mix GROUP BY columns and fields when there is no GROUP BY specification.
Added --vertical option to mysql, for printing results in vertical mode.
Index-only optimization; some queries are now resolved using only indexes. Until MySQL 4.0, this works only for numeric columns. See MySQL indexes.
Lots of new benchmarks.
A new C API chapter and lots of other improvements in the manual.
Added --tmpdir option to mysqld, for specifying the location of the temporary file directory.
MySQL now automatically changes a query from an ODBC client:
SELECT ... FROM table WHERE auto_increment_column IS NULL
to:
SELECT ... FROM table WHERE auto_increment_column == LAST_INSERT_ID()
This allows some ODBC programs (Delphi, Access) to retrieve the newly inserted row to fetch the AUTO_INCREMENT id.
DROP TABLE now waits for all users to free a table before deleting it.
Fixed small memory leak in the new connect protocol.
New functions BIN(), OCT(), HEX() and CONV() for converting between different number bases.
Added function SUBSTRING() with two arguments.
If you created a table with a record length smaller than 5, you couldn't delete rows from the table.
Added optimization to remove const reference tables from ORDER BY and GROUP BY.
mysqld now automatically disables system locking on Linux and Windows, and for systems that use MIT-pthreads. You can force the use of locking with the --enable-external-locking option.
Added --console option to mysqld, to force a console window (for error messages) when using Windows.
Fixed table locks for Windows.
Allow $ in identifiers.
Changed name of user-specific configuration file from my.cnf to .my.cnf (Unix only).
Added DATE_ADD() and DATE_SUB() functions.
Fixed a lock problem (bug in MySQL Version 3.22.1) when closing temporary tables.
Added missing mysql_ping() to the client library.
Added --compress option to all MySQL clients.
Changed byte to char in mysql.h and mysql_com.h.
Searching on multiple constant keys that matched more than 30% of the rows didn't always use the best possible key.
New functions <<, >>, RPAD() and LPAD().
You can now save default options (like passwords) in a configuration file (my.cnf).
Lots of small changes to get ORDER BY to work when no records are found when using fields that are not in GROUP BY (MySQL extension).
Added --chroot option to mysqld, to start mysqld in a chroot environment (by Nikki Chumakov <nikkic@cityline.ru>).
Trailing spaces are now ignored when comparing case-sensitive strings; this should fix some problems with ODBC and flag 512!
Fixed a core dump bug in the range optimizer.
Added --one-thread option to mysqld, for debugging with LinuxThreads (or glibc). (This replaces the -T32 flag)
Added DROP TABLE IF EXISTS to prevent an error from occurring if the table doesn't exist.
IF and EXISTS are now reserved words (they would have to be sooner or later).
Added lots of new options to mysqldump.
Server error messages are now in mysqld_error.h.
The server/client protocol now supports compression.
All bug fixes from MySQL Version 3.21.32.
Added new C API function mysql_ping().
Added new API functions mysql_init() and mysql_options(). You now MUST call mysql_init() before you call mysql_real_connect(). You don't have to call mysql_init() if you only use mysql_connect().
Added mysql_options(...,MYSQL_OPT_CONNECT_TIMEOUT,...) so you can set a timeout for connecting to a server.
Added --timeout option to mysqladmin, as a test of mysql_options().
Added AFTER column and FIRST options to ALTER TABLE ... ADD columns. This makes it possible to add a new column at some specific location within a row in an existing table.
WEEK() now takes an optional argument to allow handling of weeks when the week starts on Monday (some European countries). By default, WEEK() assumes the week starts on Sunday.
TIME columns weren't stored properly (bug in MySQL Version 3.22.0).
UPDATE now returns information about how many rows were matched and updated, and how many ``warnings'' occurred when doing the update.
Fixed incorrect result from FORMAT(-100,2).
ENUM and SET columns were compared in binary (case-sensitive) fashion; changed to be case-insensitive.
New (backward-compatible) connect protocol that allows you to specify the database to use when connecting, to get much faster connections to a specific database.
The mysql_real_connect() call is changed to:
mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, uint port, const char *unix_socket, uint client_flag)
Each connection is handled by its own thread, rather than by the master accept() thread. This fixes permanently the telnet bug that was a topic on the mail list some time ago.
All TCP/IP connections are now checked with backward-resolution of the hostname to get better security. mysqld now has a local hostname resolver cache so connections should actually be faster than before, even with this feature.
A site automatically will be blocked from future connections if someone repeatedly connects with an ``improper header'' (like when one uses telnet).
You can now refer to tables in different databases with references of the form tbl_name@db_name or db_name.tbl_name. This makes it possible to give a user read access to some tables and write access to others simply by keeping them in different databases!
Added --user option to mysqld, to allow it to run as another Unix user (if it is started as the Unix root user).
Added caching of users and access rights (for faster access rights checking)
Normal users (not anonymous ones) can change their password with mysqladmin password "new_password". This uses encrypted passwords that are not logged in the normal MySQL log!
All important string functions are now coded in assembler for x86 Linux machines. This gives a speedup of 10% in many cases.
For tables that have many columns, the column names are now hashed for much faster column name lookup (this will speed up some benchmark tests a lot!)
Some benchmarks are changed to get better individual timing. (Some loops were so short that a specific test took < 2 seconds. The loops have been changed to take about 20 seconds to make it easier to compare different databases. A test that took 1-2 seconds before now takes 11-24 seconds, which is much better)
Re-arranged SELECT code to handle some very specific queries involving group functions (like COUNT(*)) without a GROUP BY but with HAVING. The following now works:
mysql> SELECT COUNT(*) as C FROM table HAVING C > 1;
Changed the protocol for field functions to be faster and avoid some calls to malloc().
Added -T32 option to mysqld, for running all queries under the main thread. This makes it possible to debug mysqld under Linux with gdb!
Added optimization of not_null_column IS NULL (needed for some Access queries).
Allow STRAIGHT_JOIN to be used between two tables to force the optimizer to join them in a specific order.
String functions now return VARCHAR rather than CHAR and the column type is now VARCHAR for fields saved as VARCHAR. This should make the MyODBC driver better, but may break some old MySQL clients that don't handle FIELD_TYPE_VARCHAR the same way as FIELD_TYPE_CHAR.
CREATE INDEX and DROP INDEX are now implemented through ALTER TABLE. CREATE TABLE is still the recommended (fast) way to create indexes.
Added --set-variable option wait_timeout to mysqld.
Added time column to mysqladmin processlist to show how long a query has taken or how long a thread has slept.
Added lots of new variables to show variables and some new to show status.
Added new type YEAR. YEAR is stored in 1 byte with allowable values of 0, and 1901 to 2155.
Added new DATE type that is stored in 3 bytes rather than 4 bytes. All new tables are created with the new date type if you don't use the --old-protocol option to mysqld.
Fixed bug in record caches; for some queries, you could get Error from table handler: # on some operating systems.
Added --enable-assembler option to configure, for x86 machines (tested on Linux + gcc). This will enable assembler functions for the most important string functions for more speed!
Table of Contents
Version 3.21 is quite old now, and should be avoided if possible. This information is kept here for historical purposes only.
Fixed problem when sending SIGHUP to mysqld; mysqld core dumped when starting from boot on some systems.
Fixed problem with losing a little memory for some connections.
DELETE FROM tbl_name without a WHERE condition is now done the long way when you use LOCK TABLES or if the table is in use, to avoid race conditions.
INSERT INTO TABLE (timestamp_column) VALUES (NULL); didn't set timestamp.
Fixed some possible race conditions when doing many reopen/close on the same tables under heavy load! This can happen if you execute mysqladmin refresh often. This could in some very rare cases corrupt the header of the index file and cause error 126 or 138.
Fixed fatal bug in refresh() when running with the --skip-external-locking option. There was a ``very small'' time gap after a mysqladmin refresh when a table could be corrupted if one thread updated a table while another thread did mysqladmin refresh and another thread started a new update ont the same table before the first thread had finished. A refresh (or --flush-tables) will now not return until all used tables are closed!
SELECT DISTINCT with a WHERE clause that didn't match any rows returned a row in some contexts (bug only in 3.21.31).
GROUP BY + ORDER BY returned one empty row when no rows where found.
Fixed a bug in the range optimizer that wrote Use_count: Wrong count for ... in the error log file.
Fixed a sign extension problem for the TINYINT type on Irix.
Fixed problem with LEFT("constant_string",function).
Fixed problem with FIND_IN_SET().
LEFT JOIN core dumped if the second table is used with a constant WHERE/ON expression that uniquely identifies one record.
Fixed problems with DATE_FORMAT() and incorrect dates. DATE_FORMAT() now ignores '%' to make it possible to extend it more easily in the future.
mysql now returns an exit code > 0 if the query returned an error.
Saving of command-line history to file in mysql client. By Tommy Larsen <tommy@mix.hive.no>.
Fixed problem with empty lines that were ignored in mysql.cc.
Save the pid of the signal handler thread in the pid file instead of the pid of the main thread.
Added patch by <tommy@valley.ne.jp> to support Japanese characters SJIS and UJIS.
Changed safe_mysqld to redirect startup messages to 'hostname'.err instead of 'hostname'.log to reclaim file space on mysqladmin refresh.
ENUM always had the first entry as default value.
ALTER TABLE wrote two entries to the update log.
sql_acc() now closes the mysql grant tables after a reload to save table space and memory.
Changed LOAD DATA to use less memory with tables and BLOB columns.
Sorting on a function which made a division / 0 produced a wrong set in some cases.
Fixed SELECT problem with LEFT() when using the czech character set.
Fixed problem in isamchk; it couldn't repair a packed table in a very unusual case.
SELECT statements with & or | (bit functions) failed on columns with NULL values.
When comparing a field = field, where one of the fields was a part key, only the length of the part key was compared.
LOCK TABLES + DELETE from tbl_name never removed locks properly.
Fixed problem when grouping on an OR function.
Fixed permission problem with umask() and creating new databases.
Fixed permission problem on result file with SELECT ... INTO OUTFILE ...
Fixed problem in range optimizer (core dump) for a very complex query.
Fixed problem when using MIN(integer) or MAX(integer) in GROUP BY.
Fixed bug on Alpha when using integer keys. (Other keys worked on Alpha.)
Fixed bug in WEEK("XXXX-xx-01").
Fixed socket permission (clients couldn't connect to Unix socket on Linux).
Fixed bug in record caches; for some queries, you could get Error from table handler: # on some operating systems.
Added user level lock functions GET_LOCK(string,timeout), RELEASE_LOCK(string).
Added Opened_tables to show status.
Changed connect timeout to 3 seconds to make it somewhat harder for crackers to kill mysqld through telnet + TCP/IP.
Fixed bug in range optimizer when using WHERE key_part_1 >= something AND key_part_2 <= something_else.
Changed configure for detection of FreeBSD 3.0 9803xx and above
WHERE with string_col_key = constant_string didn't always find all rows if the column had many values differing only with characters of the same sort value (like e and e with an accent).
Strings keys looked up with 'ref' were not compared in case-sensitive fashion.
Added umask() to make log files non-readable for normal users.
Ignore users with old (8-byte) password on startup if not using --old-protocol option to mysqld.
SELECT which matched all key fields returned the values in the case of the matched values, not of the found values. (Minor problem.)
FROM_DAYS(0) now returns "0000-00-00".
In DATE_FORMAT(), PM and AM were swapped for hours 00 and 12.
Extended the default maximum key size to 256.
Fixed bug when using BLOB/TEXT in GROUP BY with many tables.
An ENUM field that is not declared NOT NULL has NULL as the default value. (Previously, the default value was the first enumeration value.)
Fixed bug in the join optimizer code when using many part keys on the same key: INDEX (Organization,Surname(35),Initials(35)).
Added some tests to the table order optimizer to get some cases with SELECT ... FROM many_tables much faster.
Added a retry loop around accept() to possibly fix some problems on some Linux machines.
Changed typedef 'string' to typedef 'my_string' for better portability.
You can now kill threads that are waiting on a disk-full condition.
Fixed some problems with UDF functions.
Added long options to isamchk. Try isamchk --help.
Fixed a bug when using 8 bytes long (alpha); filesort() didn't work. Affects DISTINCT, ORDER BY and GROUP BY on 64-bit processors.
Dynamic loadable functions. Based on source from Alexis Mikhailov.
You couldn't delete from a table if no one had done a SELECT on the table.
Fixed problem with range optimizer with many OR operators on key parts inside each other.
Recoded MIN() and MAX() to work properly with strings and HAVING.
Changed default umask value for new files from 0664 to 0660.
Fixed problem with LEFT JOIN and constant expressions in the ON part.
Added Italian error messages from <brenno@dewinter.com>.
configure now works better on OSF/1 (tested on 4.0D).
Added hooks to allow LIKE optimization with international character support.
Upgraded DBI to 0.93.
The following symbols are now reserved words: TIME, DATE, TIMESTAMP, TEXT, BIT, ENUM, NO, ACTION, CHECK, YEAR, MONTH, DAY, HOUR, MINUTE, SECOND, STATUS, VARIABLES.
Setting a TIMESTAMP to NULL in LOAD DATA INFILE ... didn't set the current time for the TIMESTAMP.
Fix BETWEEN to recognize binary strings. Now BETWEEN is case-sensitive.
Added --skip-thread-priority option to mysqld, for systems where mysqld's thread scheduling doesn't work properly (BSDI 3.1).
Added ODBC functions DAYNAME() and MONTHNAME().
Added function TIME_FORMAT(). This works like DATE_FORMAT(), but takes a time string ('HH:MM:SS') as argument.
Fixed unlikely(?) key optimizer bug when using OR operators of key parts inside AND expressions.
Added variables command to mysqladmin.
A lot of small changes to the binary releases.
Fixed a bug in the new protocol from MySQL Version 3.21.20.
Changed ALTER TABLE to work with Windows (Windows can't rename open files). Also fixed a couple of small bugs in the Windows version.
All standard MySQL clients are now ported to MySQL for Windows.
MySQL can now be started as a service on NT.
Starting with this version, all MySQL distributions will be configured, compiled and tested with crash-me and the benchmarks on the following platforms: SunOS 5.6 sun4u, SunOS 5.5.1 sun4u, SunOS 4.14 sun4c, SunOS 5.6 i86pc, Irix 6.3 mips5k, HP-UX 10.20 hppa, AIX 4.2.1 ppc, OSF/1 V4.0 alpha, FreeBSD 2.2.2 i86pc and BSDI 3.1 i386.
Fix COUNT(*) problems when the WHERE clause didn't match any records. (Bug from 3.21.17.)
Removed that NULL = NULL is true. Now you must use IS NULL or IS NOT NULL to test whether a value is NULL. (This is according to SQL-99 but may break old applications that are ported from mSQL.) You can get the old behavior by compiling with -DmSQL_COMPLIANT.
Fixed bug that core dumped when using many LEFT OUTER JOIN clauses.
Fixed bug in ORDER BY on string formula with possible NULL values.
Fixed problem in range optimizer when using <= on sub index.
Added functions DAYOFYEAR(), DAYOFMONTH(), MONTH(), YEAR(), WEEK(), QUARTER(), HOUR(), MINUTE(), SECOND() and FIND_IN_SET().
Added SHOW VARIABLES command.
Added support of ``long constant strings'' from SQL-99:
mysql> SELECT 'first ' 'second'; -> 'first second'
Upgraded Msql-Mysql-modules to 1.1825.
Upgraded mysqlaccess to 2.02.
Fixed problem with Russian character set and LIKE.
Ported to OpenBSD 2.1.
New Dutch error messages.
Fixed optimizer bug when using WHERE data_field = date_field2 AND date_field2 = constant.
Added SHOW STATUS command.
Removed manual.ps from the source distribution to make it smaller.
Changed the maximum table name and column name lengths from 32 to 64.
Aliases can now be of ``any'' length.
Fixed mysqladmin stat to return the right number of queries.
Changed protocol (downward compatible) to mark if a column has the AUTO_INCREMENT attribute or is a TIMESTAMP. This is needed for the new Java driver.
Added Hebrew sorting order by Zeev Suraski.
Solaris 2.6: Fixed configure bugs and increased maximum table size from 2G to 4G.
Upgraded DBD to 1.1823. This version implements mysql_use_result in DBD-Mysql.
Benchmarks updated for empress (by Luuk).
Fixed a case of slow range searching.
Configure fixes (Docs directory).
Added function REVERSE() (by Zeev Suraski).
Issue error message if client C functions are called in wrong order.
Added automatic reconnect to the libmysql.c library. If a write command fails, an automatic reconnect is done.
Small sort sets no longer use temporary files.
Upgraded DBI to 0.91.
Fixed a couple of problems with LEFT OUTER JOIN.
Added CROSS JOIN syntax. CROSS is now a reserved word.
Recoded yacc/bison stack allocation to be even safer and to allow MySQL to handle even bigger expressions.
Fixed a couple of problems with the update log.
ORDER BY was slow when used with key ranges.
Changed documentation string of --with-unix-socket-path to avoid confusion.
Added ODBC and SQL-99 style LEFT OUTER JOIN.
The following are new reserved words: LEFT, NATURAL, USING.
The client library now uses the value of the environment variable MYSQL_HOST as the default host if it's defined.
SELECT col_name, SUM(expr) now returns NULL for col_name when there are matching rows.
Fixed problem with comparing binary strings and BLOB values with ASCII characters over 127.
Fixed lock problem: when freeing a read lock on a table with multiple read locks, a thread waiting for a write lock would have been given the lock. This shouldn't affect data integrity, but could possibly make mysqld restart if one thread was reading data that another thread modified.
LIMIT offset,count didn't work in INSERT ... SELECT.
Optimized key block caching. This will be quicker than the old algorithm when using bigger key caches.
Added ODBC 2.0 & 3.0 functions POWER(), SPACE(), COT(), DEGREES(), RADIANS(), ROUND(2 arg) and TRUNCATE().
Warning: Incompatible change! LOCATE() parameters were swapped according to ODBC standard. Fixed.
Added function TIME_TO_SEC().
In some cases, default values were not used for NOT NULL fields.
Timestamp wasn't always updated properly in UPDATE SET ... statements.
Allow empty strings as default values for BLOB and TEXT, to be compatible with mysqldump.
Warning: Incompatible change! mysqlperl is now from Msql-Mysql-modules. This means that connect() now takes host, database, user, password arguments! The old version took host, database, password, user.
Allow DATE '1997-01-01', TIME '12:10:10' and TIMESTAMP '1997-01-01 12:10:10' formats required by SQL-99. Warning: Incompatible change! This has the unfortunate side-effect that you no longer can have columns named DATE, TIME or TIMESTAMP. :( Old columns can still be accessed through tablename.columnname!)
Changed Makefiles to hopefully work better with BSD systems. Also, manual.dvi is now included in the distribution to avoid having stupid make programs trying to rebuild it.
readline library upgraded to version 2.1.
A new sortorder german-1. That is a normal ISO-Latin1 with a german sort order.
Perl DBI/DBD is now included in the distribution. DBI is now the recommended way to connect to MySQL from Perl.
New portable benchmark suite with DBD, with test results from mSQL 2.0.3, MySQL, PostgreSQL 6.2.1 and Solid server 2.2.
crash-me is now included with the benchmarks; this is a Perl program designed to find as many limits as possible in an SQL server. Tested with mSQL, PostgreSQL, Solid and MySQL.
Fixed bug in range-optimizer that crashed MySQL on some queries.
Table and column name completion for mysql command-line tool, by Zeev Suraski and Andi Gutmans.
Added new command REPLACE that works like INSERT but replaces conflicting records with the new record. REPLACE INTO TABLE ... SELECT ... works also.
Added new commands CREATE DATABASE db_name and DROP DATABASE db_name.
Added RENAME option to ALTER TABLE: ALTER TABLE name RENAME TO new_name.
make_binary_distribution now includes libgcc.a in libmysqlclient.a. This should make linking work for people who don't have gcc.
Changed net_write() to my_net_write() because of a name conflict with Sybase.
New function DAYOFWEEK() compatible with ODBC.
Stack checking and bison memory overrun checking to make MySQL safer with weird queries.
Fixed a couple of small configure problems on some platforms.
Ported to SCO Openserver 5.0.4 with FSU Pthreads.
HP-UX 10.20 should work.
Added new function DATE_FORMAT().
Added NOT IN.
Added automatic removal of 'ODBC function conversions': {fn now() }
Handle ODBC 2.50.3 option flags.
Fixed comparison of DATE and TIME values with NULL.
Changed language name from germany to german to be consistent with the other language names.
Fixed sorting problem on functions returning a FLOAT. Previously, the values were converted to INT values before sorting.
Fixed slow sorting when sorting on key field when using key_column=constant.
Sorting on calculated DOUBLE values sorted on integer results instead.
mysql no longer requires a database argument.
Changed the place where HAVING should be. According to the SQL standards, it should be after GROUP BY but before ORDER BY. MySQL Version 3.20 incorrectly had it last.
Added Sybase command USE database to start using another database.
Added automatic adjusting of number of connections and table cache size if the maximum number of files that can be opened is less than needed. This should fix that mysqld doesn't crash even if you haven't done a ulimit -n 256 before starting mysqld.
Added lots of limit checks to make it safer when running with too little memory or when doing weird queries.
Added retry of interrupted reads and clearing of errno. This makes Linux systems much safer!
Fixed locking bug when using many aliases on the same table in the same SELECT.
Fixed bug with LIKE on number key.
New error message so you can check whether the connection was lost while the command was running or whether the connection was down from the start.
Added --table option to mysql to print in table format. Moved time and row information after query result. Added automatic reconnect of lost connections.
Added != as a synonym for <>.
Added function VERSION() to make easier logs.
New multi-user test tests/fork_test.pl to put some strain on the thread library.
Fixed ftruncate() call in MIT-pthreads. This made isamchk destroy the .ISM files on (Free)BSD 2.x systems.
Fixed broken __P_ patch in MIT-pthreads.
Many memory overrun checks. All string functions now return NULL if the returned string should be longer than max_allowed_packet bytes.
Changed the name of the INTERVAL type to ENUM, because INTERVAL is used in SQL-99.
In some cases, doing a JOIN + GROUP + INTO OUTFILE, the result wasn't grouped.
LIKE with '_' as last character didn't work. Fixed.
Added extended SQL-99 TRIM() function.
Added CURTIME().
Added ENCRYPT() function by Zeev Suraski.
Fixed better FOREIGN KEY syntax skipping. New reserved words: MATCH, FULL, PARTIAL.
mysqld now allows IP number and hostname for the --bind-address option.
Added SET CHARACTER SET cp1251_koi8 to enable conversions of data to and from the cp1251_koi8 character set.
Lots of changes for Windows 95 port. In theory, this version should now be easily portable to Windows 95.
Changed the CREATE COLUMN syntax of NOT NULL columns to be after the DEFAULT value, as specified in the SQL-99 standard. This will make mysqldump with NOT NULL and default values incompatible with MySQL Version 3.20.
Added many function name aliases so the functions can be used with ODBC or SQL-92 syntax.
Fixed syntax of ALTER TABLE tbl_name ALTER COLUMN col_name SET DEFAULT NULL.
Added CHAR and BIT as synonyms for CHAR(1).
Fixed core dump when updating as a user who has only SELECT privilege.
INSERT ... SELECT ... GROUP BY didn't work in some cases. An Invalid use of group function error occurred.
When using LIMIT, SELECT now always uses keys instead of record scan. This will give better performance on SELECT and a WHERE that matches many rows.
Added Russian error messages.
Configure changes.
MySQL now works with the new thread library on BSD/OS 3.0.
Added new group functions BIT_OR() and BIT_AND().
Added compatibility functions CHECK and REFERENCES. CHECK is now a reserved word.
Added ALL option to GRANT for better compatibility. (GRANT is still a dummy function.)
Added partly translated Dutch error messages.
Fixed bug in ORDER BY and GROUP BY with NULL columns.
Added function LAST_INSERT_ID() SQL function to retrieve last AUTO_INCREMENT value. This is intended for clients to ODBC that can't use the mysql_insert_id() API function, but can be used by any client.
Added --flush-logs option to mysqladmin.
Added command STATUS to mysql.
Fixed problem with ORDER BY/GROUP BY because of bug in gcc.
Fixed problem with INSERT ... SELECT ... GROUP BY.
New program mysqlaccess.
CREATE now supports all ODBC types and the mSQL TEXT type. All ODBC 2.5 functions are also supported (added REPEAT). This provides better portability.
Added text types TINYTEXT, TEXT, MEDIUMTEXT and LONGTEXT. These are actually BLOBtypes, but all searching is done in case-insensitive fashion.
All old BLOB fields are now TEXT fields. This only changes that all searching on strings is done in case-sensitive fashion. You must do an ALTER TABLE and change the datatype to BLOB if you want to have tests done in case-sensitive fashion.
Fixed some configure issues.
Made the locking code a bit safer. Fixed very unlikely deadlock situation.
Fixed a couple of bugs in the range optimizer. Now the new range benchmark test-select works.
Added --enable-unix-socket=pathname option to configure.
Fixed a couple of portability problems with include files.
Fixed bug in range calculation that could return empty set when searching on multiple key with only one entry (very rare).
Most things ported to FSU Pthreads, which should allow MySQL to run on SCO. See SCO.
Works now in Solaris 2.6.
Added handling of calculation of SUM() functions. For example, you can now use SUM(column)/COUNT(column).
Added handling of trigometric functions: PI(), ACOS(), ASIN(), ATAN(), COS(), SIN() and TAN().
New languages: Norwegian, Norwegian-ny and Portuguese.
Fixed parameter bug in net_print() in procedure.cc.
Fixed a couple of memory leaks.
Now allow also the old SELECT ... INTO OUTFILE syntax.
Fixed bug with GROUP BY and SELECT on key with many values.
mysql_fetch_lengths() sometimes returned incorrect lengths when you used mysql_use_result(). This affected at least some cases of mysqldump --quick.
Fixed bug in optimization of WHERE const op field.
Fixed problem when sorting on NULL fields.
Fixed a couple of 64-bit (Alpha) problems.
Added --pid-file=# option to mysqld.
Added date formatting to FROM_UNIXTIME(), originally by Zeev Suraski.
Fixed bug in BETWEEN in range optimizer (did only test = of the first argument).
Added machine-dependent files for MIT-pthreads i386-SCO. There is probably more to do to get this to work on SCO 3.5.
Changed Makefile.am to take advantage of Automake 1.2.
Added the beginnings of a benchmark suite.
Added more secure password handling.
Added new client function mysql_errno(), to get the error number of the error message. This makes error checking in the client much easier. This makes the new server incompatible with the 3.20.x server when running without --old-protocol. The client code is backward-compatible. More information can be found in the README file!
Fixed some problems when using very long, illegal names.
Fixed more portability issues (incorrect sigwait and sigset defines).
configure should now be able to detect the last argument to accept().
Should now work with FreeBSD 3.0 if used with FreeBSD-3.0-libc_r-1.0.diff, which can be found at http://www.mysql.com/downloads/os-freebsd.html.
Added new -O tmp_table_size=# option to mysqld.
New function FROM_UNIXTIME(timestamp) which returns a date string in 'YYYY-MM-DD HH:MM:SS' format.
New function SEC_TO_TIME(seconds) which returns a string in 'HH:MM:SS' format.
New function SUBSTRING_INDEX(), originally by Zeev Suraski.
Should now configure and compile on OSF/1 4.0 with the DEC compiler.
Configuration and compilation on BSD/OS 3.0 works, but due to some bugs in BSD/OS 3.0, mysqld doesn't work on it yet.
Configuration and compilation on FreeBSD 3.0 works, but I couldn't get pthread_create to work.
Added reverse check lookup of hostnames to get better security.
Fixed some possible buffer overflows if filenames that are too long are used.
mysqld doesn't accept hostnames that start with digits followed by a '.', because the hostname may look like an IP number.
Added --skip-networking option to mysqld, to allow only socket connections. (This will not work with MIT-pthreads!)
Added check of too long table names for alias.
Added check if database name is okay.
Added check if too long table names.
Removed incorrect free() that killed the server on CREATE DATABASE or DROP DATABASE.
Changed some mysqld -O options to better names.
Added -O join_cache_size=# option to mysqld.
Added -O max_join_size=# option to mysqld, to be able to set a limit how big queries (in this case big = slow) one should be able to handle without specifying SET SQL_BIG_SELECTS=1. A # = is about 10 examined records. The default is ``unlimited''.
When comparing a TIME, DATE, DATETIME or TIMESTAMP column to a constant, the constant is converted to a time value before performing the comparison. This will make it easier to get ODBC (particularly Access97) to work with the above types. It should also make dates easier to use and the comparisons should be quicker than before.
Applied patch from Jochen Wiedmann that allows query() in mysqlperl to take a query with \0 in it.
Storing a timestamp with a 2-digit year (YYMMDD) didn't work.
Fix that timestamp wasn't automatically updated if set in an UPDATE clause.
Now the automatic timestamp field is the FIRST timestamp field.
SELECT * INTO OUTFILE, which didn't correctly if the outfile already existed.
mysql now shows the thread ID when starting or doing a reconnect.
Changed the default sort buffer size from 2M to 1M.
The range optimizer is coded, but only 85% tested. It can be enabled with --new, but it crashes core a lot yet...
More portable. Should compile on AIX and alpha-digital. At least the isam library should be relatively 64-bit clean.
New isamchk which can detect and fix more problems.
New options for isamlog.
Using new version of Automake.
Many small portability changes (from the AIX and alpha-digital port) Better checking of pthread(s) library.
czech error messages by <snajdr@pvt.net>.
Decreased size of some buffers to get fewer problems on systems with little memory. Also added more checks to handle ``out of memory'' problems.
mysqladmin: you can now do mysqladmin kill 5,6,7,8 to kill multiple threads.
When the maximum connection limit is reached, one extra connection by a user with the process_acl privilege is granted.
Added -O backlog=# option to mysqld.
Increased maximum packet size from 512K to 1024K for client.
Almost all of the function code is now tested in the internal test suite.
ALTER TABLE now returns warnings from field conversions.
Port changed to 3306 (got it reserved from ISI).
Added a fix for Visual FoxBase so that any schema name from a table specification is automatically removed.
New function ASCII().
Removed function BETWEEN(a,b,c). Use the standard SQL syntax instead: expr BETWEEN expr AND expr.
MySQL no longer has to use an extra temporary table when sorting on functions or SUM() functions.
Fixed bug that you couldn't use tbl_name.field_name in UPDATE.
Fixed SELECT DISTINCT when using 'hidden group'. For example:
mysql> SELECT DISTINCT MOD(some_field,10) FROM test -> GROUP BY some_field;
Note: some_field is normally in the SELECT part. Standard SQL should require it.
New reserved words used: INTERVAL, EXPLAIN, READ, WRITE, BINARY.
Added ODBC function CHAR(num,...).
New operator IN. This uses a binary search to find a match.
New command LOCK TABLES tbl_name [AS alias] {READ|WRITE} ...
Added --log-update option to mysqld, to get a log suitable for incremental updates.
New command EXPLAIN SELECT ... to get information about how the optimizer will do the join.
For easier client code, the client should no longer use FIELD_TYPE_TINY_BLOB, FIELD_TYPE_MEDIUM_BLOB, FIELD_TYPE_LONG_BLOB or FIELD_TYPE_VAR_STRING (as previously returned by mysql_list_fields). You should instead use only FIELD_TYPE_BLOB or FIELD_TYPE_STRING. If you want exact types, you should use the command SHOW FIELDS.
Added varbinary syntax: 0x###### which can be used as a string (default) or a number.
FIELD_TYPE_CHAR is renamed to FIELD_TYPE_TINY.
Changed all fields to C++ classes.
Removed FORM struct.
Fields with DEFAULT values no longer need to be NOT NULL.
New field types:
ENUM | A string which can take only a couple of defined values. The value is stored as a 1-3 byte number that is mapped automatically to a string. This is sorted according to string positions! |
SET | A string which may have one or many string values separated with ','. The string is stored as a 1-, 2-, 3-, 4- or 8-byte number where each bit stands for a specific set member. This is sorted according to the unsigned value of the stored packed number. |
Now all function calculation is done with double or long long. This will provide the full 64-bit range with bit functions and fix some conversions that previously could result in precision losses. One should avoid using unsigned long long columns with full 64-bit range (numbers bigger than 9223372036854775807) because calculations are done with signed long long.
ORDER BY will now put NULL field values first. GROUP BY will also work with NULL values.
Full WHERE with expressions.
New range optimizer that can resolve ranges when some keypart prefix is constant. Example:
mysql> SELECT * FROM tbl_name -> WHERE key_part_1="customer" -> AND key_part_2>=10 AND key_part_2<=10;
Table of Contents
Version 3.20 is quite old now, and should be avoided if possible. This information is kept here for historical purposes only.
Changes from 3.20.18 to 3.20.32b are not documented here because the 3.21 release branched here. And the relevant changes are also documented as changes to the 3.21 version.
Added -p# (remove # directories from path) to isamlog. All files are written with a relative path from the database directory Now mysqld shouldn't crash on shutdown when using the --log-isam option.
New mysqlperl version. It is now compatible with msqlperl-0.63.
New DBD module available.
Added group function STD() (standard deviation).
The mysqld server is now compiled by default without debugging information. This will make the daemon smaller and faster.
Now one usually only has to specify the --basedir option to mysqld. All other paths are relative in a normal installation.
BLOB columns sometimes contained garbage when used with a SELECT on more than one table and ORDER BY.
Fixed that calculations that are not in GROUP BY work as expected (SQL-99 extension). Example:
mysql> SELECT id,id+1 FROM table GROUP BY id;
The test of using MYSQL_PWD was reversed. Now MYSQL_PWD is enabled as default in the default release.
Fixed conversion bug which caused mysqld to core dump with Arithmetic error on SPARC-386.
Added --unbuffered option to mysql, for new mysqlaccess.
When using overlapping (unnecessary) keys and join over many tables, the optimizer could get confused and return 0 records.
You can now use BLOB columns and the functions IS NULL and IS NOT NULL in the WHERE clause.
All communication packets and row buffers are now allocated dynamically on demand. The default value of max_allowed_packet is now 64K for the server and 512K for the client. This is mainly used to catch incorrect packets that could trash all memory. The server limit may be changed when it is started.
Changed stack usage to use less memory.
Changed safe_mysqld to check for running daemon.
The ELT() function is renamed to FIELD(). The new ELT() function returns a value based on an index: FIELD() is the inverse of ELT() Example: ELT(2,"A","B","C") returns "B". FIELD("B","A","B","C") returns 2.
COUNT(field), where field could have a NULL value, now works.
A couple of bugs fixed in SELECT ... GROUP BY.
Fixed memory overrun bug in WHERE with many unoptimizable brace levels.
Fixed some small bugs in the grant code.
If hostname isn't found by get_hostname, only the IP is checked. Previously, you got Access denied.
Inserts of timestamps with values didn't always work.
INSERT INTO ... SELECT ... WHERE could give the error Duplicated field.
Added some tests to safe_mysqld to make it ``safer''.
LIKE was case-sensitive in some places and case-insensitive in others. Now LIKE is always case-insensitive.
mysql.cc: Allow '#' anywhere on the line.
New command SET SQL_SELECT_LIMIT=#. See the FAQ for more details.
New version of the mysqlaccess script.
Change FROM_DAYS() and WEEKDAY() to also take a full TIMESTAMP or DATETIME as argument. Before they only took a number of type YYYYMMDD or YYMMDD.
Added new function UNIX_TIMESTAMP(timestamp_column).
More changes in MIT-pthreads to get them safer. Fixed also some link bugs at least in SunOS.
Changed mysqld to work around a bug in MIT-pthreads. This makes multiple small SELECT operations 20 times faster. Now lock_test.pl should work.
Added mysql_FetchHash(handle) to mysqlperl.
The mysqlbug script is now distributed built to allow for reporting bugs that appear during the build with it.
Changed libmysql.c to prefer getpwuid() instead of cuserid().
Fixed bug in SELECT optimizer when using many tables with the same column used as key to different tables.
Added new latin2 and Russian KOI8 character tables.
Added support for a dummy GRANT command to satisfy Powerbuilder.
Fixed fatal bug packets out of order when using MIT-pthreads.
Removed possible loop when a thread waits for command from client and fcntl() fails. Thanks to Mike Bretz for finding this bug.
Changed alarm loop in mysqld.cc because shutdown didn't always succeed in Linux.
Removed use of termbits from mysql.cc. This conflicted with glibc 2.0.
Fixed some syntax errors for at least BSD and Linux.
Fixed bug when doing a SELECT as superuser without a database.
Fixed bug when doing SELECT with group calculation to outfile.
If one gives -p or --password option to mysql without an argument, the user is solicited for the password from the tty.
Added default password from MYSQL_PWD (by Elmar Haneke).
Added command kill to mysqladmin to kill a specific MySQL thread.
Sometimes when doing a reconnect on a down connection this succeeded first on second try.
Fixed adding an AUTO_INCREMENT key with ALTER_TABLE.
AVG() gave too small value on some SELECT statements with GROUP BY and ORDER BY.
Added new DATETIME type (by Giovanni Maruzzelli <maruzz@matrice.it>).
Fixed that defining DONT_USE_DEFAULT_FIELDS works.
Changed to use a thread to handle alarms instead of signals on Solaris to avoid race conditions.
Fixed default length of signed numbers. (George Harvey <georgeh@pinacl.co.uk>.)
Allow anything for CREATE INDEX.
Add prezeros when packing numbers to DATE, TIME and TIMESTAMP.
Fixed a bug in OR of multiple tables (gave empty set).
Added many patches to MIT-pthreads. This fixes at least one lookup bug.
Added standard SQL-92 DATE and TIME types.
Fixed bug in SELECT with AND-OR levels.
Added support for Slovenian characters. The Contrib directory contains source and instructions for adding other character sets.
Fixed bug with LIMIT and ORDER BY.
Allow ORDER BY and GROUP BY on items that aren't in the SELECT list. (Thanks to Wim Bonis <bonis@kiss.de>, for pointing this out.)
Allow setting of timestamp values in INSERT.
Fixed bug with SELECT ... WHERE ... = NULL.
Added changes for glibc 2.0. To get glibc to work, you should add the gibc-2.0-sigwait-patch before compiling glibc.
Fixed bug in ALTER TABLE when changing a NOT NULL field to allow NULL values.
Added some SQL-92 synonyms as field types to CREATE TABLE. CREATE TABLE now allows FLOAT(4) and FLOAT(8) to mean FLOAT and DOUBLE.
New utility program mysqlaccess by <Yves.Carlier@rug.ac.be>. This program shows the access rights for a specific user and the grant rows that determine this grant.
Added WHERE const op field (by <bonis@kiss.de>).
When using SELECT ... INTO OUTFILE, all temporary tables are ISAM instead of HEAP to allow big dumps.
Changed date functions to be string functions. This fixed some ``funny'' side effects when sorting on dates.
Extended ALTER TABLE for SQL-92 compliance.
Some minor compatibility changes.
Added --port and --socket options to all utility programs and mysqld.
Fixed MIT-pthreads readdir_r(). Now mysqladmin create database and mysqladmin drop database should work.
Changed MIT-pthreads to use our tempnam(). This should fix the ``sort aborted'' bug.
Added sync of records count in sql_update. This fixed slow updates on first connection. (Thanks to Vaclav Bittner for the test.)
New insert type: INSERT INTO ... SELECT ...
MEDIUMBLOB fixed.
Fixed bug in ALTER TABLE and BLOB values.
SELECT ... INTO OUTFILE now creates the file in the current database directory.
DROP TABLE now can take a list of tables.
Oracle synonym DESCRIBE (DESC).
Changes to make_binary_distribution.
Added some comments to installation instructions about configure's C++ link test.
Added --without-perl option to configure.
Lots of small portability changes.
ALTER TABLE didn't copy null bit. As a result, fields that were allowed to have NULL values were always NULL.
CREATE didn't take numbers as DEFAULT.
Some compatibility changes for SunOS.
Removed config.cache from old distribution.
New commands: ALTER TABLE, SELECT ... INTO OUTFILE and LOAD DATA INFILE.
New function: NOW().
Added new field File_priv to mysql/user table.
New script add_file_priv which adds the new field File_priv to the user table. This script must be executed if you want to use the new SELECT ... INTO and LOAD DATA INFILE ... commands with a version of MySQL earlier than 3.20.7.
Fixed bug in locking code, which made lock_test.pl test fail.
New files NEW and BUGS.
Changed select_test.c and insert_test.c to include config.h.
Added status command to mysqladmin for short logging.
Increased maximum number of keys to 16 and maximum number of key parts to 15.
Use of sub keys. A key may now be a prefix of a string field.
Added -k option to mysqlshow, to get key information for a table.
Added long options to mysqldump.
Portable to more systems because of MIT-pthreads, which will be used automatically if configure cannot find a -lpthreads library.
Added GNU-style long options to almost all programs. Test with program --help.
Some shared library support for Linux.
The FAQ is now in .texi format and is available in .html, .txt and .ps formats.
Added new SQL function RAND([init]).
Changed sql_lex to handle \0 unquoted, but the client can't send the query through the C API, because it takes a str pointer. You must use mysql_real_query() to send the query.
Added API function mysql_get_client_info().
mysqld now uses the N_MAX_KEY_LENGTH from nisam.h as the maximum allowable key length.
The following now works:
mysql> SELECT filter_nr,filter_nr FROM filter ORDER BY filter_nr;
Previously, this resulted in the error: Column: 'filter_nr' in order clause is ambiguous.
mysql now outputs '\0', '\t', '\n' and '\\' when encountering ASCII 0, tab, newline or '\' while writing tab-separated output. This is to allow printing of binary data in a portable format. To get the old behavior, use -r (or --raw).
Added german error messages (60 of 80 error messages translated).
Added new API function mysql_fetch_lengths(MYSQL_RES *), which returns an array of column lengths (of type uint).
Fixed bug with IS NULL in WHERE clause.
Changed the optimizer a little to get better results when searching on a key part.
Added SELECT option STRAIGHT_JOIN to tell the optimizer that it should join tables in the given order.
Added support for comments starting with '--' in mysql.cc (Postgres syntax).
You can have SELECT expressions and table columns in a SELECT which are not used in the group part. This makes it efficient to implement lookups. The column that is used should be a constant for each group because the value is calculated only once for the first row that is found for a group.
mysql> SELECT id,lookup.text,SUM(*) FROM test,lookup -> WHERE test.id=lookup.id GROUP BY id;
Fixed bug in SUM(function) (could cause a core dump).
Changed AUTO_INCREMENT placement in the SQL query:
INSERT INTO table (auto_field) VALUES (0);
inserted 0, but it should insert an AUTO_INCREMENT value.
mysqlshow.c: Added number of records in table. Had to change the client code a little to fix this.
mysql now allows doubled '' or "" within strings for embedded ' or ".
New math functions: EXP(), LOG(), SQRT(), ROUND(), CEILING().
The configure source now compiles a thread-free client library -lmysqlclient. This is the only library that needs to be linked with client applications. When using the binary releases, you must link with -lmysql -lmysys -ldbug -lmystrings as before.
New readline library from bash-2.0.
LOTS of small changes to configure and makefiles (and related source).
It should now be possible to compile in another directory using VPATH. Tested with GNU Make 3.75.
safe_mysqld and mysql.server changed to be more compatible between the source and the binary releases.
LIMIT now takes one or two numeric arguments. If one argument is given, it indicates the maximum number of rows in a result. If two arguments are given, the first argument indicates the offset of the first row to return, the second is the maximum number of rows. With this it's easy to do a poor man's next page/previous page WWW application.
Changed name of SQL function FIELDS() to ELT(). Changed SQL function INTERVALL() to INTERVAL().
Made SHOW COLUMNS a synonym for SHOW FIELDS. Added compatibility syntax FRIEND KEY to CREATE TABLE. In MySQL, this creates a non-unique key on the given columns.
Added CREATE INDEX and DROP INDEX as compatibility functions. In MySQL, CREATE INDEX only checks if the index exists and issues an error if it doesn't exist. DROP INDEX always succeeds.
mysqladmin.c: added client version to version information.
Fixed core dump bug in sql_acl (core on new connection).
Removed host, user and db tables from database test in the distribution.
FIELD_TYPE_CHAR can now be signed (-128 to 127) or unsigned (0 to 255) Previously, it was always unsigned.
Bug fixes in CONCAT() and WEEKDAY().
Changed a lot of source to get mysqld to be compiled with SunPro compiler.
SQL functions must now have a '(' immediately after the function name (no intervening space). For example, 'USER(' is regarded as beginning a function call, and 'USER (' is regarded as an identifier USER followed by a '(', not as a function call.
The source distribution is done with configure and Automake. It will make porting much easier. The readline library is included in the distribution.
Separate client compilation: the client code should be very easy to compile on systems which don't have threads.
The old Perl interface code is automatically compiled and installed. Automatic compiling of DBD will follow when the new DBD code is ported.
Dynamic language support: mysqld can now be started with Swedish or English (default) error messages.
New functions: INSERT(), RTRIM(), LTRIM() and FORMAT().
mysqldump now works correctly for all field types (even AUTO_INCREMENT). The format for SHOW FIELDS FROM tbl_name is changed so the Type column contains information suitable for CREATE TABLE. In previous releases, some CREATE TABLE information had to be patched when re-creating tables.
Some parser bugs from 3.19.5 (BLOB and TIMESTAMP) are corrected. TIMESTAMP now returns different date information depending on its create length.
Changed parser to allow a database, table or field name to start with a number or '_'.
All old C code from Unireg changed to C++ and cleaned up. This makes the daemon a little smaller and easier to understand.
A lot of small bug fixes done.
New INSTALL files (not final version) and some information regarding porting.
Table of Contents
Version 3.19 is quite old now, and should be avoided if possible. This information is kept here for historical purposes only.
Some new functions, some more optimization on joins.
Should now compile clean on Linux (2.0.x).
Added functions DATABASE(), USER(), POW(), LOG10() (needed for ODBC).
In a WHERE with an ORDER BY on fields from only one table, the table is now preferred as first table in a multi-join.
HAVING and IS NULL or IS NOT NULL now works.
A group on one column and a sort on a group function (SUM(), AVG()...) didn't work together. Fixed.
mysqldump: Didn't send password to server.
Fixed horrible locking bug when inserting in one thread and reading in another thread.
Fixed one-off decimal bug. 1.00 was output as 1.0.
Added attribute 'Locked' to process list as information if a query is locked by another query.
Fixed full magic timestamp. Timestamp length may now be 14, 12, 10, 8, 6, 4 or 2 bytes.
Sort on some numeric functions could sort incorrectly on last number.
IF(arg,syntax_error,syntax_error) crashed.
Added functions CEILING(), ROUND(), EXP(), LOG() and SQRT().
Enhanced BETWEEN to handle strings.
Fixed SELECT with grouping on BLOB columns not to return incorrect BLOB info. Grouping, sorting and distinct on BLOB columns will not yet work as expected (probably it will group/sort by the first 7 characters in the BLOB). Grouping on formulas with a fixed string size (use MID() on a BLOB) should work.
When doing a full join (no direct keys) on multiple tables with BLOB fields, the BLOB was garbage on output.
Fixed DISTINCT with calculated columns.
This appendix will help you port MySQL to other operating systems. Do check the list of currently supported operating systems first. See Which OS. If you have created a new port of MySQL, please let us know so that we can list it here and on our web site (http://www.mysql.com/), recommending it to other users.
Note: If you create a new port of MySQL, you are free to copy and distribute it under the GPL license, but it does not make you a copyright holder of MySQL.
A working POSIX thread library is needed for the server. On Solaris 2.5 we use Sun PThreads (the native thread support in 2.4 and earlier versions is not good enough), on Linux we use LinuxThreads by Xavier Leroy, <Xavier.Leroy@inria.fr>.
The hard part of porting to a new Unix variant without good native thread support is probably to port MIT-pthreads. See mit-pthreads/README and Programming POSIX Threads (http://www.humanfactor.com/pthreads/).
Up to MySQL 4.0.2, the MySQL distribution included a patched version of Chris Provenzano's Pthreads from MIT (see the MIT Pthreads web page at http://www.mit.edu/afs/sipb/project/pthreads/ and a programming introduction at http://www.mit.edu:8001/people/proven/IAP_2000/). These can be used for some operating systems that do not have POSIX threads. See MIT-pthreads.
It is also possible to use another user level thread package named FSU Pthreads (see http://moss.csc.ncsu.edu/~mueller/pthreads/). This implementation is being used for the SCO port.
See the thr_lock.c and thr_alarm.c programs in the mysys directory for some tests/examples of these problems.
Both the server and the client need a working C++ compiler. We use gcc on many platforms. Other compilers that are known to work are SPARCworks, Sun Forte, Irix cc, HP-UX aCC, IBM AIX xlC_r), Intel ecc and Compaq cxx).
To compile only the client use ./configure --without-server.
There is currently no support for only compiling the server, nor is it likly to be added unless someone has a good reason for it.
If you want/need to change any Makefile or the configure script you will also need GNU Automake and Autoconf. See Installing source tree.
All steps needed to remake everything from the most basic files.
/bin/rm */.deps/*.P /bin/rm -f config.cache aclocal autoheader aclocal automake autoconf ./configure --with-debug=full --prefix='your installation directory' # The makefiles generated above need GNU make 3.75 or newer. # (called gmake below) gmake clean all install init-db
If you run into problems with a new port, you may have to do some debugging of MySQL! See Debugging server.
Note: Before you start debugging mysqld, first get the test programs mysys/thr_alarm and mysys/thr_lock to work. This will ensure that your thread installation has even a remote chance to work!
Table of Contents
If you are using some functionality that is very new in MySQL, you can try to run mysqld with the --skip-new (which will disable all new, potentially unsafe functionality) or with --safe-mode which disables a lot of optimization that may cause problems. See Crashing.
If mysqld doesn't want to start, you should check that you don't have any my.cnf files that interfere with your setup! You can check your my.cnf arguments with mysqld --print-defaults and avoid using them by starting with mysqld --no-defaults ....
If mysqld starts to eat up CPU or memory or if it ``hangs'', you can use mysqladmin processlist status to find out if someone is executing a query that takes a long time. It may be a good idea to run mysqladmin -i10 processlist status in some window if you are experiencing performance problems or problems when new clients can't connect.
The command mysqladmin debug will dump some information about locks in use, used memory and query usage to the mysql log file. This may help solve some problems. This command also provides some useful information even if you haven't compiled MySQL for debugging!
If the problem is that some tables are getting slower and slower you should try to optimize the table with OPTIMIZE TABLE or myisamchk. See MySQL Database Administration. You should also check the slow queries with EXPLAIN.
You should also read the OS-specific section in this manual for problems that may be unique to your environment. See Operating System Specific Notes.
If you have some very specific problem, you can always try to debug MySQL. To do this you must configure MySQL with the --with-debug or the --with-debug=full option. You can check whether MySQL was compiled with debugging by doing: mysqld --help. If the --debug flag is listed with the options then you have debugging enabled. mysqladmin ver also lists the mysqld version as mysql ... --debug in this case.
If you are using gcc or egcs, the recommended configure line is:
CC=gcc CFLAGS="-O2" CXX=gcc CXXFLAGS="-O2 -felide-constructors \ -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql \ --with-debug --with-extra-charsets=complex
This will avoid problems with the libstdc++ library and with C++ exceptions (many compilers have problems with C++ exceptions in threaded code) and compile a MySQL version with support for all character sets.
If you suspect a memory overrun error, you can configure MySQL with --with-debug=full, which will install a memory allocation (SAFEMALLOC) checker. However, running with SAFEMALLOC is quite slow, so if you get performance problems you should start mysqld with the --skip-safemalloc option. This will disable the memory overrun checks for each call to malloc() and free().
If mysqld stops crashing when you compile it with --with-debug, you have probably found a compiler bug or a timing bug within MySQL. In this case you can try to add -g to the CFLAGS and CXXFLAGS variables above and not use --with-debug. If mysqld now dies, you can at least attach to it with gdb or use gdb on the core file to find out what happened.
When you configure MySQL for debugging you automatically enable a lot of extra safety check functions that monitor the health of mysqld. If they find something ``unexpected,'' an entry will be written to stderr, which safe_mysqld directs to the error log! This also means that if you are having some unexpected problems with MySQL and are using a source distribution, the first thing you should do is to configure MySQL for debugging! (The second thing is to send mail to a MySQL mailing list and ask for help. See Mailing-list. Please use the mysqlbug script for all bug reports or questions regarding the MySQL version you are using!
In the Windows MySQL distribution, mysqld.exe is by default compiled with support for trace files.
If the mysqld server doesn't start or if you can cause the mysqld server to crash quickly, you can try to create a trace file to find the problem.
To do this you have to have a mysqld that is compiled for debugging. You can check this by executing mysqld -V. If the version number ends with -debug, it's compiled with support for trace files.
Start the mysqld server with a trace log in /tmp/mysqld.trace (or C:\mysqld.trace on Windows):
mysqld --debug
On Windows you should also use the --standalone flag to not start mysqld as a service:
In a console window do:
mysqld --debug --standalone
After this, you can use the mysql.exe command-line tool in a second console window to reproduce the problem. You can take down the above mysqld server with mysqladmin shutdown.
Note that the trace file will get very big! If you want to have a smaller trace file, you can use something like:
mysqld --debug=d,info,error,query,general,where:O,/tmp/mysqld.trace
which only prints information with the most interesting tags in /tmp/mysqld.trace.
If you make a bug report about this, please only send the lines from the trace file to the appropriate mailing list where something seems to go wrong! If you can't locate the wrong place, you can ftp the trace file, together with a full bug report, to ftp://support.mysql.com/pub/mysql/secret/ so that a MySQL developer can take a look a this.
The trace file is made with the DBUG package by Fred Fish. See The DBUG package.
On most systems you can also start mysqld from gdb to get more information if mysqld crashes.
With some older gdb versions on Linux you must use run --one-thread if you want to be able to debug mysqld threads. In this case you can only have one thread active at a time. We recommend you to upgrade to gdb 5.1 ASAP as thread debugging works much better with this version!
When running mysqld under gdb, you should disable the stack trace with --skip-stack-trace to be able to catch segfaults within gdb.
In MySQL 4.0.14 and above you should use the --gdb option to mysqld. This will install an interrupt handler for SIGINT (needed to stop mysqld with ^C to set breakpoints) and disable stack tracing and core file handling.
It's very hard to debug MySQL under gdb if you do a lot of new connections the whole time as gdb doesn't free the memory for old threads. You can avoid this problem by starting mysqld with -O thread_cache_size= 'max_connections +1'. In most cases just using -O thread_cache_size=5' will help a lot!
If you want to get a core dump on Linux if mysqld dies with a SIGSEGV signal, you can start mysqld with the --core-file option. This core file can be used to make a backtrace that may help you find out why mysqld died:
shell> gdb mysqld core gdb> backtrace full gdb> exit
See Crashing.
If you are using gdb 4.17.x or above on Linux, you should install a .gdb file, with the following information, in your current directory:
set print sevenbit off handle SIGUSR1 nostop noprint handle SIGUSR2 nostop noprint handle SIGWAITING nostop noprint handle SIGLWP nostop noprint handle SIGPIPE nostop handle SIGALRM nostop handle SIGHUP nostop handle SIGTERM nostop noprint
If you have problems debugging threads with gdb, you should download gdb 5.x and try this instead. The new gdb version has very improved thread handling!
Here is an example how to debug mysqld:
shell> gdb /usr/local/libexec/mysqld gdb> run ... backtrace full # Do this when mysqld crashes
Include the above output in a mail generated with mysqlbug and mail this to the general MySQL mailing list. See Mailing-list.
If mysqld hangs you can try to use some system tools like strace or /usr/proc/bin/pstack to examine where mysqld has hung.
strace /tmp/log libexec/mysqld
If you are using the Perl DBI interface, you can turn on debugging information by using the trace method or by setting the DBI_TRACE environment variable.
On some operating systems, the error log will contain a stack trace if mysqld dies unexpectedly. You can use this to find out where (and maybe why) mysqld died. See Error log. To get a stack trace, you must not compile mysqld with the -fomit-frame-pointer option to gcc. See Compiling for debugging.
If the error file contains something like the following:
mysqld got signal 11; The manual section 'Debugging a MySQL server' tells you how to use a stack trace and/or the core file to produce a readable backtrace that may help in finding out why mysqld died Attemping backtrace. You can use the following information to find out where mysqld died. If you see no messages after this, something went terribly wrong stack range sanity check, ok, backtrace follows 0x40077552 0x81281a0 0x8128f47 0x8127be0 0x8127995 0x8104947 0x80ff28f 0x810131b 0x80ee4bc 0x80c3c91 0x80c6b43 0x80c1fd9 0x80c1686
you can find where mysqld died by doing the following:
Copy the above numbers to a file, for example mysqld.stack.
Make a symbol file for the mysqld server:
nm -n libexec/mysqld > /tmp/mysqld.sym
Note that most MySQL binary distributions (except for the "debug" packages, where this information is included inside of the binaries themselves) already ship with the above file, named mysqld.sym.gz. In this case you can simply unpack it by doing:
gunzip < bin/mysqld.sym.gz > /tmp/mysqld.sym
Execute resolve_stack_dump -s /tmp/mysqld.sym -n mysqld.stack.
This will print out where mysqld died. If this doesn't help you find out why mysqld died, you should make a bug report and include the output from the above command with the bug report.
Note however that in most cases it will not help us to just have a stack trace to find the reason for the problem. To be able to locate the bug or provide a workaround, we would in most cases need to know the query that killed mysqld and preferable a test case so that we can repeat the problem! See Bug reports.
Note that before starting mysqld with --log you should check all your tables with myisamchk. See MySQL Database Administration.
If mysqld dies or hangs, you should start mysqld with --log. When mysqld dies again, you can examine the end of the log file for the query that killed mysqld.
If you are using --log without a file name, the log is stored in the database directory as 'hostname'.log In most cases it's the last query in the log file that killed mysqld, but if possible you should verify this by restarting mysqld and executing the found query from the mysql command-line tools. If this works, you should also test all complicated queries that didn't complete.
You can also try the command EXPLAIN on all SELECT statements that takes a long time to ensure that mysqld is using indexes properly. See EXPLAIN.
You can find the queries that take a long time to execute by starting mysqld with --log-slow-queries. See Slow query log.
If you find the text mysqld restarted in the error log file (normally named hostname.err) you have probably found a query that causes mysqld to fail. If this happens you should check all your tables with myisamchk (see MySQL Database Administration), and test the queries in the MySQL log files to see if one doesn't work. If you find such a query, try first upgrading to the newest MySQL version. If this doesn't help and you can't find anything in the mysql mail archive, you should report the bug to a MySQL mailing list. The mailing lists are described at http://lists.mysql.com/, which also has links to online list archives.
If you have started mysqld with myisam-recover, MySQL will automatically check and try to repair MyISAM tables if they are marked as 'not closed properly' or 'crashed'. If this happens, MySQL will write an entry in the hostname.err file 'Warning: Checking table ...' which is followed by Warning: Repairing table if the table needs to be repaired. If you get a lot of these errors, without mysqld having died unexpectedly just before, then something is wrong and needs to be investigated further. See Server options.
It's not a good sign if mysqld did died unexpectedly, but in this case one shouldn't investigate the Checking table... messages but instead try to find out why mysqld died.
If you get corrupted tables or if mysqld always fails after some update commands, you can test if this bug is reproducible by doing the following:
Take down the MySQL daemon (with mysqladmin shutdown).
Make a backup of the tables (to guard against the very unlikely case that the repair will do something bad).
Check all tables with myisamchk -s database/*.MYI. Repair any wrong tables with myisamchk -r database/table.MYI.
Make a second backup of the tables.
Remove (or move away) any old log files from the MySQL data directory if you need more space.
Start mysqld with --log-bin. See Binary log. If you want to find a query that crashes mysqld, you should use --log --log-bin.
When you have gotten a crashed table, stop the mysqld server.
Restore the backup.
Restart the mysqld server without --log-bin
Re-execute the commands with mysqlbinlog update-log-file | mysql. The update log is saved in the MySQL database directory with the name hostname-bin.#.
If the tables are corrupted again or you can get mysqld to die with the above command, you have found reproducible bug that should be easy to fix! FTP the tables and the binary log to ftp://support.mysql.com/pub/mysql/secret/ and enter it into our bugs system at http://bugs.mysql.com/. If you are a support customer), you can also <support@mysql.com> to alert the MySQL team about the problem and have it fixed as soon as possible.
You can also use the script mysql_find_rows to just execute some of the update statements if you want to narrow down the problem.
To be able to debug a MySQL client with the integrated debug package, you should configure MySQL with --with-debug or --with-debug=full. See configure options.
Before running a client, you should set the MYSQL_DEBUG environment variable:
shell> MYSQL_DEBUG=d:t:O,/tmp/client.trace shell> export MYSQL_DEBUG
This causes clients to generate a trace file in /tmp/client.trace.
If you have problems with your own client code, you should attempt to connect to the server and run your query using a client that is known to work. Do this by running mysql in debugging mode (assuming you have compiled MySQL with debugging on):
shell> mysql --debug=d:t:O,/tmp/client.trace
This will provide useful information in case you mail a bug report. See Bug reports.
If your client crashes at some 'legal' looking code, you should check that your mysql.h include file matches your mysql library file. A very common mistake is to use an old mysql.h file from an old MySQL installation with new MySQL library.
The MySQL server and most MySQL clients are compiled with the DBUG package originally made by Fred Fish. When one has configured MySQL for debugging, this package makes it possible to get a trace file of what the program is debugging. See Making trace files.
One uses the debug package by invoking the program with the --debug="..." or the -#... option.
Most MySQL programs has a default debug string that will be used if you don't specify an option to --debug. The default trace file is usually /tmp/programname.trace on Unix and \programname.trace on Windows.
The debug control string is a sequence of colon-separated fields as follows:
<field_1>:<field_2>:...:<field_N>
Each field consists of a mandatory flag character followed by an optional "," and comma-separated list of modifiers:
flag[,modifier,modifier,...,modifier]
The currently recognized flag characters are:
Flag | Description |
d | Enable output from DBUG_<N> macros for the current state. May be followed by a list of keywords which selects output only for the DBUG macros with that keyword. An empty list of keywords implies output for all macros. |
D | Delay after each debugger output line. The argument is the number of tenths of seconds to delay, subject to machine capabilities. That is, -#D,20 is delay two seconds. |
f | Limit debugging and/or tracing, and profiling to the list of named functions. Note that a null list will disable all functions. The appropriate "d" or "t" flags must still be given, this flag only limits their actions if they are enabled. |
F | Identify the source file name for each line of debug or trace output. |
i | Identify the process with the PID or thread ID for each line of debug or trace output. |
g | Enable profiling. Create a file called 'dbugmon.out' containing information that can be used to profile the program. May be followed by a list of keywords that select profiling only for the functions in that list. A null list implies that all functions are considered. |
L | Identify the source file line number for each line of debug or trace output. |
n | Print the current function nesting depth for each line of debug or trace output. |
N | Number each line of dbug output. |
o | Redirect the debugger output stream to the specified file. The default output is stderr. |
O | As o but the file is really flushed between each write. When needed the file is closed and reopened between each write. |
p | Limit debugger actions to specified processes. A process must be identified with the DBUG_PROCESS macro and match one in the list for debugger actions to occur. |
P | Print the current process name for each line of debug or trace output. |
r | When pushing a new state, do not inherit the previous state's function nesting level. Useful when the output is to start at the left margin. |
S | Do function _sanity(_file_,_line_) at each debugged function until _sanity() returns something that differs from 0. (Mostly used with safemalloc to find memory leaks) |
t | Enable function call/exit trace lines. May be followed by a list (containing only one modifier) giving a numeric maximum trace level, beyond which no output will occur for either debugging or tracing macros. The default is a compile time option. |
Some examples of debug control strings which might appear on a shell command-line (the "-#" is typically used to introduce a control string to an application program) are:
-#d:t -#d:f,main,subr1:F:L:t,20 -#d,input,output,files:n -#d:t:i:O,\\mysqld.trace
In MySQL, common tags to print (with the d option) are: enter,exit,error,warning,info and loop.
Currently MySQL only supports table locking for ISAM/MyISAM and HEAP tables, page-level locking for BDB tables and row-level locking for InnoDB tables. See Internal locking. With MyISAM tables one can freely mix INSERT and SELECT without locks, if the INSERT statements are non-conflicting (that is, whenever they append to the end of the table file rather than filling freespace from deleted rows/data).
Starting in version 3.23.33, you can analyse the table lock contention on your system by checking Table_locks_waited and Table_locks_immediate environment variables.
To decide if you want to use a table type with row-level locking, you will want to look at what the application does and what the select/update pattern of the data is.
Pros for row locking:
Fewer lock conflicts when accessing different rows in many threads.
Fewer changes for rollbacks.
Makes it possible to lock a single row a long time.
Cons:
Takes more memory than page level or table locks.
Is slower than page level or table locks when used on a big part of the table, because one has to do many more locks.
Is definitely much worse than other locks if you do often do GROUP BY on a large part of the data or if one has to often scan the whole table.
With higher level locks one can also more easily support locks of different types to tune the application as the lock overhead is less notable as for row level locks.
Table locks are superior to page level / row level locks in the following cases:
Mostly reads
Read and updates on strict keys; this is where one updates or deletes a row that can be fetched with one key read:
UPDATE table_name SET column=value WHERE unique_key# DELETE FROM table_name WHERE unique_key=#
SELECT combined with INSERT (and very few UPDATE and DELETE statements).
Many scans / GROUP BY on the whole table without any writers.
Other options than row / page level locking:
Versioning (like we use in MySQL for concurrent inserts) where you can have one writer at the same time as many readers. This means that the database/table supports different views for the data depending on when one started to access it. Other names for this are time travel, copy on write or copy on demand.
Copy on demand is in many case much better than page or row level locking; the worst case does, however, use much more memory than when using normal locks.
Instead of using row level locks one can use application level locks (like get_lock/release_lock in MySQL). This works only in well-behaved applications.
In many cases one can do an educated guess which locking type is best for the application, but generally it's very hard to say that a given lock type is better than another; everything depends on the application and different part of the application may require different lock types.
Here are some tips about locking in MySQL:
Most web applications do lots of selects, very few deletes, updates mainly on keys, and inserts in some specific tables. The base MySQL setup is very well tuned for this.
Concurrent users are not a problem if you don't mix updates with selects that need to examine many rows in the same table.
If you mix inserts and deletes on the same table, then INSERT DELAYED may be of great help.
You can also use LOCK TABLES to speed up things (many updates within a single lock is much faster than updates without locks). Splitting thing to different tables will also help.
If you encounter speed problems with the table locks in MySQL, you may be able to solve these by converting some of your tables to InnoDB or BDB tables. See InnoDB. See BDB.
The optimization section in the manual covers many different aspects of how to tune applications. See Tips.
I have tried to use the RTS thread packages with MySQL but stumbled on the following problems:
They use an old version of a lot of POSIX calls and it is very tedious to make wrappers for all functions. I am inclined to think that it would be easier to change the thread libraries to the newest POSIX specification.
Some wrappers are already written. See mysys/my_pthread.c for more info.
At least the following should be changed:
pthread_get_specific should use one argument. sigwait should take two arguments. A lot of functions (at least pthread_cond_wait, pthread_cond_timedwait()) should return the error code on error. Now they return -1 and set errno.
Another problem is that user-level threads use the ALRM signal and this aborts a lot of functions (read, write, open...). MySQL should do a retry on interrupt on all of these but it is not that easy to verify it.
The biggest unsolved problem is the following:
To get thread-level alarms I changed mysys/thr_alarm.c to wait between alarms with pthread_cond_timedwait(), but this aborts with error EINTR. I tried to debug the thread library as to why this happens, but couldn't find any easy solution.
If someone wants to try MySQL with RTS threads I suggest the following:
Change functions MySQL uses from the thread library to POSIX. This shouldn't take that long.
Compile all libraries with the -DHAVE_rts_threads.
Compile thr_alarm.
If there are some small differences in the implementation, they may be fixed by changing my_pthread.h and my_pthread.c.
Run thr_alarm. If it runs without any ``warning'', ``error'' or aborted messages, you are on the right track. Here is a successful run on Solaris:
Main thread: 1 Thread 0 (5) started Thread: 5 Waiting process_alarm Thread 1 (6) started Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 1 (1) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 2 (2) sec Thread: 6 Simulation of no alarm needed Thread: 6 Slept for 0 (3) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 4 (4) sec Thread: 6 Waiting process_alarm thread_alarm Thread: 5 Slept for 10 (10) sec Thread: 5 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 5 (5) sec Thread: 6 Waiting process_alarm process_alarm ... thread_alarm Thread: 5 Slept for 0 (1) sec end
MySQL is very dependent on the thread package used. So when choosing a good platform for MySQL, the thread package is very important.
There are at least three types of thread packages:
User threads in a single process. Thread switching is managed with alarms and the threads library manages all non-thread-safe functions with locks. Read, write and select operations are usually managed with a thread-specific select that switches to another thread if the running threads have to wait for data. If the user thread packages are integrated in the standard libs (FreeBSD and BSDI threads) the thread package requires less overhead than thread packages that have to map all unsafe calls (MIT-pthreads, FSU Pthreads and RTS threads). In some environments (for example, SCO), all system calls are thread-safe so the mapping can be done very easily (FSU Pthreads on SCO). Downside: All mapped calls take a little time and it's quite tricky to be able to handle all situations. There are usually also some system calls that are not handled by the thread package (like MIT-pthreads and sockets). Thread scheduling isn't always optimal.
User threads in separate processes. Thread switching is done by the kernel and all data are shared between threads. The thread package manages the standard thread calls to allow sharing data between threads. LinuxThreads is using this method. Downside: Lots of processes. Thread creating is slow. If one thread dies the rest are usually left hanging and you must kill them all before restarting. Thread switching is somewhat expensive.
Kernel threads. Thread switching is handled by the thread library or the kernel and is very fast. Everything is done in one process, but on some systems, ps may show the different threads. If one thread aborts, the whole process aborts. Most system calls are thread-safe and should require very little overhead. Solaris, HP-UX, AIX and OSF/1 have kernel threads.
In some systems kernel threads are managed by integrating user level threads in the system libraries. In such cases, the thread switching can only be done by the thread library and the kernel isn't really ``thread aware''.
Here is a list of all the environment variables that are used directly or indirectly by MySQL. Most of these can also be found in other places in this manual.
Note that any options on the command-line take precedence over values specified in configuration files and environment variables, and values in configuration files take precedence over values in environment variables.
In many cases it's preferable to use a configure file instead of environment variables to modify the behavior of MySQL. See Option files.
Variable | Description |
CXX | Set this to your C++ compiler when running configure. |
CC | Set this to your C compiler when running configure. |
CFLAGS | Flags for your C compiler when running configure. |
CXXFLAGS | Flags for your C++ compiler when running configure. |
DBI_USER | The default username for Perl DBI. |
DBI_TRACE | Used when tracing Perl DBI. |
HOME | The default path for the mysql history file is $HOME/.mysql_history. |
LD_RUN_PATH | Used to specify where your libmysqlclient.so is. |
MYSQL_DEBUG | Debug-trace options when debugging. |
MYSQL_HISTFILE | The path to the mysql history file. |
MYSQL_HOST | Default hostname used by the mysql command-line client. |
MYSQL_PS1 | Command prompt to use in the mysql command-line client. See mysql, The Command-line Tool. |
MYSQL_PWD | The default password when connecting to mysqld. Note that use of this is insecure! |
MYSQL_TCP_PORT | The default TCP/IP port. |
MYSQL_UNIX_PORT | The default socket; used for connections to localhost. |
PATH | Used by the shell to finds the MySQL programs. |
TMPDIR | The directory where temporary tables/files are created. |
TZ | This should be set to your local time zone. See Timezone problems. |
UMASK_DIR | The user-directory creation mask when creating directories. Note that this is ANDed with UMASK! |
UMASK | The user-file creation mask when creating files. |
USER | The default user on Windows to use when connecting to mysqld. |
A regular expression (regex) is a powerful way of specifying a complex search.
MySQL uses Henry Spencer's implementation of regular expressions, which is aimed at conformance with POSIX 1003.2. MySQL uses the extended version.
This is a simplistic reference that skips the details. To get more exact information, see Henry Spencer's regex(7) manual page that is included in the source distribution. See Credits.
A regular expression describes a set of strings. The simplest regexp is one that has no special characters in it. For example, the regexp hello matches hello and nothing else.
Non-trivial regular expressions use certain special constructs so that they can match more than one string. For example, the regexp hello|word matches either the string hello or the string word.
As a more complex example, the regexp B[an]*s matches any of the strings Bananas, Baaaaas, Bs, and any other string starting with a B, ending with an s, and containing any number of a or n characters in between.
A regular expression may use any of the following special characters/constructs:
^ |
Match the beginning of a string.
mysql> SELECT "fo\nfo" REGEXP "^fo$"; -> 0 mysql> SELECT "fofo" REGEXP "^fo"; -> 1 | ||||||||||||||||
$ |
Match the end of a string.
mysql> SELECT "fo\no" REGEXP "^fo\no$"; -> 1 mysql> SELECT "fo\no" REGEXP "^fo$"; -> 0 | ||||||||||||||||
. |
Match any character (including newline).
mysql> SELECT "fofo" REGEXP "^f.*"; -> 1 mysql> SELECT "fo\nfo" REGEXP "^f.*"; -> 1 | ||||||||||||||||
a* |
Match any sequence of zero or more a characters.
mysql> SELECT "Ban" REGEXP "^Ba*n"; -> 1 mysql> SELECT "Baaan" REGEXP "^Ba*n"; -> 1 mysql> SELECT "Bn" REGEXP "^Ba*n"; -> 1 | ||||||||||||||||
a+ |
Match any sequence of one or more a characters.
mysql> SELECT "Ban" REGEXP "^Ba+n"; -> 1 mysql> SELECT "Bn" REGEXP "^Ba+n"; -> 0 | ||||||||||||||||
a? |
Match either zero or one a character.
mysql> SELECT "Bn" REGEXP "^Ba?n"; -> 1 mysql> SELECT "Ban" REGEXP "^Ba?n"; -> 1 mysql> SELECT "Baan" REGEXP "^Ba?n"; -> 0 | ||||||||||||||||
de|abc |
Match either of the sequences de or abc.
mysql> SELECT "pi" REGEXP "pi|apa"; -> 1 mysql> SELECT "axe" REGEXP "pi|apa"; -> 0 mysql> SELECT "apa" REGEXP "pi|apa"; -> 1 mysql> SELECT "apa" REGEXP "^(pi|apa)$"; -> 1 mysql> SELECT "pi" REGEXP "^(pi|apa)$"; -> 1 mysql> SELECT "pix" REGEXP "^(pi|apa)$"; -> 0 | ||||||||||||||||
(abc)* |
Match zero or more instances of the sequence abc.
mysql> SELECT "pi" REGEXP "^(pi)*$"; -> 1 mysql> SELECT "pip" REGEXP "^(pi)*$"; -> 0 mysql> SELECT "pipi" REGEXP "^(pi)*$"; -> 1 | ||||||||||||||||
{1} , {2,3} | The is a more general way of writing regexps that match many occurrences of the previous atom. |
| |||||||||||||||
[a-dX] , [^a-dX] |
Matches
any character which is (or is not, if ^ is used) either a, b,
c, d or X. To include a literal ] character,
it must immediately follow the opening bracket [. To include a
literal - character, it must be written first or last. So
[0-9] matches any decimal digit. Any character that does not have
a defined meaning inside a [] pair has no special meaning and
matches only itself.
mysql> SELECT "aXbc" REGEXP "[a-dXYZ]"; -> 1 mysql> SELECT "aXbc" REGEXP "^[a-dXYZ]$"; -> 0 mysql> SELECT "aXbc" REGEXP "^[a-dXYZ]+$"; -> 1 mysql> SELECT "aXbc" REGEXP "^[^a-dXYZ]+$"; -> 0 mysql> SELECT "gheis" REGEXP "^[^a-dXYZ]+$"; -> 1 mysql> SELECT "gheisa" REGEXP "^[^a-dXYZ]+$"; -> 0 | ||||||||||||||||
[[.characters.]] | The sequence of characters of that collating element. characters is either a single character or a character name like newline. You can find the full list of character names in regexp/cname.h. | ||||||||||||||||
[=character_class=] | An equivalence class, standing for the sequences of characters of all collating elements equivalent to that one, including itself. For example, if o and (+) are the members of an equivalence class, then [[=o=]], [[=(+)=]], and [o(+)] are all synonymous. An equivalence class may not be an endpoint of a range. | ||||||||||||||||
[:character_class:] | Within a bracket expression, the name of a character class enclosed in [: and :] stands for the list of all characters belonging to that class. Standard character class names are: |
| |||||||||||||||
[[:<:]] , [[:>:]] |
These match the null string at the beginning and end of a word
respectively. A word is defined as a sequence of word characters which
is neither preceded nor followed by word characters. A word character is
an alnum character (as defined by ctype(3)) or an underscore
(_).
mysql> SELECT "a word a" REGEXP "[[:<:]]word[[:>:]]"; -> 1 mysql> SELECT "a xword a" REGEXP "[[:<:]]word[[:>:]]"; -> 0 |
mysql> SELECT "weeknights" REGEXP "^(wee|week)(knights|nights)$"; -> 1
Table of Contents
Version 2, June 1991
Copyright © 1989, 1991 Free Software Foundation, Inc.
59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software---to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The ``Program'', below, refers to any such program or work, and a ``work based on the Program'' means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term ``modification''.) Each licensee is addressed as ``you''.
Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.
You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.
You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:
You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.
You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.
If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)
These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.
In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.
You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:
Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
Accompany it with a written offer, valid for at least three years, to give any third-party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)
The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.
If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.
You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.
Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.
If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.
If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.
It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.
If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.
The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and ``any later version'', you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.
If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does. Copyright (C) yyyy name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details.
The hypothetical commands show w and show c should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than show w and show c; they could even be mouse-clicks or menu items---whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a ``copyright disclaimer'' for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice
This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.