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.