INSERT Syntax

    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 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:

INSERT ... SELECT Syntax

INSERT [LOW_PRIORITY] [IGNORE] [INTO] tbl_name [(column list)] SELECT ...

With INSERT ... SELECT statement 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 Syntax

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 only works 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:

    VariableMeaning
    Delayed_insert_threadsNumber of handler threads
    Delayed_writesNumber of rows written with INSERT DELAYED
    Not_flushed_delayed_rowsNumber 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 only use INSERT DELAYED when you are really sure you need it!