A.3.1: What are server SQL modes?
A.3.2: How many server SQL modes are there?
A.3.3: How do you determine the server SQL mode?
A.3.4: Is the mode dependent on the database or connection?
A.3.5: Can the rules for strict mode be extended?
A.3.6: Does strict mode impact performance?
A.3.7: What is the default server SQL mode when MySQL 5.5 is installed?
Questions and Answers
Server SQL 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. The MySQL Server apply these modes individually to different clients. For more information, see Section 5.1.7, “Server SQL Modes”.
Each mode can be independently switched on and off. See Section 5.1.7, “Server SQL Modes”, for a complete list of available modes.
You can set the default SQL mode (for mysqld
startup) with the
option. Using the statement
sql_mode=', you can
change the settings from within a connection, either locally to
the connection, or to take effect globally. You can retrieve the
current mode by issuing a
A mode is not linked to a particular database. Modes can be set
locally to the session (connection), or globally for the server.
you can change these settings using
When we refer to strict mode, we mean a
mode where at least one of the modes
STRICT_ALL_TABLES is enabled.
Options can be combined, so you can add restrictions to a mode.
See Section 5.1.7, “Server SQL Modes”, for more information.
The intensive validation of input data that some settings requires more time than if the validation is not done. While the performance impact is not that great, if you do not require such validation (perhaps your application already handles all of this), then MySQL gives you the option of leaving strict mode disabled. However—if you do require it—strict mode can provide such validation.
By default, no special modes are enabled. For information about all available modes and MySQL's default behavior, see Section 5.1.7, “Server SQL Modes”.