Server SQL Modes

5.1.7. Server SQL Modes

The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients. This capability enables each application to tailor the server's operating mode to its own requirements.

For answers to some questions that are often asked about server SQL modes in MySQL, see Section A.3, “MySQL 5.0 FAQ — Server SQL Mode”.

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, or by usingsql-mode="modes" in my.cnf (Unix operating systems) or my.ini (Windows). modes is a list of different modes separated by comma (“,”) characters. The default value is empty (no modes set). The modesvalue also can be empty (--sql-mode="" on the command line, or sql-mode="" in my.cnf on Unix systems or in my.ini on Windows) if you want to clear it explicitly.

You can change the SQL mode at runtime by using a SET [GLOBAL|SESSION] sql_mode='modes' statement to set the sql_mode system value. Setting the GLOBAL variable requires the SUPER privilege and affects the operation of all clients that connect from that time on. Setting the SESSION variable affects only the current client. Any client can change its own session sql_mode value at any time.

You can retrieve the current global or session sql_mode value with the following statements:

SELECT @@GLOBAL.sql_mode;
SELECT @@SESSION.sql_mode;

The most important sql_mode values are probably these:

•  ANSI

  This mode changes syntax and behavior to conform more closely to standard SQL.

•  STRICT_TRANS_TABLES

  If a value could not be inserted as given into a transactional table, abort the statement. For a non-transactional table, abort the statement if the value occurs in a single-row statement or the first row of a multiple-row statement. More detail is given later in this section. (Implemented in MySQL 5.0.2)

•  TRADITIONAL

  Make MySQL behave like a “traditional” SQL database system. A simple description of this mode is “give an error instead of a warning” when inserting an incorrect value into a column.

  Note

  The INSERT/UPDATE aborts as soon as the error is noticed. This may not be what you want if you are using a non-transactional storage engine, because data changes made prior to the error may not be rolled back, resulting in a “partially done” update. (Added in MySQL 5.0.2)

When this manual refers to “strict mode,” it means a mode where at least one ofSTRICT_TRANS_TABLES or STRICT_ALL_TABLES is enabled.

The following list describes all supported modes:

•  ALLOW_INVALID_DATES

  Don't do full checking of dates. Check only that the month is in the range from 1 to 12 and the day is in the range from 1 to 31. This is very convenient for Web applications where you obtain year, month, and day in three different fields and you want to store exactly what the user inserted (without date validation). This mode applies to DATE and DATETIME columns. It does not apply TIMESTAMP columns, which always require a valid date.

  This mode is implemented in MySQL 5.0.2. Before 5.0.2, this was the default MySQL date-handling mode. As of 5.0.2, the server requires that month and day values be legal, and not merely in the range 1 to 12 and 1 to 31, respectively. With strict mode disabled, invalid dates such as '2004-04-31' are converted to '0000-00-00' and a warning is generated. With strict mode enabled, invalid dates generate an error. To allow such dates, enable ALLOW_INVALID_DATES.

•  ANSI_QUOTES

  Treat “"” as an identifier quote character (like the “`” quote character) and not as a string quote character. You can still use “`” to quote identifiers with this mode enabled. WithANSI_QUOTES enabled, you cannot use double quotes to quote literal strings, because it is interpreted as an identifier.

•  ERROR_FOR_DIVISION_BY_ZERO

  Produce an error in strict mode (otherwise a warning) when a division by zero (or MOD(X,0)) occurs during an INSERT or UPDATE. If this mode is not enabled, MySQL instead returns NULL for divisions by zero. For INSERT IGNORE or UPDATE IGNORE, MySQL generates a warning for divisions by zero, but the result of the operation is NULL. (Implemented in MySQL 5.0.2)

•  HIGH_NOT_PRECEDENCE

  From MySQL 5.0.2 on, the precedence of the NOT operator is such that expressions such as NOT a BETWEEN b AND c are parsed as NOT (a BETWEEN b AND c). Before MySQL 5.0.2, the expression is parsed as (NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode. (Added in MySQL 5.0.2)

  mysql> SET sql_mode = '';
  mysql> SELECT NOT 1 BETWEEN -5 AND 5;
          -> 0
  mysql> SET sql_mode = 'HIGH_NOT_PRECEDENCE';
  mysql> SELECT NOT 1 BETWEEN -5 AND 5;
          -> 1
  

•  IGNORE_SPACE

  Allow spaces between a function name and the “(” character. This causes built-in 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 Section 8.2, “Schema Object Names”. For example, because there is a COUNT()function, the use of count as a table name in the following statement causes an error:

  mysql> CREATE TABLE count (i INT);
  ERROR 1064 (42000): You have an error in your SQL syntax
  

  The table name should be quoted:

  mysql> CREATE TABLE `count` (i INT);
  Query OK, 0 rows affected (0.00 sec)
  

  The IGNORE_SPACE SQL mode applies to built-in functions, not to user-defined functions or stored functions. It is always allowable to have spaces after a UDF or stored function name, regardless of whether IGNORE_SPACE is enabled.

  For further discussion of IGNORE_SPACE, see Section 8.2.3, “Function Name Parsing and Resolution”.

•  NO_AUTO_CREATE_USER

  Prevent the GRANT statement from automatically creating new users if it would otherwise do so, unless a non-empty password also is specified. (Added in MySQL 5.0.2)

•  NO_AUTO_VALUE_ON_ZERO

  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_ZEROsuppresses 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. (Storing 0 is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters the 0 values, resulting in a table with contents different from the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. mysqldump now automatically includes in its output a statement that enables NO_AUTO_VALUE_ON_ZERO, to avoid this problem.

•  NO_BACKSLASH_ESCAPES

  Disable the use of the backslash character (“\”) as an escape character within strings. With this mode enabled, backslash becomes an ordinary character like any other. (Implemented in MySQL 5.0.1)

•  NO_DIR_IN_CREATE

  When creating a table, ignore all INDEX DIRECTORY and DATA DIRECTORY directives. This option is useful on slave replication servers.

•  NO_ENGINE_SUBSTITUTION

  Control automatic substitution of the default storage engine when a statement such as CREATE TABLE orfont-family: monospace, fixed; font-weight: bold; colo

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