5.1.8 Server SQL Modes

The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients, depending on the value of the sql_mode system variable. DBAs can set the global SQL mode to match site server operating requirements, and each application can set its session SQL mode to its own requirements.

Modes affect the SQL syntax MySQL supports and the data validation checks it performs. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers.

• Setting the SQL Mode

• The Most Important SQL Modes

• Full List of SQL Modes

• Combination SQL Modes

• Strict SQL Mode

For answers to questions often asked about server SQL modes in MySQL, see Section A.3, “MySQL 5.6 FAQ: Server SQL Mode”.

When working with InnoDB tables, consider also the innodb_strict_mode system variable. It enables additional error checks for InnoDB tables.

Setting the SQL Mode

The default SQL mode is NO_ENGINE_SUBSTITUTION.

To set the SQL mode at server startup, use the --sql-mode="modes" option on the command line, or sql-mode="modes" in an option file such as my.cnf (Unix operating systems) or my.ini (Windows). modes is a list of different modes separated by commas. To clear the SQL mode explicitly, set it to an empty string using --sql-mode="" on the command line, or sql-mode="" in an option file.

Note

MySQL installation programs may configure the SQL mode during the installation process. For example, mysql_install_db creates a default option file named my.cnf in the base installation directory. This file contains a line that sets the SQL mode; see Section 4.4.3, “mysql_install_db — Initialize MySQL Data Directory”.

If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.

To change the SQL mode at runtime, set the global or session sql_mode system variable using a SET statement:

SET GLOBAL sql_mode = 'modes';
SET SESSION sql_mode = 'modes';

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. Each client can change its session sql_mode value at any time.

To determine the current global or session sql_mode setting, select its value:

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

Important

SQL mode and user-defined partitioning.  Changing the server SQL mode after creating and inserting data into partitioned tables can cause major changes in the behavior of such tables, and could lead to loss or corruption of data. It is strongly recommended that you never change the SQL mode once you have created tables employing user-defined partitioning.

When replicating partitioned tables, differing SQL modes on the master and slave can also lead to problems. For best results, you should always use the same server SQL mode on the master and slave.

For more information, see Section 19.6, “Restrictions and Limitations on Partitioning”.

The Most Important SQL Modes

The most important sql_mode values are probably these:

• ANSI

  This mode changes syntax and behavior to conform more closely to standard SQL. It is one of the special combination modes listed at the end of this section.

• STRICT_TRANS_TABLES

  If a value could not be inserted as given into a transactional table, abort the statement. For a nontransactional table, abort the statement if the value occurs in a single-row statement or the first row of a multiple-row statement. More details are given later in this section.

• 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. It is one of the special combination modes listed at the end of this section.

  Note

  With TRADITIONAL mode enabled, an INSERT or UPDATE aborts as soon as an error occurs. If you are using a nontransactional storage engine, this may not be what you want because data changes made prior to the error may not be rolled back, resulting in a “partially done” update.

When this manual refers to “strict mode,” it means a mode with either or both STRICT_TRANS_TABLES or STRICT_ALL_TABLES enabled.

Full List of SQL Modes

The following list describes all supported SQL modes:

• ALLOW_INVALID_DATES

  Do not perform 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 may be useful for Web applications that obtain year, month, and day in three different fields and 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.

  With ALLOW_INVALID_DATES enabled, 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 permit 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. With ANSI_QUOTES enabled, you cannot use double quotation marks to quote literal strings because they are interpreted as identifiers.

• ERROR_FOR_DIVISION_BY_ZERO

  The ERROR_FOR_DIVISION_BY_ZERO mode affects handling of division by zero, which includes MOD(N,0). For data-change operations (INSERT, UPDATE), its effect also depends on whether strict SQL mode is enabled.

  • If this mode is not enabled, division by zero inserts NULL and produces no warning.

  • If this mode is enabled, division by zero inserts NULL and produces a warning.

  • If this mode and strict mode are enabled, division by zero produces an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, division by zero inserts NULL and produces a warning.

  For SELECT, division by zero returns NULL. Enabling ERROR_FOR_DIVISION_BY_ZERO causes a warning to be produced as well, regardless of whether strict mode is enabled.

  As of MySQL 5.6.17, ERROR_FOR_DIVISION_BY_ZERO is deprecated and setting the sql_mode value to include it generates a warning.

• HIGH_NOT_PRECEDENCE

  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). In some older versions of MySQL, the expression was parsed as (NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode.

  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

  Permit 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 9.2, “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 permissible 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 9.2.4, “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 authentication information is specified. The statement must specify a nonempty password using IDENTIFIED BY or an authentication plugin using IDENTIFIED WITH.

• 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_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. (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. For this reason, mysqldump automatically includes in its output a statement that enables NO_AUTO_VALUE_ON_ZERO.

• 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.

• 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 or ALTER TABLE specifies a storage engine that is disabled or not compiled in.

  Because storage engines can be pluggable at runtime, unavailable engines are treated the same way:

  With NO_ENGINE_SUBSTITUTION disabled, for CREATE TABLE the default engine is used and a warning occurs if the desired engine is unavailable. For ALTER TABLE, a warning occurs and the table is not altered.

  With NO_ENGINE_SUBSTITUTION enabled, an error occurs and the table is not created or altered if the desired engine is unavailable.

• NO_FIELD_OPTIONS

  Do not print MySQL-specific column options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

• NO_KEY_OPTIONS

  Do not print MySQL-specific index options in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

• NO_TABLE_OPTIONS

  Do not print MySQL-specific table options (such as ENGINE) in the output of SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.

• NO_UNSIGNED_SUBTRACTION

  Subtraction between integer values, where one is of type UNSIGNED, produces an unsigned result by default. If the result would otherwise have been negative, an error results:

  mysql> SET sql_mode = '';
  Query OK, 0 rows affected (0.00 sec)
  
  mysql> SELECT CAST(0 AS UNSIGNED) - 1;
  ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(cast(0 as unsigned) - 1)'

  If the NO_UNSIGNED_SUBTRACTION SQL mode is enabled, the result is negative:

  mysql> SET sql_mode = 'NO_UNSIGNED_SUBTRACTION';
  mysql> SELECT CAST(0 AS UNSIGNED) - 1;
  +-------------------------+
  | CAST(0 AS UNSIGNED) - 1 |
  +-------------------------+
  |                      -1 |
  +-------------------------+

  If the result of such an operation is used to update an UNSIGNED integer column, the result is clipped to the maximum value for the column type, or clipped to 0 if NO_UNSIGNED_SUBTRACTION is enabled. With strict SQL mode enabled, an error occurs and the column remains unchanged.

  When NO_UNSIGNED_SUBTRACTION is enabled, the subtraction result is signed, even if any operand is unsigned. For example, compare the type of column c2 in table t1 with that of column c2 in table t2:

  mysql> SET sql_mode='';
  mysql> CREATE TABLE test (c1 BIGINT UNSIGNED NOT NULL);
  mysql> CREATE TABLE t1 SELECT c1 - 1 AS c2 FROM test;
  mysql> DESCRIBE t1;
  +-------+---------------------+------+-----+---------+-------+
  | Field | Type                | Null | Key | Default | Extra |
  +-------+---------------------+------+-----+---------+-------+
  | c2    | bigint(21) unsigned | NO   |     | 0       |       |
  +-------+---------------------+------+-----+---------+-------+
  
  mysql> SET sql_mode='NO_UNSIGNED_SUBTRACTION';
  mysql> CREATE TABLE t2 SELECT c1 - 1 AS c2 FROM test;
  mysql> DESCRIBE t2;
  +-------+------------+------+-----+---------+-------+
  | Field | Type       | Null | Key | Default | Extra |
  +-------+------------+------+-----+---------+-------+
  | c2    | bigint(21) | NO   |     | 0       |       |
  +-------+------------+------+-----+---------+-------+

  This means that BIGINT UNSIGNED is not 100% usable in all contexts. See Section 12.10, “Cast Functions and Operators”.

• NO_ZERO_DATE

  The NO_ZERO_DATE mode affects whether the server permits '0000-00-00' as a valid date. Its effect also depends on whether strict SQL mode is enabled.

  • If this mode is not enabled, '0000-00-00' is permitted and inserts produce no warning.

  • If this mode is enabled, '0000-00-00' is permitted and inserts produce a warning.

  • If this mode and strict mode are enabled, '0000-00-00' is not permitted and inserts produce an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, '0000-00-00' is permitted and inserts produce a warning.

  As of MySQL 5.6.17, NO_ZERO_DATE is deprecated and setting the sql_mode value to include it generates a warning.

• NO_ZERO_IN_DATE

  The NO_ZERO_IN_DATE mode affects whether the server permits dates in which the year part is nonzero but the month or day part is 0. (This mode affects dates such as '2010-00-01' or '2010-01-00', but not '0000-00-00'. To control whether the server permits '0000-00-00', use the NO_ZERO_DATE mode.) The effect of NO_ZERO_IN_DATE also depends on whether strict SQL mode is enabled.

  • If this mode is not enabled, dates with zero parts are permitted and inserts produce no warning.

  • If this mode is enabled, dates with zero parts are inserted as '0000-00-00' and produce a warning.

  • If this mode and strict mode are enabled, dates with zero parts are not permitted and inserts produce an error, unless IGNORE is given as well. For INSERT IGNORE and UPDATE IGNORE, dates with zero parts are inserted as '0000-00-00' and produce a warning.

  As of MySQL 5.6.17, NO_ZERO_IN_DATE is deprecated and setting the sql_mode value to include it generates a warning.

• ONLY_FULL_GROUP_BY

  Reject queries for which the select list, HAVING condition, or ORDER BY list refer to nonaggregated columns that are not named in the GROUP BY clause.

  A MySQL extension to standard SQL permits references in the HAVING clause to aliased expressions in the select list. Enabling ONLY_FULL_GROUP_BY disables this extension, thus requiring the HAVING clause to be written using unaliased expressions.

  For additional discussion and examples, see Section 12.18.3, “MySQL Handling of GROUP BY”.

• PAD_CHAR_TO_FULL_LENGTH

  By default, trailing spaces are trimmed from CHAR column values on retrieval. If PAD_CHAR_TO_FULL_LENGTH is enabled, trimming does not occur and retrieved CHAR values are padded to their full length. This mode does not apply to VARCHAR columns, for which trailing spaces are retained on retrieval.

  mysql> CREATE TABLE t1 (c1 CHAR(10));
  Query OK, 0 rows affected (0.37 sec)
  
  mysql> INSERT INTO t1 (c1) VALUES('xy');
  Query OK, 1 row affected (0.01 sec)
  
  mysql> SET sql_mode = '';
  Query OK, 0 rows affected (0.00 sec)
  
  mysql> SELECT c1, CHAR_LENGTH(c1) FROM t1;
  +------+-----------------+
  | c1   | CHAR_LENGTH(c1) |
  +------+-----------------+
  | xy   |               2 |
  +------+-----------------+
  1 row in set (0.00 sec)
  
  mysql> SET sql_mode = 'PAD_CHAR_TO_FULL_LENGTH';
  Query OK, 0 rows affected (0.00 sec)
  
  mysql> SELECT c1, CHAR_LENGTH(c1) FROM t1;
  +------------+-----------------+
  | c1         | CHAR_LENGTH(c1) |
  +------------+-----------------+
  | xy         |              10 |
  +------------+-----------------+
  1 row in set (0.00 sec)

• PIPES_AS_CONCAT

  Treat || as a string concatenation operator (same as CONCAT()) rather than as a synonym for OR.

• REAL_AS_FLOAT

  Treat REAL as a synonym for FLOAT. By default, MySQL treats REAL as a synonym for DOUBLE.

• STRICT_ALL_TABLES

  Enable strict SQL mode for all storage engines. Invalid data values are rejected. For details, see Strict SQL Mode.

• STRICT_TRANS_TABLES

  Enable strict SQL mode for transactional storage engines, and when possible for nontransactional storage engines. For details, see Strict SQL Mode.

Combination SQL Modes

The following special modes are provided as shorthand for combinations of mode values from the preceding list.

• ANSI

  Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE.

  ANSI mode also causes the server to return an error for queries where a set function S with an outer reference S(outer_ref) cannot be aggregated in the outer query against which the outer reference has been resolved. This is such a query:

  SELECT * FROM t1 WHERE t1.a IN (SELECT MAX(t1.b) FROM t2 WHERE ...);

  Here, MAX(t1.b) cannot aggregated in the outer query because it appears in the WHERE clause of that query. Standard SQL requires an error in this situation. If ANSI mode is not enabled, the server treats S(outer_ref) in such queries the same way that it would interpret S(const).

  See Section 1.7, “MySQL Standards Compliance”.

• DB2

  Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

• MAXDB

  Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER.

• MSSQL

  Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

• MYSQL323

  Equivalent to MYSQL323, HIGH_NOT_PRECEDENCE. This means HIGH_NOT_PRECEDENCE plus some SHOW CREATE TABLE behaviors specific to MYSQL323:

  • TIMESTAMP column display does not include DEFAULT or ON UPDATE attributes.

  • String column display does not include character set and collation attributes. For CHAR and VARCHAR columns, if the collation is binary, BINARY is appended to the column type.

  • The ENGINE=engine_name table option displays as TYPE=engine_name.

  • For MEMORY tables, the storage engine is displayed as HEAP.

• MYSQL40

  Equivalent to MYSQL40, HIGH_NOT_PRECEDENCE. This means HIGH_NOT_PRECEDENCE plus some behaviors specific to MYSQL40. These are the same as for MYSQL323, except that SHOW CREATE TABLE does not display HEAP as the storage engine for MEMORY tables.

• ORACLE

  Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER.

• POSTGRESQL

  Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS.

• TRADITIONAL

  Equivalent to STRICT_TRANS_TABLES, STRICT_ALL_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_DIVISION_BY_ZERO, NO_AUTO_CREATE_USER, and NO_ENGINE_SUBSTITUTION.

Strict SQL Mode

Strict mode controls how MySQL handles invalid or missing values in data-change statements such as INSERT or UPDATE. A value can be invalid for several reasons. For example, it might have the wrong data type for the column, or it might be out of range. A value is missing when a new row to be inserted does not contain a value for a non-NULL column that has no explicit DEFAULT clause in its definition. (For a NULL column, NULL is inserted if the value is missing.) Strict mode also affects DDL statements such as CREATE TABLE.

If strict mode is not in effect, MySQL inserts adjusted values for invalid or missing values and produces warnings (see Section 13.7.5.41, “SHOW WARNINGS Syntax”). In strict mode, you can produce this behavior by using INSERT IGNORE or UPDATE IGNORE.

For statements such as SELECT that do not change data, invalid values generate a warning in strict mode, not an error.

As of MySQL 5.6.11, strict mode produces an error for attempts to create a key that exceeds the maximum key length. Previously, this resulted in a warning and truncation of the key to the maximum key length (the same as when strict mode is not enabled).

Strict mode does not affect whether foreign key constraints are checked. foreign_key_checks can be used for that. (See Section 5.1.5, “Server System Variables”.)

Strict SQL mode is in effect if either STRICT_ALL_TABLES or STRICT_TRANS_TABLES is enabled, although the effects of these modes differ somewhat:

• For transactional tables, an error occurs for invalid or missing values in a data-change statement when either STRICT_ALL_TABLES or STRICT_TRANS_TABLES is enabled. The statement is aborted and rolled back.

• For nontransactional tables, the behavior is the same for either mode if the bad value occurs in the first row to be inserted or updated: The statement is aborted and the table remains unchanged. If the statement inserts or modifies multiple rows and the bad value occurs in the second or later row, the result depends on which strict mode is enabled:

  • For STRICT_ALL_TABLES, MySQL returns an error and ignores the rest of the rows. However, because the earlier rows have been inserted or updated, the result is a partial update. To avoid this, use single-row statements, which can be aborted without changing the table.

  • For STRICT_TRANS_TABLES, MySQL converts an invalid value to the closest valid value for the column and inserts the adjusted value. If a value is missing, MySQL inserts the implicit default value for the column data type. In either case, MySQL generates a warning rather than an error and continues processing the statement. Implicit defaults are described in Section 11.6, “Data Type Default Values”.

Strict mode also affects handling of division by zero, zero dates, and zeros in dates, in conjunction with the ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, and NO_ZERO_IN_DATE modes. For details, see the descriptions of those modes.