# SQL Mode

TiDB servers operate in different SQL modes and apply these modes differently for different clients. SQL mode defines the SQL syntaxes that TiDB supports and the type of data validation check to perform, as described below:

• Before TiDB is started, modify the --sql-mode="modes" configuration item to set SQL mode.

• After TiDB is started, modify SET [ SESSION | GLOBAL ] sql_mode='modes' to set SQL mode.

Ensure that you have SUPER privilege when setting SQL mode at GLOBAL level, and your setting at this level only affects the connections established afterwards. Changes to SQL mode at SESSION level only affect the current client.

Modes are a series of different modes separated by commas (','). You can use the SELECT @@sql_mode statement to check the current SQL mode. The default value of SQL mode: ONLY_FULL_GROUP_BY, STRICT_TRANS_TABLES, NO_ZERO_IN_DATE, NO_ZERO_DATE, ERROR_FOR_DIVISION_BY_ZERO, NO_AUTO_CREATE_USER, NO_ENGINE_SUBSTITUTION.

## Important sql_mode values

• ANSI: This mode complies with standard SQL. In this mode, data is checked. If data does not comply with the defined type or length, the data type is adjusted or trimmed and a warning is returned.
• STRICT_TRANS_TABLES: Strict mode, where data is strictly checked. When any incorrect data is inserted into a table, an error is returned.
• TRADITIONAL: In this mode, TiDB behaves like a “traditional” SQL database system. An error instead of a warning is returned when any incorrect value is inserted into a column. Then, the INSERT or UPDATE statement is immediately stopped.

## SQL mode table

Name Description
PIPES_AS_CONCAT Treats “||” as a string concatenation operator (+) (the same as CONCAT()), not as an OR (full support)
ANSI_QUOTES Treats " as an identifier. If ANSI_QUOTES is enabled, only single quotes are treated as string literals, and double quotes are treated as identifiers. Therefore, double quotes cannot be used to quote strings. (full support)
IGNORE_SPACE If this mode is enabled, the system ignores space. For example: “user” and “user " are the same. (full support)
ONLY_FULL_GROUP_BY If a non-aggregated column that is referred to in SELECT, HAVING, or ORDER BY is absent in GROUP BY, this SQL statement is invalid, because it is abnormal for a column to be absent in GROUP BY but displayed by query. (full support)
NO_UNSIGNED_SUBTRACTION Does not mark the result as UNSIGNED if an operand has no symbol in subtraction. (full support)
NO_DIR_IN_CREATE Ignores all INDEX DIRECTORY and DATA DIRECTORY directives when a table is created. This option is only useful for slave replication servers (syntax support only)
NO_KEY_OPTIONS When you use the SHOW CREATE TABLE statement, MySQL-specific syntaxes such as ENGINE are not exported. Consider this option when migrating across DB types using mysqldump. (syntax support only)
NO_FIELD_OPTIONS When you use the SHOW CREATE TABLE statement, MySQL-specific syntaxes such as ENGINE are not exported. Consider this option when migrating across DB types using mysqldump. (syntax support only)
NO_TABLE_OPTIONS When you use the SHOW CREATE TABLE statement, MySQL-specific syntaxes such as ENGINE are not exported. Consider this option when migrating across DB types using mysqldump. (syntax support only)
NO_AUTO_VALUE_ON_ZERO If this mode is enabled, when the value passed in the AUTO_INCREMENT column is 0 or a specific value, the system directly writes this value to this column. When NULL is passed, the system automatically generates the next serial number. (full support)
NO_BACKSLASH_ESCAPES If this mode is enabled, the \ backslash symbol only stands for itself. (full support)
STRICT_TRANS_TABLES Enables the strict mode for the transaction storage engine and rolls back the entire statement after an illegal value is inserted. (full support)
STRICT_ALL_TABLES For transactional tables, rolls back the entire transaction statement after an illegal value is inserted. (full support)
NO_ZERO_IN_DATE Strict mode, where dates with a month or day part of 0 are not accepted. If you use the IGNORE option, TiDB inserts ‘0000-00-00’ for a similar date. In non-strict mode, this date is accepted but a warning is returned. (full support)
NO_ZERO_DATE Does not use ‘0000-00-00’ as a legal date in strict mode. You can still insert a zero date with the IGNORE option. In non-strict mode, this date is accepted but a warning is returned. (full support)
ALLOW_INVALID_DATES In this mode, the system does not check the validity of all dates. It only checks the month value ranging from 1 to 12 and the date value ranging from 1 to 31. The mode only applies to DATE and DATATIME columns. All TIMESTAMP columns need a full validity check. (full support)
ERROR_FOR_DIVISION_BY_ZERO If this mode is enabled, the system returns an error when handling division by 0 in data-change operations (INSERT or UPDATE).
If this mode is not enabled, the system returns a warning and NULL is used instead. (full support)
NO_AUTO_CREATE_USER Prevents GRANT from automatically creating new users, except for the specified password (full support)
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, this expression is parsed as (NOT a) BETWEEN b AND c. (full support)
NO_ENGINE_SUBSTITUTION Prevents the automatic replacement of storage engines if the required storage engine is disabled or not compiled. (syntax support only)
PAD_CHAR_TO_FULL_LENGTH If this mode is enabled, the system does not trim the trailing spaces for CHAR types. (full support)
REAL_AS_FLOAT Treats REAL as the synonym of FLOAT, not the synonym of DOUBLE (full support)
POSTGRESQL Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS (full support)
MSSQL Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS (full support)
DB2 Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS (full support)
MAXDB Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER (full support)
MySQL323 Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE (full support)
MYSQL40 Equivalent to NO_FIELD_OPTIONS, HIGH_NOT_PRECEDENCE (full support)
ANSI Equivalent to REAL_AS_FLOAT, PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE (full support)
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 (full support)
ORACLE Equivalent to PIPES_AS_CONCAT, ANSI_QUOTES, IGNORE_SPACE, NO_KEY_OPTIONS, NO_TABLE_OPTIONS, NO_FIELD_OPTIONS, NO_AUTO_CREATE_USER (full support)