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MySQL Globalization
MySQL Information Schema
MySQL Installation Guide
MySQL and Linux/Unix
MySQL and macOS
MySQL Partitioning
MySQL Performance Schema
MySQL Replication
Using the MySQL Yum Repository
MySQL Restrictions and Limitations
Security in MySQL
MySQL and Solaris
Building MySQL from Source
Starting and Stopping MySQL
MySQL Tutorial
MySQL and Windows
MySQL NDB Cluster 7.5
The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients, depending on the value of thesql_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.
For answers to questions often asked about server SQL modes in MySQL, seeSection A.3, “MySQL 5.7 FAQ: Server SQL Mode”.
When working withInnoDB tables, consider also theinnodb_strict_mode system variable. It enables additional error checks forInnoDB tables.
The default SQL mode in MySQL 5.7 includes these modes:ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER, andNO_ENGINE_SUBSTITUTION.
These modes were added to the default SQL mode in MySQL 5.7: TheONLY_FULL_GROUP_BY andSTRICT_TRANS_TABLES modes were added in MySQL 5.7.5. TheNO_AUTO_CREATE_USER mode was added in MySQL 5.7.7. TheERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATE modes were added in MySQL 5.7.8. For additional discussion regarding these changes to the default SQL mode value, seeSQL Mode Changes in MySQL 5.7.
To set the SQL mode at server startup, use the--sql-mode=" option on the command line, ormodes"sql-mode=" in an option file such asmodes"my.cnf (Unix operating systems) ormy.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, orsql-mode="" in an option file.
MySQL installation programs may configure the SQL mode during the installation process. 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 sessionsql_mode system variable using aSET statement:
SET GLOBAL sql_mode = 'modes';SET SESSION sql_mode = 'modes'; Setting theGLOBAL variable requires theSUPER privilege and affects the operation of all clients that connect from that time on. Setting theSESSION variable affects only the current client. Each client can change its sessionsql_mode value at any time.
To determine the current global or sessionsql_mode setting, select its value:
SELECT @@GLOBAL.sql_mode;SELECT @@SESSION.sql_mode;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 source and replica can also lead to problems. For best results, you should always use the same server SQL mode on the source and replica.
For more information, seeSection 22.6, “Restrictions and Limitations on Partitioning”.
The most importantsql_mode values are probably these:
This mode changes syntax and behavior to conform more closely to standard SQL. It is one of the specialcombination modes listed at the end of this section.
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.
As of MySQL 5.7.5, the default SQL mode includes
STRICT_TRANS_TABLES.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 specialcombination modes listed at the end of this section.
NoteWith
TRADITIONALmode enabled, anINSERTorUPDATEaborts 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 bothSTRICT_TRANS_TABLES orSTRICT_ALL_TABLES enabled.
The following list describes all supported SQL modes:
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
DATEandDATETIMEcolumns. It does not apply toTIMESTAMPcolumns, which always require a valid date.With
ALLOW_INVALID_DATESdisabled, 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, enableALLOW_INVALID_DATES.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_QUOTESenabled, you cannot use double quotation marks to quote literal strings because they are interpreted as identifiers.The
ERROR_FOR_DIVISION_BY_ZEROmode affects handling of division by zero, which includesMOD(. For data-change operations (N,0)INSERT,UPDATE), its effect also depends on whether strict SQL mode is enabled.If this mode is not enabled, division by zero inserts
NULLand produces no warning.If this mode is enabled, division by zero inserts
NULLand produces a warning.If this mode and strict mode are enabled, division by zero produces an error, unless
IGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE, division by zero insertsNULLand produces a warning.
For
SELECT, division by zero returnsNULL. EnablingERROR_FOR_DIVISION_BY_ZEROcauses a warning to be produced as well, regardless of whether strict mode is enabled.ERROR_FOR_DIVISION_BY_ZEROis deprecated.ERROR_FOR_DIVISION_BY_ZEROis not part of strict mode, but should be used in conjunction with strict mode and is enabled by default. A warning occurs ifERROR_FOR_DIVISION_BY_ZEROis enabled without also enabling strict mode or vice versa. For additional discussion, seeSQL Mode Changes in MySQL 5.7.Because
ERROR_FOR_DIVISION_BY_ZEROis deprecated; expect it to be removed in a future release of MySQL as a separate mode name and its effect included in the effects of strict SQL mode.The precedence of the
NOToperator is such that expressions such asNOT a BETWEEN b AND care parsed asNOT (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 theHIGH_NOT_PRECEDENCESQL mode.mysql> SET sql_mode = '';mysql> SELECT NOT 1 BETWEEN -5 AND 5; -> 0mysql> SET sql_mode = 'HIGH_NOT_PRECEDENCE';mysql> SELECT NOT 1 BETWEEN -5 AND 5; -> 1Permit 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 inSection 9.2, “Schema Object Names”. For example, because there is aCOUNT()function, the use ofcountas 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 syntaxThe table name should be quoted:
mysql> CREATE TABLE `count` (i INT);Query OK, 0 rows affected (0.00 sec)The
IGNORE_SPACESQL mode applies to built-in functions, not to loadable functions or stored functions. It is always permissible to have spaces after a loadable function or stored function name, regardless of whetherIGNORE_SPACEis enabled.For further discussion of
IGNORE_SPACE, seeSection 9.2.5, “Function Name Parsing and Resolution”.Prevent the
GRANTstatement from automatically creating new user accounts if it would otherwise do so, unless authentication information is specified. The statement must specify a nonempty password usingIDENTIFIED BYor an authentication plugin usingIDENTIFIED WITH.It is preferable to create MySQL accounts with
CREATE USERrather thanGRANT.NO_AUTO_CREATE_USERis deprecated and the default SQL mode includesNO_AUTO_CREATE_USER. Assignments tosql_modethat change theNO_AUTO_CREATE_USERmode state produce a warning, except assignments that setsql_modetoDEFAULT. ExpectNO_AUTO_CREATE_USERto be be removed in a future release of MySQL, and its effect to be enabled at all times (and forGRANTnot to create accounts any longer).Previously, before
NO_AUTO_CREATE_USERwas deprecated, one reason not to enable it was that it was not replication safe. Now it can be enabled and replication-safe user management performed withCREATE USER IF NOT EXISTS,DROP USER IF EXISTS, andALTER USER IF EXISTSrather thanGRANT. These statements enable safe replication when replicas may have different grants than those on the source. SeeSection 13.7.1.2, “CREATE USER Statement”,Section 13.7.1.3, “DROP USER Statement”, andSection 13.7.1.1, “ALTER USER Statement”.NO_AUTO_VALUE_ON_ZEROaffects handling ofAUTO_INCREMENTcolumns. Normally, you generate the next sequence number for the column by inserting eitherNULLor0into it.NO_AUTO_VALUE_ON_ZEROsuppresses this behavior for0so that onlyNULLgenerates the next sequence number.This mode can be useful if
0has been stored in a table'sAUTO_INCREMENTcolumn. (Storing0is not a recommended practice, by the way.) For example, if you dump the table withmysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters the0values, resulting in a table with contents different from the one that was dumped. EnablingNO_AUTO_VALUE_ON_ZERObefore reloading the dump file solves this problem. For this reason,mysqldump automatically includes in its output a statement that enablesNO_AUTO_VALUE_ON_ZERO.Enabling this mode disables the use of the backslash character (
\) as an escape character within strings and identifiers. With this mode enabled, backslash becomes an ordinary character like any other, and the default escape sequence forLIKEexpressions is changed so that no escape character is used.When creating a table, ignore all
INDEX DIRECTORYandDATA DIRECTORYdirectives. This option is useful on replica replication servers.Control automatic substitution of the default storage engine when a statement such as
CREATE TABLEorALTER TABLEspecifies a storage engine that is disabled or not compiled in.By default,
NO_ENGINE_SUBSTITUTIONis enabled.Because storage engines can be pluggable at runtime, unavailable engines are treated the same way:
With
NO_ENGINE_SUBSTITUTIONdisabled, forCREATE TABLEthe default engine is used and a warning occurs if the desired engine is unavailable. ForALTER TABLE, a warning occurs and the table is not altered.With
NO_ENGINE_SUBSTITUTIONenabled, an error occurs and the table is not created or altered if the desired engine is unavailable.Do not print MySQL-specific column options in the output of
SHOW CREATE TABLE. This mode is used bymysqldump in portability mode.NoteAs of MySQL 5.7.22,
NO_FIELD_OPTIONSis deprecated. It is removed in MySQL 8.0.Do not print MySQL-specific index options in the output of
SHOW CREATE TABLE. This mode is used bymysqldump in portability mode.NoteAs of MySQL 5.7.22,
NO_KEY_OPTIONSis deprecated. It is removed in MySQL 8.0.Do not print MySQL-specific table options (such as
ENGINE) in the output ofSHOW CREATE TABLE. This mode is used bymysqldump in portability mode.NoteAs of MySQL 5.7.22,
NO_TABLE_OPTIONSis deprecated. It is removed in MySQL 8.0.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_SUBTRACTIONSQL 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
UNSIGNEDinteger column, the result is clipped to the maximum value for the column type, or clipped to 0 ifNO_UNSIGNED_SUBTRACTIONis enabled. With strict SQL mode enabled, an error occurs and the column remains unchanged.When
NO_UNSIGNED_SUBTRACTIONis enabled, the subtraction result is signed,even if any operand is unsigned. For example, compare the type of columnc2in tablet1with that of columnc2in tablet2: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 UNSIGNEDis not 100% usable in all contexts. SeeSection 12.10, “Cast Functions and Operators”.The
NO_ZERO_DATEmode 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, unlessIGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE,'0000-00-00'is permitted and inserts produce a warning.
NO_ZERO_DATEis deprecated.NO_ZERO_DATEis not part of strict mode, but should be used in conjunction with strict mode and is enabled by default. A warning occurs ifNO_ZERO_DATEis enabled without also enabling strict mode or vice versa. For additional discussion, seeSQL Mode Changes in MySQL 5.7.Because
NO_ZERO_DATEis deprecated; expect it to be removed in a future release of MySQL as a separate mode name and its effect included in the effects of strict SQL mode.The
NO_ZERO_IN_DATEmode 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 theNO_ZERO_DATEmode.) The effect ofNO_ZERO_IN_DATEalso 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
IGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE, dates with zero parts are inserted as'0000-00-00'and produce a warning.
NO_ZERO_IN_DATEis deprecated.NO_ZERO_IN_DATEis not part of strict mode, but should be used in conjunction with strict mode and is enabled by default. A warning occurs ifNO_ZERO_IN_DATEis enabled without also enabling strict mode or vice versa. For additional discussion, seeSQL Mode Changes in MySQL 5.7.Because
NO_ZERO_IN_DATEis deprecated; expect it to be removed in a future release of MySQL as a separate mode name and its effect included in the effects of strict SQL mode.Reject queries for which the select list,
HAVINGcondition, orORDER BYlist refer to nonaggregated columns that are neither named in theGROUP BYclause nor are functionally dependent on (uniquely determined by)GROUP BYcolumns.As of MySQL 5.7.5, the default SQL mode includes
ONLY_FULL_GROUP_BY. (Before 5.7.5, MySQL does not detect functional dependency andONLY_FULL_GROUP_BYis not enabled by default.)A MySQL extension to standard SQL permits references in the
HAVINGclause to aliased expressions in the select list. Before MySQL 5.7.5, enablingONLY_FULL_GROUP_BYdisables this extension, thus requiring theHAVINGclause to be written using unaliased expressions. As of MySQL 5.7.5, this restriction is lifted so that theHAVINGclause can refer to aliases regardless of whetherONLY_FULL_GROUP_BYis enabled.For additional discussion and examples, seeSection 12.19.3, “MySQL Handling of GROUP BY”.
By default, trailing spaces are trimmed from
CHARcolumn values on retrieval. IfPAD_CHAR_TO_FULL_LENGTHis enabled, trimming does not occur and retrievedCHARvalues are padded to their full length. This mode does not apply toVARCHARcolumns, 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)Treat
||as a string concatenation operator (same asCONCAT()) rather than as a synonym forOR.Treat
REALas a synonym forFLOAT. By default, MySQL treatsREALas a synonym forDOUBLE.Enable strict SQL mode for all storage engines. Invalid data values are rejected. For details, seeStrict SQL Mode.
From MySQL 5.7.4 through 5.7.7,
STRICT_ALL_TABLESincludes the effect of theERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEmodes. For additional discussion, seeSQL Mode Changes in MySQL 5.7.Enable strict SQL mode for transactional storage engines, and when possible for nontransactional storage engines. For details, seeStrict SQL Mode.
From MySQL 5.7.4 through 5.7.7,
STRICT_TRANS_TABLESincludes the effect of theERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEmodes. For additional discussion, seeSQL Mode Changes in MySQL 5.7.
The following special modes are provided as shorthand for combinations of mode values from the preceding list.
Equivalent to
REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE, and (as of MySQL 5.7.5)ONLY_FULL_GROUP_BY.ANSImode also causes the server to return an error for queries where a set functionSwith an outer referencecannot be aggregated in the outer query against which the outer reference has been resolved. This is such a query:S(outer_ref)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 theWHEREclause of that query. Standard SQL requires an error in this situation. IfANSImode is not enabled, the server treatsin such queries the same way that it would interpretS(outer_ref).S(const)Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS.NoteAs of MySQL 5.7.22,
DB2is deprecated. It is removed in MySQL 8.0.Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS,NO_AUTO_CREATE_USER.NoteAs of MySQL 5.7.22,
MAXDBis deprecated. It is removed in MySQL 8.0.Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS.NoteAs of MySQL 5.7.22,
MSSQLis deprecated. It is removed in MySQL 8.0.Equivalent to
MYSQL323,HIGH_NOT_PRECEDENCE. This meansHIGH_NOT_PRECEDENCEplus someSHOW CREATE TABLEbehaviors specific toMYSQL323:TIMESTAMPcolumn display does not includeDEFAULTorON UPDATEattributes.String column display does not include character set and collation attributes. For
CHARandVARCHARcolumns, if the collation is binary,BINARYis appended to the column type.The
ENGINE=table option displays asengine_nameTYPE=.engine_nameFor
MEMORYtables, the storage engine is displayed asHEAP.
NoteAs of MySQL 5.7.22,
MYSQL323is deprecated. It is removed in MySQL 8.0.Equivalent to
MYSQL40,HIGH_NOT_PRECEDENCE. This meansHIGH_NOT_PRECEDENCEplus some behaviors specific toMYSQL40. These are the same as forMYSQL323, except thatSHOW CREATE TABLEdoes not displayHEAPas the storage engine forMEMORYtables.NoteAs of MySQL 5.7.22,
MYSQL40is deprecated. It is removed in MySQL 8.0.Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS,NO_AUTO_CREATE_USER.NoteAs of MySQL 5.7.22,
ORACLEis deprecated. It is removed in MySQL 8.0.Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS.NoteAs of MySQL 5.7.22,
POSTGRESQLis deprecated. It is removed in MySQL 8.0.Before MySQL 5.7.4, and in MySQL 5.7.8 and later,
TRADITIONALis equivalent toSTRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER, andNO_ENGINE_SUBSTITUTION.From MySQL 5.7.4 though 5.7.7,
TRADITIONALis equivalent toSTRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_AUTO_CREATE_USER, andNO_ENGINE_SUBSTITUTION. TheNO_ZERO_IN_DATE,NO_ZERO_DATE, andERROR_FOR_DIVISION_BY_ZEROmodes are not named because in those versions their effects are included in the effects of strict SQL mode (STRICT_ALL_TABLESorSTRICT_TRANS_TABLES). Thus, the effects ofTRADITIONALare the same in all MySQL 5.7 versions (and the same as in MySQL 5.6). For additional discussion, seeSQL Mode Changes in MySQL 5.7.
Strict mode controls how MySQL handles invalid or missing values in data-change statements such asINSERT orUPDATE. 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 explicitDEFAULT clause in its definition. (For aNULL column,NULL is inserted if the value is missing.) Strict mode also affects DDL statements such asCREATE TABLE.
If strict mode is not in effect, MySQL inserts adjusted values for invalid or missing values and produces warnings (seeSection 13.7.5.40, “SHOW WARNINGS Statement”). In strict mode, you can produce this behavior by usingINSERT IGNORE orUPDATE IGNORE.
For statements such asSELECT that do not change data, invalid values generate a warning in strict mode, not an error.
Strict mode produces an error for attempts to create a key that exceeds the maximum key length. When strict mode is not enabled, this results in a warning and truncation of the key to the maximum key length.
Strict mode does not affect whether foreign key constraints are checked.foreign_key_checks can be used for that. (SeeSection 5.1.7, “Server System Variables”.)
Strict SQL mode is in effect if eitherSTRICT_ALL_TABLES orSTRICT_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_TABLESorSTRICT_TRANS_TABLESis 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 inSection 11.6, “Data Type Default Values”.
Strict mode affects handling of division by zero, zero dates, and zeros in dates as follows:
Strict mode affects handling of division by zero, which includes
MOD(:N,0)For data-change operations (
INSERT,UPDATE):If strict mode is not enabled, division by zero inserts
NULLand produces no warning.If strict mode is enabled, division by zero produces an error, unless
IGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE, division by zero insertsNULLand produces a warning.
For
SELECT, division by zero returnsNULL. Enabling strict mode causes a warning to be produced as well.Strict mode affects whether the server permits
'0000-00-00'as a valid date:If strict mode is not enabled,
'0000-00-00'is permitted and inserts produce no warning.If strict mode is enabled,
'0000-00-00'is not permitted and inserts produce an error, unlessIGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE,'0000-00-00'is permitted and inserts produce a warning.
Strict mode affects whether the server permits dates in which the year part is nonzero but the month or day part is 0 (dates such as
'2010-00-01'or'2010-01-00'):If strict mode is not enabled, dates with zero parts are permitted and inserts produce no warning.
If strict mode is enabled, dates with zero parts are not permitted and inserts produce an error, unless
IGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE, dates with zero parts are inserted as'0000-00-00'(which is considered valid withIGNORE) and produce a warning.
For more information about strict mode with respect toIGNORE, seeComparison of the IGNORE Keyword and Strict SQL Mode.
Before MySQL 5.7.4, and in MySQL 5.7.8 and later, strict mode affects handling of division by zero, zero dates, and zeros in dates in conjunction with theERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATE modes. From MySQL 5.7.4 though 5.7.7, theERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATE modes do nothing when named explicitly and their effects are included in the effects of strict mode. For additional discussion, seeSQL Mode Changes in MySQL 5.7.
This section compares the effect on statement execution of theIGNORE keyword (which downgrades errors to warnings) and strict SQL mode (which upgrades warnings to errors). It describes which statements they affect, and which errors they apply to.
The following table presents a summary comparison of statement behavior when the default is to produce an error versus a warning. An example of when the default is to produce an error is inserting aNULL into aNOT NULL column. An example of when the default is to produce a warning is inserting a value of the wrong data type into a column (such as inserting the string'abc' into an integer column).
| Operational Mode | When Statement Default is Error | When Statement Default is Warning |
|---|---|---|
WithoutIGNORE or strict SQL mode | Error | Warning |
WithIGNORE | Warning | Warning (same as withoutIGNORE or strict SQL mode) |
| With strict SQL mode | Error (same as withoutIGNORE or strict SQL mode) | Error |
WithIGNORE and strict SQL mode | Warning | Warning |
One conclusion to draw from the table is that when theIGNORE keyword and strict SQL mode are both in effect,IGNORE takes precedence. This means that, althoughIGNORE and strict SQL mode can be considered to have opposite effects on error handling, they do not cancel when used together.
The Effect of IGNORE on Statement Execution
Several statements in MySQL support an optionalIGNORE keyword. This keyword causes the server to downgrade certain types of errors and generate warnings instead. For a multiple-row statement, downgrading an error to a warning may enable a row to be processed. Otherwise,IGNORE causes the statement to skip to the next row instead of aborting. (For nonignorable errors, an error occurs regardless of theIGNORE keyword.)
Example: If the tablet has a primary key columni containing unique values, attempting to insert the same value ofi into multiple rows normally produces a duplicate-key error:
mysql> CREATE TABLE t (i INT NOT NULL PRIMARY KEY);mysql> INSERT INTO t (i) VALUES(1),(1);ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY' WithIGNORE, the row containing the duplicate key still is not inserted, but a warning occurs instead of an error:
mysql> INSERT IGNORE INTO t (i) VALUES(1),(1);Query OK, 1 row affected, 1 warning (0.01 sec)Records: 2 Duplicates: 1 Warnings: 1mysql> SHOW WARNINGS;+---------+------+---------------------------------------+| Level | Code | Message |+---------+------+---------------------------------------+| Warning | 1062 | Duplicate entry '1' for key 'PRIMARY' |+---------+------+---------------------------------------+1 row in set (0.00 sec) Example: If the tablet2 has aNOT NULL columnid, attempting to insertNULL produces an error in strict SQL mode:
mysql> CREATE TABLE t2 (id INT NOT NULL);mysql> INSERT INTO t2 (id) VALUES(1),(NULL),(3);ERROR 1048 (23000): Column 'id' cannot be nullmysql> SELECT * FROM t2;Empty set (0.00 sec) If the SQL mode is not strict,IGNORE causes theNULL to be inserted as the column implicit default (0 in this case), which enables the row to be handled without skipping it:
mysql> INSERT INTO t2 (id) VALUES(1),(NULL),(3);mysql> SELECT * FROM t2;+----+| id |+----+| 1 || 0 || 3 |+----+ These statements support theIGNORE keyword:
CREATE TABLE ... SELECT:IGNOREdoes not apply to theCREATE TABLEorSELECTparts of the statement but to inserts into the table of rows produced by theSELECT. Rows that duplicate an existing row on a unique key value are discarded.DELETE:IGNOREcauses MySQL to ignore errors during the process of deleting rows.INSERT: WithIGNORE, rows that duplicate an existing row on a unique key value are discarded. Rows set to values that would cause data conversion errors are set to the closest valid values instead.For partitioned tables where no partition matching a given value is found,
IGNOREcauses the insert operation to fail silently for rows containing the unmatched value.LOAD DATA,LOAD XML: WithIGNORE, rows that duplicate an existing row on a unique key value are discarded.UPDATE: WithIGNORE, rows for which duplicate-key conflicts occur on a unique key value are not updated. Rows updated to values that would cause data conversion errors are updated to the closest valid values instead.
TheIGNORE keyword applies to the following ignorable errors:
The Effect of Strict SQL Mode on Statement Execution
The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients, depending on the value of thesql_mode system variable. In“strict” SQL mode, the server upgrades certain warnings to errors.
For example, in non-strict SQL mode, inserting the string'abc' into an integer column results in conversion of the value to 0 and a warning:
mysql> SET sql_mode = '';Query OK, 0 rows affected (0.00 sec)mysql> INSERT INTO t (i) VALUES('abc');Query OK, 1 row affected, 1 warning (0.01 sec)mysql> SHOW WARNINGS;+---------+------+--------------------------------------------------------+| Level | Code | Message |+---------+------+--------------------------------------------------------+| Warning | 1366 | Incorrect integer value: 'abc' for column 'i' at row 1 |+---------+------+--------------------------------------------------------+1 row in set (0.00 sec)In strict SQL mode, the invalid value is rejected with an error:
mysql> SET sql_mode = 'STRICT_ALL_TABLES';Query OK, 0 rows affected (0.00 sec)mysql> INSERT INTO t (i) VALUES('abc');ERROR 1366 (HY000): Incorrect integer value: 'abc' for column 'i' at row 1 For more information about possible settings of thesql_mode system variable, seeSection 5.1.10, “Server SQL Modes”.
Strict SQL mode applies to the following statements under conditions for which some value might be out of range or an invalid row is inserted into or deleted from a table:
Within stored programs, individual statements of the types just listed execute in strict SQL mode if the program was defined while strict mode was in effect.
Strict SQL mode applies to the following errors, which represent a class of errors in which an input value is either invalid or missing. A value is invalid if it has the wrong data type for the column or might be out of range. A value is missing if a new row to be inserted does not contain a value for aNOT NULL column that has no explicitDEFAULT clause in its definition.
ER_BAD_NULL_ERRORER_CUT_VALUE_GROUP_CONCATER_DATA_TOO_LONGER_DATETIME_FUNCTION_OVERFLOWER_DIVISION_BY_ZEROER_INVALID_ARGUMENT_FOR_LOGARITHMER_NO_DEFAULT_FOR_FIELDER_NO_DEFAULT_FOR_VIEW_FIELDER_TOO_LONG_KEYER_TRUNCATED_WRONG_VALUEER_TRUNCATED_WRONG_VALUE_FOR_FIELDER_WARN_DATA_OUT_OF_RANGEER_WARN_NULL_TO_NOTNULLER_WARN_TOO_FEW_RECORDSER_WRONG_ARGUMENTSER_WRONG_VALUE_FOR_TYPEWARN_DATA_TRUNCATEDBecause continued MySQL development defines new errors, there may be errors not in the preceding list to which strict SQL mode applies.
In MySQL 5.7.22, these SQL modes are deprecated and are removed in MySQL 8.0:DB2,MAXDB,MSSQL,MYSQL323,MYSQL40,ORACLE,POSTGRESQL,NO_FIELD_OPTIONS,NO_KEY_OPTIONS,NO_TABLE_OPTIONS.
In MySQL 5.7, theONLY_FULL_GROUP_BY SQL mode is enabled by default becauseGROUP BY processing has become more sophisticated to include detection of functional dependencies. However, if you find that havingONLY_FULL_GROUP_BY enabled causes queries for existing applications to be rejected, either of these actions should restore operation:
If it is possible to modify an offending query, do so, either so that nonaggregated columns are functionally dependent on
GROUP BYcolumns, or by referring to nonaggregated columns usingANY_VALUE().If it is not possible to modify an offending query (for example, if it is generated by a third-party application), set the
sql_modesystem variable at server startup to not enableONLY_FULL_GROUP_BY.
In MySQL 5.7, theERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATE SQL modes are deprecated. The long term plan is to have the three modes be included in strict SQL mode and to remove them as explicit modes in a future release of MySQL. For compatibility in MySQL 5.7 with MySQL 5.6 strict mode and to provide additional time for affected applications to be modified, the following behaviors apply:
ERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEare not part of strict SQL mode, but it is intended that they be used together with strict mode. As a reminder, a warning occurs if they are enabled without also enabling strict mode or vice versa.ERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEare enabled by default.
With the preceding changes, stricter data checking is still enabled by default, but the individual modes can be disabled in environments where it is currently desirable or necessary to do so.
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