sql_mode
为什么会有各种各样的sqlmode呢?不外乎标准与非标准的问题!标准的东西贵在普适,但不是最合适的!各种各样的dbms总会加入自己的理 解,扩展自己的产品功能,这就会引起非标准的问题。所以一个成熟的dbms总会提供sql_mode这一解决方案形式,使dbms系统具有某种行为模式以 便实现 和 标准、其他dbms系统的兼容!
mysql的sql_mode
mysql的sql_mode的设置方式
mysql的各种mode
mysql的预定义模式
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 5.1 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="
option, or by using modes
"sql-mode="
in modes
"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 modes
value 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='
statement to set the modes
'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.
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.
See Section 18.5, “Restrictions and Limitations on Partitioning”, for more information.
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:
This mode changes syntax and behavior to conform more closely to standard SQL.
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.
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.
When this manual refers to “strict mode,” it means a mode where at least one of STRICT_TRANS_TABLES
or STRICT_ALL_TABLES
is enabled.
The following list describes all supported modes:
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.
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
.
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 quotes to quote literal strings, because it is interpreted as an identifier.
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
.
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
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 8.2.4, “Function Name Parsing and Resolution”.
Prevent the GRANT
statement from automatically creating new users if it would otherwise do so, unless a non-empty password also is specified.
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. mysqldump now automatically includes in its output a statement that enables NO_AUTO_VALUE_ON_ZERO
, to avoid this problem.
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.
When creating a table, ignore all INDEX DIRECTORY
and DATA DIRECTORY
directives. This option is useful on slave replication servers.
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.
Up through MySQL 5.1.11, with NO_ENGINE_SUBSTITUTION
disabled, the default engine is used and a warning occurs if the desired engine is known but disabled or not compiled in. If the desired engine is invalid (not a known engine name), an error occurs and the table is not created or altered.
With NO_ENGINE_SUBSTITUTION
enabled, an error occurs and the table is not created or altered if the desired engine is unavailable for any reason (whether disabled or invalid).
As of MySQL 5.1.12, storage engines can be pluggable at runtime, so the distinction between disabled and invalid no longer applies. All 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.
Do not print MySQL-specific column options in the output of SHOW CREATE TABLE
. This mode is used by mysqldump in portability mode.
Do not print MySQL-specific index options in the output of SHOW CREATE TABLE
. This mode is used by mysqldump in portability mode.
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.
In integer subtraction operations, do not mark the result as UNSIGNED
if one of the operands is unsigned. In other words, the result of a subtraction is always signed whenever this mode is in effect, even if one of the operands 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 | | | 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) | | | 0 | |
+-------+------------+------+-----+---------+-------+
Note that this means that BIGINT UNSIGNED
is not 100% usable in all contexts. See Section 11.9, “Cast Functions and Operators”.
mysql>SET SQL_MODE = '';
mysql>SELECT CAST(0 AS UNSIGNED) - 1;
+-------------------------+
| CAST(0 AS UNSIGNED) - 1 |
+-------------------------+
| 18446744073709551615 |
+-------------------------+
mysql>SET SQL_MODE = 'NO_UNSIGNED_SUBTRACTION';
mysql>SELECT CAST(0 AS UNSIGNED) - 1;
+-------------------------+
| CAST(0 AS UNSIGNED) - 1 |
+-------------------------+
| -1 |
+-------------------------+
In strict mode, don't allow '0000-00-00'
as a valid date. You can still insert zero dates with the IGNORE
option. When not in strict mode, the date is accepted but a warning is generated.
In strict mode, do not accept dates where the year part is non-zero but the month or day part is 0 (for example, '0000-00-00'
is legal but '2010-00-01'
and '2010-01-00'
are not). If used with the IGNORE
option, MySQL inserts a '0000-00-00'
date for any such date. When not in strict mode, the date is accepted but a warning is generated.
Do not allow queries for which the SELECT
list refers to non-aggregated columns that are not named in the GROUP BY
clause. The following query is invalid with this mode enabled because address
is not named in the GROUP BY
clause:
SELECT name, address, MAX(age) FROM t GROUP BY name;
As of MySQL 5.1.11, this mode also restricts references to non-aggregated columns in the HAVING
clause that are not named in the GROUP BY
clause.
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. This mode was added in MySQL 5.1.20.
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 as CONCAT()
) rather than as a synonym for OR
.
Treat REAL
as a synonym for FLOAT
. By default, MySQL treats REAL
as a synonym for DOUBLE
.
Enable strict mode for all storage engines. Invalid data values are rejected. Additional detail follows.
Enable strict mode for transactional storage engines, and when possible for non-transactional storage engines. Additional details follow.
Strict mode controls how MySQL handles input values that are invalid or missing. 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.)
For transactional tables, an error occurs for invalid or missing values in a statement when either of the STRICT_ALL_TABLES
or STRICT_TRANS_TABLES
modes are enabled. The statement is aborted and rolled back.
For non-transactional 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 option is enabled:
For STRICT_ALL_TABLES
, MySQL returns an error and ignores the rest of the rows. However, in this case, the earlier rows still have been inserted or updated. This means that you might get a partial update, which might not be what you want. To avoid this, it is best to use single-row statements because these 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 insert 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 10.1.4, “Data Type Default Values”.
Strict mode disallows invalid date values such as '2004-04-31'
. It does not disallow dates with zero month or day parts such as '2004-04-00'
or “zero” dates. To disallow these as well, enable the NO_ZERO_IN_DATE
and NO_ZERO_DATE
SQL modes in addition to strict mode.
If you are not using strict mode (that is, neither STRICT_TRANS_TABLES
nor STRICT_ALL_TABLES
is enabled), MySQL inserts adjusted values for invalid or missing values and produces warnings. In strict mode, you can produce this behavior by using INSERT IGNORE
or UPDATE IGNORE
. See Section 12.5.5.42, “SHOW WARNINGS
Syntax”.
Strict mode does not affect whether foreign key constraints are checked. foreign_key_checks
can be used for that. (See Section 5.1.4, “Session System Variables”.)
The following special modes are provided as shorthand for combinations of mode values from the preceding list.
The descriptions include all mode values that are available in the most recent version of MySQL. For older versions, a combination mode does not include individual mode values that are not available except in newer versions.
Equivalent to REAL_AS_FLOAT
, PIPES_AS_CONCAT
, ANSI_QUOTES
, IGNORE_SPACE
.
As of MySQL 5.1.18, ANSI
mode also causes the server to return an error for queries where a set function S
with an outer reference
cannot 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 the WHERE
clause of that query. Standard SQL requires an error in this situation. If ANSI
mode is not enabled, the server treats
in such queries the same way that it would interpret S
(outer_ref
)
, as was always done prior to 5.1.18. S
(const
)
Equivalent to PIPES_AS_CONCAT
, ANSI_QUOTES
, IGNORE_SPACE
, NO_KEY_OPTIONS
, NO_TABLE_OPTIONS
, NO_FIELD_OPTIONS
.
Equivalent to PIPES_AS_CONCAT
, ANSI_QUOTES
, IGNORE_SPACE
, NO_KEY_OPTIONS
, NO_TABLE_OPTIONS
, NO_FIELD_OPTIONS
, NO_AUTO_CREATE_USER
.
Equivalent to PIPES_AS_CONCAT
, ANSI_QUOTES
, IGNORE_SPACE
, NO_KEY_OPTIONS
, NO_TABLE_OPTIONS
, NO_FIELD_OPTIONS
.
Equivalent to NO_FIELD_OPTIONS
, HIGH_NOT_PRECEDENCE
.
Equivalent to NO_FIELD_OPTIONS
, HIGH_NOT_PRECEDENCE
.
Equivalent to PIPES_AS_CONCAT
, ANSI_QUOTES
, IGNORE_SPACE
, NO_KEY_OPTIONS
, NO_TABLE_OPTIONS
, NO_FIELD_OPTIONS
, NO_AUTO_CREATE_USER
.
Equivalent to PIPES_AS_CONCAT
, ANSI_QUOTES
, IGNORE_SPACE
, NO_KEY_OPTIONS
, NO_TABLE_OPTIONS
, NO_FIELD_OPTIONS
.
Equivalent to STRICT_TRANS_TABLES
, STRICT_ALL_TABLES
, NO_ZERO_IN_DATE
, NO_ZERO_DATE
, ERROR_FOR_DIVISION_BY_ZERO
, NO_AUTO_CREATE_USER
.