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Mysql：命令选项、配置选项、，全局、会话系统变量、状态变量：SQL模式

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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可以同时运行在各种sqlmode下，尤其是可以在会话级别进行模式设置，提供了最大的应用程序灵活性！
  • mysql的sqlmode定义了：语法支持规则、执行何种数据有效性验证处理。
  • mysql的sqlmode可以叠加，例如在strict模式下允许部分其他行为...
  • mysql的sqlmode有很多预定义的模式！

mysql的sql_mode的设置方式

  • 启动mysqld服务器是指定： --sql-mode="modes"
  • 在选项文件里设置：sql-mode="modes"
  • 运行时设置全局系统变量：set global sql_mode="modes"　　--需要super权限
  • 运行时设置会话系统变量：set [session] sql_mode="modes"
  • 可以将sqlmode设为空，mysql将使用编译时默认的行为方式

mysql的各种mode

  • STRICT_ALL_TABLES　　--对所有的存储引擎应用 严格 模式。行为：拒绝无效数据或缺失数据。对于事务性引擎：如果输入无效数据或位提供数据，语句终止，事务回滚，错误发生。对于非非非事务性引擎：如果是第一行数据就发生数据无效或丢失，语句终止，表数据不改变；如果不是第一行数据，保留之前影响数据，终止语句执行，错误发生！部分啊，数据不完整！
  • STRICT_TRANS_TABLES　　--对事务性存储引擎应用 严格 模式。可能的话，对非事物性存储引擎应用 严格 模式！行为：拒绝无效数据或缺失数据。对于事务性引擎：如果输入无效数据或位提供数据，语句终止，事务回滚，错误发生。对于非非非事务性引擎：如果是第一行数据就发生数据无效或丢失，语句终止，表数据不改变；如果不是第一行数据，mysql会以 数据类型的隐式默认值 插入，语句成功执行，有警告！
  • ALLOW_INVALID_DATES　　--允许：非法的日期时间、"0000-00-00“日期。否则出错
  • NO_ZERO_DATE　　--禁止"0000-00-00“日期。但是你仍然可以通过ignore选项插入0日期
  • NO_ZERO_IN_DATE　　--禁止日期中的month、day部分出现”00“。但是你仍然可以通过ignore选项插入0日期
  • ANSI_QUOTES　　--双引号引用标识符，而不是表示字符串
  • ERROR_FOR_DIVISION_BY_ZERO　　--被0除出错，而不是警告后返回null
  • HIGH_NOT_PRECEDENCE　　--NOT具有较高的操作符优先顺序，主要是兼容较低版本的mysql。例如在此模式下：not a and b 依据 （not a） and b解析，而不是较高版本的not （a and b）的解析顺序
  • IGNORE_SPACE　　--对于部分内置函数名称作为保留字处理，不能直接当做用户标识符！这样这些函数的括号“（”前面可以有若干空白 ——不必紧紧跟随着其函数名称。在“非IGNORE_SPACE”的默认模式下，部分内置函数名称不作为保留字处理，如果其后紧跟“（”就认为是函数，否 则认为是用户的标识符。其他mysql就不应该出现这个使事情复杂化的东西——一律当做保留字处理岂不更简单！
  • NO_AUTO_CREATE_USER　　--禁止grant语句在没有指定 非空白 密码的情况下创建目前尚不存在的用户
  • NO_AUTO_VALUE_ON_ZERO　　--禁止在auto_increment列上通过赋值“0"自增！该模式主要是解决自增列存储有意义的0列值，或数据导入时可能将有意义的0当做自增值的情况下
  • NO_BACKSLASH_ESCAPES　　--禁止字符转义，“\”仅仅作为普通字符使用
  • NO_DIR_IN_CREATE　　--在创建table时，忽略inex directory 和 data directory语句
  • NO_ENGINE_SUBTITUTION　　--在创建或修改table时，当指定的引擎不可用是，语句出错，禁止mysql使用用默认的引擎。默认情况下，mysql发出警告进行无效引擎的替换
  • NO_FIELD_OPTIONS、NO_KEY_OPTIONS、NO_TABLE_OPTIONS　　--控制mysqldump和show语句是否显示额外的信息
  • NO_UNSIGNED_SUBTRACTION　　--在含有unsigned 整数 的整数减法（-）运算中，禁止将结果result当做unsigned整数处理。小心这个雷啊！
  • ONLY_FULL_GROUP_BY　　--select 列表中的非聚合列 必须是在group by中出现的列！自mysql5.1.11后，还限制having子句中的非聚合列也必须是group by中的列
  • PAD_CHAR_TO_FULL_LENGTH　　--保留char列的尾随空格（不trim掉），注意：varchar列总是trim！。该模式自5.1.20加入
  • PIPES_AS_CONCAT　　--"||"操作符当做字符串连接符，类似于concat（str,...）；而不是逻辑 or！
  • REAL_AS_FLOAT　　--将real类型作为float类型；而不是douoble

mysql的预定义模式

  • ANSI　　　　　<==>　　PIPES_AS_CONCAT、ANSI_QUOTE、IGNORE_SPACE、REAL_AS_FLOAT　
  • TRADITIONAL <==>　STRICT_TRANS_TABLES、STRICT_ALL_TABLES、NO_ZERO_IN_DATE、NO_ZERO_DATE、ERROR_FOR_DIVISION_BY_ZERO、NO_AUTO_CREATE_USER　
  1. MYSQL323　<==>　　NO_FIELD_OPTIONS、HIGH_NOT_PRECDEDENCE
  2. MYSQL40 　<==>　　NO_FIELD_OPTIONS、HIGH_NOT_PRECDEDENCE
  3. MSSQL　　　<==>　　PIPES_AS_CONCAT、ANSI_QUOTE、IGNORE_SPACE、NO_KEY_OPTIONS、NO_TABLE_OPTIONS、NO_FIELD_OPTIONS、REAL_AS_FLOAT
  4. DB2　　　　 <==>　　PIPES_AS_CONCAT、ANSI_QUOTE、IGNORE_SPACE、NO_KEY_OPTIONS、NO_TABLE_OPTIONS、NO_FIELD_OPTIONS
  5. MAXDB　　　 <==>　　PIPES_AS_CONCAT、ANSI_QUOTE、IGNORE_SPACE、NO_KEY_OPTIONS、NO_TABLE_OPTIONS、NO_FIELD_OPTIONS、NO_AUTO_CREATE_USER
  6. ORACLE 　　 <==>　　PIPES_AS_CONCAT、ANSI_QUOTE、IGNORE_SPACE、NO_KEY_OPTIONS、NO_TABLE_OPTIONS、NO_FIELD_OPTIONS、NO_AUTO_CREATE_USER
  7. POSTGRESQL<==>　 PIPES_AS_CONCAT、ANSI_QUOTE、IGNORE_SPACE、NO_KEY_OPTIONS、NO_TABLE_OPTIONS、NO_FIELD_OPTIONS

附件：

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 5.1 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="modes" option, or by using sql-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 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='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.

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.

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:

  • 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.

  • 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.

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:

  • 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.

    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. With ANSI_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.

  • 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

    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”.

  • 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.

  • 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. 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.

  • 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.

    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.

  • 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

    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 |
    +-------------------------+

  • NO_ZERO_DATE

    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.

  • NO_ZERO_IN_DATE

    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.

  • ONLY_FULL_GROUP_BY

    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.

  • 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. 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)

  • 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 mode for all storage engines. Invalid data values are rejected. Additional detail follows.

  • STRICT_TRANS_TABLES

    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.

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