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1、mysql 有众多的存储引擎,然而只有一个默认的存储引擎,通常来说它是innodb
2、mysql 可以通过sql_mode 来控制mysql 数据库的行为,今天我们要讲的就是no_engine_substitution
3、no_engine_subtitution的作用:mysql 在create table 时可以指定engine子句;这个engine子句用于指定表的存储引擎,那么问题就来了。
如果我把引擎指定成一个并不存在的引擎!这个时候mysql可以有两种行为供选择 1、直接报错;2、把表的存储引擎替换成innodb
例子:
1、环境检查(查看mysql所支持的存储引擎,sql_mode模式)
001:存储引擎,由下图可以看出在这个mysql上不支持federated 引擎
mysql> show engines; +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | Engine | Support | Comment | Transactions | XA | Savepoints | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | MyISAM | YES | MyISAM storage engine | NO | NO | NO | | CSV | YES | CSV storage engine | NO | NO | NO | | MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO | | BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO | | MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO | | PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO | | ARCHIVE | YES | Archive storage engine | NO | NO | NO | | InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES | | FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ 9 rows in set (0.00 sec)
002:sql_mode
mysql> show variables like ‘sql_mode‘; +---------------+---------------------+ | Variable_name | Value | +---------------+---------------------+ | sql_mode | STRICT_TRANS_TABLES | +---------------+---------------------+ 1 row in set (0.00 sec)
003:测试
mysql> create table t(x int) engine=federated; Query OK, 0 rows affected, 2 warnings (0.11 sec) mysql> show create table t; +-------+--------------------------------------------------------------------------------------+ | Table | Create Table | +-------+--------------------------------------------------------------------------------------+ | t | CREATE TABLE `t` ( `x` int(11) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1 | +-------+--------------------------------------------------------------------------------------+ 1 row in set (0.00 sec) mysql>
结论001:在sql_mode中不包涵no_engine_subtitution 且create table 中engine子句指定的存储引擎不被支持时,mysql会把表的引擎改为innodb。
例子:
在sql_mode包涵有no_engine_subtitution时
引擎支持情况:
mysql> show engines; +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | Engine | Support | Comment | Transactions | XA | Savepoints | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | MyISAM | YES | MyISAM storage engine | NO | NO | NO | | CSV | YES | CSV storage engine | NO | NO | NO | | MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO | | BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO | | MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO | | PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO | | ARCHIVE | YES | Archive storage engine | NO | NO | NO | | InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES | | FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ 9 rows in set (0.00 sec)
sql_mode情况:
mysql> show variables like ‘sql_mode‘; +---------------+--------------------------------------------+ | Variable_name | Value | +---------------+--------------------------------------------+ | sql_mode | STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION | +---------------+--------------------------------------------+ 1 row in set (0.00 sec)
测试:
mysql> create table t2(x int) engine=federated; ERROR 1286 (42000): Unknown storage engine ‘federated‘
结论002:当sql_mode中包涵no_engine_subtitution时,如果create table 时指定的engine项不被支持,这个时候mysql会支持报错。
mysql sql_mode 之 NO_ENGINE_SUBSTITUTION
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原文地址:http://www.cnblogs.com/JiangLe/p/5621856.html