ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be def

将一个MyISAM 引擎的表转为InnoDB引擎时出现如下错误：

ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

mysql> CREATE TABLE `t_myisam` (

`id` int(10) NOT NULL AUTO_INCREMENT,

`a` varchar(10) NOT NULL DEFAULT '',

PRIMARY KEY (a,id) ) 

ENGINE=MyISAM DEFAULT CHARSET=utf8;

Query OK, 0 rows affected (0.00 sec)

mysql> ALTER TABLE `t_myisam` ENGINE=InnoDB;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

参考上述表结构重新创建一个InnDB引擎的表也不行。

mysql> CREATE TABLE `t_innodb` (

`id` int(10) NOT NULL AUTO_INCREMENT,

`a` varchar(10) NOT NULL DEFAULT '',

 PRIMARY KEY (a,id)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

改变索引的顺序重新建表

CREATE TABLE `t_innodb` (

  `id` int(10) NOT NULL AUTO_INCREMENT,

  `a` varchar(10) NOT NULL DEFAULT '',

  PRIMARY KEY (id,a)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

原来在InnoDB引擎中，自增长的列必须是索引，而且必须是索引的第一个列。