mysql 出现错误 Duplicate entry for key PRIMARY 解决办法

原来是没有主键的，想增加一列为主键。

mysql> desc t111;+-------+-------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+-------+-------------+------+-----+---------+-------+| name | varchar(24) | YES || robert | || age | int | YES || NULL | |+-------+-------------+------+-----+---------+-------+2 rows in set (0.00 sec)

执行代码，结果报错：

mysql> alter table t111 add stu_id tinyint primary key first;ERROR 1062 (23000): Duplicate entry '0' for key 't111.PRIMARY'

解决办法，把它设置为自增auto_increment：

mysql> alter table t111 add stu_id int(4) primary key auto_increment first;Query OK, 0 rows affected, 1 warning (0.06 sec)Records: 0 Duplicates: 0 Warnings: 1