mysql怎样删除主键?【MySQL教程】,mysql,主键
起首我们来看看删除主键的语法:
ALTER TABLE TABLE_NAME DROP PRIMARY KEY;
在MySQL中删除主键要斟酌两种状况:
1、主键列不带任何束缚,能够直接删除主键的状况
例:
mysql> create table test1_3( -> id int not null primary key, -> name char(10) -> ); Query OK, 0 rows affected (0.01 sec)
我们能够直接运用drop来删除主键
mysql> alter table test1_3 drop primary key; Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0
2、假如是自增(AUTO_INCREMENT属性)的主键
例:
mysql> create table test1_2( -> id int not null auto_increment, -> name char(10),-> primary key(id) -> ); Query OK, 0 rows affected (0.00 sec) mysql> desc test1_2; +-------+----------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+----------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | char(10) | YES | | NULL | | +-------+----------+------+-----+---------+----------------+ 2 rows in set (0.00 sec)
假如直接删除,会报错
mysql> alter table test1_2 drop primary key;
输出:
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key #这说明此列是自动增进列,没法直接删除
列的属性还带有AUTO_INCREMENT,那末要先将这个列的自动增进属性去掉,才能够删除主键。
mysql> alter table test1_2 modify id int; Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table test1_2 drop primary key; Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0
以上就是mysql怎样删除主键?的细致内容,更多请关注ki4网别的相干文章!