mysql怎样删除主键?
发布时间:08/01 来源:未知 浏览:
关键词:
第一我们来看看删除主键的语法:
ALTER TABLE TABLE_NAME DROP PRIMARY KEY;
在MySQL中删除主键要考虑两种状况:
1、主键列不带任何束缚,可以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)
我们可以直接运用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、要是是自增(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)
要是直接删除,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 #这注明此列是主动增长列,没法直接删除
列的属性还带有AUTO_INCREMENT,那么要先将这个列的主动增长属性去除,才可以删除主键。
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
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