mysql如何删除主键？(2)-木庄网络博客

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)

如果直接删除，会报错

1	`mysql>` `alter` `table` `test1_2` `drop` `primary` `key;`

输出：

1 2	`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长列，无法直接删除`

列的属性还带有AUTO_INCREMENT，那么要先将这个列的自动增长属性去掉，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