我们如何删除应用于现有 MySQL 表的多个列的复合 PRIMARY KEY 约束?
摘要:
示例假设我们有一个表“Room_allotment”,在“ID”和“RoomNo”列上具有复合主键约束,如下-mysql>describeroom_allotment;+--------+-------------+------+-----+---------+-------+|Field|Type|Nu...
示例
假设我们有一个表“Room_allotment”,在“ID”和“RoomNo”列上具有复合主键约束,如下 -
mysql> describe room_allotment; +--------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+-------------+------+-----+---------+-------+ | id | int(11) | NO | PRI | 0 | | | Name | varchar(20) | NO | PRI | | | | RoomNo | int(11) | YES | | NULL | | +--------+-------------+------+-----+---------+-------+ 3 rows in set (0.06 sec)
现在,如果我们想删除复合 PRIMARY KEY 约束,那么我们可以使用 ALTER TABLE 语句,如下所示 -
mysql> Alter table room_allotment DROP PRIMARY KEY; Query OK, 0 rows affected (0.19 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> describe room_allotment; +--------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+-------------+------+-----+---------+-------+ | id | int(11) | NO | | 0 | | | Name | varchar(20) | NO | | | | | RoomNo | int(11) | YES | | NULL | | +--------+-------------+------+-----+---------+-------+ 3 rows in set (0.07 sec)
上面的结果集显示列“ID”和“RoomNo”的复合 PRIMARY KEY 约束已被删除。
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