mysql多个key，我们如何在现有MySQL表的多个列上设置
英语之声PRIMARYKEY？
我们可以通过使⽤ADD关键字和ALTER TABLE语句在现有表的多个列上设置PRIMARY KEY约束。
观音灵感歌原唱⽰例
假设我们有⼀个表“ Room_allotment”，如下所⽰：
mysql> Create table Room_allotment(Id Int, Name Varchar(20), RoomNo Int);
mysql> Describe Room_allotment;
+--------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| Id | int(11) | YES | | NULL | |注射器图片
刻骨铭心的回忆
| Name | varchar(20) | YES | | NULL | |
| RoomNo | int(11) | YES | | NULL | |
+--------+-------------+------+-----+---------+-------+
3 rows in t (0.11 c)
现在，我们可以使⽤以下查询在多个列“ id”和“ Name”上添加复合PRIMARY
KEYmysql> Alter Table Room_allotment ADD PRIMARY KEY(Id, Name);
Records: 0 Duplicates: 0 Warnings: 0
mysql> Describe Room_allotment;
+--------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |率性而为的意思
火鸡用英语怎么说+--------+-------------+------+-----+---------+-------+
眼袋去除
| Id | int(11) | NO | PRI | 0 | |
| Name | varchar(20) | NO | PRI | | |
| RoomNo | int(11) | YES | | NULL | |
+--------+-------------+------+-----+---------+-------+
防诈骗观后感
3 rows in t (0.12 c)
从上⾯的结果集中可以看出，PRIMARY KEY已添加到多列中。
