mysql 将唯一键更改为主键 (mariadb)
mysql changing unique key to primary (mariadb)
我有 table 个用户：
+--------------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------+------+-----+---------+-------+
| userid | varchar(30) | YES | | NULL | |
| lname | varchar(40) | YES | | NULL | |
| fname | varchar(20) | YES | | NULL | |
| system_id | varchar(12) | YES | | NULL | |
+--------------------+--------------+------+-----+---------+-------+
我想将 system_id 和 userid 更改为唯一键。
如果我通过 ALTER TABLE users MODIFY userid varchar(30) NOT NULL UNIQUE KEY; 更改它们，我得到：
+--------------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------+------+-----+---------+-------+
| userid | varchar(30) | NO | PRI | NULL | |
| lname | varchar(40) | YES | | NULL | |
| fname | varchar(20) | YES | | NULL | |
| system_id | varchar(12) | YES | | NULL | |
+--------------------+--------------+------+-----+---------+-------+
然后如果我更改 system_id ALTER TABLE users MODIFY system_id varchar(30) NOT NULL UNIQUE KEY;
+--------------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------+------+-----+---------+-------+
| userid | varchar(30) | NO | PRI | NULL | |
| lname | varchar(40) | YES | | NULL | |
| fname | varchar(20) | YES | | NULL | |
| system_id | varchar(12) | NO | UNI | NULL | |
+--------------------+--------------+------+-----+---------+-------+
为什么 MySQL 将我的 UNIQUE 键更改为 PRI 而我从未指定过它？
"A UNIQUE index may be displayed as PRI if it cannot contain NULL values and there is no PRIMARY KEY in the table. A UNIQUE index may display as MUL if several columns form a composite UNIQUE index; although the combination of the columns is unique, each column can still hold multiple occurrences of a given value."
https://dev.mysql.com/doc/refman/5.7/en/show-columns.html
找到我的答案。
我有 table 个用户：
+--------------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------+------+-----+---------+-------+
| userid | varchar(30) | YES | | NULL | |
| lname | varchar(40) | YES | | NULL | |
| fname | varchar(20) | YES | | NULL | |
| system_id | varchar(12) | YES | | NULL | |
+--------------------+--------------+------+-----+---------+-------+
我想将 system_id 和 userid 更改为唯一键。
如果我通过 ALTER TABLE users MODIFY userid varchar(30) NOT NULL UNIQUE KEY; 更改它们，我得到：
+--------------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------+------+-----+---------+-------+
| userid | varchar(30) | NO | PRI | NULL | |
| lname | varchar(40) | YES | | NULL | |
| fname | varchar(20) | YES | | NULL | |
| system_id | varchar(12) | YES | | NULL | |
+--------------------+--------------+------+-----+---------+-------+
然后如果我更改 system_id ALTER TABLE users MODIFY system_id varchar(30) NOT NULL UNIQUE KEY;
+--------------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------+------+-----+---------+-------+
| userid | varchar(30) | NO | PRI | NULL | |
| lname | varchar(40) | YES | | NULL | |
| fname | varchar(20) | YES | | NULL | |
| system_id | varchar(12) | NO | UNI | NULL | |
+--------------------+--------------+------+-----+---------+-------+
为什么 MySQL 将我的 UNIQUE 键更改为 PRI 而我从未指定过它？
"A UNIQUE index may be displayed as PRI if it cannot contain NULL values and there is no PRIMARY KEY in the table. A UNIQUE index may display as MUL if several columns form a composite UNIQUE index; although the combination of the columns is unique, each column can still hold multiple occurrences of a given value."
https://dev.mysql.com/doc/refman/5.7/en/show-columns.html
找到我的答案。