MySQL 如何在MySQL中使一对列唯一

为了使一对列唯一，使用ALTER TABLE命令和UNIQUE关键字。以下是语法−

alter table 你的表名 add unique 你想要的唯一约束名(列名1,列名2,...N);

让我们先创建一个表−

mysql> create table DemoTable
(
   StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   StudentFirstName varchar(100),
   StudentLastName varchar(100),
   StudentAge int,
   StudentPhoneNumber varchar(20)
);
Query OK, 0 rows affected (0.81 sec)

以下是在MySQL中创建一对唯一列的查询−

mysql> alter table DemoTable add unique DemoTable_unique_StudentFirstName_StudentPhoneNumber(StudentFirstName,StudentPhoneNumber);
Query OK, 0 rows affected (0.40 sec)
Records: 0 Duplicates: 0 Warnings: 0

使用insert命令在表中插入一些记录−

mysql> insert into DemoTable(StudentFirstName,StudentLastName,StudentAge,StudentPhoneNumber) values('John','Doe',21,'9878567878');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable(StudentFirstName,StudentLastName,StudentAge,StudentPhoneNumber) values('John','Smith',23,'7654674545');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable(StudentFirstName,StudentLastName,StudentAge,StudentPhoneNumber)
values('John','Brown',21,'9878567878');
ERROR 1062 (23000): Duplicate entry 'John-9878567878' for key 'DemoTable_unique_StudentFirstName_StudentPhoneNumber'

使用select语句从表中显示所有记录−

mysql> select *from DemoTable;

这将产生以下输出−

+-----------+------------------+-----------------+------------+--------------------+
| StudentId | StudentFirstName | StudentLastName | StudentAge | StudentPhoneNumber |
+-----------+------------------+-----------------+------------+--------------------+
|         1 | John             | Doe             | 21         | 9878567878         |
|         2 | John             | Smith           | 23         | 7654674545         |
+-----------+------------------+-----------------+------------+--------------------+
2 rows in set (0.00 sec)

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