如何使一对列在MySQL中唯一？
要使一对列唯一，请使用带有ALTERTABLE命令的UNIQUE。以下是语法-
alter table yourTableName add unique yourUniqueName(yourColumnName1,yourColumnName2,...N);
让我们首先创建一个表-
create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentFirstName varchar(100), StudentLastName varchar(100), StudentAge int, StudentPhoneNumber varchar(20) );
以下是在MySQL中创建一对唯一列的查询-
alter table DemoTable add unique DemoTable_unique_StudentFirstName_StudentPhoneNumber(StudentFirstName,StudentPhoneNumber); Records: 0 Duplicates: 0 Warnings: 0
使用插入命令在表中插入一些记录-
insert into DemoTable(StudentFirstName,StudentLastName,StudentAge,StudentPhoneNumber) values('John','Doe',21,'9878567878');
insert into DemoTable(StudentFirstName,StudentLastName,StudentAge,StudentPhoneNumber) values('John','Smith',23,'7654674545');
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语句显示表中的所有记录-
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)