To make a pair of columns unique, use UNIQUE with ALTER TABLE command. Following is the syntax −
alter table yourTableName add unique yourUniqueName(yourColumnName1,yourColumnName2,...N);
Let us first create a table −
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)
Following is the query to make a pair of unique columns in MySQL −
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
Insert some records in the table using insert command −
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'Display all records from the table using select statement −
mysql> select *from DemoTable;
This will produce the following output −
+-----------+------------------+-----------------+------------+--------------------+ | StudentId | StudentFirstName | StudentLastName | StudentAge | StudentPhoneNumber | +-----------+------------------+-----------------+------------+--------------------+ | 1 | John | Doe | 21 | 9878567878 | | 2 | John | Smith | 23 | 7654674545 | +-----------+------------------+-----------------+------------+--------------------+ 2 rows in set (0.00 sec)