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Using UNIQUE for varchar columns with some conditions in MySQL?
For this, you can use UNIQUE constraint on one or more columns −
alter table yourTablleName add unique(yourColumnName1,yourColumnName2,...N);
Let us first create a table −
mysql> create table DemoTable1598 -> ( -> EmployeeId int, -> EmployeeName varchar(20), -> EmployeeCountryName varchar(20) -> ); Query OK, 0 rows affected (0.52 sec)
Here is the query to implement UNIQUE on varchar columns −
mysql> alter table DemoTable1598 add unique(EmployeeName,EmployeeCountryName); Query OK, 0 rows affected (0.55 sec) Records: 0 Duplicates: 0 Warnings: 0
Insert some records in the table using insert command −
mysql> insert into DemoTable1598 values(101,'Adam','AUS'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable1598 values(102,'John','US'); Query OK, 1 row affected (0.64 sec) mysql> insert into DemoTable1598 values(103,'Adam','US'); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable1598 values(104,'Adam','AUS'); ERROR 1062 (23000): Duplicate entry 'Adam-AUS' for key 'EmployeeName'
Display all records from the table using select statement −
mysql> select * from DemoTable1598;
This will produce the following output −
+------------+--------------+---------------------+ | EmployeeId | EmployeeName | EmployeeCountryName | +------------+--------------+---------------------+ | 101 | Adam | AUS | | 102 | John | US | | 103 | Adam | US | +------------+--------------+---------------------+ 3 rows in set (0.00 sec)
Updated on: 16-Dec-2019
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