How to avoid inserting duplicate rows in MySQL?

To avoid inserting duplicate rows in MySQL, you can use UNIQUE(). The syntax is as follows −

ALTER TABLE yourTableName ADD UNIQUE(yourColumnName1,yourColumnName2,...N);

To understand the above syntax, let us create a table. 

The query to create a table is as follows −

mysql> create table avoidInsertingDuplicateRows    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> FirstValue int,    -> SecondValue int    -> ); Query OK, 0 rows affected (0.53 sec)

Now check the description of table using desc command. 

The query is as follows −

mysql> desc avoidInsertingDuplicateRows;

Sample The following is The output −

+-------------+---------+------+-----+---------+----------------+ | Field       | Type    | Null | Key | Default | Extra          | +-------------+---------+------+-----+---------+----------------+ | Id          | int(11) | NO   | PRI | NULL    | auto_increment | | FirstValue  | int(11) | YES  |     | NULL    | | | SecondValue | int(11) | YES  |     | NULL   | | +-------------+---------+------+-----+---------+----------------+ 3 rows in set (0.00 sec)

Here is the query to avoid inserting duplicate rows in MySQL. We will set it with the insert command to insert records in the table −

mysql> insert into avoidInsertingDuplicateRows(FirstValue,SecondValue) values(10,20); Query OK, 1 row affected (0.24 sec) mysql> insert into avoidInsertingDuplicateRows(FirstValue,SecondValue) values(10,20); ERROR 1062 (23000): Duplicate entry '10-20' for key 'FirstValue'

Display all records from the table using select statement. 

The query is as follows −

mysql> select *from avoidInsertingDuplicateRows;

Here is the output −

+----+------------+-------------+ | Id | FirstValue | SecondValue | +----+------------+-------------+ | 1 | 10 | 20 | +----+------------+-------------+ 1 row in set (0.00 sec)