Find and display duplicate values only once from a column in MySQL

Let us first create a table −

mysql> create table DemoTable -> ( -> value int -> ); Query OK, 0 rows affected (0.82 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(100); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.28 sec) mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.34 sec) mysql> insert into DemoTable values(30); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable values(40); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.07 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

Output

This will produce the following output −

+-------+ | value | +-------+ | 10 | | 100 | | 20 | | 10 | | 30 | | 40 | | 20 | +-------+ 7 rows in set (0.00 sec)

Following is the query to find the duplicate values and display them once −

mysql> select *from DemoTable group by value having count(*) > 1;

Output

This will produce the following output −

+-------+ | value | +-------+ | 10 | | 20 | +-------+ 2 rows in set (0.00 sec)