Count duplicate ids and display the result in a separate column with MySQL

Let us first create a table −

mysql> create table DemoTable1453    -> (    -> CustomerId int,    -> CustomerReviewNumber int    -> ); Query OK, 0 rows affected (0.58 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable1453 values(10,4); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable1453 values(10,4); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable1453 values(11,5); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1453 values(11,5); Query OK, 1 row affected (0.07 sec) mysql> insert into DemoTable1453 values(11,5); Query OK, 1 row affected (0.06 sec) mysql> insert into DemoTable1453 values(13,2); Query OK, 1 row affected (0.27 sec) mysql> insert into DemoTable1453 values(11,5); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1453 values(10,4); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1453 values(13,2); Query OK, 1 row affected (0.14 sec)

Display all records from the table using select statement −

mysql> select * from DemoTable1453;

This will produce the following output −

+------------+----------------------+ | CustomerId | CustomerReviewNumber | +------------+----------------------+ |         10 |                    4 | |         10 |                    4 | |         11 |                    5 | |         11 |                    5 | |         11 |                    5 | |         13 |                    2 | |         11 |                    5 | |         10 |                    4 | |         13 |                    2 | +------------+----------------------+ 9 rows in set (0.00 sec)

Following is the query to count duplicate ids −

mysql> select CustomerId,count(distinct CustomerReviewNumber)    -> from DemoTable1453    -> group by CustomerId;

This will produce the following output −

+------------+--------------------------------------+ | CustomerId | count(distinct CustomerReviewNumber) | +------------+--------------------------------------+ |         10 |                                    1 | |         11 |                                    1 | |         13 |                                    1 | +------------+--------------------------------------+ 3 rows in set (0.14 sec)