MySQL query to count the duplicate ID values and display the result in a separate column

To count the duplicate ID values, use aggregate function COUNT() and GROUP BY. Let us first create a table −

mysql> create table DemoTable (    Id int,    Name varchar(100) ); Query OK, 0 rows affected (1.30 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values(50,'Chris'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(51,'David'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(51,'Mike'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable values(50,'Sam'); Query OK, 1 row affected (0.17 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+------+-------+ | Id   | Name  | +------+-------+ |   50 | Chris | |   51 | David | |   51 | Mike  | |   50 | Sam   | +------+-------+ 4 rows in set (0.00 sec)

Following is the query to display the count of duplicate ID values in a new column −

mysql> select Id,count(Name) as Count    from DemoTable    group by Id;

This will produce the following output −

+------+-------+ | Id   | Count | +------+-------+ |   50 | 2 | |   51 | 2 | +------+-------+ 2 rows in set (0.00 sec)