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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)
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