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Perform count with CASE WHEN statement in MySQL?
For this, you can use CASE WHEN statement. Let us first create a table −
mysql> create table DemoTable1910 ( FirstName varchar(20), Marks int ); Query OK, 0 rows affected (0.00 sec)
Insert some records in the table using insert command −
mysql> insert into DemoTable1910 values('Chris',45); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1910 values('David',85); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1910 values('Chris',55); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1910 values('Chris',98); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1910 values('David',98); Query OK, 1 row affected (0.00 sec)
Display all records from the table using select statement −
mysql> select * from DemoTable1910;
This will produce the following output −
+-----------+-------+ | FirstName | Marks | +-----------+-------+ | Chris | 45 | | David | 85 | | Chris | 55 | | Chris | 98 | | David | 98 | +-----------+-------+ 5 rows in set (0.00 sec)
Here is the query to count column values efficiently −
mysql> select FirstName, sum(case when Marks=45 then 1 else 0 end), sum(case when Marks=98 then 1 else 0 end) from DemoTable1910 group by FirstName;
This will produce the following output −
+-----------+-------------------------------------------+-------------------------------------------+ | FirstName | sum(case when Marks=45 then 1 else 0 end) | sum(case when Marks=98 then 1 else 0 end) | +-----------+-------------------------------------------+-------------------------------------------+ | Chris | 1 | 1 | | David | 0 | 1 | +-----------+-------------------------------------------+-------------------------------------------+ 2 rows in set (0.00 sec)
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