Why should we use MySQL CASE Statement?

Use MySQL CASE for a fixed number of arguments.

The syntax is as follows

SELECT *, CASE WHEN yourColumName1>yourColumName2 THEN 'yourMessage1' ELSE 'yourMessage2' END AS anyAliasName FROM yourTableName;

To understand the above syntax, let us create a table. The query to create a table is as follows

mysql> create table CaseFunctionDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> Value1 int,
   -> Value2 int
   -> );
Query OK, 0 rows affected (0.56 sec)

Insert some records in the table using insert command.

The query is as follows

mysql> insert into CaseFunctionDemo(Value1,Value2) values(10,20);
Query OK, 1 row affected (0.21 sec)
mysql> insert into CaseFunctionDemo(Value1,Value2) values(100,40);
Query OK, 1 row affected (0.10 sec)
mysql> insert into CaseFunctionDemo(Value1,Value2) values(0,20);
Query OK, 1 row affected (0.15 sec)
mysql> insert into CaseFunctionDemo(Value1,Value2) values(0,-50);
Query OK, 1 row affected (0.12 sec)

Display all records from the table using select statement.

The query is as follows

mysql> select *from CaseFunctionDemo;

The following is the output

+----+--------+--------+
| Id | Value1 | Value2 |
+----+--------+--------+
| 1  | 10     | 20     |
| 2  | 100    | 40     |
| 3  | 0      | 20     |
| 4  | 0      | -50    |
+----+--------+--------+
4 rows in set (0.00 sec)

Here is the query for CASE statement

mysql> select*, case when Value1>Value2 then 'Value1 is Greater' else 'Value2 is Greater' end AS Comparision from CaseFunctionDemo;

The following is the output

+----+--------+--------+-------------------+
| Id | Value1 | Value2 | Comparision       |
+----+--------+--------+-------------------+
| 1  | 10     | 20     | Value2 is Greater |
| 2  | 100    | 40     | Value1 is Greater |
| 3  | 0      | 20     | Value2 is Greater |
| 4  | 0      | -50    | Value1 is Greater |
+----+--------+--------+-------------------+
4 rows in set (0.00 sec)