MySQL Programming Interview Question:

How To Use CASE Expression?

Submitted by: Administrator

There are 2 ways to use the CASE expression. The first way is to return one of the predefined values based on the comparison of a given value to a list of target values. The second way is to return one of the predefined values based on a list of conditions. Here is the syntax of both types of CASE expressions:

CASE value WHEN target_value THEN result
WHEN target_value THEN result
WHEN target_value THEN result
...
ELSE result
END

CASE WHEN condition THEN result
WHEN condition THEN result
WHEN condition THEN result
...
ELSE result
END

The tutorial exercise below gives two good examples:

SELECT CASE 'Sun' WHEN 'Mon' THEN 'Open'
WHEN "Fri" THEN "Open" ELSE 'Closed' END FROM DUAL;
Closed

SELECT CASE WHEN HOUR(CURRENT_TIME())<9 THEN 'Closed'
WHEN HOUR(CURRENT_TIME())>17 THEN 'Closed'
ELSE 'Open' END FROM DUAL;
Closed
Submitted by: Administrator