How do I use properly CASE..WHEN in MySQL

71

Here is a demo query, notice it is very simple, Fetches only where base_price is 0, And still, it chooses the condition 3:

SELECT
   CASE course_enrollment_settings.base_price
    WHEN course_enrollment_settings.base_price = 0      THEN 1
    WHEN course_enrollment_settings.base_price<101      THEN 2
    WHEN course_enrollment_settings.base_price>100 AND   
                      course_enrollment_settings.base_price<201 THEN 3
        ELSE 6
   END AS 'calc_base_price',
   course_enrollment_settings.base_price
FROM
    course_enrollment_settings
WHERE course_enrollment_settings.base_price = 0

base_price is decimal(8,0)

When run this on my DB, I get:

3 0
3 0
3 0
3 0
3 0

This question is tagged with mysql sql conditional switch-statement case

~ Asked on 2012-03-06 16:41:38

The Best Answer is


71

Remove the course_enrollment_settings.base_price immediately after CASE:

SELECT
   CASE
    WHEN course_enrollment_settings.base_price = 0      THEN 1
    ...
    END

CASE has two different forms, as detailed in the manual. Here, you want the second form since you're using search conditions.

~ Answered on 2012-03-06 16:45:36


39

CASE case_value
    WHEN when_value THEN statements
    [WHEN when_value THEN statements]
    ELSE statements
END 

Or:

CASE
WHEN <search_condition> THEN statements
[WHEN <search_condition> THEN statements] 
ELSE statements
END 

here CASE is an expression in 2nd scenario search_condition will evaluate and if no search_condition is equal then execute else

SELECT
   CASE course_enrollment_settings.base_price
    WHEN course_enrollment_settings.base_price = 0      THEN 1

should be

SELECT
   CASE 
    WHEN course_enrollment_settings.base_price = 0      THEN 1

~ Answered on 2013-07-17 05:47:44


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