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MySQL | CASE

Database
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MySQL
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Documentation
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Operators
schedule Jul 1, 2022
Last updated
local_offer MySQL
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tocTable of Contents
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MySQL's CASE operator allows us to add multiple conditions to our query and return a value for the first condition met.

Syntax

-- Syntax 1: Return result for first comparison of value = compare_value that is true
SELECT column(s),
CASE value
WHEN compare_value THEN result1
WHEN compare_value2 THEN result2
ELSE result3
END
FROM table;
-- Syntax 2: Return result for first condition that is true
SELECT column(s),
CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
ELSE result3
END
FROM table;

NOTE

In both cases if no comparison/condition is true, the result after ELSE is returned or NULL if there is no ELSE part.

Examples

Consider the following table about students' extracurricular activities:

student_id

club

date_entered

1

Football

2016-02-13

2

Boxing

2016-05-25

3

Apple

2018-08-17

4

Fishing

2017-01-01

5

NULL

NULL

The above sample table can be created using the code here.

Syntax 1

To check whether student_id is 1 and return a string depending on the result of the comparison:

SELECT student_id,
CASE student_id
WHEN 1 THEN "student1"
ELSE "Not student1"
END
AS 'Case Outcome'
FROM extracurricular;
+------------+--------------+
| student_id | Case Outcome |
+------------+--------------+
| 1 | student1 |
| 2 | Not student1 |
| 3 | Not student1 |
| 4 | Not student1 |
| 5 | Not student1 |
+------------+--------------+

For student_id=1 as the comparison is true we return "student1". For all other students, as the comparison is false, we return the ELSE block return value "Not student1".

Syntax 2

To return "Not student1" for all student_id greater than 1:

SELECT student_id,
CASE
WHEN student_id > 1 THEN "Not student1"
ELSE "student1"
END
AS 'Case Outcome'
FROM extracurricular;
+------------+--------------+
| student_id | Case Outcome |
+------------+--------------+
| 1 | student1 |
| 2 | Not student1 |
| 3 | Not student1 |
| 4 | Not student1 |
| 5 | Not student1 |
+------------+--------------+

For student_id=1 as the condition is false, we return the ELSE block return value "student1". For all other students, as the condition is true, we return "Not student1".

robocat
Published by Arthur Yanagisawa
Edited by 0 others
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