The usage of case when and select case when is very easy to use

Case There are two formats . Simple Case Functions and Case The search function .
Simple Case function
CASE sex
WHEN ‘1’ THEN ‘ male ’
WHEN ‘2’ THEN ‘ Woman ’
ELSE ‘ other ’ END

–Case The search function
CASE WHEN sex = ‘1’ THEN ‘ male ’
WHEN sex = ‘2’ THEN ‘ Woman ’
ELSE ‘ other ’ END
Ways of planting , Can achieve the same function . Simple Case The writing of function is relatively simple , But and Case Search function , There will be some functional limitations , For example, write judgment . There is another problem that needs attention ,Case Function returns only the first value that matches the condition , The rest Case Parts will be automatically ignored .
– for instance , The following paragraph SQL, You'll never get “ The second category ” This result

CASE WHEN col_1 IN ( 'a', 'b') THEN ' The first category '
WHEN col_1 IN ('a')  THEN ' The second category '
ELSE' other ' END

There are scores score,score<60 Return to fail ,score>=60 Return to pass ,score>=80 Return to excellence

SELECT
    STUDENT_NAME,
    (CASE WHEN score < 60 THEN ' fail, '
        WHEN score >= 60 AND score < 80 THEN ' pass '
        WHEN score >= 80 THEN ' good '
        ELSE ' abnormal ' END) AS REMARK
FROM
    TABLE

That's all for simple use , similar if function .