SQL Case When Then Else End 多条件判断

1.、简单CASE WHEN函数

CASE SCORE WHEN A THEN 优 ELSE 不及格 END
CASE SCORE WHEN B THEN 良 ELSE 不及格 END
CASE SCORE WHEN C THEN 中 ELSE 不及格 END

2、CASE WHEN条件表达式函数

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

condition是一个返回布尔类型的表达式，如果表达式返回true，则整个函数返回相应result的值，如果表达式皆为false，则返回ElSE后result的值，如果省略了ELSE子句，则返回NULL 3、使用场景

场景1 有分数score，score<60返回不及格，score>=60返回及格，score>=80返回优秀

SELECT
    STUDENT_NAME,
    (CASE WHEN score < 60 THEN 不及格
        WHEN score >= 60 AND score < 80 THEN 及格
        WHEN score >= 80 THEN 优秀
        ELSE 异常 END) AS REMARK
FROM
    TABLE

场景2 现老师要统计班中，有多少男同学，多少女同学，并统计男同学中有几人及格，女同学中有几人及格，要求用一个SQL输出结果。

SELECT 
    SUM (CASE WHEN STU_SEX = 0 THEN 1 ELSE 0 END) AS MALE_COUNT,
    SUM (CASE WHEN STU_SEX = 1 THEN 1 ELSE 0 END) AS FEMALE_COUNT,
    SUM (CASE WHEN STU_SCORE >= 60 AND STU_SEX = 0 THEN 1 ELSE 0 END) AS MALE_PASS,
    SUM (CASE WHEN STU_SCORE >= 60 AND STU_SEX = 1 THEN 1 ELSE 0 END) AS FEMALE_PASS
FROM 
    THTF_STUDENTS

场景3

ELECT 
    E_CODE,
    SUM(CASE WHEN E_TYPE = 0 THEN E_VALUE ELSE 0 END) AS WATER_ENERGY,--水耗
    SUM(CASE WHEN E_TYPE = 1 THEN E_VALUE ELSE 0 END) AS ELE_ENERGY,--电耗
    SUM(CASE WHEN E_TYPE = 2 THEN E_VALUE ELSE 0 END) AS HEAT_ENERGY--热耗
FROM 
    THTF_ENERGY_TEST
GROUP BY
    E_CODE