SQL 之关于case 函数的使用

废话不多，直接上SQL

case 形式一：

SELECT
            f.series_id,
            <!-- f.fuel_flag, -->
            (CASE f.fuel_flag
            WHEN 1 THEN ‘汽油‘
            WHEN 2 THEN ‘柴油‘
            WHEN 3 THEN ‘油电混合‘
            WHEN 4 THEN ‘纯电动‘
            WHEN 5 THEN ‘油气混合‘
            WHEN 6 THEN ‘液化石油气‘
            WHEN 7 THEN ‘压缩天然气‘
            WHEN 8 THEN ‘甲醇‘
            WHEN 9 THEN ‘乙醇‘
            ELSE ‘‘
            END
            ) as fuel_flag,
            f.car_age
        FROM
            series_fuel_flag f

case 形式二：

SELECT
            f.series_id,
            <!-- f.fuel_flag, -->
            (CASE
            WHEN f.fuel_flag = 1 THEN ‘汽油‘
            WHEN f.fuel_flag = 2 THEN ‘柴油‘
            WHEN f.fuel_flag = 3 THEN ‘油电混合‘
            WHEN f.fuel_flag = 4 THEN ‘纯电动‘ 　　　　　　　　......
            ELSE ‘‘
            END
            ) as fuel_flag,
            f.car_age
        FROM
            series_fuel_flag f

形式二比形式一要灵活 “=” 可以换成其他表达式 如 “>,<” 等 还 可以

(case 

WHEN f.fuel_flag in (1,2,3) THEN ‘非电动‘

ELSE ‘‘  END

)但是如果是

(case 

WHEN f.fuel_flag in (1,2,3) THEN ‘非电动‘

WHEN f.fuel_flag in (1,2,3) THEN ‘燃油‘

ELSE ‘‘  END

)

只能获取到 非电动  而获取不到 燃油

原文地址：https://www.cnblogs.com/xingtangxiaoga/p/9714940.html