SQL 之关于case 函数的使用

Posted 2021-01-09 XT_小嘎

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