题解 | #计算25岁以上和以下的用户数量#

#第一种

SELECT

    IF (age >= 25, "25岁及以上", "25岁以下") AS age_cut,

    count(*) AS number

FROM

    user_profile

GROUP BY

    IF (age >= 25, "25岁及以上", "25岁以下") ; #group by 执行顺序在select之前，MySQL中是特例，严格上不能直接用别名

#第二种

select

    age_cut,

    count(*)

from

    (

        select

            if (age >= 25, "25岁及以上", "25岁以下") as age_cut

        from

            user_profile

    ) as a #MySQL在执行子查询的时候需要加上as 别名

group by

    age_cut