题解 | #计算25岁以上和以下的用户数量#

# 子查询--在user_profile添加分组列，为各行添加年龄分组标记
select *, case 
when age<25 or age is null then '25岁以下'
else '25岁及以上'
end as age_cut
from user_profile
# 完整查询--返回这两个年龄段的用户数量
select age_cut, count(*) number
from (
    select *, case 
    when age<25 or age is null then '25岁以下'
    else '25岁及以上'
    end as age_cut
    from user_profile
) age_f
group by age_cut;