题解 | #计算25岁以上和以下的用户数量#

select (case 
            when age>=25 then '25岁及以上' 
            when age>=0 and age<25 or age is NULL then '25岁以下' 
        end 
        ) as age_cut,
        count(*) as number
    from `user_profile`
    group by age_cut

select up.age_cut,count(*) as number 
  from (
      select (case 
            when age>=25 then '25岁及以上' 
            when age>=0 and age<25 or age is NULL then '25岁以下' 
        end 
        ) as age_cut
    from `user_profile`
  ) as up
  group by up.age_cut

条件表达式

case

when condition then result1 else result2

end

可与聚合函数使用，实现更加复杂的统计功能：