题解 | 计算25岁以上和以下的用户数量

/* select
    '25岁以下' as age_cut,
    count(id) as number
from
    user_profile
where
    age < 25
    or age is null
union
select
    '25岁及以上' as age_cut,
    count(id) as number
from
    user_profile
where
    age >= 25 */

/* select 
    if(age>=25,'25岁及以上','25岁以下') as age_cut,
    count(device_id) as number 
from user_profile
group by age_cut */
select 
    (case when age>=25 then '25岁及以上' else '25岁以下' end) as age_cut,
    count(device_id)
from user_profile
group by age_cut