题解 | #计算25岁以上和以下的用户数量#

select if (age<25 or age is null,'25岁以下','25岁及以上') as age_cut, count(device_id) as number
from user_profile
group by age_cut

if函数 if（条件，则是，否则为）

或

select '25岁以下' as age_cut, count(device_id) as number

from user_profile

where age < 25 or age is null

union all

select '25岁及以上' as age_cut, count(device_id) as number

from user_profile

where age >= 25