题解 | #计算25岁以上和以下的用户数量#
计算25岁以上和以下的用户数量
https://www.nowcoder.com/practice/30f9f470390a4a8a8dd3b8e1f8c7a9fa
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
