题解 | 计算25岁以上和以下的用户数量

方法一：使用if语句
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;

方法二：使用case语句
select 
case 
when age <25 then '25岁以下'
when age is null then '25岁以下'
else '25岁及以上'
end
as age_cut,
count(device_id) as number
from user_profile
group by age_cut;