select
    device_id,
    gender,
    (
        case
            when age < 20 then '20岁以下'
            when age between 20 and 24  then '20-24岁'
            when age >= 25 then '25岁及以上'
            when age is null then '其他'
        end
    ) as age_cut
from
    user_profile;

case when的使用。