``` select device_id, gender, case when age >= 25 then '25岁及以上' when age >= 20 then '20-24岁' when age < 20 then '20岁以下' else '其他' end as age_cut from user_profile ```  ``` select DATE_FORMAT(date, '%d') as day, count(question_id) as question_cut from question_practice_detail where DATE_FORMAT(date, '%Y-%m') = '2021-08' group by date ```