题解 | 所有用户对高难度题目的刷题数
所有用户对高难度题目的刷题数
https://www.nowcoder.com/practice/e8b66c069376405bb7524b217c890b23
select a.device_id, count(case when c.difficult_level='hard' then 1 else null end) as question_cnt from user_profile a left join question_practice_detail b on a.device_id=b.device_id left join question_detail c on b.question_id=c.question_id group by a.device_id order by question_cnt asc