题解 | #统计每个学校各难度的用户平均刷题数#
统计每个学校各难度的用户平均刷题数
https://www.nowcoder.com/practice/5400df085a034f88b2e17941ab338ee8
select u.university,d.difficult_level,count(q.question_id)/count(distinct q.device_id) avg_answer_cnt from user_profile u,question_practice_detail q,question_detail d where u.device_id=q.device_id and q.question_id=d.question_id group by u.university,d.difficult_level;
