题解 | #统计每个用户的平均刷题数#
统计每个用户的平均刷题数
https://www.nowcoder.com/practice/f4714f7529404679b7f8909c96299ac4
select a.university,c.difficult_level, (count(b.question_id)/count(distinct(a.device_id))) as avg_answer_cnt from user_profile as a, question_practice_detail as b, question_detail as c where a.device_id=b.device_id and b.question_id=c.question_id group by a.university,c.difficult_level having university='山东大学'