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 university,difficult_level,count(b.device_id)/count(distinct(b.device_id)) as avg_answer_cnt from user_profile a,question_practice_detail b,question_detail c where a.device_id = b.device_id and b.question_id = c.question_id and university = "山东大学" group by difficult_level