题解 | #统计每个学校的答过题的用户的平均答题数#
统计每个学校的答过题的用户的平均答题数
http://www.nowcoder.com/practice/88aa923a9a674253b861a8fa56bac8e5
select u.university,(COUNT(q.question_id))/(count(distinct q.device_id)) as avg_answer_cnt from user_profile as u join question_practice_detail as q on u.device_id=q.device_id group by u.university