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 university, (count(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