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 up.university,
COUNT(qpd.question_id) / COUNT(DISTINCT(qpd.device_id))
AS avg_answer_cnt
FROM user_profile AS up JOIN question_practice_detail AS qpd
ON up.device_id = qpd.device_id
GROUP BY up.university