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
https://www.nowcoder.com/practice/88aa923a9a674253b861a8fa56bac8e5
# 2个表都需要 # select * from user_profile u,question_practice_detail q where u.device_id=q.device_id; # select university,count(u.device_id) d from user_profile u,question_practice_detail q where u.device_id=q.device_id group by university select a.university,b.q1/a.d from (select university,count(distinct u.device_id) d from user_profile u,question_practice_detail q where u.device_id=q.device_id group by university) a , (select university,count(question_id) q1 from user_profile u,question_practice_detail q where u.device_id=q.device_id group by university) b where a.university=b.university
先查询总人数(需要去重),在查询总题数