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(c.gpa) / count( DISTINCT c.device_id) FROM ( select a.university , b.device_id , b.result , a.gpa from user_profile as a inner join question_practice_detail as b on a.device_id = b.device_id ) as c group by c.university