题解 | #统计每个学校各难度的用户平均刷题数#
统计每个学校各难度的用户平均刷题数
http://www.nowcoder.com/practice/5400df085a034f88b2e17941ab338ee8
select u.university ,q2.difficult_level, COUNT(answer_cnt)/ count(DISTINCT u.device_id) as avg_answer_cnt from user_profile u inner join question_practice_detail q1 on u.device_id = q1.device_id inner join question_detail q2 ON q1.question_id= q2.question_id group by u.university,q2.difficult_level;
