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
https://www.nowcoder.com/practice/5400df085a034f88b2e17941ab338ee8
select #通过筛选及分组的方式计算每个学校的同学平均答题数 b.university, b.difficult_level, sum(b.result_cnt)/count(distinct b.device_id) as avg_answer_cnt from ( select #关联每个同学所属的学校 a.device_id, a.difficult_level, a.result_cnt, up.university from( select #计算每位同学在不同难度下的答题数; qpd.device_id, qd.difficult_level, count(qpd.result) as result_cnt from question_practice_detail as qpd left join question_detail as qd on qpd.question_id=qd.question_id group by qpd.device_id,qd.difficult_level ) as a left join user_profile as up on a.device_id=up.device_id ) as b group by university,difficult_level