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 university,difficult_level, (sum(cou_diff)/count(cou_diff)) as avg_answer_cnt from(select university,difficult_level,cou_diff from (select difficult_level,device_id, count(difficult_level) as cou_diff from (select device_id,a.question_id,difficult_level from question_practice_detail as a inner join question_detail as b on a.question_id=b.question_id) as c group by difficult_level,device_id) as d inner join user_profile as e on d.device_id=e.device_id ) as f group by university,difficult_level order by university,difficult_level