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 a.university,c.difficult_level,
count(a.device_id)/count(distinct a.device_id) ave_answer_cnt
from question_practice_detail b
inner join user_profile a on a.device_id=b.device_id
inner join question_detail c on c.question_id=b.question_id
group by a.university,c.difficult_level;
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