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, count(qpd.id)/count(distinct qpd.device_id) from user_profile up, question_practice_detail qpd, question_detail qd where up.device_id = qpd.device_id and qpd.question_id = qd.question_id group by university, difficult_level
原来多表查询也可以不用Join 然后用户平均刷题数 所以是用户做分母
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