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(c.question_id)/count(distinct b.device_id) from (select device_id,university from user_profile)a join (select device_id,question_id from question_practice_detail)b on a.device_id=b.device_id join question_detail c on b.question_id=c.question_id group by university, difficult_level
我写的时候遇到的问题：貌似join 和where将两个表连接不能同时出现？？？希望解答
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