题解 | #统计每个用户的平均刷题数#
统计每个用户的平均刷题数
http://www.nowcoder.com/practice/f4714f7529404679b7f8909c96299ac4
select university,difficult_level,count(t1.device_id)/count(distinct t1.device_id) from question_practice_detail t1 left join user_profile t2 on t1.device_id=t2.device_id left join question_detail t3 on t1.question_id=t3.question_id where t2.university='山东大学' group by university,difficult_level;
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