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, round(count(qq.question_id)/count(distinct qq.device_id),4) avg_answer_cnt from user_profile uu join question_practice_detail qq on uu.device_id=qq.device_id join question_detail qt on qq.question_id=qt.question_id where university='山东大学' group by university,difficult_level
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