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
https://www.nowcoder.com/practice/f4714f7529404679b7f8909c96299ac4
select university,difficult_level,count(qpd.question_id)/count( distinct(qpd.device_id)) avg_answer_cnt from question_practice_detail qpd inner join user_profile up on up.device_id=qpd.device_id inner join question_detail qd on qpd.question_id = qd.question_id group by university, difficult_level having university= "山东大学"
捯饬半天，以为where还是having出问题了，结果发现表链接写错了
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