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(difficult_level) / count(distinct device_id)) as avg_answer_cnt from user_profile join question_practice_detail using (device_id) join question_detail using (question_id) group by university, difficult_level HAVING university = '山东大学'
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