题解 | #统计每个学校的答过题的用户的平均答题数#
统计每个学校的答过题的用户的平均答题数
https://www.nowcoder.com/practice/88aa923a9a674253b861a8fa56bac8e5
不用join on连接即可，count(非去重) / count(去重) 求平均值
select university,count(b.device_id) / count(distinct b.device_id) as avg_answer_cnt from user_profile a,question_practice_detail b where a.device_id=b.device_id group by university order by university
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