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
SELECT user_profile.university, round(count(question_practice_detail.question_id)/count(DISTINCT question_practice_detail.device_id),4) as avg_answer_cnt from user_profile inner join question_practice_detail on user_profile.device_id = question_practice_detail.device_id group by university order by university;
两个表按照device_id 取交集
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