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
up.university,
count(qpd.device_id)/count(DISTINCT qpd.device_id) AS avg_answer_cnt
FROM question_practice_detail AS qpd
INNER JOIN user_profile AS up
ON up.device_id = qpd.device_id
GROUP BY university
ORDER BY university
**distinct**用于去重
注意是question_practice_detail表中数量的统计，因为可能存在有人没有答过题目
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