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
http://www.nowcoder.com/practice/88aa923a9a674253b861a8fa56bac8e5
SELECT university,
(COUNT(question_practice_detail.question_id)/COUNT(DISTINCT question_practice_detail.device_id))
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
distinct与列名称之间不需要括号
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