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_id)/count(DISTINCT a.device_id) as avg_answer_cnt
FROM(
SELECT
device_id,
university
FROM user_profile
) a
JOIN(
SELECT
device_id,
question_id
FROM question_practice_detail
) b
on a.device_id = b.device_id
GROUP BY university
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