题解 | #统计每个学校各难度的用户平均刷题数#
统计每个学校各难度的用户平均刷题数
http://www.nowcoder.com/practice/5400df085a034f88b2e17941ab338ee8
SELECT
t1.university,
t3.difficult_level,
COUNT(t2.question_id)/COUNT(distinct(t2.device_id)) as avg_answer_cnt
FROM
user_profile t1,
question_practice_detail t2,
question_detail t3
WHERE
t1.device_id = t2.device_id
and
t2.question_id = t3.question_id
GROUP BY t1.university,t3.difficult_level;
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