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
没啥说的跟上一道题差不多我看的视频还没到join所以直接where筛选就完事了
SELECT
university,
difficult_level,
COUNT(q_p.question_id) / COUNT(DISTINCT q_p.device_id) avg_answer_cnt
FROM user_profile u,
question_detail q,
question_practice_detail q_p
WHERE
u.device_id = q_p.device_id
and q_p.question_id = q.question_id
GROUP BY
university,difficult_level;
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