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
https://www.nowcoder.com/practice/5400df085a034f88b2e17941ab338ee8
SELECT up.university,
qd.difficult_level,
count(qpd.question_id) / count(DISTINCT qpd.device_id) AS avg_answer_cnt
FROM user_profile up,
question_practice_detail qpd,
question_detail qd
WHERE qpd.question_id = qd.question_id
AND qpd.device_id = up.device_id
GROUP BY up.university,
qd.difficult_level
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