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 university, difficult_level, COUNT(qpd.question_id) / COUNT(DISTINCT qpd.device_id) AS avg_answer_cnt
from question_practice_detail qpd
LEFT JOIN user_profile u on qpd.device_id = u.device_id
LEFT JOIN question_detail qd on qpd.question_id = qd.question_id
GROUP BY university, difficult_level;
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