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 user_profile up
inner join question_practice_detail qpd
on up.device_id = qpd.device_id
inner join question_detail qd
on qpd.question_id = qd.question_id
group by university,difficult_level;
from user_profile up
inner join question_practice_detail qpd
on up.device_id = qpd.device_id
inner join question_detail qd
on qpd.question_id = qd.question_id
group by university,difficult_level;
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