题解 | #统计每个用户的平均刷题数#
统计每个用户的平均刷题数
http://www.nowcoder.com/practice/f4714f7529404679b7f8909c96299ac4
select u.university,
d.difficult_level,
count(q.question_id)/count(distinct q.device_id) as avg_answer_cnt
from user_profile u
left join question_practice_detail q
on u.device_id=q.device_id
left join question_detail d
on q.question_id=d.question_id
where u.university='山东大学'
group by d.difficult_level;
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