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 a.university,c.difficult_level,count(b.question_id)/count(distinct(b.device_id)) as avg_answer_cnt
from question_practice_detail as b
inner join user_profile as a on b.device_id=a.device_id
inner join question_detail as c on b.question_id=c.question_id
group by university,difficult_level
HAVING a.university='山东大学'
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