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
https://www.nowcoder.com/practice/f4714f7529404679b7f8909c96299ac4
select university,difficult_level,
count(*)/count( distinct a.device_id) as avg_answer_cnt
from user_profile as a left join question_practice_detail as b
on a.device_id=b.device_id left join question_detail as c
on b.question_id=c.question_id where university ="山东大学"
group by difficult_level having difficult_level is not null ;
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