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
u.university,
t.difficult_level,
count(d.question_id)/count(distinct d.device_id)
from
user_profile as u,
question_practice_detail as d,
question_detail as t
where u.university = '山东大学' and
u.device_id =d.device_id and
d.question_id =t.question_id
group by t.difficult_level
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