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
a.university,
c.difficult_level,
(count(b.question_id)/count(distinct(b.device_id))) as avg_answer_cnt
from
user_profile a,
question_practice_detail b,
question_detail c
where
a.university = '山东大学'
AND a.device_id = b.device_id
AND b.question_id = c.question_id
GROUP BY difficult_level
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