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
错误原因：
好几次都没有看清楚表的结构，导致浪费大量时间找出错误
select
university,
t3.difficult_level,
count(t2.question_id)/count(distinct t2.device_id) as avg_answer_cnt
from
user_profile t1,
question_practice_detail t2,
question_detail t3
where
t1.device_id = t2.device_id
and t2.question_id = t3.question_id
and university = '山东大学'
group by t3.difficult_level;
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