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,
sum(date) / count(u.device_id) avg_answer_cnt
from
(
select
*
from
user_profile
where
university = '山东大学'
) u,
(
select
device_id,
COUNT(a.question_id) date,
difficult_level
from
question_practice_detail a,
question_detail b
where
a.question_id = b.question_id
group by
device_id,
difficult_level
) p
where
u.device_id = p.device_id
group by
difficult_level;
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