题解 | #统计每个学校各难度的用户平均刷题数#
统计每个学校各难度的用户平均刷题数
https://www.nowcoder.com/practice/5400df085a034f88b2e17941ab338ee8
select
university,
difficult_level,
sum(date) / count(university)
from
user_profile a,
(
select
device_id,
count(b.question_id) date,
difficult_level
from
question_detail a,
question_practice_detail b
where
a.question_id = b.question_id
group by
device_id,
difficult_level
) b
where
a.device_id = b.device_id
group by
university,
b.difficult_level
order by
university;
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