题解 | #统计每个学校的答过题的用户的平均答题数#
统计每个学校的答过题的用户的平均答题数
https://www.nowcoder.com/practice/88aa923a9a674253b861a8fa56bac8e5
select university,sum(q_idnum)/count(q.device_id) avg_answer_cnt
from user_profile uf join (
select device_id,count(question_id) q_idnum
from question_practice_detail
group by device_id)q on uf.device_id=q.device_id
group by university
order by university
1、建立一个子查询表,求出各用户id和各用户id答题数目
2、将子查询表与user_profile以device_id连接
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