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, count(question_id)/count(DISTINCT qpd.device_id) as avg_answer_cnt from question_practice_detail as qpd inner join user_profile as up on qpd.device_id = up.device_id group by university
- 表联合。将未答过题的用户筛掉
- DISTINCT去除重复答题用户的device_id
- count(question_id)/count(DISTINCT qpd.device_id) as avg_answer_cnt 平均答题数量计算方式为该学校用户答题总次数除以答过题的不同用户个数
- group by university 每个学校