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 up.university , qd.difficult_level ,count(qpd.question_id)/count(distinct qpd.device_id) as avg_answer_cnt from user_profile as up join question_practice_detail as qpd on up.device_id = qpd.device_id left join question_detail as qd on qpd.question_id = qd.question_id where up.university = '山东大学' group by qd.difficult_level
select 。。（字段运算）。 from 表
join表 on 连接条件 。。
where 筛选条件
group by 分组的字段
having 聚合的运算
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