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
http://www.nowcoder.com/practice/88aa923a9a674253b861a8fa56bac8e5
select university, count(result)/count(distinct question_practice_detail.device_id) as avg_answer_cnt from user_profile,question_practice_detail where question_practice_detail.device_id = user_profile.device_id group by university order by university #主要是计算平均值容易绕的头晕