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 u.university,COUNT(q.question_id)/COUNT(DISTINCT q.device_id) FROM user_profile u JOIN question_practice_detail q ON u.device_id = q.device_id GROUP BY u.university;
内连接、左连接、右连接都试过了,即“FROM user_profile u JOIN question_practice_detail q ON u.device_id = q.device_id”这里,(LEFT/RIGHT)JOIN都能运行成功
还是不太懂内连接和左右连接