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 z.* FROM (SELECT up.university, qd.difficult_level, COUNT(qp.question_id) / COUNT(DISTINCT qp.device_id) FROM question_practice_detail AS qp LEFT OUTER JOIN question_detail AS qd ON qp.question_id = qd.question_id LEFT OUTER JOIN user_profile AS up ON qp.device_id = up.device_id GROUP BY up.university, qd.difficult_level) AS z WHERE z.university = '山东大学';
将上一题的结果作为一个新表，命名为z，查询university = '山东大学'。
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