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, round(count(qpd.question_id)/count(distinct qpd.device_id),4) as avg_answer_cnt from question_practice_detail as qpd left join user_profile as up on up.device_id=qpd.device_id left join question_detail as qd on qd.question_id=qpd.question_id group by university,difficult_level having up.university='山东大学'
注意，这里使用having，而不是where
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