题解 | #统计每个用户的平均刷题数#

SELECT university,
    difficult_level,
    ROUND(COUNT(qpd.question_id)/COUNT(DISTINCT qpd.device_id),4) as avg_answer_cnt
   
FROM user_profile up,
    question_practice_detail qpd,
    question_detail qd

WHERE 
    up.device_id = qpd.device_id
    and qpd.question_id = qd.question_id
    and university = '山东大学'

GROUP BY difficult_level