题解 | #统计每个学校的答过题的用户的平均答题数#

SELECT a.university,count(q.question_id)/count(distinct q.device_id) AS avg_answer_cnt
FROM user_profile AS a
JOIN question_practice_detail AS q
ON a.device_id=q.device_id
GROUP BY a.university

这里一直有个小点卡住，就是把distinct q.device_id写成了distinct. q.device_id。注意distinct不用标点.