题解 | #统计每个学校的答过题的用户的平均答题数#

WITH CTE1 AS 
    (
        SELECT  *
        FROM    question_practice_detail
        JOIN    user_profile
        USING(device_id)
    )
    

SELECT  university, 
        ROUND(COUNT(*) / COUNT(DISTINCT device_id), 4) AS avg_answer_cnt
FROM    CTE1
GROUP BY    university