题解 | #分组过滤练习题#

SELECT university,avg_question_cnt,avg_answer_cnt from  (select
    user_profile.university,
    sum(question_cnt) / cn  avg_question_cnt,
   sum(answer_cnt) / cn avg_answer_cnt
from
    user_profile,
    (
        select
            university,
            count(*) cn
        from
            user_profile
        GROUP BY
            university
    ) a
where
    a.university = user_profile.university 
GROUP BY
    a.university) b where b.avg_question_cnt < '5' or b.avg_answer_cnt < '20';