题解 | #分组过滤练习题#

select
    university,
    avg(question_cnt) as avg_question_cnt,
    avg(answer_cnt) as avg_answer_cnt
from
    user_profile
group by
    university
having
    avg(question_cnt) < 5 or avg(answer_cnt) < 20

最后输出三列：university，university对应的avg_question_cnt，university对应的avg_answer_cnt

可以看出以university为聚合依据，求发帖均值和回帖均值仅需一个简单的avg聚合函数，而满足筛选条件仅需一个having子句。