先按学校分组，再按性别分组，再用count,avg计算
分组计算练习题
https://www.nowcoder.com/practice/009d8067d2df47fea429afe2e7b9de45
select
gender,university,
count(id) as user_num,
avg(active_days_within_30) as avg_active_day,
avg(question_cnt) as avg_question_cnt
from
user_profile
group by university,gender
order by gender asc,university asc
