1、groupby用法：根据性别和学校来分组

select 
	gender,university,
	count(gender)as user_num,
	avg(active_days_within_30) as avg_active_day,
	avg(question_cnt) as avg_question_cnt
from 
	user_profile 
group by gender,university

2、groupby 结合having语法，进行分组过滤

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

3、groupby结合orderby 分组排序（升序是asc，降序是desc）

select 
	university,avg(question_cnt) as avg_question_cnt 
from 
	user_profile group by university 
order by avg_question_cnt asc