select university,avg_age,avg_gpa from
(select ifnull(university,"总体") university,round(avg(age),3) avg_age,round(avg(gpa),3) avg_gpa from
user_profile
group by university 
with rollup) AS a
order by (case when university="总体" then 1 else 2 end)

wih rollup 用在group by 后面，对分组后的数值进行求和。

由于不能求和的字段会变为 null 需要用ifnull函数进行填充

为了保证总和可以排在第一排，用case when以后做升序排序