方法一：left join

select p.device_id, u.university, u.gpa
from (select university, min(gpa) as gpa from user_profile group by university) u
left join user_profile p 
on u.university = p.university and u.gpa = p.gpa 
order by u.university;

方法二：join

select a.device_id, a.university, a.gpa 
from user_profile a 
join
    (select university,min(gpa) gpa 
     from user_profile 
     group by university
    ) b 
on 
a.gpa = b.gpa and a.university = b.university 
order by a.university;

方法三：子查询

select device_id, university, gpa 
from user_profile u
where gpa in (
            select min(gpa) from user_profile 
            where university = u.university
             )
order by university