题解 | 找出每个学校GPA最低的同学

select
    up.device_id,
    up.university,
    up.gpa
from
    user_profile  up
join (
    select
        university,
        min(gpa) as min_gpa
    from
        user_profile
    group by
        university
    ) as sub 
on 
    up.university = sub.university
    and up.gpa = sub.min_gpa
order by
    up.university asc

• 画张图，帮助自己更好地理解，这题没做出来