题目：现在运营想要找到每个学校gpa最低的同学来做调研，请你取出每个学校的最低gpa。

drop table if exists user_profile;
CREATE TABLE `user_profile` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`gender` varchar(14) NOT NULL,
`age` int ,
`university` varchar(32) NOT NULL,
`gpa` float,
`active_days_within_30` int ,
`question_cnt` int ,
`answer_cnt` int 
);
INSERT INTO user_profile VALUES(1,2138,'male',21,'北京大学',3.4,7,2,12);
INSERT INTO user_profile VALUES(2,3214,'male',null,'复旦大学',4.0,15,5,25);
INSERT INTO user_profile VALUES(3,6543,'female',20,'北京大学',3.2,12,3,30);
INSERT INTO user_profile VALUES(4,2315,'female',23,'浙江大学',3.6,5,1,2);
INSERT INTO user_profile VALUES(5,5432,'male',25,'山东大学',3.8,20,15,70);
INSERT INTO user_profile VALUES(6,2131,'male',28,'山东大学',3.3,15,7,13);
INSERT INTO user_profile VALUES(7,4321,'male',28,'复旦大学',3.6,9,6,52);

方案

select b.device_id ,a.university,a.gpa
from 
(select university,min(gpa) as gpa 
from user_profile
group by university
 )a left join user_profile b on b.university = a.university and  b.gpa = a.gpa
 order by a.university 
 
select device_id,university,gpa
from (
select 
*
,row_number() over(partition by university order by gpa) as rn
from user_profile
)a
where a.rn = 1