窗口函数最简单的解法
找出每个学校GPA最低的同学
https://www.nowcoder.com/practice/90778f5ab7d64d35a40dc1095ff79065
SELECT device_id, university, gpa
FROM (
SELECT *,
ROW_NUMBER() OVER(PARTITION BY university ORDER BY gpa) AS rnk
FROM user_profile
) AS t
WHERE rnk = 1
ORDER BY university;