https://leetcode-cn.com/problems/highest-grade-for-each-student/
select
a.student_id
,a.course_id
,a.grade
from
(
select
student_id
,course_id
,grade
,row_number() over(partition by student_id order by grade desc,course_id )rn
from Enrollments
)a where a.rn=1
