rank() over(partition by）记录

查询出每个班级成绩是第一名的同学

--其中partition by 为分组，即通过class分组，然后根据score排序
select s.name,s.class rank() over(partition by s.class order by s.score) as S from student as s
select s.name,s.class densen_rank() over(partition by s.class order by s.score) as S from student as s
select s.name,s.class row_number() over(partition by s.class order by s.score) as S from student as s

rank搜索出来的结果直接1，1，3了，而densen_rank搜索出来直是1，1，2,row_number()搜索出来是1，2，3