DENSE_RANK()，允许并列名次、名次不间断，如122344456

将score按ID分组排名：dense_rank() over(partition by id order by score desc)

将score不分组排名：dense_rank() over(order by score desc)

select id,area,score,

dense_rank() over(partition by id order by score desc) 分组id排序,

dense_rank() over(order by score desc) 不分组排序

from students order by id,area;