cume_dist()，允许并列名次、复制名次自动空缺，取并列后较大名次，结果如22355778……

将score按ID分组排名：cume_dist() over(partition by id order by score desc)*sum(1) over(partition by id)

将score不分组排名：cume_dist() over(order by score desc)*sum(1) over()

select id,area,score,

sum(1) over() as 总数,

sum(1) over(partition by id) as 分组个数,

(cume_dist() over(partition by id order by score desc))*(sum(1) over(partition by id)) 分组id排序,

(cume_dist() over(order by score desc))*(sum(1) over()) 不分组排序

from students order by id,area