知识点

1. 使用窗函数对grade进行分组然后，使用sum() over (order by ) 开窗函数，sum(a) over (order by b) 的含义是：按照b列排序，将a依次相加

代码

select grade, sum(number) over(order by grade) as t_rank 
from class_grade 
order by grade