select emp_no,salary,sum(salary) over (order by emp_no) as running_total from 
salaries
where to_date ='9999-01-01'

窗口函数的使用

sum(a) over (order by b) 的含义是:

例如：

a b

1 2

3 4

5 6

按照b列排序，将a依次相加，得到结果，如下:

a b sum(a) over (order by b)：

1 2 1

3 4 1+3

5 6 1+3+5