SQL题目

Year Salary
2000 1000
2001 2000
2002 3000
2003 4000
想得到如下形式的查询结果
Year Salary
2000 1000
2001 3000
2002 6000
2003 10000
sql语句怎么写?

create table TT
(
  YEARS  NUMBER(4) not null,
  SALARY VARCHAR2(20) not null
)

select b.years , sum(a.salary) salary 
from tt a, tt b 
where a.years<=b.years 
group by b.years