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