已知原表(t_salary) year salary 2000 1000 2001 2000 2002 3000 2003 4000 先要实现显示结果(salary为以前的工资和) year salary 2000 1000 2001 3000
答案：
select year, (select sum(salary) from t_salary b where b.year <= a.year) salary from t_salary a group by year