统计salary的累计和running_total

CREATE TABLE `salaries` ( 
`emp_no` int(11) NOT NULL,
`salary` int(11) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`from_date`));

select s2.emp_no,s2.salary,sum(s1.salary) running_total from (select emp_no,salary from salaries where to_date = '9999-01-01') s1 inner join (select emp_no,salary from salaries where to_date = '9999-01-01') s2 on s1.emp_no <= s2.emp_no group by s2.emp_no

select emp_no,salary from salaries where to_date = '9999-01-01'

s1 inner join (select emp_no,salary from salaries where to_date = '9999-01-01') s2 on s1.emp_no <= s2.emp_no

select s2.emp_no,s2.salary,sum(s1.salary) running_total from s1 inner join s2 on s1.emp_no <= s2.emp_no group by s2.emp_no