题解 | #统计salary的累计和running_total#

SELECT c.emp_no,c.salary,s.running_total
FROM salaries AS c INNER JOIN(
SELECT a.emp_no,SUM(b.salary) AS running_total
FROM salaries AS a INNER JOIN salaries AS b
ON a.emp_no>=b.emp_no AND a.to_date = '9999-01-01' AND b.to_date = '9999-01-01'
GROUP BY a.emp_no
) AS s
ON c.emp_no=s.emp_no AND c.to_date='9999-01-01'

/*
select emp_no,salary,
sum(salary) over(order by emp_no) as running_total
from salaries
where to_date= '9999-01-01';
*/
首先找到不比职工号大的元组，然后按照职工号分组求和