题解 | #统计salary的累计和running_total#

法一：sum聚合窗口函数

select emp_no,salary,sum(salary)over(order by emp_no) running_total 
from salaries where to_date='9999-01-01'

法二：

select emp_no,salary,(select sum(salary) from salaries s2 where s2.emp_no<=s1.emp_no and to_date='9999-01-01') running_total 
from salaries s1 where to_date='9999-01-01'

法三：也可以用join+group by

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