题解 | #统计salary的累计和running_total#

1.先查出to_date ='9999-01-01'的员工（a1,a2）

select * from salaries b where b.to_date='9999-01-01'

2.a1表左外连接a2表，条件：a1.emp_no >= a2.emp_no (a、b表都是以emp_no 升序排),再group by a1.emp_no

select a1.emp_no,a1.salary,sum(a2.salary) 
from (select * from salaries b where b.to_date='9999-01-01') a1  
     left outer join
     (select * from salaries b where b.to_date='9999-01-01') a2
on a1.emp_no >= a2.emp_no
group by a1.emp_no;