搞不懂大家查询当前工资的时候为什么要用连接查询

验证时删除注释

select s1.emp_no,(s1.salary-e1.salary) as growth
from 
# 查询当前工资
(select emp_no,salary
from salaries
where to_date='9999-01-01') as s1 
# 内连接2次查询结果
inner join 
# 查询入职时候的工资
(select s.emp_no,s.salary
from salaries as s
inner join employees as e
on s.emp_no = e.emp_no and s.from_date=e.hire_date) as e1

on s1.emp_no=e1.emp_no
order by growth

我就想问你们怎么知道to_date=2099-01-01的?

我就想问你们怎么知道to_date=2099-01-01的?

我就想问你们怎么知道to_date=2099-01-01的?

我就想问你们怎么知道to_date=2099-01-01的?

我就想问你们怎么知道to_date=2099-01-01的?

我就想问你们怎么知道to_date=2099-01-01的?