/*#查询员工的信息
select
de.emp_no,
s1.salary
from dept_emp de join salaries s1
on de.emp_no = s1.emp_no and s1.to_date = '9999-01-01'
and de.to_date = '9999-01-01'#为什么是s1 

#查询manager的信息
select
dm.emp_no,
s2.salary
from dept_manager dm, salaries s2
where dm.emp_no = s2.emp_no and s2.to_date = '9999-01-01'
and dm.to_date = '9999-01-01'
*/
#筛选员工薪水 > manager 薪水
select 
de.emp_no,
dm.emp_no manager_no,
s1.salary emp_salary,
s2.salary manager_salary
from dept_emp de, dept_manager dm, salaries s1, salaries s2
where de.emp_no = s1.emp_no 
and s1.to_date = '9999-01-01'
and de.to_date = '9999-01-01'
and dm.emp_no = s2.emp_no 
and s2.to_date = '9999-01-01'
and dm.to_date = '9999-01-01'
and s1.salary > s2.salary
and de.dept_no = dm.dept_no

没做出来，看了讲解后懂了

有几个要点：

1、学到了from后面也可以用逗号间隔多个表，然后用where限定进行连接

2、虽然只给了三个表，但是表都是可以反复利用的

3、自己的思路挺清晰的，主要是后面将二者连起来，再限定s1.salary > s2.salary，这种想法需要加强