step1：拿到要的字段 step2：内关联起来

select last_name
      ,first_name
      ,p1.dept_no as dept_no     
  from (
		select dept_no
		      ,emp_no
		  from dept_emp
        ) p1

 inner join

       ( 
		select emp_no
		      ,first_name
		      ,last_name
		  from employees
       ) p2
    on p1.emp_no = p2.emp_no