子查询+两次外连接

select
dept_no,emp.emp_no,salary
from
    (
        select
            e.emp_no as emp_no
        from
            employees e
            left join dept_manager dm on e.emp_no = dm.emp_no
        where
            dept_no is null
    ) as emp
    left join dept_emp de on emp.emp_no = de.emp_no
    left join salaries s on de.emp_no = s.emp_no
where de.to_date = '9999-01-01'