员工的上司的编号
获取所有员工当前的manager
http://www.nowcoder.com/questionTerminal/e50d92b8673a440ebdf3a517b5b37d62
select dept_emp.emp_no as emp_no, dept_manager.emp_no as manager_no from dept_emp, dept_manager where dept_emp.dept_no=dept_manager.dept_no and dept_emp.emp_no!=dept_manager.emp_no and dept_manager.to_date='9999-01-01';