SQL11 获取所有员工当前的manager

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SELECT
  de.emp_no,
  dm.emp_no AS manager_no 
FROM
  dept_emp de
LEFT JOIN dept_manager dm ON de.dept_no = dm.dept_no 
WHERE
  de.to_date = '9999-01-01'
AND dm.to_date = '9999-01-01'
AND de.emp_no <> dm.emp_no;