SELECT
    O.DEPT_CODE AS DEPT_CODE
    ,D.DEPT_NAME
FROM
    TBL_ORDERS AS O
LEFT OUTER JOIN
    TBL_DEPT AS D
  ON
    O.DEPT_CODE = D.DEPT_CODE
UNION
SELECT
    S.DEPT_CODE AS DEPT_CODE
    ,D.DEPT_NAME
FROM
    TBL_SALES AS S
LEFT OUTER JOIN
    TBL_DEPT AS D
  ON
    S.DEPT_CODE = D.DEPT_CODE
    
ORDER BY
    DEPT_CODE ASC;