SELECT
    TBO.DEPT_CODE AS DEPT_CODE,
    TBD.DEPT_NAME AS DEPT_NAME
FROM
    TBL_ORDERS AS TBO
    LEFT OUTER JOIN TBL_DEPT AS TBD
    ON TBO.DEPT_CODE = TBD.DEPT_CODE


UNION

SELECT 
    TBS.DEPT_CODE AS DEPT_CODE,
    TBD.DEPT_NAME AS DEPT_NAME
FROM
    TBL_SALES AS TBS
    LEFT JOIN TBL_DEPT AS TBD
    ON TBS.DEPT_CODE = TBD.DEPT_CODE
ORDER BY DEPT_CODE;