SELECT
    DEPT_CODE,
    DEPT_NAME
FROM
    (
        SELECT
            TOR.DEPT_CODE,
            TD.DEPT_NAME
        FROM
            TBL_ORDERS TOR
        LEFT JOIN TBL_DEPT TD ON TOR.DEPT_CODE = TD.DEPT_CODE
        UNION
        SELECT
            TS.DEPT_CODE,
            TD.DEPT_NAME
        FROM
            TBL_SALES TS
            LEFT JOIN TBL_DEPT TD ON TS.DEPT_CODE = TD.DEPT_CODE
    )
GROUP BY
    DEPT_CODE,DEPT_NAME
ORDER BY
    DEPT_CODE ASC