SELECT
    DEPT.DEPT_CODE AS DEPT_CODE,
    TBL_DEPT.DEPT_NAME AS DEPT_NAME
FROM
    TBL_DEPT
RIGHT JOIN
(
    SELECT
        DEPT_CODE
    FROM
        TBL_ORDERS
    UNION
    SELECT
        DEPT_CODE
    FROM
        TBL_SALES
) AS DEPT
ON  DEPT.DEPT_CODE = TBL_DEPT.DEPT_CODE
ORDER BY
    DEPT_CODE