WITH T1 AS(
    SELECT
        DEPT_CODE
    FROM
        TBL_ORDERS
), T2 AS(
    SELECT
        DEPT_CODE
    FROM
        TBL_SALES
), T3 AS(
    SELECT
        *
    FROM
        T1
    UNION ALL
    SELECT
        *
    FROM
        T2
), T4 AS(
    SELECT
        DISTINCT T3.DEPT_CODE,
        DEPT_NAME
    FROM
        T3
    LEFT OUTER JOIN
        TBL_DEPT ON T3.DEPT_CODE = TBL_DEPT.DEPT_CODE
    ORDER BY
        T3.DEPT_CODE ASC
)
SELECT
    *
FROM
    T4