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