SELECT
    T1.DEPT_CODE AS DEPT_CODE,
    T2.DEPT_NAME 
FROM
    TBL_ORDERS AS T1 
    LEFT OUTER JOIN TBL_DEPT AS T2 
        ON T2.DEPT_CODE = T1.DEPT_CODE 
UNION 
SELECT
    T3.DEPT_CODE AS DEPT_CODE
    , T4.DEPT_NAME 
FROM
    TBL_SALES AS T3 
    LEFT OUTER JOIN TBL_DEPT AS T4 
        ON T4.DEPT_CODE = T3.DEPT_CODE 
ORDER BY
    DEPT_CODE ASC;