SELECT OD.DEPT_CODE AS DEPT_CODE, DP.DEPT_NAME
FROM TBL_ORDERS OD
LEFT JOIN TBL_DEPT DP
ON OD.DEPT_CODE = DP.DEPT_CODE

UNION

SELECT SA.DEPT_CODE AS DEPT_CODE, DP.DEPT_NAME
FROM TBL_SALES SA
LEFT JOIN TBL_DEPT DP
ON SA.DEPT_CODE = DP.DEPT_CODE

ORDER BY DEPT_CODE;