SELECT O.DEPT_CODE AS DEPT_CODE ,D.DEPT_NAME,D.DEPT_CODE 
FROM TBL_ORDERS O
LEFT JOIN TBL_DEPT D ON D.DEPT_CODE = O.DEPT_CODE

UNION

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