SELECT OD.DEPT_CODE AS DEPT_CODE, DP.DEPT_NAME 
FROM TBL_ORDERS AS OD LEFT OUTER JOIN TBL_DEPT AS DP ON DP.DEPT_CODE = OD.DEPT_CODE 
UNION 
SELECT SA.DEPT_CODE AS DEPT_CODE, DP.DEPT_NAME 
FROM TBL_SALES AS SA LEFT OUTER JOIN TBL_DEPT AS DP ON DP.DEPT_CODE = SA.DEPT_CODE 
ORDER BY DEPT_CODE ASC;