SELECT b.DEPT_CODE AS DEPT_CODE ,  a.DEPT_NAME
FROM TBL_ORDERS AS b

LEFT OUTER JOIN TBL_DEPT AS a
ON a.DEPT_CODE = b.DEPT_CODE

UNION

SELECT c.DEPT_CODE as DEPT_CODE ,  a.DEPT_NAME
FROM TBL_SALES AS c 
LEFT  OUTER JOIN TBL_DEPT AS a
ON a.DEPT_CODE = c.DEPT_CODE


ORDER BY DEPT_CODE ASC