SELECT OD.DEPT_CODE AS DEPT_CODE,DP.DEPT_NAME AS DEPT_NAME

FROM TBL_ORDERS AS OD

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