select
  D.DEPT_CODE AS DEPT_CODE
  , D.DEPT_NAME
from
  TBL_ORDERS AS O
  left outer join TBL_DEPT AS D
    on D.DEPT_CODE = O.DEPT_CODE
union
select
  S.DEPT_CODE AS DEPT_CODE
  , D.DEPT_NAME
from
  TBL_SALES AS S
  left outer join TBL_DEPT AS D
    on D.DEPT_CODE = S.DEPT_CODE
order by
  DEPT_CODE
;