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;