select 
    OD.DEPT_CODE,
    DP.DEPT_NAME

from TBL_ORDERS as OD
    left join TBL_DEPT as DP
        on OD.DEPT_CODE = DP.DEPT_CODE

union 

select 
    SL.DEPT_CODE,
    DP.DEPT_NAME
    
from TBL_SALES as SL
    left join TBL_DEPT as DP
        on SL.DEPT_CODE = DP.DEPT_CODE

order by OD.DEPT_CODE asc;