select O.DEPT_CODE as DEPT_CODE, TBL_DEPT.DEPT_NAME
from TBL_ORDERS O
left join TBL_DEPT
on O.DEPT_CODE = TBL_DEPT.DEPT_CODE
union
select S.DEPT_CODE as DEPT_CODE, TBL_DEPT.DEPT_NAME
from TBL_SALES S
left join TBL_DEPT
on S.DEPT_CODE = TBL_DEPT.DEPT_CODE 
order by 1 asc ;