select * from (
select distinct
 T2.DEPT_CODE
 ,T1.DEPT_NAME
from
tbl_dept T1
full outer join tbl_orders T2 on
T1.DEPT_CODE = T2.DEPT_CODE
union
select distinct
 T4.DEPT_CODE
 ,T3.DEPT_NAME
from
tbl_dept T3
full outer join tbl_sales T4 on
T3.DEPT_CODE = T4.DEPT_CODE
) order by DEPT_CODE asc;