select do.dept_code, do.dept_name, do.order_no, do.cust_code, cust.cust_name, do.order_amt
from (
    select * from tbl_dept as dept
    inner join tbl_orders as orders 
    on dept.dept_code = orders.dept_code
) do
left outer join tbl_cust as cust
on do.cust_code = cust.cust_code
order by do.dept_code asc, do.order_no asc;