How can I show the values from my input that don't exist in a table?
create table order_table(order_number number);
insert into order_table values (43454235423);
commit;

with input_values as
(
  select
    to_number(column_value) as order_number
  from
    xmltable('43454235423, 785686847856, 1243215421, 6437647, 978423454')
)
select
  v.order_number, 'not found' as status
from
  input_values v
left join
  order_table o on (v.order_number = o.order_number)
where
  o.order_number is null
;

        ORDER_NUMBER STATUS
-------------------- ---------
        785686847856 not found
          1243215421 not found
             6437647 not found
           978423454 not found