"biggest" character in an order by operation using NLS_SORT=WEST_EUROPEAN

Question

I thought this would be simple to find out, but it isn't.
I'd like to find the single character that comes out last in a "sort by" on a varchar field. If I use the normal ASCII sort order everything works as expected and the characters like ~ and } come after all other characters and numbers:
select * from my_table order by nlssort(my_field, 'nls_sort=ASCII7')
However, I can't always use the "order by nlssort" clause (the db is a data warehouse and there are hundreds of reports). The NLS_SORT parameter is set to WEST_EUROPEAN and it seems that numbers come after all letters (i.e. 0 is bigger than z).
My questions is: does anybody know a special character that comes after the number 9?
Or, in alternative, does anybody know a link to a complete table that shows the sort order for WEST_EUROPEAN?

Answer 1

Massimo,
with the term "unknown" records I meant the codes that are null or that do not are not found in dimensions (we are tallking about a data warehouse), so they are assigned an "unknown" or "N/A" value.
The second hint that you gave me is also useful, I didn't know about the existance of "nulls first" and "nulls last" clause, but data warehouse best practices say that there should be no fields left Null in the dimensions, so I have to find a different solution. One possible alternative is to add another columns to the table, to be used for sorting purposes only.
Andrea