Checking number of entries

Hello,

Is it possible to restrict the number of entries in a table? I have attempted
to write a check like so:

CREATE TABLE mytable (
id integer NOT NULL,
CHECK (COUNT(id) <= 10)
);

This is not allowed, I get an error saying:

ERROR: ExecEvalAggref: no aggregates in this expression context

What is the proper way of doing this? I want to be able to force a minimum and
maximum number of entries.

Wade Oberpriller
StorageTek
oberpwd(at)network(dot)com