md5 of table

Is there a way to get an md5 or other hash of an entire table?

I want to be able to easily compare 2 tables in different databases.

I thought about using dblink and the EXCEPT query, but then I need to
know the field list of each query result, which is a pain in the butt.

If I could return an md5 of the entire table, then I could check if the
tables have the same hash and be confident enough that the tables were
identical.


Thanks
Sim