Novice needs help - Mailing list pgsql-sql

I have loaded over 29,000 customer records into a database. I'm trying 
to apply a referential foreign key that validates the country code and 
the province code in another table. It won't work because somewhere in 
that 29,000 records there is a province code or country code that 
doesn't match. Is there a way to use a select statement to find out 
which customer records has the invalid data? Here is the partial table 
layout:

cust                                                            province
--------                                                 -------
country                      ===>                       country
province                    ===>                       code

Thanks in advance...

-- 
Terry Lee Tucker