How to get a count() where column < ''?

Hi,

I want the number of customers that have a zipCode smaller tha a given
value. The foolowing query doe snot work : I get an error (ERROR:
column "addresses.zipcode" must appear in the GROUP BY clause or be used
in an aggregate function) and I do not know how to solve it.

SELECT COUNT(customers.objectid) FROM prototype.customers,
prototype.addresses
WHERE
customers.contactaddress = addresses.objectid
AND
zipCode < '2716BN'
ORDER By zipCode, houseNumber

Anyone an idea?

TIA

--
Groeten,

Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
e-mail: J(dot)Kraaijeveld(at)Askesis(dot)nl
web: www.askesis.nl