help on a query

Hi all,

This is one of those things I know I should know, but it's not coming to 
me. It's probably really simple.

I have two related tables, registrations and receipts, related by the 
field registration_id.

So registrations looks kinda like:

registration_id bigint (primary key)
foo varchar(10)
bar varchar(20)

and receipts looks like:

receipt_id bigint (primary key)
registration_id bigint (foreign key)
amount float
baz varchar(10)

If someone has paid, there is a row in the receipts table for that 
registration ID#.

I need to find a list of the registration IDs that *don't* have an entry 
in the receipts table.

Thanks in advance!!!
-- 
.Michelle

--------------------------
Michelle Murrain
mmurrain at dbdes dot com
413-222-6350 ph
617-889-0929 ph
952-674-7253 fax <--- new
Page: pageme@murrain.net
AIM:pearlbear0 ICQ:129250575
Skype: pearlbear
Jabber: pearlbear@transactim.net

"I see all the different religious traditions as paths for the 
development of inner peace, which is the true foundation of world peace. 
These ancient traditions come to us as a gift from our common past. Will 
we continue to cherish it as a gift and hand it over to the future 
generations as a legacy of our shared desire for peace?"  - His Holiness 
the Dalai Lama