Hiding columns used in GROUP BY and HAVING clauses

[Edward Kay]

I have a table of addresses. Each address is associated with a primary
entity and a primary entity can have n different addresses. For each primary
entity, one address is marked as the main address.

I need a query to return all addresses that are the only address associated
with the primary entity but aren't marked as the main address.

At the moment, I have this and it works:

	select * from contact_address
	group by primary_entity_id
	having count(primary_entity_id) = 1
	and is_primary = 0;

This is fine except I want to use the result in a sub-query. Since it
returns two columns this doesn't work:

	update contact_address set is_primary = 1 where address_id in (
		select * from contact_address
		group by primary_entity_id
		having count(primary_entity_id) = 1
		and is_primary = 0
	);

Normally, I'd only return the address_id in the sub-SELECT, but I need the
is_primary column for the HAVING clause.

Any ideas on how to achieve this?

Thanks,
Edward