On Fri, 10 Feb 2006, Sergei Dubov wrote:
> I have two tables, let's say A and B.
>
> B is a child of a in one to many relationship. A contains records that are
> not referenced by B.
>
> I am running a query:
>
> select * from A t1 where t1.id not in (select t2.A_id from B t2);
>
> It returns 0 rows.
>
> Now I run
> (select t1.id from A t1) except (select t2.A_id from B t2);
>
> And now Postgres correctly returns records from A that are not referenced by
> B.
This may not be a bug, since these two queries will do different things if
there are any nulls in B.A_id according to spec AFAIK. The short form is
that rvc NOT IN (<subselect returning nulls>) will not return true.