On Tue, Jun 30, 2009 at 1:22 PM, Erik Jones<ejones@engineyard.com> wrote:
>> and if I have a row in table C where c.id is null? A don't know.
>
> No, it's perfectly clear as 'NULL = NULL' evaluates to false:
>
> postgres=# select null = null;
> ?column?
> ----------
>
you can test for that with 'is distinct from':
select null is distinct from null; -- false
select null is distinct from 1; -- true