Re: unexpected results with NOT IN query

Thanks -- that was it -- last_feed_download_task_id can indeed be null.

- Mason

On Thu, Mar 20, 2008 at 10:17 AM, Stephan Szabo <
sszabo(at)megazone(dot)bigpanda(dot)com> wrote:

> On Thu, 20 Mar 2008, Mason Hale wrote:
>
> > Hello --
> >
> > I'm getting some unexpected results with a NOT IN query -- this is on
> 8.2.5.
> >
> > This is the query in question:
> >
> > prod_2=> select id from feed_download_task where id in
> (111102466,141701504)
> > and id not in (select last_feed_download_task_id from subscription);
>
> Is it possible for last_feed_download_task_id be NULL? If so, then then id
> not in (...) will not ever return true due to the way comparisons with
> NULLs work -- basically, it can't tell if the id is in the other table
> because id = NULL is unknown, so it thus can't tell that it's not in the
> other table either, so you could end up with neither in nor not in
> returning the row.
>
>