From: | "Mason Hale" <masonhale(at)gmail(dot)com> |
---|---|
To: | "Stephan Szabo" <sszabo(at)megazone(dot)bigpanda(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: unexpected results with NOT IN query |
Date: | 2008-03-20 17:10:02 |
Message-ID: | 8bca3aa10803201010pc2207as9a65bbb1adf967e@mail.gmail.com |
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Thread: | |
Lists: | pgsql-general |
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.
>
>
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