| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Michael Meskes <meskes(at)postgresql(dot)org>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: Re: Does PostgreSQL support EXISTS? |
| Date: | 2001-06-13 15:09:09 |
| Message-ID: | 200106131509.f5DF99V08176@candle.pha.pa.us |
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| Lists: | pgsql-general |
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > I thought NOT IN was the only one that was concerned about any NULL?
>
> No, they both are: in the presence of NULLs, IN can return TRUE or NULL,
> NOT IN can return FALSE or NULL.
>
> The reason the FAQ is always about NOT NULL is that WHERE treats NULL as
> FALSE, so the average newbie writing an IN doesn't even realize he's
> getting a NULL rather than a FALSE. With NOT NULL, he can't ignore it.
Got it. How does an IN subquery returning NULL behave differently from
one returning FALSE? I can't think of a test that would be affected.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
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