Re: Re: Does PostgreSQL support EXISTS?

> Bruce Momjian <pgman@candle.pha.pa.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.

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