Re: Re: Does PostgreSQL support EXISTS?

> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > 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.
>
> After we fix IS TRUE and friends to respond to nulls correctly (Conway's
> promised to do that, IIRC) it'll be possible to write
>
>     (foo IN (SELECT ...)) IS NOT FALSE
>
> and get the "intuitive" behavior.  But right now that doesn't work.

OK, so I wasn't missing anything in our current code.  I can see how
this capability would change things.

> Hm.  Maybe we could recognize that construct as a whole, and translate
> it to an optimizable join?  It'd become the usual locution, I imagine.

Are we anywhere with optimizing IN to EXISTS?  I didn't think there was
any work being done in that area.

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