Re: join removal

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Greg Stark <stark(at)mit(dot)edu>, "<pgsql-hackers(at)postgresql(dot)org>" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: join removal
Date: 2010-03-28 15:56:28
Message-ID: 22143.1269791788@sss.pgh.pa.us
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Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I'm alarmed by your follow-on statement that the current code can't
> handle the two-levels of removable join case. Seems like it ought to
> form {B C} as a path over {B} and then {A B C} as a path over {A}.

Actually I think it ought to form {A B} as a no-op join and then be able
to join {A B} to {C} as a no-op join. It won't recognize joining A to
{B C} as a no-op because the RHS isn't a baserel. But yeah, I was quite
surprised at the failure too. We should take the time to understand why
it's failing before we go further. I ran out of steam last night but
will have a look into that today.

regards, tom lane

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