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RE: [HACKERS] RE: [GENERAL] Long update query ? (also Re: [GENERAL] CNF vs. DNF)

From: "Taral" <taral(at)mail(dot)utexas(dot)edu>
To: "Bruce Momjian" <maillist(at)candle(dot)pha(dot)pa(dot)us>
Cc: <jwieck(at)debis(dot)com>, <hackers(at)postgreSQL(dot)org>
Subject: RE: [HACKERS] RE: [GENERAL] Long update query ? (also Re: [GENERAL] CNF vs. DNF)
Date: 1998-10-04 02:26:20
Message-ID: 000501bdef3e$5f5293a0$3b291f0a@taral (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers
> however if A and C are identical, this could become:
>
> 	(A OR A) AND (A OR D) AND (B OR A) AND (B OR D)
>
> and A OR A is A:
>
> 	A AND (A OR D) AND (B OR A) AND (B OR D)
>
> and since we are now saying A has to be true, we can remove OR's with A:
>
> 	A AND (B OR D)

Very nice... and you could do that after each iteration of the rewrite,
preventing the size from getting too big. :)

I have a symbolic expression tree evaluator that would be perfect for
this... I'll see if I can't adapt it.

Can someone mail me the structures for expression trees? I don't want to
have to excise them from the source. Please?

Taral


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