From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
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To: | Tzahi Fadida <Tzahi(dot)ML(at)gmail(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org, Brandon Aiken <BAiken(at)winemantech(dot)com>, Richard Broersma Jr <rabroersma(at)yahoo(dot)com> |
Subject: | Re: 8.2 contrib. "Full Disjunction" |
Date: | 2007-06-23 21:04:53 |
Message-ID: | 20070623210453.GG11248@svana.org |
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Lists: | pgsql-general |
On Fri, Jun 22, 2007 at 07:38:01PM +0300, Tzahi Fadida wrote:
> Let me simplify it in lamer terms.
> Basically, you have a cycle in your relations schema. i.e.
> rel A: att-x, att-y
> rel B: att-y, att-z
> rel C: att-z, att-x
>
> The only way to join these three without loosing a lot of information (aside
> from some very weird corner cases which i won't mention here), is to use my
> full disjunctions which is probably most certainly the only implementation of
> the operation in existence to calculate the general case (which you can see
> above).
FWIW, with this simple description I finally worked out what full
disjunctions are and why you can't do them (efficiently) in SQL.
Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.
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