Hi,
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).
Btw, it also applies to more than 3 relations, but be careful, it can be a
costly operation. I would try it on very small relations and gradually move
up to see how it performs.
You can see examples in the contrib module dist in pgfoundry.
On Wednesday 06 December 2006 17:37:58 Brandon Aiken wrote:
> Download the contrib module .tgz from PGFoundry and check out the
> readme. Syntax is explained therein. It's a multi-step process, it
> appears.
>
> I don't especially care for the term 'full disjunction' to describe this
> operation, but it seems to be an understood relational operation.
>
> --
> Brandon Aiken
> CS/IT Systems Engineer
> -----Original Message-----
> From: pgsql-general-owner@postgresql.org
> [mailto:pgsql-general-owner@postgresql.org] On Behalf Of Richard
> Broersma Jr
> Sent: Wednesday, December 06, 2006 1:30 AM
> To: Richard Broersma Jr; General PostgreSQL List
> Subject: Re: [GENERAL] 8.2 contrib. "Full Disjunction"
>
> > 1) what is its application?
>
> I guess I found part of my "laymans" answer:
> http://www.cs.toronto.edu/~yaron/Presentations/pods2003.ppt#468,39,Examp
> le
>
> > 2) how is it used?
>
> Maybe this question should have been, what is the syntax?
>
> Regards,
>
> Richard Broersma Jr.
>
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--
Regards,
Tzahi.
--
Tzahi Fadida
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