Обсуждение: 8.2 contrib. "Full Disjunction"
I see that a new contrib module was added with the release of 8.2: http://pgfoundry.org/projects/fulldisjunction/ I found this article that describes the set theory behind it: http://dbpubs.stanford.edu:8090/pub/showDoc.Fulltext?lang=en&doc=1996-58&format=pdf&compression=&name=1996-58.pdf Most of it is over my head since I do not have a deep knowledge of set theory as well as all of the weird squiggly symbols that are used in this paper. Understanding the concepts of inner, outer, full outer, and cross joins are straight forward to me as to their application and use. However, since full disjunction is apparently some kind of join: 1) what is its application? 2) how is it used? Regards, Richard Broersma Jr.
> 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,Example > 2) how is it used? Maybe this question should have been, what is the syntax? Regards, Richard Broersma Jr.
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. ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to majordomo@postgresql.org so that your message can get through to the mailing list cleanly
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. > > ---------------------------(end of broadcast)--------------------------- > TIP 1: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@postgresql.org so that your > message can get through to the mailing list cleanly > > ---------------------------(end of broadcast)--------------------------- > TIP 2: Don't 'kill -9' the postmaster -- Regards, Tzahi. -- Tzahi Fadida Blog: http://tzahi.blogsite.org | Home Site: http://tzahi.webhop.info WARNING TO SPAMMERS: see at http://members.lycos.co.uk/my2nis/spamwarning.html
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@svana.org> http://svana.org/kleptog/ > From each according to his ability. To each according to his ability to litigate.
Вложения
"Martijn van Oosterhout" <kleptog@svana.org> writes: > 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. I'm still lost. I can see how it would be hard to join these together but I'm not sure what result I would be after. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com
On Sat, Jun 23, 2007 at 10:33:49PM +0100, Gregory Stark wrote: > "Martijn van Oosterhout" <kleptog@svana.org> writes: > > 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 > > I'm still lost. I can see how it would be hard to join these together but I'm > not sure what result I would be after. Well, the way I understand it is if you had the following data: rel A x : y 1 : 2 5 : 6 rel B: y : z 2 : 3 7 : 8 rel C: z : x 3 : 1 10 : 9 That the result would be: x : y : z 1 : 2 : 3 5 : 6 : : 7 : 8 9 : : 10 Now, I can't off the top of my head think of a schema where you would need this, but if you have this problem then I don't see the solution in plain SQL. Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > From each according to his ability. To each according to his ability to litigate.