Re: Join types
Date: Fri, 25 Jan 2008 13:46:10 -0400
Message-ID: <479a2067$0$4069$9a566e8b_at_news.aliant.net>
JOG wrote:
> On Jan 25, 11:04 am, Gints Plivna <gints.pli..._at_gmail.com> wrote:
>
>>I'm a bit studying join types and trying to make a visualisation of
>>relations among them. As a result I've created an ER diagram
>>describing relations among them and it can be found herehttp://gplivna.blogspot.com/2008/01/sql-join-types-im-studying-bit-sq...
>>I've tried to find something like that using google however the best I
>>could get was textual description. I'm not mathematician and studied
>>set theory a bit 10 years ago in university and almost all have no
>>forgotten :) so maybe it has some problems from set theory viewpoint.
>>So question is - is it generally ok? If you know anything similar
>>please add link either here or in my blog post. All comments welcome!
>>Thanks!
>>Gints
> > Having only looked at your breakdown briefly, I can't give you much > comment (although I thought your time-bomb discussion of natural joins > was entertaining). However, I would say that in general I view natural > joins, equi-joins, etc. as specializations of the generalized theta > join. I'd be interested if other's share this perspective.
I do not share the perspective. I prefer to view theta join as natural join followed by restrict.
One might argue it's just a question of one's choice of primitives. I would argue that both natual join and restrict are simpler operations than theta join. Received on Fri Jan 25 2008 - 18:46:10 CET