Path: utzoo!mnetor!uunet!steinmetz!ge-dab!codas!pdn!ard
From: ard@pdn.UUCP (Akash Deshpande)
Newsgroups: comp.databases
Subject: Re: SQL question
Message-ID: <2376@pdn.UUCP>
Date: 2 Mar 88 14:50:23 GMT
References: <34358UH2@PSUVM> <43005@sun.uucp> <34586UH2@PSUVM>
Organization: Paradyne Corporation, Largo, Florida
Lines: 24

In article <34586UH2@PSUVM>, UH2@PSUVM.BITNET (Lee Sailer) writes:
> One of the characterisitcs of SQL, I thought, was that there are ONLY
> 4 operators, SELECT, INSERT, DELETE, and UPDATE.  I figured that
> there would be some tricky way to use a SELECT to do a Union, Intersect,
> Difference, etc.
> 
> So, how come it is said that SQL has only 4 operators, when obviously
> there are more?
> 
>                lee

	There are two separate issues here - completeness and expressiveness.
	Relational algebra, relational calculus and set calculus are all
	equivalently complete. Operations in one can be expressed in terms
	of operations in another. However, for more expressiveness, one may
	want to have operations from more than one groups in a language.

	Details can be found in 'An Introduction to Database Systems' Date.

-- 
Akash Deshpande					Paradyne Corporation
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(813) 530-8307 o				P.O. Box 2826
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