Path: utzoo!dciem!nrcaer!sce!cognos!nigelc
From: nigelc@cognos.UUCP (Nigel Campbell)
Newsgroups: comp.databases
Subject: Re: Join Contest
Message-ID: <8619@cognos.UUCP>
Date: 20 Jul 90 03:18:38 GMT
References: <5265@plains.UUCP> <933@dgis.dtic.dla.mil>
Reply-To: nigelc@cognos.UUCP (Nigel Campbell)
Organization: Cognos Inc., Ottawa, Canada
Lines: 37

In article <933@dgis.dtic.dla.mil> jkrueger@dgis.dtic.dla.mil (Jon) writes:
>gus@plains.NoDak.edu writes:
>
>>Recently I heard that an IBM-type db person claimed that it's
>>not uncommon in commercial db applications to join as many as
>>10-15 (maybe even 30) tables in a single query.
>

>It is uncommon. 

	really ..... 

>Ask your IBM-type db person to substantiate
>his claim.  "Extraordinary claims require extraordinary
>justification".  In fact it's difficult to design a query that
>makes sense with more than about five joins.

	Quite an extraordinary claim 

> Try it.

	I just took a peek at the 40+ reports in a large bus
scheduling/driver bidding system I have worked on . Most reports
are non trivial (but real-life) and have 4-8 tables . Not much
above 5 I admit but those larger joins do make sense . Given that
most SQL implementations do not support a recusive join I would
not find it unusual to see 5+ reflexive joins in BOM style structures.
In fact a museums Taxonomic dictionary can be up to 24 levels deep
depending upon the discipline .



-- 
Nigel Campbell          Voice: (613) 783-6828                P.O. Box 9707
Cognos Incorporated       FAX: (613) 738-0002                3755 Riverside Dr.
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