Via va Viaindex

[Deskin, Bob]

Strictly speaking, VIAINDEX for relational is misleading. What happens is
that the index specified is broken down into the composit segments/columns
and the net is a VIA by those columns. If the relational DB decides to do an
indexed retrieval, fine, but it's left to the database. We did think about
taking it out or changing the keyword many years ago, but it never happened.

There are other effects from VIAINDEX, but I'm not the expert. As with most
things, if you understand what's happening, then it can work for you.
However, since some of the effects aren't obvious, you may be able to get
better control by using VIA, USING, and ORDERBY.

Bob Deskin              
PowerHouse Web Product Manager and Senior Product Advisor
Application Development Tools, Cognos Inc.
bob.deskin@cognos.com (613) 738-1338 ext 4205 FAX: (613) 228-3149
3755 Riverside Drive P.O. Box 9707 Stn. T, Ottawa ON K1G 4K9 CANADA


> ----------
> From: 	stewm@canada.com[SMTP:stewm@canada.com]
> Sent: 	August 10, 1999 11:05 PM
> To: 	powerh-l@lists.swau.edu
> Subject: 	Via va Viaindex
> 
> G'day,
> 
> I would never think to use Viaindex with relational tables simply because
> Cognos doesn't recommend it.  However I just seen a case where a fellow
> worker used Viaindex with RDB.  I attended the code review meeting for his
> enhancements and mentioned the fact that even the 'Qdesign' manual states
> that you shouldn't use Viaindex with relational linkages.  
> 
> What are the reasons why Via is the better choice with relational
> databases.  The manual only states that it is better because indexes may
> change and thus code changes are not needed or something like that.  This
> can't be the only reason because Cognos has recommended to some companies
> to remove all Viaindex occurrances through out their apps when relational
> tables are involved.  I've also heard that data retrieval results can be
> unpredictable with the database optimizer in conjuction with Viaindex.
> Can someone tell me what ALL the drawbacks associated with using Viaindex
> with relational tables are?
> 
> Thanks in advance,
> 
> Mark Stewart
> Consultants Club Corp.
> Windsor, Ontario
> Canada
> 
> Current Site:
> 7.10.G2 OpenVms
> RDB
> Bannockburn, Il
> 
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