Re: Oracle Myths

From: D.Y. <dyou98_at_aol.com>
Date: 21 May 2002 12:19:41 -0700
Message-ID: <f369a0eb.0205211119.5b4b6b90@posting.google.com>

nsouto_at_optushome.com.au (Nuno Souto) wrote in message news:<dd5cc559.0205151535.cef9399_at_posting.google.com>...
> "Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote in message news:<3ce21b71$0$8510$ed9e5944_at_reading.news.pipex.net>...
> > Suggested list to be added to, deleted from etc
>
> Oh yeah, almost forgot:
>
> - Put the most selective column first in a concatenated index.
> (this one AFAIK was never true, but somehow it stuck)
>

I found myself on the opposite side again :-)

There is one reason to do this: the most selective column is more likely to be part of the criteria of many queries. Therefore having the most selective column first will likely allow you to serve many queries with one index. As for performance, compressed index with the least selective column first may be better. So do what's best for your application.

>
> Cheers
> Nuno
Received on Tue May 21 2002 - 14:19:41 CDT