Re: index usage

From: Richard Foote <richard.foote_at_bigpond.nospam.com>
Date: Thu, 20 Jan 2005 21:18:51 GMT
Message-ID: <%eVHd.126355$K7.76849@news-server.bigpond.net.au>

"Niall Litchfield" <niall.litchfield_at_dial.pipex.com> wrote in message

news:41f01b1e$0$16583$cc9e4d1f_at_news-text.dial.pipex.com...

> "Richard Foote" <richard.foote_at_bigpond.nospam.com> wrote in message
> news:fJMHd.126019$K7.84069_at_news-server.bigpond.net.au...
>> I can easily give you an example where an index is most efficient when
>> reading 0% of data
>
> snip all the rest of the good stuff to say
>
> 1. welcome back. and

Hi Niall

Thank you

> 2. er, wouldnt not executing the query at all be more efficient in the 0%
> case?
>

Possibly but then how can you determine that there are no space seats left on flight Q123 from Canberra to Brisbane on Jan 26 2005 without first querying the database and selecting no rows ...

An index is the perfect way to select no rows (btw, Oracle uses them all the time to do the same thing when validating a value in a unique constraint).

Cheers ;)

Richard Received on Thu Jan 20 2005 - 15:18:51 CST