Re: Why would an index not be used if specified as a hint in a query?

From: Niall Litchfield <niall.litchfield_at_dial.pipex.com>
Date: Sat, 12 Feb 2005 09:24:56 -0000
Message-ID: <420dd025$0$19158$cc9e4d1f@news-text.dial.pipex.com>

"DA Morgan" <damorgan_at_x.washington.edu> wrote in message news:1108185875.191030_at_yasure...
> Craig & Co. wrote:
>
>> Hi,
>>
>> Running Oracle 8.1.7.4 on Solaris 2.8.
>>
>> Running explain plan, and then a query (I don't have a copy to show at
>> this
>> point), apparently
>> the index is not used.
>>
>> I assume it is because the optimiser thinks the index is not required
>> even
>> though it is specified.
>>
>> Cheers
>> Craig.
>
> A reasonable presumption.
>
> On the other hand it could be lack of statistics for the optimizer or
> any one of a number of things. Small matters like the number of rows
> in the table, the applicability of the index to the query, the
> cardinality, and the percentage of rows to be returned could also be
> affecting the outcome.

A reasonable presumption indeed, but an incorrect one - assuming I understand 'not required' correctly - equally only one of your factors should be relevant.

Using an INDEX hint *WILL* cause the index to be used *IF IT CAN BE* Received on Sat Feb 12 2005 - 03:24:56 CST