Re: Vagaries of the CBO: Out-of-Range Predicates

Hi,

Thanks Wolfgang, you are right i got a bit entangled in the terminology and hence ended up formulating a wrong question.

Yes, selectivity is what i should be worried about and ultimately the cost factor. because, i my case CBO is choosing the wrong index due to the NDV being 1 and i don't have histograms.

so, looks like i have resign myself to the fact that an NDV hack is the only way to make CBO choose the right index (without hinting the query).

many thanks,
anand

On 18/12/06, Wolfgang Breitling <breitliw_at_centrexcc.com> wrote:
>
> At 12:11 AM 12/18/2006, Anand Rao wrote:
>
> adding one more question,
>
> 3) How does CBO calculate the density in cases of bind variables when the
> value is out of range?
>
> or is this a RTFM / RTFB ... ??
>
>
> density is a "property" of the column and is roughly related to the
> probability of finding a particular value in the rows of the table. It is
> calculated when statistics are collected, *not* at parse time. density is
> in no way dependent on bind variables - or literals for that matter. You may
> be mistaking density with selectivity.
>
> Regards
>
> Wolfgang Breitling
> Centrex Consulting Corporation
> www.centrexcc.com
>

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