RE: wrong cardinality

From: Wolfgang Breitling <breitliw_at_centrexcc.com>
Date: Tue, 14 Feb 2006 07:06:13 -0700
Message-Id: <6.2.3.4.2.20060214070358.04026358@pop.centrexcc.com>

At 02:21 AM 2/14/2006, Christian Antognini wrote:
>Wolfgang
>
> >The correction comes from the fact that Christian's formula for OR
> >predicates is correct for predicates involving different columns.
> >Expressing it in probability terms:
> >
> >p( A or B ) = p(A) + P(B) - p(A and B)
> >
> >In this case the optimizer knows that the two sides of the OR can not
> >both be true, i.e. p(A and B) = selectivity1*selectivity2 = 0
>
>I stand corrected. Thank you. I should probably avoid replying to
>email after 2am ;-)

No, please don't. I hope nothing I wrote sounded patronizing. In fact I stumbled on the answer more by accident than by deep analytical thought. I'll tell you the details at Hotsos.

Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com

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Received on Tue Feb 14 2006 - 08:06:13 CST