RE: wrong cardinality
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- Date: Tue, 14 Feb 2006 07:06:13 -0700
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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