Re: multi-column indexes, statistics and selectivity

From: Mladen Gogala <>
Date: Sat, 5 Dec 2009 21:35:37 +0000 (UTC)
Message-ID: <hfejn9$hh6$>

On Sat, 05 Dec 2009 14:18:38 +0100, Robert Klemme wrote:

> Are there cases where it makes sense to use a FBI to get "multi column"
> histogram information?

Hmmm, let me quote from the 11g book: if the columns are related in the way that breaks the 3rd normal form, such statistics would make sense. The famous example by Jonatan was about zodiac signs and months of birth. The 10g CBO would produce an incorrect estimate for the number of people with the sign of Capricorn born in June. There are, of course, none, but you can't know that without a multi-column histogram.

Received on Sat Dec 05 2009 - 15:35:37 CST

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