Re: multi-column indexes, statistics and selectivity
From: Robert Klemme <shortcutter_at_googlemail.com>
Date: Sun, 06 Dec 2009 13:33:06 +0100
Message-ID: <7o1mk3F3n9576U3_at_mid.individual.net>
On 05.12.2009 22:35, Mladen Gogala wrote:
> On Sat, 05 Dec 2009 14:18:38 +0100, Robert Klemme wrote:
>
>
> 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.
Date: Sun, 06 Dec 2009 13:33:06 +0100
Message-ID: <7o1mk3F3n9576U3_at_mid.individual.net>
On 05.12.2009 22:35, Mladen Gogala wrote:
> 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.
That makes a lot of sense! Thank you, Mladen!
Kind regards
robert
-- remember.guy do |as, often| as.you_can - without end http://blog.rubybestpractices.com/Received on Sun Dec 06 2009 - 06:33:06 CST