RE: Count(*) not doing a FTS??

From: Lex de Haan <lex.de.haan_at_naturaljoin.nl>
Date: Fri, 3 Sep 2004 10:59:40 +0200
Message-ID: <JFEEIGBIDOCCDALDIPLNEEADCIAA.lex.de.haan@naturaljoin.nl>

I think the instructor (in case he/she wasn't joking in the first place) mixed things up a little here.
I am guessing, but I assume he/she was referring to the fact that the CBO may use segment header info to estimate the costs of a full table scan in the absence of table statistics.

well, there is some distinct relationship between the two queries "select count(*) from T" and "how expensive you think a FTS of table T will be" ...

Kind regards,
Lex.

visit http://www.naturaljoin.nl

skype me <callto://lexdehaan>

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Steve Rospo Sent: Friday, September 03, 2004 01:17
To: Oracle Discussion List
Subject: Re: Count(*) not doing a FTS??

Did your instructor say this with a straight face? There's no such voodoo as a rowcount in a segment header. The two ways you can do it are a FTS or fast full scan of a not null index.

On Thu, 2 Sep 2004, rjamya wrote:

> I am sitting in a class and instructor told us that count(*) reads
> rowcount from segment header in some (or most?) cases ...

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Received on Fri Sep 03 2004 - 03:55:24 CDT