RE: Count(*) not doing a FTS??
- From: "Lex de Haan" <lex.de.haan@xxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 3 Sep 2004 10:59:40 +0200
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.
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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]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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