Re: question about seq scan and index scan

Le Vendredi 25 Octobre 2002 20:17, Stephan Szabo a écrit :
> On Fri, 25 Oct 2002, [iso-8859-15] Hervé Piedvache wrote:
> > Thanks for you help ... to "explain" us why Postgresql do not use all the
> > time the index scan for this kind of request for 3 tables with the same
> > primary key id.
>
> Depending on the number of rows returned, index scan may not be faster
> than a sequential scan. As you up the constant, the estimated number of
> rows drops which make the index scan a better and better plan. Are
> the estimated number of rows for the scan of a (4379, 3987, and 29)
> realistic for mynumber>(23000, 23500, 24000)

I'm surpise about this answer for

>23000
result is 98

>23350
result is 96

>24000
result is 93

With a table of 471 413 records and most of the values for mynumber are
< of 2500 result is 467 902 records ...

I do not understand the explain result sorry ! ;o/

Regards,
--
Hervé Piedvache

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