From: Michael Fuhr <mike@fuhr.org>
To: Bo Lorentsen <bl@netgroup.dk>
Cc: Russell Simpkins <russellsimpkins@hotmail.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Number of rows in a cursor ?
Date: Wed, 24 Aug 2005 11:46:12 -0600
Message-ID: <20050824174612.GB80642@winnie.fuhr.org> (raw)
In-Reply-To: <430C842C.8000504@netgroup.dk>
References: <B74B7433CDDD2C4AA41D94832E32E19D92EE9A@EMEXM1112.dir.svc.accenture.com>
<430C4C70.2010005@netgroup.dk>
<BAY103-DAV72BF461390EA073012267B5A80@phx.gbl>
<430C6CFF.9070304@netgroup.dk>
<20050824131921.GA39444@winnie.fuhr.org>
<430C842C.8000504@netgroup.dk>
On Wed, Aug 24, 2005 at 04:29:00PM +0200, Bo Lorentsen wrote:
> Michael Fuhr wrote:
> >...which is the same reason a cursor doesn't know how many rows it will
> >fetch until you fetch them all (or MOVE to the end of the cursor,
> >which fetches the rows internally).
>
> So, Postgresql is not hidding something for me, it just, like me, don't
> know ?
Right -- when you open a cursor PostgreSQL doesn't know how many
rows it will return. PostgreSQL selects a query plan based on an
*estimate* of how many rows the query will return, but until you
fetch all the rows you can't know for sure how many rows there will
be.
--
Michael Fuhr
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To: pgsql-sql@postgresql.org
Cc: mike@fuhr.org, bl@netgroup.dk, russellsimpkins@hotmail.com
Subject: Re: Number of rows in a cursor ?
In-Reply-To: <20050824174612.GB80642@winnie.fuhr.org>
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