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Re: LIMIT Question

From: "Gurjeet Singh" <singh(dot)gurjeet(at)gmail(dot)com>
To: "Martijn van Oosterhout" <kleptog(at)svana(dot)org>, "Gurjeet Singh" <singh(dot)gurjeet(at)gmail(dot)com>, "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>, "Terry Lee Tucker" <terry(at)chosen-ones(dot)org>, pgsql-general(at)postgresql(dot)org
Subject: Re: LIMIT Question
Date: 2008-02-29 11:58:29
Message-ID: 65937bea0802290358m64976999m2d0c7c428eeadbea@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-general
On Fri, Feb 29, 2008 at 3:55 PM, Martijn van Oosterhout <kleptog(at)svana(dot)org>
wrote:

> On Fri, Feb 29, 2008 at 02:53:05PM +0530, Gurjeet Singh wrote:
> > In my opinion (without looking at the code), if you have a
> grouping-function
> > or ORDER BY or GROUP BY clause, then yes, the whole query has to be
> executed
> > to show the first row of the result-set. But if the query doesn't have
> any
> > of these clauses, then the DB has the ability to send back the first row
> > from the result as soon as it processes it (i.e after WHERE clause
> > processing), and stop the query execution there.
>
> Except if you have an index on the column you're ordering by. Then the
> server can really return the first row quickly.


Quickly for sure... but I don't think 'without processing all the rows that
qualify'. I think it will still process all the rows and return just one.

Best regards,
-- 
gurjeet[(dot)singh](at)EnterpriseDB(dot)com
singh(dot)gurjeet(at){ gmail | hotmail | indiatimes | yahoo }.com

EnterpriseDB      http://www.enterprisedb.com

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