Content-Type: text/plain; charset="utf-8"
Date: Mon, 13 Sep 2010 02:03:06 +0200
From: "Steve" <steeeeeveee@gmx.net>
In-Reply-To: <i6g60e$345$1@news.albasani.net>
Message-ID: <20100913000306.202150@gmx.net>
MIME-Version: 1.0
References: <20100911122923.75010@gmx.net> <i6g60e$345$1@news.albasani.net>
Subject: Re: Question regarding indices
To: pgsql-sql@postgresql.org
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-------- Original-Nachricht --------
> Datum: Sat, 11 Sep 2010 11:08:00 -0400
> Von: Lew <noone@lewscanon.com>
> An: pgsql-sql@postgresql.org
> Betreff: Re: [SQL] Question regarding indices

> On 09/11/2010 08:29 AM, Steve wrote:
> > I have a small question about the order of values in a query.
> > Assume I have a table with the following fields:
> >    uid INT,
> >    data BIGINT,
> >    hits INT
> > And an unique index on (uid, data). I use libpq C API to query
> > data from the table. The query is something like this:
> > SELECT uid,data,hits FROM mytable WHERE uid=2
> > AND data IN (2033,2499,590,19,201,659)
> >
> > Would the speed of the query be influenced if I would sort the data?
> 
> What do you mean by "sort the data"?  Which data?
> 
I mean sorting the values in the brackets. Instead of:
SELECT uid,data,hits FROM mytable WHERE uid=2 AND data IN (2033,2499,590,19,201,659)

I would then send this here:
SELECT uid,data,hits FROM mytable WHERE uid=2 AND data IN (19,201,590,659,2033,2499)

Off course this is a small dataset but the query usually has thousands of elements and not only the above 6 elements.


> > I can imagine that just querying a bunch of bigint would not make a
> > big difference but what about several thousand of values? Would sorting
> > them and sending the SQL query with ordered data influence the speed of
> the query?
> 
> Send the query from where to where?
> 
Sending the query from my application to the PostgreSQL server.


> Are you referring to a sort of the items in the IN subselect?
>
Yes.


> My guess is
> that sorting that won't matter but it's only a WAG.
> 
What is "WAG"?


> -- 
> Lew
> 
SteveB
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