Re: Question regarding indices

-------- Original-Nachricht --------
> Datum: Sat, 11 Sep 2010 11:08:00 -0400
> Von: Lew <noone(at)lewscanon(dot)com>
> An: pgsql-sql(at)postgresql(dot)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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