Re: Suitable Index for my Table

On Mon, Nov 04, 2013 at 07:21:11PM +0100, Janek Sendrowski wrote:
> Hi,
>
> I've got a table with many Values of the Type REAL.
> These are my metric distances or my pivots to my sentences.
> The table looks like this:
>
> ID INTEGER, distance1 REAL, distance2 REAL, distance3 REAL, distance4 REAL, ..., distance24 REAL
>
> The range of the Value is in between 0 and 1. So it looks like this 0.196 or 0.891
>
> That my query
>
> WHERE value BETWEEN (distance1 - radius) AND (distance1 + radius)
> WHERE value BETWEEN (distance2 - radius) AND (distance2 + radius)
> WHERE value BETWEEN (distance3 - radius) AND (distance3 + radius)
> WHERE value BETWEEN (distance4 - radius) AND (distance4 + radius)
> ...
>
> Now I'm searching for a suitable index.

This sounds like a job for a geometric datatype, a la GiST.

http://www.postgresql.org/docs/9.3/static/cube.html

CREATE INDEX foo ON bar USING GIST ( cube( ARRAY(distance1), ARRAY(distance1) ) );

The you can do lookups with:

SELECT * FROM bar WHERE
      cube( ARRAY(distance1), ARRAY(distance1) )
      &&
      cube( ARRAY(value-radius), ARRAY(value+radius) )

If you commonly use sets of columns you can go multiple dimensional for
extra benefit.

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> He who writes carelessly confesses thereby at the very outset that he does
> not attach much importance to his own thoughts.
   -- Arthur Schopenhauer