Re: hint unique result fro union

Yes, the "LIMIT 1" is OK, thanks!

I didn't noticed the "not executed" in the explain output!

I have done some test comparing a plain table and a partitioned table
performance in a particular statistical hypothesis (something explained here
too: http://tagschema.com ).

Mainly, data is produced and asked following an exponential distribution. So
there a few very frequently accessed items and a lot of uncommon items.

Partitioning the two sets in different tables, the performance gain is
interesting only after a few thousand rows.

http://www.slug.it/pgsqlpart

Sorry, the text is Italian, the code (sql schema and python test code) will
be released in a few days (and you will need plpython from CVS if you are
using 8.1), nevertheless pictures are already self explaining :-P
... I have seen a similar benchmark online but I cannot find it now to
compare.

Sorry for my English, and open to comment about my simple benchmark,
Matteo Bertini

2006/8/16, Steve Atkins <steve(at)blighty(dot)com>:
>
>
> On Aug 16, 2006, at 8:23 AM, Matteo Bertini wrote:
>
> > Hello all!
> >
> > I'm quite new to pg, but I'm using it quite a lot in the last few
> > monts.
> >
> > Deeping in new features, I found a question: is it possible to hint
> > an unique result from a select?
> >
> > Mainly, thinking about partitions, I'd like to create a small,
> > frequently accessed partition and a big, rarely accessed partition.
> >
> > I'd like to hint pg to stop the query on the parent partition at
> > the first found item (and so hint not to analyze all the childs),
> > because I know the index I'm using is unique.
> >
> > Possible? Usefull?
> >
>
> "select foo from bar limit 1" ?
>
> I don't know if there's any guaranteed ordering of results from
> a union query, though, and that's what a query on a set of
> inherited tables will expand to, pretty much.
>
> Cheers,
> Steve
>
>
>
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