Re: Why we don't want hints Was: Slow count(*) again...

Kevin Grittner wrote:
> Shaun Thomas <sthomas(at)peak6(dot)com> wrote:
>
> > how difficult would it be to add that syntax to the JOIN
> > statement, for example?
>
> Something like this syntax?:
>
> JOIN WITH (correlation_factor=0.3)
>
> Where 1.0 might mean that for each value on the left there was only
> one distinct value on the right, and 0.0 would mean that they were
> entirely independent? (Just as an off-the-cuff example -- I'm not
> at all sure that this makes sense, let alone is the best thing to
> specify. I'm trying to get at *syntax* here, not particular knobs.)

I am not excited about the idea of putting these correlations in
queries. What would be more intesting would be for analyze to build a
correlation coeffficent matrix showing how columns are correlated:

a b c
a 1 .4 0
b .1 1 -.3
c .2 .3 1

and those correlations could be used to weigh how the single-column
statistics should be combined.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +