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

Kevin Grittner wrote:
> Shaun Thomas <sthomas@peak6.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@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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