Re: Thinking About Correlated Columns (again)

On 16/05/13 04:23, Craig James wrote:
> On Wed, May 15, 2013 at 8:31 AM, Shaun Thomas
> <sthomas(at)optionshouse(dot)com <mailto:sthomas(at)optionshouse(dot)com>> wrote:
>
> [Inefficient plans for correlated columns] has been a pain point
> for quite a while. While we've had several discussions in the
> area, it always seems to just kinda trail off and eventually
> vanish every time it comes up.
>
[...]
>
> It's a very hard problem. There's no way you can keep statistics
> about all possible correlations since the number of possibilities is
> O(N^2) with the number of columns.
Actually far worse: N!/(N - K)!K! summed over K=1...N, assuming the
order of columns in the correlation is unimportant (otherwise it is N
factorial) - based on my hazy recollection of the relevant maths...

[...]

Cheers,
Gavin