Re: Correlation in cost_index()

On Fri, 08 Aug 2003 18:25:41 -0400, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
wrote:
> Two examples: [...]

One more example:
X Y

A A
a B
A C
b A
B B
b C
C A
c B
C C

Correlation for column X is something less than 1.0, OTOH correlation
for an index on upper(X) is 1.0.

>I don't really see
>a way to do this without actually examining the multi-column ordering
>relationship during ANALYZE.

So did we reach consensus to add a TODO item?

* Compute index correlation on CREATE INDEX and ANALYZE,
use it for index scan cost estimation

Servus
Manfred