Re: FETCH FIRST clause WITH TIES option

On Tue, Jan 15, 2019 at 2:51 PM Tomas Vondra <tomas.vondra@2ndquadrant.com>
wrote:


> What do you mean by "raw statistic"?
>

I mean without further calculation to consider other operation


>
> IMHO the best thing you can do is call estimate_num_groups() and combine
> that with the number of input rows. That shall benefit from ndistinct
> coefficients when available, etc. I've been thinking that considering
> the unreliability of grouping estimates we should use a multiple of the
> average size (because there may be much larger groups), but I think
> that's quite unprecipled and I'd much rather try without it first.
>
>
thank you for clarifying.

The attache patch use your suggestion uptread

regards

Surafel