Re: FETCH FIRST clause WITH TIES option

On Wed, Jan 2, 2019 at 6:19 PM Tomas Vondra <tomas.vondra@2ndquadrant.com>
wrote:

> After looking at the "FETCH FIRST ... PERCENT" patch, I wonder if this
> patch should tweak estimates in some way. Currently, the cardinality
> estimate is the same as for plain LIMIT, using the requested number of
> rows. But let's say there are very few large groups - that will
> naturally increase the number of rows produced.
>
> As an example, let's say the subplan produces 1M rows, and there are
> 1000 groups (when split according to the ORDER BY clause).
>



can we use ORDER BY column raw statistic in limit node reliably? because it
seems to me it can be affected by other operation in a subplan like filter
condition

regards

Surafel