Re: [HACKERS] Re: order by and index path

> >     We  do  not  have  this statistical information. So the whole
> >     thing is at this time academic.
>
> I recall that Commercial Ingres made the assumption that one row (or 1%
> of rows? My memory of Ingres is fading :) would be returned from a
> qualified query if no statistics were available to suggest otherwise.
>
> It did collect statistics on data distribution to try to help make those
> optimizer choices.
>
> It may be reasonable to assume that if there is an index, then using it
> with any qualified query would be a win. Since the alternative is to
> decide to _not_ use an index, a decision for which we have no support
> with existing statistics.

For =, the assumion is 1 row, for > the assumption is 1/3 of the table.
With pg_statistic, it uses that.

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