On Tue, 2009-05-19 at 08:58 -0400, Tom Lane wrote:
> Simon Riggs <simon@2ndQuadrant.com> writes:
> > Both plans for this query show an IndexScan on a two column-index, with
> > an Index Condition of equality on the leading column. The ORDER BY
> > specifies a sort by the second index column, so the top-level Sort is
> > superfluous in this case.
>
> > My understanding is that we don't currently eliminate superfluous
> > additional sorts of this kind.
>
> Nonsense. The planner might think some other plan is cheaper, but
> it definitely knows how to do this, and has since at least 8.1.
Please look at Dimitri's plan. If it can remove the pointless sort, why
does it not do so?
I agree that it will remove a Sort when the data is already has the
exact same interesting sort order. In this case the sort order is not
exactly the same, but looks fully removable to me.
--
Simon Riggs www.2ndQuadrant.com
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