Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Oct 22, 2012 at 11:57 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Don't hold your breath. There are two ways the system could implement
>> the DISTINCT clause: either sort and uniq, or hashaggregate.
>> hashaggregate will destroy any input ordering, so there's no value in
>> using the index as input.
> Isn't that an implementation limitation though, rather than a
> fundamental limitation?
Perhaps, but it's not a simple one to surmount, and I'm dubious about
putting the amount of work that'd be required into such a corner case.
regards, tom lane