On Sun, Dec 15, 2013 at 12:48 PM, Greg Stark <stark@mit.edu> wrote:
On 14 Dec 2013 15:40, "Tom Lane" <tgl@sss.pgh.pa.us> wrote: > > David Rowley <dgrowleyml@gmail.com> writes: > > The attached patch is not quite finished yet, I've not yet fully covered > > SUM and AVG for all types. > > I think you *can't* cover them for the float types; roundoff error > would mean you don't get the same answers as before.
I was going to say the same thing. But then I started to wonder.... What's so special about the answers we used to give? They are also subject to round off and the results are already quite questionable in those cases.
I guess they probably shouldn't be, subject to rounding / influenced by errors from tuples that are out of scope of the aggregate context.
Though saying that it would be a shame to have this optimisation for all but float and double. I can imagine the questions in [GENERAL].. Why is SUM(<int>) OVER ().. fast but SUM(<float>) OVER () slow? I wonder what other RDBMS' do here...
