<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Tue, Jan 14, 2014 at 2:29 PM, Tom Lane <span
dir="ltr"><<ahref="mailto:tgl@sss.pgh.pa.us" target="_blank">tgl@sss.pgh.pa.us</a>></span> wrote:<br
/><blockquoteclass="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div
class="im"><br/></div> One reason I'm thinking this is that whatever we do to ameliorate<br /> the semantic issues is
goingto slow down the forward transition<br /> function --- to no benefit unless the aggregate is being used as a<br />
windowfunction in a moving window. So I'm less than convinced<br /> that we *should* implement any of these designs in
thedefault<br /> aggregates, even if we get to the point where we arguably *could*<br /> do it with little risk of
functionaldifferences.<br /><br /> regards, tom lane<br /></blockquote></div><br /></div><div
class="gmail_extra">Iwas thinking about this earlier today and came up with an idea that perhaps aggregates could
support2 transition functions. 1 for normal aggregation and for windows with UNBOUNDED PRECEDING. The 2nd transition
functioncould be used when there is a possibility that we would need to perform an inverse transition. This 2nd
transitionfunction could do all the extra tracking it needed without having to worry that it would slow down normal
aggregation.With numeric that might be tracking each numeric's scale as it enters and exits the window frame. It might
evenbe possible to perform inverse transitions with float and double here, we could just internally use numeric, and
havethe final function convert back to the original type. Though perhaps that might have the side effect of making
floatingpoint calculations too accurate? Or at least not matching the IEEE standards.</div><div class="gmail_extra"><br
/></div><divclass="gmail_extra">Of course, I'm not thinking this could be part of this patch, but I thought that I'd
postthe idea while all this is fresh in people's heads.</div><div class="gmail_extra"><br /></div><div
class="gmail_extra">David</div><divclass="gmail_extra"><br /></div><div class="gmail_extra"><br /></div><div
class="gmail_extra"><br/></div></div>