Re: The Future of Aggregation

David Rowley <david.rowley@2ndquadrant.com> wrote: 

> The idea I discussed in the link in item 5 above gets around this
> problem, but it's a perhaps more surprise filled implementation
> as it will mean "select avg(x),sum(x),count(x) from t" is
> actually faster than "select sum(x),count(x) from t" as the agg
> state for avg() will satisfy sum and count too.

I'm skeptical that it will be noticeably faster.  It's easy to see
why this optimization will make a query *with all three* faster,
but I would not expect the process of accumulating the sum and
count to be about the same speed whether performed by one
transition function or two.  Of course I could be persuaded by a
benchmark showing otherwise.