Re: [patch] bit XOR aggregate functions

Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> But this is offtopic in this discussion :)

The whole topic is off-topic. As a general rule, things that depend on
input order shouldn't be declared as aggregates --- they should be window
functions or ordered-set aggregates, for which the syntax forces you to
specify input order. All of the standard aggregates, and most of our
custom ones (including BIT_XOR) do not depend on input order (... mumble
floating-point roundoff error mumble ...), so forcing users to write an
ordering clause would be useless, not to mention being a SQL spec
violation.

There are a small minority like array_agg that do have such a dependency,
but as far as I recall our docs for each of those warn about the need to
sort the input for reproducible results. I think that's sufficient.
Who's to say whether a particular query actually requires reproducible
results? Seeing that we don't provide reproducible row ordering
without an ORDER BY, I'm not sure why we should apply a different
standard to array_agg.

regards, tom lane