Isaac Morland <isaac(dot)morland(at)gmail(dot)com> writes:
> Out of curiosity, was there any thought given to the idea that it should be
> an attribute of the aggregate itself?
SUM over no rows has been defined to return NULL for decades. They
can't just up and change that. They could have instead defined a
new aggregate (SUM0, maybe) but chose not to.
regards, tom lane