TODO has an entry
o Allow UPDATE to handle complex aggregates [update]?
which I think is now obsolete, because we've settled on rejecting
aggregates at the top level of UPDATE, as the spec tells us to do.
Also, there's one remaining unfinished feature in the multi-argument
aggregate patch, which I think we should have a TODO item for:
* Allow DISTINCT to work in multiple-argument aggregate calls
The SQL2003 spec doesn't require this (it forbids DISTINCT in all its
two-argument aggregates) but it seems like we should do it someday
for orthogonality's sake.
regards, tom lane
