On Fri, Nov 13, 2009 at 10:35 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Greg Stark <gsst...@mit.edu> writes: >> On Fri, Nov 13, 2009 at 7:54 AM, Heikki Linnakangas >> <heikki.linnakan...@enterprisedb.com> wrote: >>> Andrew Gierth wrote: >>>> Herewith a patch to implement agg(foo ORDER BY bar) with or without >>>> DISTINCT, etc. >>> >>> What does that mean? Aggregate functions are supposed to be commutative, >>> right? > >> We certainly have non-commutative agggregates currently, notably array_agg() > > Right. The fact that none of the standard aggregates are > order-sensitive doesn't mean that it's not useful to have user-defined > ones that are. Currently we suggest fetching from an ordered sub-select > if you want to use an aggregate that is input order sensitive. This > patch just provides an alternative (and equally nonstandard) notation > for that. > > I'm not entirely convinced that adding ORDER BY here is a good idea, > partly because it goes so far beyond the spec and partly because it's > not going to be easily optimizable. But I can see that there is a > use-case.
Yeah, for sure. I currently handle this, when necessary, by using subselects, but it would sure be nice to have a more compact notation, if there's a good way to do that. ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
