2009/11/14 Andrew Gierth <and...@tao11.riddles.org.uk>: >>>>>> "Heikki" == Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> >>>>>> writes: > > >> No artificial restrictions are imposed on what syntactical > >> combinations are allowed. However, ORDER BY is not allowed with > >> aggregates used as window functions (as per the existing > >> restriction on DISTINCT). > > Heikki> How is this different from window functions? > > Window functions return a row for each row of input, aggregates don't. > > The reason I didn't tackle the case of aggregate functions used as > window functions is that the spec allows constructs like this: > > array_agg(a order by b) over (order by c) > > which can't be represented using the aggregate-as-window-function > mechanism as it currently stands, since you'd have to re-sort the > window each time. > Now I'm about to send my patch to introduce more frame types, aggregate cache mechanism in window functions may be broken sometimes, and it is *possible* to put order-by clause in argument list if we prepare tuplesort as in nodeAgg. But I don't see useful cases and it seems so hard task that I'm not sold.
Regards, -- Hitoshi Harada -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
