2009/12/15 David Fetter <da...@fetter.org>: > On Tue, Dec 15, 2009 at 10:28:49PM +0100, Pavel Stehule wrote: >> Hello >> >> I am looking on new feature - ORDER clause in aggregate, and I thing, >> so we are able to effectively implement some non standard, but well >> known aggregates. >> >> a) function median - it is relative frequent request - with usually >> slow implementation > > Makes a lot of sense. I suspect we'll have to provide several > different medians, as there are several precise, useful, and > conflicting definitions. Some examples below: > > http://www.simple-talk.com/sql/t-sql-programming/median-workbench/
In this article the are two medians - statistical and financial. I am for both. But only one can be named "median". > >> b) function listagg (it is analogy of group_concat from MySQL) - it >> should simplify report generating and some other > > This is redundant, as it's equivalent to array_to_string(array_agg()). when I implement it in orafce - the almost all code was parameters checking. Implementation is trivial, because important part of work was done with array_agg support. It is wrapper over stringInfo. > > If it's done as syntactic sugar over that, it's fine. If it's a > separate implementation, it's a bad idea. Probably best as an > optional module of some kind I am not sure if implementation as syntactic sugar is best. It needs parser changes. And final implementation will not be effective. listagg should be faster - string operations are significantly simpler than array op. What more - PostgreSQL cannot well wrap SRF and aggregates. The implementation could be analogy with functions generate_series and generate_subscripts. generate_subscripts is redundant, but well implementation needs C coding. Implementation as syntactic sugar is possible - it could be nice too - listagg is more shorter than array_to_string(array_agg()) - but it has overhead with array. There could be some steps. First - implementation as wrapper over arrays, second - if this functionality will be popular - native implementation in C? Regards Pavel > > Cheers, > David. > -- > David Fetter <da...@fetter.org> http://fetter.org/ > Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter > Skype: davidfetter XMPP: david.fet...@gmail.com > iCal: webcal://www.tripit.com/feed/ical/people/david74/tripit.ics > > Remember to vote! > Consider donating to Postgres: http://www.postgresql.org/about/donate > -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
