2010/8/19 David Fetter <da...@fetter.org>: > On Thu, Aug 19, 2010 at 12:49:45PM -0400, Robert Haas wrote: >> On Thu, Aug 19, 2010 at 11:33 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> > Greg Stark <gsst...@mit.edu> writes: >> >> On Thu, Aug 19, 2010 at 11:59 AM, Pavel Stehule <pavel.steh...@gmail.com> >> >> wrote: >> >>> I am sending a prototype implementation of functions median and >> >>> percentile. This implementation is very simple and I moved it to >> >>> contrib for this moment - it is more easy maintainable. Later I'll >> >>> move it to core. >> > >> >> So if the entire result set fits in memory it would be nice to use the >> >> O(n) Quickselect algorithm -- which would only be a small change to >> >> the existing Quicksort code -- instead of sorting the entire set. >> > >> > That seems like rather a lot of added infrastructure for functions whose >> > popularity is at best unknown. I think we should KISS for the first >> > implementation. >> >> +1. I think the functions are useful, but the perfect is the enemy of the >> good. > > Percentile is already there as NTILE, a windowing function. Median
I don't think it. The purpose is same, but usage is different - aggregate functions can be used as window func, but window functions cannot be used as aggregates. > may be useful, but we pretty much can't just call it "median." > Instead, we need to call it something like "left_median" or > "arithmetic_median." I put some time to deep searching in this area - and I talked with my kolegues mathematican and everywhere use a just median. Some longer or different name isn't barrier for me, but people can be confused. 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
