Re: Median - Mailing list pgsql-sql

omid omoomi wrote:
> Hi,
> I'll be glad if you describe more details about the problem. Is it a kind of
> statistical analysis or what?
> Omid Omoomi
   Sorry to respond that slow.
   It's something, Ulf Mehlig described to me a couple of months   ago.  The median is the  value,  below  and  above
of which   exactly  half  of  the  sorted  items would be. Having an odd   number of entries, it's exactly the one in
themiddle like
 
       1 2 3 4 5 6 7       ------|------             M = 4
   Having an even number of entries, it's  the  average  between   the two in the middle like
       1 2 3 4 5 6 7 8       -------|-------              M = (4 + 5) / 2
   As  he  said,  other ranges like Quartile (the position where   25% of the entries are below and 75% are above)
wouldalso be   of  interest.  So the most useful thing would be an aggregate   like qantil(n), where n is value between
0.0 and  100.0,  so   that  quantil(50.0) is the Median, quantil(25.0) is the first   Quartile and so on.
 
   I don't see any quick solution how to solve this problem with   an aggregate.  Aggregates get all selected values in
unsorted  order, and don't know ahead how many  items  there  will  be.   Even if, all this wouldn't be of any use,
becauseyou need to   look at the entire sorted list of selected items.
 
   Maybe someone else has an idea.

>
> >From: "Kermani, Bahram" <BKermani@illumina.com>
> >To: "'pgsql-sql@postgresql.org'" <pgsql-sql@postgresql.org>
> >Subject: [SQL] Median
> >Date: Fri, 30 Jun 2000 17:37:06 -0700
> >
> >Hello,
> >
> >I am trying to do a Median or Trimmed-mean operation in postgreSQL. I was
> >wondering if anybody knew how to do it. I appreciate it if you reply to my
> >email address.
> >
> >Thanks,
> >Bahram Kermani
> >bkermani@illumina.com <mailto:bkermani@illumina.com>
>
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>


Jan

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