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Re: wip: functions median and percentile

From: David Fetter <david(at)fetter(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>,Robert Haas <robertmhaas(at)gmail(dot)com>,Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>,Greg Stark <gsstark(at)mit(dot)edu>,PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: wip: functions median and percentile
Date: 2010-08-19 17:47:59
Message-ID: 20100819174759.GC17368@fetter.org (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-rrreviewers
On Thu, Aug 19, 2010 at 01:25:36PM -0400, Tom Lane wrote:
> David Fetter <david(at)fetter(dot)org> writes:
> > On Thu, Aug 19, 2010 at 12:12:12PM -0500, Kevin Grittner wrote:
> >> http://www.merriam-webster.com/dictionary/median
> >> 
> >> If you do a google search for "median" and poke around, you'll find
> >> many places where this is the only definition mentioned; the others
> >> seem to be rather infrequently used.  Why not make the commone usage
> >> convenient?
> 
> > The reason not to is the same reason that MEDIAN doesn't appear in the
> > SQL standard, namely that what's common in one field is wrong in
> > another.
> 
> Hmm, do you have any *evidence* that that's why it's not in the standard?

Only from Joe Celko, who was on the standards committee, and has
written on the subject.  There's nothing I've found in the standard
itself for this, if that's what you're looking for.

> My own take on that is that it's reasonably probable that the SQL
> committee might standardize a function by that name someday.  What
> we need to be worrying about is the prospect that if there are
> multiple definitions for the term, they might pick a different one
> than we did.

Exactly :)

> A name like "arithmetic_median" seems much less likely to get
> blindsided by future standardization.

Yep.

Cheers,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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