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Re: aggregate function stddev

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: Kemin Zhou <kemin(dot)zhou(at)ferring(dot)com>, pgsql-sql(at)postgresql(dot)org
Subject: Re: aggregate function stddev
Date: 2004-09-10 21:48:30
Message-ID: 200409102148.i8ALmU129696@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-sql
Is this a TODO?

---------------------------------------------------------------------------

Josh Berkus wrote:
> Kemin,
> 
> > Just noticed that the postgres stddev is the stddev_sample formula.
> > There are two different ways to calculate this value.
> > Their difference is very small with large samle size.  It would be nice
> > to distinguish the two different versions.
> 
> Note sent to PGSQL-DOCS.
> 
> > I also noticed that oracle has stddev_sample and stddev_population.
> > This is just a wish list.
> 
> Were you aware that in PostgreSQL you can write your own aggregates?   It's 
> relatively easy to do.
> 
> -- 
> Josh Berkus
> Aglio Database Solutions
> San Francisco
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 9: the planner will ignore your desire to choose an index scan if your
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-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
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