aggregate function stddev

Implementers:

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.

I also noticed that oracle has stddev_sample and stddev_population.
This is just a wish list.

Kemin



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Re: aggregate function stddev

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

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Re: aggregate function stddev

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
> joining column's datatypes do not match
>

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