Hi Pierre,
Looking at your Excel document I think I misinterpreted, and you are
trying to take the stddev of each column separately (which makes a lot
more sense!). In the case you can say this:
select id, stddev(a), stddev(b), stddev(c) from foo group by id;
Paul
On Wed, Jan 21, 2015 at 10:15 AM, Paul Jungwirth
<pj@illuminatedcomputing.com> wrote:
> Hi Pierre,
>
> It looks like you're saying that each row has an id plus three numeric
> columns, and you want the stddev calculated from the three numeric
> columns? In that case you could do this:
>
> create table foo (id integer, a float, b float, c float);
> insert into foo values (1, 2,3,4);
> insert into foo values (2, 2,3,4);
> select id, stddev(x) from (select id, unnest(array[a,b,c]) x from foo)
> bar group by id;
> id | stddev
> ----+--------
> 1 | 1
> 2 | 1
> (2 rows)
>
> But if that's correct, then I think your table is badly structured for
> a relational database. It might be better to have just two columns: an
> id and *one* numeric value. Or perhaps an id and an array of numeric
> values if you really want all values in one row.
>
> At a higher level, if you are really taking the stddev of a sample of
> size 3, you should reconsider applying statistical analysis to your
> problem at all.
>
> I hope this helps!
>
> Paul
>
>
>
>
>
>
>
>
> On Wed, Jan 21, 2015 at 10:09 AM, Raymond O'Donnell <rod@iol.ie> wrote:
>> On 21/01/2015 18:02, Pierre Hsieh wrote:
>>> Hi Raymond,
>>>
>>> Thanks for your reply. Please see detail as following. Thanks again.
>>
>> Can you describe *in words* what sort of calculation you want to do?
>>
>> Ray.
>>
>>
>> --
>> Raymond O'Donnell :: Galway :: Ireland
>> rod@iol.ie
>>
>>
>> --
>> Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
>> To make changes to your subscription:
>> http://www.postgresql.org/mailpref/pgsql-general
>
>
>
> --
> _________________________________
> Pulchritudo splendor veritatis.
--
_________________________________
Pulchritudo splendor veritatis.