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@xxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxx> 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@xxxxxx >> >> >> -- >> Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) >> To make changes to your subscription: >> http://www.postgresql.org/mailpref/pgsql-general > > > > -- > _________________________________ > Pulchritudo splendor veritatis. -- _________________________________ Pulchritudo splendor veritatis. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
