--- In firebird-support@yahoogroups.com, Milan Babuskov wrote:

> PenWin wrote:
> > Dne 25.6.2010 14:29, Michael Ludwig napsal(a):
> >> Svein Erling schrieb am 25.06.2010 um 11:16 (-0000):
> >>> [...] isn't it an aggregate function that requires 'going
> >>> through' records twice (first finding the average and then how
> >>> much each value deviates from this value)?
> >>
> >> Yes, exactly. Conceptually, it cannot be done in one pass.
> >
> > Actually, it can.
> >
> > STDDEV(x) = AVG(x^2) - (AVG(x))^2
> >
> > AVG can be calculated in one pass.
>
> Isn't it rather:
>
> STDDEV(x) = AVG( x^2 - (AVG(x))^2 )
>
> ?

Nothing is like trying, and to me, PenWins suggestions seems OK - except that he forgot the square root. At least, the following produced a sensible result for my first (and only) test:

with CTE(MySum) as
(select avg(MyField*MyField)-(avg(MyField)*avg(MyField))
from TEST_TABLE)
select sqrt(MySum)
from CTE

So no need for any stored procedure,
Set