Re: stddev returns 0 when there is one row

Tom Lane wrote:

>Joe Conway <mail@joeconway.com> writes:
>
>>Tom Lane wrote:
>>
>>>I don't have a real strong feeling about whether we should change the
>>>behavior at N=1 or not.  Does the SQL200x spec provide any guidance?
>>>
>>The spec does have specific guidance in section
>>10.9 <aggregate function>:
>>
>>       1) If VAR_POP is specified, then the result is (S2-S1*S1/N)/N.
>>       2) If VAR_SAMP is specified, then:
>>          A) If N is 1 (one), then the result is the null value.
>>          B) Otherwise, the result is (S2-S1*S1/N)/(N-1)
>>
>
>Okay, that probably trumps the Oracle precedent, especially seeing that
>it seems mathematically sounder.  I'll make the changes.
>
The above is indeed the right thing to do for samples!
(Oracle must do something else as a convenience for programmers who
don't write code that checks for a sample size of at least two.)

What's really interesting to me is that StarOffice 6.0's spreadsheet
functions,
both the standard deviation of a sample (=STDEV) and variance of a sample
(=VAR) are bug-for-bug compatible with Excel 2002!  That is, Excel has a
bug, and StarOffice has the same bug to be compatible with Excel's bug.
I assume the functions are buggy in OpenOffice as well, but I haven't
checked.

For example, both of these calculations produce answers of 0 (zero)
but they should produce answers of 1 (one):

    =stdev(80000000,80000001,80000002)
    =var(80000000,80000001,80000002)

When the numbers are smaller, like this:

    =stdev(0,1,2)
    =var(0,1,2)

They produce correct answers.

    douglas "trying to exploit the R and PostgreSQL synergy" trainor