mdv 9731 (1/28/2011)
I do not agree that the answer is right.Think it is supposed to be 0.
the standard deviation s (sigma) is the square root of the average value of (X - µ)2.
Which means s = sqrt(((1-1)^2)/1) = 0
Or in other words std. deviation equals sqrt of (population-avarage) sq / number of population values
Please correct me if im wrong on the formula it has been a while since i used my statistics 😀
What you state is correct for a population standard deviation. Then you devide by the number of samples N, which is one for a single record. You do this with the function STDEVP.
When using STDEV however, you take the sample standard deviation in which you devide by N - 1 which would result in a division by zero. Hence the NULL.
SELECT STDEV(100)
Results in NULL
SELECT STDEVP(100)
Results in 0