The VARP function finds the variance by using all of values in a field.
In comaparison, the VAR function only uses a portion, called a sample, of the values to calculate the variance. There must be at least two values in the field or the standard deviation will not be calculated and a NULL value is returned.
SELECT VARP(Age) AS [VarAge]
FROM MediCarePatients
VarAge
369.3328
(1 row(s) affected)
This code finds the variance of the age for all MediCare patients in a hospital and stores that information in 'VarAge'.