The STDEV function finds the standard deviation by using a portion, called a sample, of the total number of values in a field.
This is a time saver when dealing with extremely large tables and can be shown to be statistically valid. In comparison, the STDEVP function uses all of the values to calculate the standard deviation. There must be at least two values in the field or the standard deviation will not be calculated and a NULL is returned.
SELECT STDEV(Age) AS [SDAge]
FROM MediCarePatients
SDAge
19.59862
(1 row(s) affected)
This code finds the standard deviation of the age of the MediCare patients in a hospital (by using a sample) and stores that information in 'SDAge'.