VARIANCE function [Aggregate]

Returns the variance of a set of numbers.

VARIANCE ( [ ALL ] expression )

Given this data:

SELECT Salary FROM Employees WHERE DepartmentID = 300

The following statement returns the value 1063923790.99999994:

SELECT VARIANCE ( Salary ) FROM Employees
WHERE DepartmentID = 300

Given this data:

SELECT UnitPrice FROM Products WHERE name = 'Tee Shirt'

The following statement returns the value 8.33333333333334327:

SELECT VARIANCE ( UnitPrice ) FROM Products
WHERE name = 'Tee Shirt'

The formula used to calculate VARIANCE is

VARIANCE returns a result of data type double-precision floating-point. If applied to the empty set, the result is NULL, which returns NULL for a one-element input set.