STDEV ( [ ALL | DISTINCT ] expression )
Applies the function to all values. ALL is the default.
Specifies that each unique value is considered.
Is a numeric expression. Aggregate functions and subqueries are not permitted. expression is an expression of the exact numeric or approximate numeric data type category, except for the bit data type.
If STDEV is used on all items in a SELECT statement, each value in the result set is included in the calculation. STDEV can be used with numeric columns only. Null values are ignored.
The following example returns the standard deviation for all bonus values in the SalesPerson table.