stddev returns sample standard deviation of expr, a set of numbers. You can use it as both an aggregate and analytic function. It differs from stddev_samp in that stddev returns zero when it has only 1 row of input data, whereas stddev_samp returns a null.

Oracle calculates the standard deviation as the square root of the variance defined for the variance aggregate function.

If you specify distinct, then you can specify only the query_partition_clause of the analytic_clause. The order_by_clause and windowing_clause are not allowed.