STDDEV_SAMP

Syntax

stddev_samp::=

Text description of stddev_samp

See Also: "Analytic Functions" for information on syntax, semantics, and restrictions

Purpose

STDDEV_SAMP computes the cumulative sample standard deviation and returns the square root of the sample variance. You can use it as both an aggregate and analytic function.

The expr is a number expression, and the function returns a value of type NUMBER. This function is same as the square root of the VAR_SAMP function. When VAR_SAMP returns null, this function returns null.

See Also: "Aggregate Functions" and VAR_SAMP "About SQL Expressions" for information on valid forms of expr

Aggregate Example

The following example returns the population and sample standard deviations of the amount of sales in the sample table sh.sales:

SELECT STDDEV_POP(amount_sold) "Pop", 
   STDDEV_SAMP(amount_sold) "Samp"
   FROM sales;

       Pop       Samp
---------- ----------
896.355151 896.355592

Analytic Example

The following example returns the sample standard deviation of salaries in the employees table by department:

SELECT department_id, last_name, hire_date, salary, 
   STDDEV_SAMP(salary) OVER (PARTITION BY department_id 
      ORDER BY hire_date 
      ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS cum_sdev 
   FROM employees;

DEPARTMENT_ID LAST_NAME       HIRE_DATE     SALARY   CUM_SDEV
------------- --------------- --------- ---------- ----------
           10 Whalen          17-SEP-87       4400
           20 Hartstein       17-FEB-96      13000
           20 Goyal           17-AUG-97       6000 4949.74747
           30 Raphaely        07-DEC-94      11000
           30 Khoo            18-MAY-95       3100 5586.14357
           30 Tobias          24-JUL-97       2800  4650.0896
           30 Baida           24-DEC-97       2900 4035.26125
.
.
.
          100 Chen            28-SEP-97       8200 2003.33056
          100 Sciarra         30-SEP-97       7700 1925.91969
          100 Urman           07-MAR-98       7800 1785.49713
          100 Popp            07-DEC-99       6900 1801.11077
          110 Higgens         07-JUN-94      12000
          110 Gietz           07-JUN-94       8300 2616.29509