STDDEV_SAMP
This function calculates the cumulative sample standard deviation and returns the square root of the overall variable with the same return value as the square root of the VAR_POP function.
Example:
begin; CREATE TABLE employees (manager_id INT,last_name varchar(50),hiredate varchar(50),SALARY INT); INSERT INTO employees VALUES(100, 'Raphaely', '2017-07-01', 1700); INSERT INTO employees VALUES(100, 'De Haan', '2018-05-01',11000); INSERT INTO employees VALUES(100, 'Errazuriz', '2017-07-21', 1400); INSERT INTO employees VALUES(100, 'Hartstein', '2019-05-01',14000); INSERT INTO employees VALUES(100, 'Raphaely', '2017-07-22', 1700); INSERT INTO employees VALUES(100, 'Weiss', '2019-07-11',13500); INSERT INTO employees VALUES(100, 'Russell', '2019-10-05', 13000); INSERT INTO employees VALUES(100, 'Partners', '2018-12-01',14000); INSERT INTO employees VALUES(200, 'Ross', '2019-06-11',13500); INSERT INTO employees VALUES(200, 'Bell', '2019-05-25', 13000); INSERT INTO employees VALUES(200, 'Part', '2018-08-11',14000); COMMIT; SELECT manager_id, last_name, hiredate, salary,STDDEV_SAMP(salary) OVER (PARTITION BY manager_id ORDER BY hiredate ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS cum_sdev FROM employees ORDER BY manager_id, last_name, hiredate, salary, cum_sdev; MANAGER_ID | LAST_NAME | HIREDATE | SALARY | CUM_SDEV ------------+-----------+------------+--------+-------------------- 100 | De Haan | 2018-05-01 | 11000 | 4702.127178203499 100 | Errazuriz | 2017-07-21 | 1400 | 212.132034355964 100 | Hartstein | 2019-05-01 | 14000 | 6340.346993658943 100 | Partners | 2018-12-01 | 14000 | 6064.899009876422 100 | Raphaely | 2017-07-01 | 1700 | 100 | Raphaely | 2017-07-22 | 1700 | 173.205080756888 100 | Russell | 2019-10-05 | 13000 | 6026.474330580265 100 | Weiss | 2019-07-11 | 13500 | 6244.31169717116 200 | Bell | 2019-05-25 | 13000 | 707.106781186548 200 | Part | 2018-08-11 | 14000 | 200 | Ross | 2019-06-11 | 13500 | 500 (11 rows) 
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