STDDEV
Returns the standard deviation of all the values in a specified expression.
May be used as a window function and with the frame clause.
Syntax
Aggregate Function
STDDEV( [ DISTINCT ] <expression>
Window Function & Window Frame Clause
STDDEV( [DISTINCT ] (col | expr ) OVER ( [ PARTITION BY (col | expr )] [ ORDER BY (col | expr ) [ <window_frame> ] ] )
Arguments
expression: numeric expression
Return Type
Returns the standard deviation of the expression or NULL if there are no matching rows.
Examples
The following table and values were used for the examples:
CREATE TABLE player_scores(player_name VARCHAR(50), player_id VARCHAR(10),
1st_qtr_score DECIMAL(5,2), 2nd_qtr_score DECIMAL(5,2),
3rd_qtr_score DECIMAL(5,2), 4th_qtr_score DECIMAL(5,2),
yearly_total AS 1st_qtr_score + 2nd_qtr_score + 3rd_qtr_score + 4th_qtr_score PERSISTED DECIMAL(5,2));
INSERT INTO player_scores VALUES
('Steve', '119','22.50','72.00', '63.00', '45.00'),
('Jack', '432', '90.10', '78.00','88.20', '92.20'),
('Jim', '779','75.00', '68.90','55.70', '72.00'),
('Eve', '189','91.50', '88.10', '95.00', '94.50'),
('Shelia','338', '75.60', '72.00', '81.10', '78.40'),
('June', '521', '81.00', '87.30','76.80','82.20'),
('Martin', '674','98.80', '95.10', '88.00', '96.40');
Aggregate Function
SELECT STDDEV(yearly_total) FROM player_scores; **** +----------------------+ | STDDEV(yearly_total) | +----------------------+ | 57.083158 | +----------------------+
Window Function
SELECT player_name, yearly_total, ROUND(stddev(yearly_total) OVER (ORDER BY player_name, yearly_total)) AS stddev FROM player_scores ORDER BY player_name; **** +-------------+--------------+--------+ | player_name | yearly_total | stddev | +-------------+--------------+--------+ | Eve | 369.10 | 0 | | Jack | 348.50 | 10 | | Jim | 271.60 | 42 | | June | 327.30 | 36 | | Martin | 378.30 | 38 | | Shelia | 307.10 | 37 | | Steve | 202.50 | 57 | +-------------+--------------+--------+
Window Frame Clause
SELECT player_name, yearly_total, ROUND(stddev(yearly_total) OVER (ORDER BY player_name, yearly_total ROWS UNBOUNDED PRECEDING)) AS stddev FROM player_scores ORDER BY player_name; **** +-------------+--------------+--------+ | player_name | yearly_total | stddev | +-------------+--------------+--------+ | Eve | 369.10 | 0 | | Jack | 348.50 | 10 | | Jim | 271.60 | 42 | | June | 327.30 | 36 | | Martin | 378.30 | 38 | | Shelia | 307.10 | 37 | | Steve | 202.50 | 57 | +-------------+--------------+--------+