VARIANCE
Calculates the population variance value from a set of numbers.
VARIANCE has synonym VAR_POP which is equivalent. VARIANCE returns NULL if there are not matching rows.
May be used as a window function and with the frame clause.
Syntax
Aggregate Function
VARIANCE ( expression )
Window Function & Window Frame Clause
VARIANCE( [ DISTINCT ] expr ) OVER ( [PARTITION BY expr] [ORDER BY expr] [<window_frame_function>])
Arguments
expression: any expression. This may be a column name, the result of another function, or a math operation.
Return Type
A double.
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 VARIANCE(yearly_total) FROM player_scores; **** +------------------------+ | VARIANCE(yearly_total) | +------------------------+ | 3258.486939 | +------------------------+
Window Function
SELECT player_name, 3rd_qtr_score, 4th_qtr_score, ROUND(VARIANCE(3rd_qtr_score) OVER (ORDER BY player_name)) AS VARIANCE FROM player_scores ORDER BY player_name; **** +-------------+---------------+---------------+----------+ | player_name | 3rd_qtr_score | 4th_qtr_score | VARIANCE | +-------------+---------------+---------------+----------+ | Eve | 95.00 | 94.50 | 0 | | Jack | 88.20 | 92.20 | 12 | | Jim | 55.70 | 72.00 | 294 | | June | 76.80 | 82.20 | 222 | | Martin | 88.00 | 96.40 | 191 | | Shelia | 81.10 | 78.40 | 159 | | Steve | 63.00 | 45.00 | 175 | +-------------+---------------+---------------+----------+
Window Frame Clause
SELECT player_name, 1st_qtr_score, 2nd_qtr_score, ROUND(VARIANCE(1st_qtr_score) OVER (ORDER BY player_name, 1st_qtr_score, 2nd_qtr_score ROWS UNBOUNDED PRECEDING)) AS VARIANCE FROM player_scores ORDER BY player_name; **** +-------------+---------------+---------------+----------+ | player_name | 1st_qtr_score | 2nd_qtr_score | VARIANCE | +-------------+---------------+---------------+----------+ | Eve | 91.50 | 88.10 | 0 | | Jack | 90.10 | 78.00 | 0 | | Jim | 75.00 | 68.90 | 56 | | June | 81.00 | 87.30 | 46 | | Martin | 98.80 | 95.10 | 70 | | Shelia | 75.60 | 72.00 | 77 | | Steve | 22.50 | 72.00 | 549 | +-------------+---------------+---------------+----------+