Categories:
Aggregate Functions (General) , Window Functions

COVAR_POP

Returns the population covariance for non-null pairs in a group. It is computed for non-null pairs using the following formula:

(SUM(x*y) - SUM(x) * SUM(y) / COUNT(*)) / COUNT(*)

Where x is the independent variable and y is the dependent variable.

See also:
COVAR_SAMP , COUNT , SUM

Syntax

COVAR_POP( y , x )

Usage Notes

  • DISTINCT is not supported for this function.

Examples

CREATE OR REPLACE TABLE aggr(k int, v decimal(10,2), v2 decimal(10, 2));
INSERT INTO aggr VALUES(1, 10, NULL);
INSERT INTO aggr VALUES(2, 10, 11), (2, 20, 22), (2, 25, NULL), (2, 30, 35);

SELECT * FROM aggr;

+---+-------+---------+
| K |     V |      V2 |
|---+-------+---------|
| 1 | 10.00 | NULL    |
| 2 | 10.00 |   11.00 |
| 2 | 20.00 |   22.00 |
| 2 | 25.00 | NULL    |
| 2 | 30.00 |   35.00 |
+---+-------+---------+
SELECT k, COVAR_POP(v, v2) FROM aggr GROUP BY k;

+---+------------------+
| K | COVAR_POP(V, V2) |
|---+------------------|
| 1 |           NULL   |
| 2 |             80.0 |
+---+------------------+