iAnywhere.com - COVAR_POP function [Aggregate]

COVAR_POP function [Aggregate]

Function

Returns the population covariance of a set of number pairs.

Syntax

COVAR_POP ( dependent-expression, independent-expression )

Parameters

dependent-expression The variable that is affected by the independent variable.

independent-expression The variable that influences the outcome.

Usage

The function returns a numeric value. If the function is applied to an empty set, then it returns NULL.

Both dependent-expression and independent-expression are numeric. The function is applied to the set of (dependent-expression, independent-expression) pairs after eliminating all pairs for which either dependent-expression or independent-expression is NULL. The following computation is then made:

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

where x represents the dependent-expression and y represents the independent-expression.

Standards and compatibility

SQL/92 Vendor extension.
SQL/99 SQL/foundation feature outside of core SQL.
Sybase Not supported by Adaptive Server Enterprise.

Example

The following example measures the strength of association between employees' age and salary. This function returns the value 73785.84005866687.

SELECT COVAR_POP (salary, (year(now()) - year(birth_date)))
FROM employee