Returns the population covariance of a set of number pairs.
Parameter |
Description |
|---|---|
dependent-expression |
The variable that is affected by the independent variable. |
independent-expression |
The variable that influences the outcome. |
The following example measures the strength of association between employee age and salary. This function returns the value 73785.840059:
SELECT COVAR_POP( Salary, ( YEAR( NOW( ) ) - YEAR( BirthDate ) ) ) FROM Employees;
This function converts its arguments to DOUBLE, performs the computation in double-precision floating-point, and returns a DOUBLE as the result. If applied to an empty set, then COVAR_POP returns NULL.
dependent-expression and independent-expression are both numeric. The function is applied to the set of (dependent-expression, independent-expression) after eliminating the pairs for which either dependent-expression or independent-expression is NULL. The following computation is made:
(SUM(x*y) - SUM(x) * SUM(y) / n) / n
where x represents the dependent-expression and y represents the independent-expression.
Syntax 2 represents usage as a window function in a SELECT statement. As such, you can specify elements of window-spec either in the function syntax (inline), or with a WINDOW clause in the SELECT statement.