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SQL Anywhere 10.0.1 » SQL Anywhere Server - SQL Reference » SQL Functions » Alphabetical list of functions

### COVAR_POP function [Aggregate]

Returns the population covariance of a set of number pairs.

###### Syntax 1

COVAR_POP( dependent-expression, independent-expression )

###### Syntax 2

COVAR_POP( dependent-expression, independent-expression )
OVER (
window-spec )

window-spec : see Syntax 2 instructions in the Usage section below

###### Parameters

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

independent-expression    The variable that influences the outcome.

###### Remarks

This function converts its arguments to DOUBLE, performs the computation in double-precision floating point, and returns a DOUBLE as the result. 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( y ) / n ) / n`

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

For more information about the statistical computation performed, see Mathematical formulas for the aggregate functions.

Syntax 2 represents usage as a window function in a SELECT statement. As such, elements of window-spec can be specified either in the function syntax (inline), or in conjunction with a WINDOW clause in the SELECT statement. See the window-spec definition provided in WINDOW clause.

For more information about using window functions in SELECT statements, including working examples, see Window functions.

###### Standards and compatibility
• SQL/2003    SQL foundation feature (T621) outside of core SQL.

###### 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( BirthDate ) ) )
FROM Employees;
```