VAR_POP Function [Aggregate]

Computes the statistical variance of a population consisting of a numeric-expression, as a DOUBLE.

Syntax

VAR_POP ( [ ALL ] expression )

Parameters

Parameter	Description
expression	The expression (commonly a column name) whose population-based variance is calculated over a set of rows.

Returns

DOUBLE

Examples

The following statement lists the average and variance in the number of items per order in different time periods:

SELECT year( ShipDate ) AS Year, quarter( ShipDate )
  AS Quarter, AVG( Quantity ) AS Average, 
  VAR_POP( Quantity ) AS Variance 
FROM SalesOrderItems GROUP BY Year, Quarter 
  ORDER BY Year, Quarter

Year	Quarter	Average	Variance
2000	1	25.775148	203.9021
2000	2	27.050847	225.8109
...	...	...	...

Usage

Computes the population variance of the provided value expression evaluated for each row of the group or partition (if DISTINCT was specified, then each row that remains after duplicates have been eliminated), defined as the sum of squares of the difference of value expression, from the mean of value expression, divided by the number of rows (remaining) in the group or partition.

Population-based variances are computed according to the following formula:

Standards and Compatibility

SQL—Vendor extension to ISO/ANSI SQL grammar.
Sybase—Not supported by Adaptive Server Enterprise.