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SQL Anywhere 11.0.1 (Français) » SQL Anywhere Server - SQL Reference » Using SQL » SQL functions » SQL functions (P-Z)

 

VAR_SAMP function [Aggregate]

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

Syntax 1
VAR_SAMP( numeric-expression )
Syntax 2
VAR_SAMP( numeric-expression ) OVER ( window-spec )
window-spec : see Syntax 2 instructions in the Remarks section below
Parameters
  • numeric-expression   The expression whose sample-based variance is calculated over a set of rows. The expression is commonly a column name.

Returns

DOUBLE

Remarks

This function converts its argument to DOUBLE, performs the computation in double-precision floating point, and returns a DOUBLE as the result.

The variance (s2) of numeric-expression (x) is computed according to the following formula, which assumes a normal distribution:

s2 = (1/( N - 1 )) * SUM( xI - mean( x ) )2

This variance does not include rows where numeric-expression is NULL. It returns NULL for a group containing either 0 or 1 rows.

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.

See also
Standards and compatibility
  • SQL/2003   SQL foundation feature outside core SQL. The VARIANCE syntax is a vendor extension.

Example

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_SAMP( quantity ) AS Variance
FROM SalesOrderItems
GROUP BY Year, Quarter
ORDER BY Year, Quarter;
Year Quarter Average Variance
2000 1 25.775148 205.1158...
2000 2 27.050847 227.0939...
... ... ... ...