VAR_SAMP function [Aggregate]

Function

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

NoteVAR_SAMP is an alias of VARIANCE.

Syntax

VAR_SAMP ( [ALL] expression )

Parameters

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

NULL Returns null values on one-element input sets in Sybase IQ versions prior to 12.7.

Examples

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

SELECT year( ship_date ) AS Year, quarter( ship_date )
  AS Quarter, AVG( quantity ) AS Average,  
  VAR_POP( quantity ) AS Variance 
FROM sales_order_items GROUP BY Year, Quarter 
  ORDER BY Year, Quarter

Year

Quarter

Average

Variance

2000

1

25.775148

205.1158

2000

2

27.050847

227.0939

...

...

...

...

Usage

Computes the sample variance of 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 one less than the number of rows (remaining) in the group or partition.

Variances are computed according to the following formula, which assumes a normal distribution:

Computes the sample variance of 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 one less than the number of rows remaining in the group or partition

Standards and compatibility

See also

“Analytical functions”

“VARIANCE function [Aggregate]”

Chapter 4, “Using OLAP” in the Sybase IQ Performance and Tuning Guide