STDDEV_SAMP Function [Aggregate]

Computes the standard deviation of a sample consisting of a numeric-expression, as a DOUBLE.

Syntax

STDDEV_SAMP ( [ ALL ] expression )

Parameters

Parameter	Description
expression	The expression (commonly a column name) whose sample-based standard deviation 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( ship_date ) AS Year, quarter( ship_date )
  AS Quarter, AVG( quantity ) AS Average, 
  STDDEV_SAMP( quantity ) AS Variance 
FROM SalesOrderItems GROUP BY Year, Quarter 
  ORDER BY Year, Quarter;

Year	Quarter	Average	Variance
2000	1	25.775148	14.3218
2000	2	27.050847	15.0696
...	...	...	...

Usage

Note: STDDEV_SAMP is an alias for STDDEV.

Computes the sample standard deviation 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 square root of the sample variance.

NULL returns NULL for a one-element input set.

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

Computes the sample standard deviation 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 square root of the sample variance

Standards and compatibility

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