stddev_samp

Description

Computes the standard deviation of a sample consisting of a numeric expression, as a double. stdev and stddev are aliases for stddev_samp, and use the same syntax.

Syntax

stddev_samp ( [ all | distinct ] expression )

Parameters

all

applies stddev_samp to all values. all is the default.

distinct

eliminates duplicate values before stddev_samp is applied.

expression

is any numeric datatype (float, real, or double precision) expression.

Examples

Example 1

The following statement lists the average and standard deviation of the advances for each type of book in the pubs2 database.

select type, avg(advance) as "avg",
  stddev_samp(advance) as "stddev" from titles
  where total_sales > 2000 group by type order by type

Usage

Computes the sample standard deviation of the provided value expression evaluated for each row of the group (if distinct was specified, then each row that remains after duplicates have been eliminated), defined as the square root of the sample variance.

Figure 2-4: The formula for sample-related statistical aggregate functions

The formula for sample-related statistical aggregate functions.

Standards

ANSI SQL – Compliance level: Transact-SQL extension.

Permissions

Any user can execute stddev_samp.

See also

For general information about aggregate functions, see “Aggregate functions”.

Functions stddev_pop, var_pop, var_samp