STDDEV_POP

Computes the population standard deviation of all non-NULL numeric values produced by an expression. The population standard deviation shows how spread out the values in a population are, by measuring the average distance of each value from the population’s mean. For information about the sample standard deviation, which estimates the spread of values across sample rather than the full population, see STDDEV_SAMP.

Syntax

STDDEV_POP(<expression>)

Parameters

Parameter	Description	Supported input types
<expression>	An expression producing numeric values for which to calculate the population standard deviation.	REAL, DOUBLE PRECISION

Return Type

STDDEV_POP returns a result of type DOUBLE PRECISION.

Special cases

• If there are no non-NULL input values, the result is NULL.
• If the input contains an Inf or NaN value, the result will be NaN.

Example

The following code creates an exams table with a grade column of type DOUBLE PRECISION, and inserts five grade values into it:

CREATE TABLE exams (grade DOUBLE PRECISION);
INSERT INTO exams VALUES (4.0), (3.7), (3.3), (2.7), (2.7);

The following code calculates the population standard deviation of the grade values from the exams table, rounds the result to three decimal places, and returns it as stddev:

SELECT ROUND(STDDEV_POP(grade), 3) as stddev from exams;

Returns The previous code returns the following result:

stddev (DOUBLE PRECISION)
0.523