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 populationā€™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.

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Syntax

STDDEV_POP(<expression>)

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Parameters

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

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Return Type

STDDEV_POP returns a result of type DOUBLE PRECISION.

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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.

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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