stddev_pop ​

Calculates the population standard deviation.

The result is the square root of the population variance, var_pop. It has the same units as the observations.

Syntax

stddev_pop(x)

Arguments

• x — A numeric column or expression. NULL values are skipped.

Calculation

sqrt(sum((x - mean) * (x - mean)) / (n))

mean is the arithmetic mean of the non-NULL values, and n is their count. The population calculation uses n because the observations describe the entire population.

Returned value

An approximate REAL value. Empty or all-NULL input returns NULL; one non-NULL input returns 0.0. Nonfinite inputs return NULL; finite arithmetic overflow raises NUMERIC_OVERFLOW.

Examples

Measuring the spread of readings

CREATE TABLE readings (value INTEGER);
INSERT INTO readings VALUES (1), (3), (5), (7), (9), (NULL);

SELECT round(stddev_pop(value), 6) AS result
FROM readings
FORMAT csv;

2.828427

A single observation

CREATE TABLE single_reading (value INTEGER);
INSERT INTO single_reading VALUES (7), (NULL);

SELECT stddev_pop(value)
FROM single_reading
FORMAT csv;

0.0