stddev_samp ​

Calculates the sample standard deviation.

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

Syntax

stddev_samp(x)

Arguments

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

Calculation

sqrt(sum((x - mean) * (x - mean)) / (n - 1))

mean is the arithmetic mean of the non-NULL values, and n is their count. The sample calculation uses n - 1 because the observations estimate a larger population.

Returned value

An approximate REAL value. Fewer than two non-NULL inputs returns NULL. 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_samp(value), 6) AS result
FROM readings
FORMAT csv;

3.162278

A single observation

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

SELECT stddev_samp(value)
FROM single_reading
FORMAT csv;

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