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Overview

The VARIANCE() aggregate function calculate the sample variance of a set of numeric values. Variance measures the spread of data points around the mean, providing insight into how much the values deviate from the average.

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Syntax

The syntax for this function is as follows:

VARIANCE(expression)

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Parameters

  • expression: numeric expression or column for which the variance is calculated

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Example

For the needs of this section, we’re going to use a simplified version of the film table from the Pagila database, containing only the title, length and rating columns. The complete schema for the film table can be found on the Pagila database website.

DROP TABLE IF EXISTS film;
CREATE TABLE film (
  title text NOT NULL,
  rating int,
  length int
);
INSERT INTO film(title, length, rating) VALUES
  ('ATTRACTION NEWTON', 83, 5),
  ('CHRISTMAS MOONSHINE', 150, 7),
  ('DANGEROUS UPTOWN', 121, 4),
  ('KILL BROTHERHOOD', 54, 3),
  ('HALLOWEEN NUTS', 47, 5),
  ('HOURS RAGE', 122, 7),
  ('PIANIST OUTFIELD', 136, 7),
  ('PICKUP DRIVING', 77, 3),
  ('INDEPENDENCE HOTEL', 157, 7),
  ('PRIVATE DROP', 106, 4),
  ('SAINTS BRIDE', 125, 3),
  ('FOREVER CANDIDATE', 131, 7),
  ('MILLION ACE', 142, 5),
  ('SLEEPY JAPANESE', 137, 4),
  ('WRATH MILE', 176, 7),
  ('YOUTH KICK', 179, 7),
  ('CLOCKWORK PARADISE', 143, 5);

The query below uses the VARIANCE() function to calculate the variance for the length column:

SELECT
    VARIANCE(length) AS LengthVariance
FROM film;

By executing the code above, we will get the following output:

   lengthvariance   
--------------------
 1473.0955882352937
(1 row)
STDDEV_SAMPVAR_POP