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Overview

The VAR_SAMP() aggregate function calculates the sample variance of a set of numeric values. This function measures the spread of data points around the mean, assuming the data is a sample of a larger population.

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Syntax

The syntax for this function is as follows: 
VAR_SAMP(expression)

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Parameters

  • expression: numeric expression or column for which the sample 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,
  length int,
  rating 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);
They query below uses the VAR_SAMP() function to calculate the sample variance for the length column where rating is greater than or equal to 4: 
SELECT
    VAR_SAMP(length) AS LengthSampleVariance
FROM film
WHERE rating >= 4;
By running the above code, we will get the following output: 
 lengthsamplevariance 
----------------------
   1219.7582417582407
(1 row)