# Source: https://docs.oxla.com/sql-reference/sql-functions/aggregate-functions/var-samp.md

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# VAR_SAMP()

## 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.

## Syntax

The syntax for this function is as follows:

```sql  theme={null}
VAR_SAMP(expression)
```

## Parameters

* `expression`: numeric expression or column for which the sample variance is calculated

## 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
<a href="https://www.postgresql.org/ftp/projects/pgFoundry/dbsamples/pagila/pagila/" target="_blank">Pagila</a> database website.

```sql  theme={null}
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:

```sql  theme={null}
SELECT
    VAR_SAMP(length) AS LengthSampleVariance
FROM film
WHERE rating >= 4;
```

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

```sql  theme={null}
 lengthsamplevariance 
----------------------
   1219.7582417582407
(1 row)
```