> ## Documentation Index
> Fetch the complete documentation index at: https://docs.oxla.com/llms.txt
> Use this file to discover all available pages before exploring further.

# STDDEV_SAMP()

## Overview

The `STDDEV_SAMP()` aggregate function calculates the sample standard deviation of a set of numeric values. This function measures how much the values deviate from their mean, assuming the data is a sample of a larger population.

## Syntax

The syntax for this function is as follows:

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

## Parameters

* `expression`: numeric expression or column for which the sample standard deviation 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);
```

The query below uses the `STDDEV_SAMP()` function to calculate the sample standard deviation for the `length` column where `rating` is greater than or equal to 4:

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

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

```sql theme={null}
 lengthsamplestddev 
--------------------
  34.92503746251735
(1 row)
```