# MySQL STDDEV_POP() function

## STDDEV_POP() function

MySQL STDDEV_POP() function returns the population standard deviation of an expression ( the square root of VAR_POP()). Statistically, the population standard deviation quantifies how much variation there is in a dataset.

It returns NULL if no matching row is found.

This function is useful in -

- The primary purpose of the STDDEV_POP() function is to accurately calculate the population standard deviation.
- STDDEV_POP() quantifies the spread or dispersion of values around the mean (average) in a dataset.
- The population standard deviation helps you understand the variability or consistency of data points within the entire population.
- Population standard deviation is used to calculate confidence intervals for population parameters.
- You can use population standard deviation to compare the variability of different populations or datasets and assess their similarity or difference.
- In finance and risk analysis, population standard deviation is used to measure the volatility or risk associated with investment returns or financial instruments.

**Syntax:**

STDDEV_POP(expr);

Where expr is an expression.

**MySQL Version:** 8.0

**Example: MySQL STDDEV_POP() function **

The following statement returns the standard deviation of 'total_cost' from purchase table.

Sample table: purchase

Code:

```
-- This query calculates the population standard deviation of the 'total_cost' column in the 'purchase' table.
SELECT STDDEV_POP(total_cost)
-- This statement selects the population standard deviation of the 'total_cost' column.
FROM purchase;
-- This part of the query specifies the table from which data is being retrieved, which is 'purchase'.
```

**Explanation:**

- The purpose of this SQL query is to compute the population standard deviation of the 'total_cost' values in the 'purchase' table.
- SELECT STDDEV_POP(total_cost): This part of the query selects the population standard deviation of the 'total_cost' column. Population standard deviation is a statistical measure of the amount of variation or dispersion in a population.
- FROM purchase: This part specifies the table from which the data is being selected, which is the 'purchase' table.
- The query will return a single value, which is the population standard deviation of the 'total_cost' values in the 'purchase' table. This value provides insight into the spread or dispersion of the 'total_cost' values in the entire population represented by the 'purchase' table.

Output:

mysql> SELECT STDDEV_POP(total_cost) -> FROM purchase; +------------------------+ | STDDEV_POP(total_cost) | +------------------------+ | 315.392172 | +------------------------+ 1 row in set (0.00 sec)

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STD()

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STDDEV_SAMP()

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