# How the STDDEV_POP() function works in Mariadb?

The `STDDEV_POP()`

function is a statistical aggregate function in MariaDB that computes the population standard deviation of a set of values.

The `STDDEV_POP()`

function is a statistical aggregate function in MariaDB that computes the population standard deviation of a set of values. It measures the spread of a data set by calculating how much each data point differs from the mean (average) of the population.

## Syntax

The syntax for the MariaDB `STDDEV_POP()`

function is as follows:

```
STDDEV_POP(expression)
```

The `STDDEV_POP()`

function takes one argument, `expression`

, which is typically a column name containing numeric data. The function returns the population standard deviation as a double-precision value.

## Examples

### Example 1: STDDEV_POP() with a Condition

In this example, we calculate the population standard deviation of values that meet a certain condition.

```
DROP TABLE IF EXISTS students;
CREATE TABLE students (id INT, test_score INT);
INSERT INTO students VALUES (1, 90), (2, 80), (3, 70), (4, 60);
SELECT STDDEV_POP(test_score) FROM students WHERE test_score >= 70;
```

The output for this statement is:

```
+------------------------+
| STDDEV_POP(test_score) |
+------------------------+
| 8.1650 |
+------------------------+
```

The population standard deviation is calculated for test scores greater than or equal to 70.

### Example 2: Grouped STDDEV_POP()

Here, we calculate the population standard deviation for different groups of data.

```
DROP TABLE IF EXISTS class_scores;
CREATE TABLE class_scores (class_id INT, score INT);
INSERT INTO class_scores VALUES (1, 88), (1, 92), (2, 75), (2, 85);
SELECT class_id, STDDEV_POP(score) FROM class_scores GROUP BY class_id;
```

The output for this statement is:

```
+----------+-------------------+
| class_id | STDDEV_POP(score) |
+----------+-------------------+
| 1 | 2.0000 |
| 2 | 5.0000 |
+----------+-------------------+
```

This shows the population standard deviation of scores for each class.

## Related Functions

Below are a few functions related to the MariaDB `STDDEV_POP()`

function:

- MariaDB
`AVG()`

function calculates the average value of a set of values. - MariaDB
`VARIANCE()`

function computes the population variance of a set of values, which is the square of the population standard deviation.

## Conclusion

The `STDDEV_POP()`

function is an essential tool for statistical analysis in MariaDB, providing a measure of the variability within a population. It is crucial for data analysts to understand the difference between population and sample standard deviation (`STDDEV_SAMP()`

) to apply the correct function for their analysis. Accurate use of `STDDEV_POP()`

can help in understanding the distribution and consistency of data across a population.