MySQL STDDEV_SAMP() function

STDDEV_SAMP() function

MySQL STDDEV_SAMP() function returns the sample standard deviation of an expression ( the square root of VAR_SAMP()). Statistically, sample standard deviation quantifies the amount of variation or dispersion in a dataset for which you have a sample of the whole population.

It returns NULL if no matching rows are found.

This function is useful in -

• It's used when you have a sample of data and want to estimate the variability in the entire population.
• Data Analysis: The primary purpose of the STDDEV_SAMP() function is to accurately calculate the sample standard deviation.
• When comparing different samples or groups, STDDEV_SAMP() is used to assess the significance of differences between the groups.
• Sample standard deviation is used to calculate confidence intervals for population parameters based on sample data.
• STDDEV_SAMP() is used to explore the variation and distribution of data in sample datasets, helping in initial data analysis.
• Sample standard deviation is used in hypothesis testing to test the validity of assumptions and draw conclusions about population characteristics.

Syntax:

STDDEV_SAMP(expr);

Where expr is an expression.

MySQL Version: 8.0

Example: MySQL STDDEV_SAMP() function

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

Sample table: purchase

Code:

-- This query calculates the sample standard deviation of the 'total_cost' column in the 'purchase' table.
SELECT STDDEV_SAMP(total_cost)
-- This statement selects the sample 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 sample standard deviation of the 'total_cost' values in the 'purchase' table.


• SELECT STDDEV_SAMP(total_cost): This part of the query selects the sample standard deviation of the 'total_cost' column. Sample standard deviation is a statistical measure of the amount of variation or dispersion in a sample.


• 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 sample 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 sample represented by the 'purchase' table. It's important to note that sample standard deviation is used when the data is a subset (sample) of a larger population, whereas population standard deviation considers the entire population.

Output:

mysql> SELECT STDDEV_SAMP(total_cost)
    -> FROM purchase;
+-------------------------+
| STDDEV_SAMP(total_cost) |
+-------------------------+
|              345.494814 | 
+-------------------------+
1 row in set (0.00 sec)

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