MySQL STDDEV_SAMP() function

Last update on May 01 2024 12:45:14 (UTC/GMT +8 hours)

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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