Name
STDDEV_SAMP()
Synopsis
STDDEV_SAMP(expression
)
This function returns the sample standard deviation of the
given column. It’s normally used in conjunction with a GROUP
BY
clause specifying a unique column, so that values are
compared for each unique item separately. It returns NULL if no
matching rows are found. It was added in version 5.0.3 of MySQL for
compliance with SQL standards. Here is an example:
SELECT CONCAT(name_first, SPACE(1), name_last) AS rep_name, AVG(sale_amount) AS avg_sale_per_ticket, STDDEV_POP(sale_amount) AS population_std_dev, STDDEV_SAMP(sale_amount) AS sample_std_dev FROM sales JOIN sales_reps USING(sales_rep_id) GROUP BY sales_rep_id;
This SQL statement uses several aggregate functions: AVG() to determine the average sale for each sales
rep; STDDEV_POP() to determine how much each sale
made by each sales rep tends to vary from each rep’s average sale; and
STDDEV_SAMP()
to determine the standard
deviation from the average based on a sample of the data.
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