Syntax
------

STDDEV_SAMP(expr)

Description
-----------

Returns the sample standard deviation of expr (the square root of VAR_SAMP()).

It is an aggregate function, and so can be used with the GROUP BY clause.

STDDEV_SAMP() can be used as a window function.

STDDEV_SAMP() returns NULL if there were no matching rows.

URL: https://mariadb.com/kb/en/stddev_samp/