Syntax:
VAR_SAMP(expr) [over_clause]

Returns the sample variance of expr. That is, the denominator is the
number of rows minus one.

If there are no matching rows, or if expr is NULL, VAR_SAMP() returns
NULL.

This function executes as a window function if over_clause is present.
over_clause is as described in
https://dev.mysql.com/doc/refman/8.0/en/window-functions-usage.html.

URL: https://dev.mysql.com/doc/refman/8.0/en/aggregate-functions.html

