Syntax:
VARIANCE(expr) [over_clause]

Returns the population standard variance of expr. VARIANCE() is a
synonym for the standard SQL function VAR_POP(), provided as a MySQL
extension.

If there are no matching rows, VARIANCE() 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/group-by-functions.html

