DROP FUNCTION [IF EXISTS] f_name
DROP FUNCTION statement is used to drop a stored function or a user-defined function (UDF). That is, the
specified routine is removed from the server. You must have the
ALTER ROUTINE privilege for the routine. If the automatic_sp_privileges server system variable is set, that privilege and
granted automatically to the routine creator - see Stored Routine Privileges.
IF EXISTS clause is a MySQL/MariaDB extension. It
prevents an error from occurring if the function does not exist. A
NOTE is produced that can be viewed with SHOW WARNINGS.