Update mysql ( small fix pls )

function reward(){
	$current_user = wp_get_current_user();
	$grade = $current_user->points - 1;
	$sql = "UPDATE wp_users SET points = '$grade' WHERE ID = '$current_user->ID' ";
	$res = mysql_query($sql);
}
add_action('added_postmeta','reward');

what is wrong here?
Please help I’m having a headache lol.Thx