mysql_num_rows error

[hubert]

As I'm in the process of upgrading to 1.5.4 on a server running PHP 5.6 this

if( mysql_num_rows( mysql_query("SHOW TABLES LIKE '".DB_PREFIX."so_payment_types'"))){
    $sql = "TRUNCATE TABLE ".DB_PREFIX."so_payment_types";
    $db->Execute($sql);
}

(which is Super_orders' init_so_config.php) fire me with

PHP Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in /ADMIN/includes/init_includes/init_so_config.php on line 13

.

Would this replacement work and is it the write syntax ?

$sql = "SHOW TABLES LIKE '".DB_PREFIX."so_payment_types'";
	$result = $db->Execute($sql);
	$row_cnt = $result->num_rows;
	if($row_cnt){
    $sql = "TRUNCATE TABLE ".DB_PREFIX."so_payment_types";
    $db->Execute($sql);
}

Thanks for your help

Hubert