Using WPDB class

You can’t mix wpdb with mysql_fetch_array. They are not compatible. You need to use wpdb methods, plus PHP functions like while, foreach, and for. wpdb does not return the references that PHP’s mysql functions use. It returns an object, and array, or sometimes a string.

In your case, though, the database part is done. You just want to foreach over the result set.

foreach ($products as $op) {
    // do stuff
}