If you use assignment in this way, it won't actually copy the resource, simply both variables refer to the same one.
To copy a resource you must use a method specific to the resource type; many resource types are not copyable at all, probably including mysql results.
I'm not sure why you WANT to copy the resource, but if you know your result set is of reasonable size (e.g. will fit in RAM), you may want to read the entire result set into a variable and copy that instead.
Mark