I haven't tried something like this in CR. I would try creating a stored proc to do the processing as you can make the selection into several steps. Your data has 2 dates and ratings and I don't think that CR can group/compare on the 2 values...at least I don't see a easy simple solution in CR.
Again, a stored proc is much more flexible in this regard and you can return only the data that you need making the logic of the report much simpler.
HTH