I am using Toad Data Point in Oracle. 5.4.0. Does Toad allow Compare Key be a hash key? Is there a size limit on the compare key?
So, sounds like you are using the Data Compare wizard. I'm not aware of any limitations on which keys to use for comparison, but UNIQUENESS is pretty important for any comparison. So a hash key may not give you proper results if the hash values are not unique.
By default, TDP's Compare wizard chooses an existing primary or unique key, but the end user can override this with any combination of columns s/he thinks will give them relevant results. Note again, that uniqueness of your "key" column/s selection is super important.