Copy both databases to one Excel worksheet preferably in the same column(s).
Then the massaging starts.
What do you want to do with duplicates if/when found?
Keep one of each and delete the extras?
Use Advanced filter and check "unique records" and "copy to another place"
See Debra Dalgleish's site for more on this. http://www.contextures.on.ca/xladvfilter01.html