Without context, it makes it a little hard to give you a straight answer but I'll try:
If you're building a fourth table reconciling the data from the three tables, I'd ask you to simply join the dups and create additional fields with aggregations -- or the numbers you're insteresting in.
If you're thinking "If it exists on all three, I don't care about the records" -- usually when you're checking what rows have not replicated to the other zones - then you can do a set analysis on your dashboard where the count of your rows are < 2 ...
You can do it on the Qlik Script too, and on the database too.
If you can provide more context (maybe your data models) and your actual result (on a Dashboard, or a physical deletion of the data), I htink I can be more precise on my response.