Joining two tables

I have two tables named TrackerOrders and TrackerFax. All orders coming thru fax are being tracked on table TrackerFax. Now these orders are being processed and being tracked on table TrackerOrders. Both tables have POnumber column and I wanted to join these tables to match if all PO received on  TrackerFax are processed on TrackerOrders. Any idea how to do this? Appreciate any help.
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