I have a very simple setup:

Table 1 = Accounts

Field1 = AccountID

Field2 = AccountName

Table 1 will have Account named entered manually. There are not many, 6 accounts.

Table 2 = Opportunity

Field 1 = OpportunityID

Field 2 = AccountName - This will come from the import

Field 3 = AccountID

Table 2 will have weekly imported opportunity data. With the imported data comes the AccountName.

What I would like to have happen is when the Opportunity table is populated with the imported data then the Opportunity:AccountID is populated by the Accounts:AccountID

Solved!

I had my relationships incorrect.

I had it between Opportunity:AccountID and Accounts:AccountID.

I changed to Opportunity:AccountName and Accounts:AccountName and now my data is populated.