Inverted question

I have table A and table B. I need to use an update question to give the field Avrakn in table B the value 2 for every record that is a exact match in table A and B. To find the exact match there are 4 fields in both tables that has to match. We can call them field1, field2, field3 and field4.
If I use the unmatch question I will get all records that does'nt match but I need the inverted result.
How can this be done?