Tcepsa's Thoughts

I'm trying to update one database table (A) with data from another table (B). The two tables' definitions are identical. I only want to copy a row from table B into table A if not all key fields are identical (i.e. if a row with that key does not already exist in table A). In other words if A.keyfield1 = B.keyfield1 AND A.keyfield2 = B.keyfield2, do not copy the row, but if A.keyfield1 <> B.keyfield1 OR A.keyfield2 <> B.keyfield2, copy the row. I tried doing this:

INSERT INTO A
SELECT B.keyfield1, B.keyfield2, B.otherfield
FROM B
INNER JOIN A
ON A.keyfield1 <> B.keyfield1 OR A.keyfield2 <> B.keyfield2

But no rows are copied (A is currently empty)

Plus I'm not sure that the logic is correct anyway, because I only want the data to be copied if there are NO rows for which A.keyfield1 = B.keyfield1 AND A.keyfield2 = B.keyfield2, not if there are ANY rows where A.keyfield1 <> B.keyfield1 OR A.keyfield2 <> B.keyfield2...