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I solved it. All I need was a night of sleep and breakfast.

Code:
SELECT B.BID
FROM TableA A, TableB B
WHERE A.AID = B.BID AND A.A1 = 1
HAVING COUNT(B.AID) = (
SELECT FROM COUNT(A.AID)
FROM...

TableA(AID,A1)
TableB(BID, AID)

SELECT AID FROM TABLEA WHERE A1 = 1;

SELECT B.BID, A.AID FROM AID A, BID B WHERE A.AID = B.BID AND A1 = 1;

The first code above will give a list. (Ex....