Hi every body,
Could u plz. take a look to these two quries, they seems to me that they r equal, but they return different result sets back WHY?.
Note: - i v got the correct result from the first one.
        - i need to return tuples in Rel1 who have (a1,a2,a3) values not in Rel2
I
SELECT a0, a1, a2, a3
  FROM Rel1 WHERE (a1, a2, a3) NOT IN
      (SELECT b1, b2, b3 FROM Rel2)

II
SELECT a0, a1, a2, a3
  FROM Rel1 WHERE NOT EXISTS
   (SELECT r1.a1, r1.a2, r1.a3
       FROM Rel1 r1, Rel2 r2
          WHERE r1.a1=r2.b1 AND r1.a2=r2.b2 AND r1.a3=r2.b3)

For ur requirement, the first query is correct. The second query does not return any results if it finds any rows in inner query. Run the inner query separately and test it out. Then u will understand the problem with second one.