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)

Hey,

The second one you could use not in also in your query. Does that match them up?

Brian

Hi Brian,
First thanks for replaying; Second, what exactly, i am trying to do is using "NOT EXISTS" instead of "NOT IN" (more efficient ).
So, i have rewritten the first one using "NOT EXISTS", but it returns a different result set. My question is are they equivalent? or not? .
thanks

Hey,

From this article: http://www.devx.com/dbzone/Article/9570. It seems like that they may not be quite the exact same thing...

Brian