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Date: Mon, 6 Apr 92 11:18:02 -0700
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From: joseash@bush.tamu.edu (Alfredo Sanchez)
Subject: Re: class difference
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	>> how do i find the instances in A but not in B?

	>can you elaborate a little.  Right now I would say that
	>you are asking how to retrieve from class A instead of
	>from class B and that can't be what you are really asking.

	>Jeff Meredith

Actually, I needed something like the SQL minus operation.
I finally implemented it by creating a temporary class, and then
deleting the unwanted instances.

E.g. given

Class A
x  y
1  10
2  20
3  30

Class B
x  y
1  10
3  30

I wanted A - B = ({2,20}), so i did

retrieve into t unique (A.x, A.y) where A.x != B.x
delete t where t.x = B.x
(leaving the tuples i wanted in t)

Is there a better way to do it?

Thanks,

J Alfredo Sanchez H
-------------------
Hypermedia Research Lab
Department of Computer Science
Texas A&M University