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Re: How to do a difference on two sets from same table?

From: Laconic2 <laconic2_at_comcast.net>
Date: Tue, 31 Aug 2004 10:38:51 -0400
Message-ID: <2IadnZOYKbBuEancRVn-rw@comcast.com>

"Alan" <not.me_at_uhuh.rcn.com> wrote in message news:2eSYc.10965$Tq.9705_at_trndny02...

> FROM same_place
> WHERE other_condition

As usual, your comments are excellent.

I do have a quibble with you on this one. The "FROM same_place" is misleading. You don't always have
to draw the second set from the same source as the first, just as you don't necessarily have to draw both sets
from the same source in UNION.

When the sets are both drawn from the same source, it's possbile to express the result without a MINUS,
by just saying WHERE some_condition AND NOT other_condition. This leaves the learner in a quandary about
why the MINUS had to be added to the already complex bag of things to be learned. The MINUS is more useful,
and sometimes necessary, when the two sets are drawn from different sources. The same comment applies to UNION. Received on Tue Aug 31 2004 - 09:38:51 CDT

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