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

From: Alan <alan_at_erols.com>
Date: Tue, 31 Aug 2004 13:02:47 -0400
Message-ID: <2pjp9mFlafflU1@uni-berlin.de>

"Laconic2" <laconic2_at_comcast.net> wrote in message news:2IadnZOYKbBuEancRVn-rw_at_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.
>
>
>

I agree- I was debating whether or not to get into it- but I decided just to give a very simple (unintimidating) example. I am surprised that Brio doesn't offer MINUS. It could be that there is an end-user version and a developer's version. I've seen this with several other tools. Received on Tue Aug 31 2004 - 12:02:47 CDT

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