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Re: The Practical Benefits of the Relational Model

From: --CELKO-- <71062.1056_at_compuserve.com>
Date: 7 Oct 2002 08:50:17 -0700
Message-ID: <c0d87ec0.0210070750.1256b704@posting.google.com> 





>> Union and intersection are dual operations in the set theory.

Suddenly, this symmetry is broken in the relational theory. <<



There is no problem.  Dr. Codd had intersection, union and set
difference as three of the eight basic relational operators.



SQL-86 and SQL-89 had only UNION [ALL], but we added INTERSECT [ALL]
and EXCEPT [ALL] in the SQL-92 standard.  We were slow catching up,
that's all.
Received on Mon Oct 07 2002 - 10:50:17 CDT












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