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_at_posting.google.com>
Date: 7 Oct 2002 08:50:17 -0700
Message-ID: <c0d87ec0.0210070750.1256b704_at_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 - 17:50:17 CEST