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Set Operators in SQL
Relational database design has strong roots within Set Theory, as can be seen in the seminal work of E.F. Codd more than 40 years ago. Most people recall encountering Venn diagrams during their school days, a pictorial excursion into this realm. Codd codified his relational ideals into a series of well-known rules, which represent an extreme case, not taking account of the often necessary pragmatic or performance reasons for selective denormalization. But his principles are still instructive and serve as a starting point for designing business schemas. Continue…