Set Operators Defined

A set operator appears between two independent queries. It is used to - in some way - reconcile the results of the two queries into a single result set. These operations are based upon principles in elementry mathematical set theory.

- MINUS is used to produce the
*difference*between two result sets. - INTERSECT is used to show the
*commonalities*between two result sets. - UNION combines two results sets, but
*removes*any duplicates. - UNION ALL combines two results sets, but
*preserves*any duplicates.

These relationships can be visualized using *Venn Diagrams* which
represent the logical relations between sets in a visual form. A Venn diagram
uses circles to show areas of commonality and exclusivity between sets.