Relational Algebra
This chapter describes and illustrates a set of generic, read-only operators on relations that together constitute what’s called the relational algebra. The algebraic closure property is explained and its significance discussed in detail. Operators described include RENAME, restrict, project, UNION, INTERSECT, MINUS, JOIN, TIMES, MATCHING, NOT MATCHING, EXTEND (two versions), GROUP, and UNGROUP. Image relations are explained, including in particular a discussion of their usefulness in formulating summarization queries. Relational comparisons (relation equality, relation inclusion, etc.) are discussed, as are primitive operations and the important notion of relational completeness. The use of WITH in formulating complicated ...
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