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Optimization of Real Conjunctive Queries

Chaudhuri, Surajit; Vardi, Moshe Y.



Abstract: The optimization problem for conjunctive queries has been studied extensively. Unfortunately, this research almost invariably assumes set-theoretic semantics (i.e., duplicates are eliminated). In contrast, SQL queries have bag-theoretic semantics (i.e., in general duplicates are not eliminated). In this paper we study the optimization problems for conjunctive queries under bag-theoretic semantics. We show that optimization techniques from the set-theoretic setting do not carry over to the bag-theoretic setting.

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