Containment of Conjunctive Queries: Beyond Relations as Sets
Yannis Ioannidis
Raghu Ramakrishnan
Date published: 
Published In: 
ACM Transactions on Database Systems (TODS), Vol. 20, No. 3, Sept. 1995, pp. 288-324
Journal Article

Conjuctive queries are queries over a relational database and are at the core of relational query languages such as SQL. Testing for containment (and equivalence) of such queries arises as part of many advanced features of query optimization, for example, using rnaterialized views, processing correlated nested queries, semantic query optimization, and global query optimization. Earlier formal work on the topic has examined conjunctive queries over sets of tuples, where each query can be viewed as a function from sets to sets. Containment (and equivalence) of conjunctive queries has been naturally defined based on set incluslon and has been shown to be an NP-complete problem.

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