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dc.contributor.authorFarre C
dc.contributor.authorNutt W
dc.contributor.authorTeniente E
dc.contributor.authorUrpi T
dc.contributor.editorSchwentick T
dc.contributor.editorSuciu D
dc.date2016-12-15T00:00:00Z
dc.date.accessioned2017-03-30T13:38:30Z
dc.date.available2017-03-30T13:38:30Z
dc.date.issued2006
dc.identifier.isbn978-3-540-69269-0
dc.identifier.issn0302-9743
dc.identifier.urihttp://dx.doi.org/10.1007/11965893_27
dc.identifier.urihttp://link.springer.com/chapter/10.1007/11965893_27
dc.identifier.urihttp://hdl.handle.net/10863/2092
dc.description.abstractWe study containment of conjunctive queries that are evaluated over databases that may contain tuples with null values. We assume the semantics of SQL for single block queries with a SELECT DISTINCT clause. This problem ("null containment" for short) is different from containment over databases without null values and sometimes more difficult. We show that null-containment for boolean conjunctive queries is NP-complete while it is Pi(P)(2)-complete for queries with distinguished variables. However, if no relation symbol is allowed to appear more than twice, then null-containment is polynomial, as it is for databases without nulls. If we add a unary test predicate IS NULL, as it is available in SQL, then containment becomes Pi(P)(2)-hard for boolean queries, while it remains in Pi(P)(2) for arbitrary queries.en_US
dc.language.isoenen_US
dc.publisherSpringeren_US
dc.relation.ispartofseriesSpringer LNCS;
dc.titleContainment of Conjunctive Queries over Databases with Null Valuesen_US
dc.typeBook chapteren_US
dc.date.updated2016-12-19T14:05:37Z
dc.publication.titleDatabase Theory – ICDT 2007: 11th International Conference, Barcelona, Spain, January 10-12, 2007. Proceedings
dc.journal.titleLecture Notes in Computer Science
dc.description.fulltextopenen_US


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