Decidability of Equivalence of Aggregate Count-Distinct Queries
arXiv (Cornell University)(2015)
摘要
We address the problem of equivalence of count-distinct aggregate queries, prove that the problem is decidable, and can be decided in the third level of Polynomial hierarchy. We introduce the notion of core for conjunctive queries with comparisons as an extension of the classical notion for relational queries, and prove that the existence of isomorphism among cores of queries is a sufficient and necessary condition for equivalence of conjunctive queries with comparisons similar to the classical relational setting. However, it is not a necessary condition for equivalence of count-distinct queries. We introduce a relaxation of this condition based on a new notion, which is a potentially new query equivalent to the initial query, introduced to capture the behavior of count-distinct operator.
更多查看译文
关键词
equivalence,count-distinct
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络