The theory of joins in relational databases
Authors:
Open Access
- 1 September 1979
- journal article
- research article
- Published by Association for Computing Machinery (ACM) in ACM Transactions on Database Systems
- Vol. 4 (3) , 297-314
Abstract
Answering queries in a relational database often requires that the natural join of two or more relations be computed. However, the result of a join may not be what one expects. In this paper we give efficient algorithms to determine whether the join of several relations has the intuitively expected value (is lossless ) and to determine whether a set of relations has a subset with a lossy join. These algorithms assume that all data dependencies are functional. We then discuss the extension of our techniques to the case where data dependencies are multivalued.Keywords
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