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Redundant join elimination and sub-query elimination using subsumption

  • US 7,587,383 B2
  • Filed: 02/27/2003
  • Issued: 09/08/2009
  • Est. Priority Date: 03/01/2002
  • Status: Active Grant
First Claim
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1. A computer-implemented method for optimizing a query in a relational database management system, wherein the computer performs the following functions comprising:

  • evaluating the query to determine whether a sub-expression of the query is being joined to itself and whether a predicate of the query comprises an equality test between a same column of the sub-expression;

    determining whether a first row set producible from a first set of references of the query to the sub-expression is subsumed by a second row set producible from a second set of references of the query to the sub-expression; and

    reforming the query to eliminate the joining of the sub-expression to itself based on evaluation of the query and determination of whether the first row set is subsumed by the second row set.

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