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Matching and compensation tests for optimizing correlated subqueries within query using automatic summary tables

  • US 7,167,853 B2
  • Filed: 11/05/2002
  • Issued: 01/23/2007
  • Est. Priority Date: 05/20/1999
  • Status: Expired due to Fees
First Claim
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1. A method of optimizing a query in a computer system, the query being performed by the computer system to retrieve data from a database stored on the computer system, the method comprising the steps of:

  • (a) generating an automatic summary table for use in optimizing the query;

    (b) analyzing the query using matching and compensation tests between the query, at least one correlated subquery within the query and the automatic summary table to determine whether there is a match between the query, the correlated subquery and the automatic summary table using a bottom-up traversal of boxes in query graph models (QGMs) for the query, correlated subquery and automatic summary table that tries to establish matches between the query, correlated subquery and automatic summary table, until it reaches a top of the QGM for the automatic summary table, so that expressions occurring in the query including the correlated subquery, but not in the automatic summary table, can be derived using the automatic summary table; and

    (c) rewriting the query so that the automatic summary table is used when there is a match, wherein the rewritten query is performed by the computer system to retrieve data from the database.

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