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Query optimizer system that detects and prevents mutating table violations of database integrity in a query before execution plan generation

  • US 5,546,576 A
  • Filed: 02/17/1995
  • Issued: 08/13/1996
  • Est. Priority Date: 02/17/1995
  • Status: Expired due to Fees
First Claim
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1. A method for optimizing the execution plan of a query that enforces database integrity in a relational database processing system having a stored database including a plurality of base tables {T} and a data processor for processing queries represented by query graphs {G}, wherein each said query graph G includes a plurality of quantifier nodes {Ni } each representing a relational operation, wherein each said quantifier node Ni receives from each of one or more other said quantifier nodes {Nj } a flow of records represented by a directed data-flow arc Aji forming part of a data-flow path and wherein i and j are positive integers, said method comprising the steps of:

  • (a) evaluating said query graph G for each said base table Teach to identify common-referencing pairs of said quantifier nodes for which said each base table Teach is the object;

    (b) reforming said query graph G to restrict said data-flow path to sequence the execution of each said common-referencing pair of quantifier nodes to produce a query graph GMTI that enforces database integrity during table mutation;

    (c) generating a plurality of plans for executing said query graph GMTI ; and

    (d) evaluating the execution cost of each said query execution plan and selecting said optimal execution plan.

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