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Method for performing joins between different record types in a database system

  • US 5,625,813 A
  • Filed: 06/27/1995
  • Issued: 04/29/1997
  • Est. Priority Date: 08/27/1994
  • Status: Expired due to Term
First Claim
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1. In a database system comprising a database storing a plurality of records of a plurality of different record types, a method of executing a database query involving a join between a plurality of said record types, the method comprising the steps:

  • (a) processing the query to create a data structure comprising a plurality of nodes, linked together to form a plurality of chains, each of said nodes representing one of said data types, said processing comprising;

    (i) identifying a starting set of record types each of which contains a key that is equated to a literal in said query, or contains a field that is equated to a key of another record type in said query;

    (ii) creating a node in said data structure for each of said starting set of record types;

    (iii) identifying a further set of record types each of which can be accessed from a record type represented by an existing node; and

    (iv) creating a new node in said data structure for each of said further set of record types, and linking said new node to said existing node;

    (b) constructing a virtual row of said join by accessing said nodes in sequence and, for each of said nodes, reading a record of the record type represented by that node; and

    (c) testing said virtual row to determine whether it satisfies said database query.

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