Patent
1995-06-05
1998-05-12
Black, Thomas G.
G06F 1730
Patent
active
057520178
ABSTRACT:
A method and apparatus for reordering complex SQL queries containing joins, outer and full outer joins. The method and apparatus first translates the query into a hypergraph representation. Required sets, conflict sets and preserved sets are then generated for the query hypergraph. Using the required sets, a plurality of plans are enumerated, wherein the plans represent associative reorderings of relations in the query. SQL operators are selectively assigned to each of the enumerated plans using the conflict sets and/or preserved sets, so that the results from the plans are identical to the original query. A novel Modified General Outer Join (MGOJ) operator may be assigned to the root of a sub-tree, wherein the MGOJ operator is a compensation operator. The operator assignment is performed recursively for the root of each sub-tree in the plan. One of the enumerated plans (generally the most optimal) is then selected for execution.
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Bhargava Gautam
Goel Piyush
Iyer Balakrishna Ragmavendra
Black Thomas G.
Choules Jack M.
International Business Machines - Corporation
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