Evaluation of existential and universal subquery in a relational

Details Evaluation of existential and universal subquery in a relational Evaluation of existential and universal subquery in a relational

1997-06-30

1999-01-26

Von Buhr, Maria N.

Data processing: database and file management or data structures

Database design

Data structure types

707 10, G06F 1730

Patent

active

058648402

ABSTRACT:
A relational data base management system includes a query processor that permits consideration of alternative query plans by the query optimizer so one table can be sent to a selected network location for subquery evaluation in consideration of maximum processing efficiency. Subqueries are converted from "predicate push-down" form to scalar subqueries, enabling upper tables to be sent to nodes of lower tables and vice versa, thereby permitting selection of the node direction depending on the least cost alternative. The optimizer of the query processor is presented with rewritten query code that permits more than one alternative for sending tables for evaluation. The optimizer evaluates the alternatives permitted by the rewritten code, determines the optimal plan for each alternative, and selects the least-cost plan from among the plans evaluated. Thus, the optimizer can decide to send an outer table to where a subquery table is located, or can decide to send a subquery table to where an outer table is located, depending on which is more efficient.

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