Dropping tautological predicates from SQL queries for...

Details Dropping tautological predicates from SQL queries for... Dropping tautological predicates from SQL queries for...

2011-01-25

2011-01-25

Breene, John E (Department: 2162)

Data processing: database and file management or data structures

Database and file access

Query optimization

C707S719000

Reexamination Certificate

active

07877377

ABSTRACT:
A database query optimizer creates a main access plan for a query, and also creates one or more subplans for the same query. The subplans are used in executing a query. When a subplan is generated, all tautological predicates (i.e., predicates that do not narrow the query) are dropped, thereby enhancing the reusability of stored subplans. When a query is processed, its tautological predicates are dropped, and if a subplan for the query with the dropped tautological predicates is found, the subplan is used to execute the query. If the query to be run has no main access plan in the cache, a main access plan is generated, and a subplan is also generated that corresponds to the query to be run, with all tautological predicates dropped. The same query may thus generate many subplans, enhancing the reusability of the query by storing each subplan in the access plan cache.

REFERENCES:
patent: 5548755 (1996-08-01), Leung et al.
patent: 6275818 (2001-08-01), Subramanian et al.
patent: 6466931 (2002-10-01), Attaluri et al.
patent: 2002/0143754 (2002-10-01), Paulley et al.
patent: 2005/0097078 (2005-05-01), Lohman et al.

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