Simplification of sql queries using generalized inference propagation

Abstract

A method and apparatus for query simplification by applying generalization inference propagation and transitive closure in SQL queries having intersection operations combined with inner and outer join operations further combined with selection and/or projection operations. First a strong set of predicates is calculated, typically a selection or join predicate which is null-intolerant. Second the strong set of attributes is used to select and replace a full, left, or right outer join operation found as the operand of an intersection operation in the query. A less expensive outer or inner join replaces the selected join and the process is repeated until no further simplification if possible. Inferences are propagated from one operand to the other of an intersection operation. Selection operators are applied through transitive closure to reduce the size of intermediate results. The transformations are applied to the query to produces a set of operations that perform more efficiently than that of the original query while providing the same results.