Optimization of SQL queries using universal quantifiers, set intersection, and max/min aggregation in the presence of nullable columns

摘要

A method and apparatus for optimizing SQL queries by propagating and exploiting column nullability. Column nullability is identified and propagated using a three-valued logic, wherein a column of a table can be identified nullability information is exploited to optimize query operations through transformations. In one aspect of the present invention, quantified predicates (such as " ALL") are transformed into simple predicates involving singleton subqueries so that indexing can be exploited. In another aspect of the present invention, "is not null" predicates are generated and pushed for certain aggregate queries. In still another aspect of the present invention, intersect operations are transformed into joins. The end result is that the present invention can significantly enhance the performance of the queries.