Transforming correlated scalar subqueries
US8521723B1 · kind B1 · utility
Assignee
Inventor
Key dates
| Filing date | Jul 18, 2012 |
| Grant date | Aug 27, 2013 |
| Priority date | — |
| Expiry date | Jul 18, 2032 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06F16/24534
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A method, apparatus, and stored instructions are provided for transforming an initial query having a scalar subquery with correlated predicates into a transformed query having transformed predicates that are not in the scalar subquery. The transformed predicates correspond to the correlated predicates, but the transformed predicates are no longer correlated. The transformed predicates reference an outer join operation to preserve null values that may have been generated by the correlated predicates that were in the scalar subquery of the initial query. The transformed query is semantically equivalent to the initial query. When creating an execution plan for the transformed query, the query processor may choose from a much larger set of access paths, join methods, and join permutations than those that were available for the initial query. The transformed query may qualify for other transformations or optimizations, or may otherwise be executed or optimized differently from the initial query.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.