Refining SQL Queries based on Why-Not Polynomials

Explaining why some data are not part of a query result has recently gained significant interest. One use of why-not explanations is adapting queries to meet user expectations. We propose an algorithm to automatically generate changes to a query, by using Why-Not polynomials, one form of why-not explanations based on query operators.We improve on the state of the art in three aspects: (i) we refine both selection and join predicates, (ii) we guarantee a maximum similarity to the original query, and (iii) we cover all possible cases of why the desired data was missing. A prototype implementation shows the applicability of our approach in practice.