A Truncating Hash Algorithm for Processing Band-Join Queries

A non-equijoin of relations R and S is a band join if the join predicate requires values in the join attribute of R to fall within a specified band about the values in the join attribute of S. This paper describes a new algorithm, termed a truncating-hash band join, for evaluating band joins. This algorithm is based on the idea of truncating join attribute values in order to ezecute band joins in a way similar to hash join algorithms for equijoins. Unlike previously proposed algorithms for band joins, it does not sort either of the input relations during its ezecution. We present a comparison between the truncating-hash band join algorithm andprevious algorithms for band joins using an analytical model. The model also compares an evaluation of band join algorithms for a pamllel implementation on a ”shared-nothing” multiprocessor system. The results show that the truncating-hash band join algorithm outperforms the other band join algorithms because of a significantly lower CPU cost.