期刊名称：International Journal of Computer Science and Information Technologies
电子版ISSN：0975-9646
出版年度：2012
卷号：3
期号：2
页码：3483-3487
出版社：TechScience Publications
摘要：Existing SQL aggregations have limitations to prepare data sets because they return one column per aggregated group using group functions. A significant manual effort using a compliant programming language is required to build data sets, where a horizontal layout is required. Earlier a simple, yet powerful, methods(CASE,PIVOT,SPJ) to generate aggregated columns in a horizontal tabular layout were developed. Both CASE and PIVOT evaluation methods are significantly faster than the SPJ method. We propose to use a technique called generalized projections (GPs) to improve the performance of SPJ method. The proposed technique pushes down to the lowest levels of a query tree aggregation computation, function computation and duplicate elimination. It also creates aggregations in queries that did not use aggregation to begin with. It unifies set and duplicate semantics, and helps in better understanding aggregations. It improves SPJ performance significantly since applying aggregations early in query processing can provide significant performance improvements.p
