How to extend a conventional optimizer to handle one- and two-sidedouterjoin

摘要

The authors provide a nearly complete theory for reorderingnjoin/outerjoin queries. The theory is used to describe modularnextensions that strengthen a conventional optimizer to handle nearly allnselect/project/join/outerjoin queries. Unlike previous work, thesenresults are not limited to queries possessing a nice structure, ornqueries that are nicely represented in relational calculus. Thentheoretical results concern query simplification and reassociation usingna generalized outerjoin