QUERY OPTIMIZATION IN RELATIONAL DATA BASES

Abstract

Over the last decade, the data base technology and specially the Relational model in this technology has been extensively explored from the theoritical as well as imple-mentation point of view. The field of Relational data bases continues to evolve, at a ever increasing rate, so much so, that several subfields within it are beginning to emerge as disciplines in their own right. Codd [1972] first proposed tuple relational calculus as a bench mark for evaluating modern data mainpulation languages. The concept of 'Tableau set'. by Sagiv and Yannakakis [1978] and the idea of domain relational calculus by Gallaire and Minker [1979] have given rise to a number of higher level guery language like Information arystem Base Language (ISBL), Query By Example (QBE), QUEL and SQL. The gueries expressed in these languages are 'non—procedural' in nature: they express what the value of query should be, but do not express how to compute the value. Hence the first modification which is necessary on such types of queries is their translation into relational algebra (this is a procedural way of expressing queries). But the translated algebraic expression is not, and can not expected to be most efficient. Hence as a part of its analysis, the query processor has to modify the query, usually for the reasons for computational efficiency. This is the concept of query optimization.