Introduction to Query Processing and Optimization Michael L. Rupley, Jr. Indiana University at South Bend
[email protected] owned_by 10 No ABSTRACT All database systems must be able to respond to The drivers relation: requests for information from the user—i.e. process Attribute Length Key? queries. Obtaining the desired information from a driver_id 10 Yes database system in a predictable and reliable fashion is first_name 20 No the scientific art of Query Processing. Getting these last_name 20 No results back in a timely manner deals with the age 2 No technique of Query Optimization. This paper will introduce the reader to the basic concepts of query processing and query optimization in the relational The car_driver relation: database domain. How a database processes a query as Attribute Length Key? well as some of the algorithms and rule-sets utilized to cd_car_name 15 Yes* produce more efficient queries will also be presented. cd_driver_id 10 Yes* In the last section, I will discuss the implementation plan to extend the capabilities of my Mini-Database Engine program to include some of the query 2. WHAT IS A QUERY? optimization techniques and algorithms covered in this A database query is the vehicle for instructing a DBMS paper. to update or retrieve specific data to/from the physically stored medium. The actual updating and 1. INTRODUCTION retrieval of data is performed through various “low-level” operations. Examples of such operations Query processing and optimization is a fundamental, if for a relational DBMS can be relational algebra not critical, part of any DBMS. To be utilized operations such as project, join, select, Cartesian effectively, the results of queries must be available in product, etc.