Introduction

When an end user submits an SQL query to a database, in general any database engine does the parsing and then validates the syntax and semantics of the given query. Once the query passes through the parsing levels, it will enter into the optimizer section. This optimizer section is responsible for generating the execution plan of the submitted query, by reading the table statistics. An execution plan of the same query can be varied while executing the query multiple times. Since the plan that the optimizer is generating is based on the amount of data, the query is about to process. In this chapter, we will be discussing various aspects of the optimizer by discussing a few query processing algorithms.