SQL for MySQL Developers: A Comprehensive Tutorial and Reference

Chapter 25. Using Indexes

25.1 Introduction

Some SQL statements, such as the CREATE TABLE and GRANT statements, have a reasonably constant execution time. It does not matter under which circumstances such statements are executed; they always need a certain execution time, and it cannot be reduced. However, this is not the case for all statements. The time required to process SELECT, UPDATE, and DELETE statements varies. One SELECT statement might be processed in two seconds, and another could take minutes. You can influence the required execution time for this type of statement.

Many techniques exist for reducing the execution time of SELECT, UPDATE, and DELETE statements, ranging from reformulating statements to purchasing faster computers. ...