Practical SQL Handbook, The: Using SQL Variants, Fourth Edition

Creating Indexes

In a relational database management system, an index is a mechanism for boosting performance. Just as an index in a book helps you quickly find the pages you want to read, an index on a column helps the system find data. When you're looking for a particular subject in a book, you don't want to read every page to find the topic of interest. Similarly, when you're searching for a given piece of data, an index can serve as a logical pointer to its physical location.

There are several important differences, however, between an index in a book and an index in a relational database management system. The reader of a book decides whether to consult the index. The user of a relational database management system decides whether to create ...