As a database administrator (DBA) or developer, one of your most important goals is to ensure that the query times are consistent with the service-level agreement (SLA) and are meeting user expectations. Along with other performance enhancement techniques, creating indexes for your queries on underlying tables is one of the most effective and common ways to achieve this objective.

The indexes of underlying relational tables are very similar in purpose to an index section at the back of a book. For example, instead of flipping through each page of the book, you use the index section at the back of the book to quickly find the particular information or topic within the book. In the same way, instead of scanning each individual row on the data page, SQL Server uses indexes to quickly find the data for the qualifying query. Therefore, by indexing an underlying relational table, you can significantly enhance the performance of your database.

Indexing affects the processing speed for both...