Choosing and Optimizing Indexes
An index is a database object used primarily to improve the performance of SQL queries. The function of a database index is similar to an index in the back of a book. A book index associates a topic with a page number. When you’re locating information in a book, it’s usually much faster to inspect the index first, find the topic of interest, and identify associated page numbers. With this information, you can navigate directly to specific page numbers in the book. In this situation, the number of pages you need to inspect is minimal.
If there were no index, you would have to inspect every page of the ...