Imagine a small book of 100 pages. Let's say that this hypothetical book is about the SQL language. Your only navigation through the book is via the Table of Contents (TOC) with page numbers. Now, imagine that you need to find where the word DDL is mentioned in the book. The TOC is useless. You can find a chapter about DDL commands, if it exists, but there is no guarantee that DDL is not mentioned anywhere else. You have to conclude that the only way to find all DDL words is by reading all 100 pages, page by page.

Now, let's imagine the same book with an Index of Terms. It means you will have all the book's related words in some order (for example, ascending) with the number of the page(s) where that word is positioned in the book. In our example, let's say that DDL is mentioned on pages 33, 56, and 78 of the book. Now there is no need to read each page; you can look at the index and quickly locate the required data.

The same concept is applied in the database world. Tables...