What Is an Index?
Simply put, an index is a pointer to data in a table. An index in a database is very similar to an index in the back of a book. For example, if you want to reference all pages in a book that discuss a certain topic, you first refer to the index, which lists all topics alphabetically, and are then referred to one or more specific page numbers. An index in a database works the same way in that a query is pointed to the exact physical location of data in a table. You are actually being directed to the data's location in an underlying file of the database, but as far as you are concerned, you are referring to a table.
Which would be faster, looking through a book page by page for some information or searching the book's index and ...
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