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Index Fragmentation in SQL

Instructor: David Gloag

David has over 40 years of industry experience in software development and information technology and a bachelor of computer science

Maintaining quick access to information is rather important these days. In this lesson, we'll take a look at SQL, indexes, and the fragmentation that can occur within indexes.

Accessing Information

Have you ever wondered how businesses can access information so fast? It seems like it is virtually at their fingertips. You ask someone for a report, and they return minutes later with a printout. Your boss asks you to search the customer base for a specific client, and with a few key clicks, you get the result. And you ask a store clerk for a price, and moments later they have it. If you're like most, you know that there is database technology behind the magic. But have you ever asked yourself what the specifics are? It's true that the computers are getting bigger and faster. And in some respects, this contributes to faster information retrieval. But the most significant contributor is SQL, and the associated indexes.

What is SQL?

SQL is a placeholder. It represents the phrase Structured Query Language, and it is the language used to perform various operations on a database management system. It was developed in 1974 by IBM, and released five years later as commercial product by Oracle. The language is composed of a set of commands performing a specific operation on a database. The type and purpose varies depending on the intended result. Common examples include:

  • CREATE - create a new object in a database, such as a table.
  • SELECT - find and return information in a database.
  • INSERT - add information to a database.
  • UPDATE - change the data that already exists in the database.
  • DELETE - remove information from the database.

What is an Index?

An index is a list of values that provides the means to order the information in a database, without physically modifying it. The list of values is made up of indicators that show the physical position of the information in the database. Now, you're probably wondering why one doesn't simply insert new information in the correct order. Well, you could. There isn't anything stopping you. But performance would suffer because it is faster to add new information to the end of the database, and update the index, than it is to insert the data in the correct position. Also, databases often need multiple orderings, which compound the problem.

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