Database Index

Database Index / Define index in database / What is index? / Example of an index / Purpose of a database index

Index

An index is an auxiliary data structure that is used to find records that meet a selection condition. Index is used especially to speed up the selection process where a selection condition to be verified on records. Index works the same way as the indexes found in end of the pages of most of the books.

Some of the indexes that you might have used are,

• Card catalog in libraries
• Telephone directory
• Book last page indexes

Example

Book last page index

We can easily observe from the above image about an index. Yes, it has certain properties;

Index is sorted

Each entry (ex. Basic operation 14) contains the page number along with it

All the index keys are listed.

This type of arrangement speeds up our process by directly giving us the page where the required data are available.

Indexes usually are of two broad types. They are;

• Ordered indices – sorted values
• Hash indices – distribution based on hash function

You can click on "How to choose the type of index for your application" to know about applications where these types can fit.