Indexes, Part 1: Main Types

What Is Index

This is what I found in Wikipedia

A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure.

But let's use plain English instead.

We live in the world with enormous amount of data. It is hell to search for data in that is not ordered in any way.

Index is just some logical ordering and storing, so we can later find the right phone/email/name easier

Main Types of Indexes

Hash Index

Hash index is easy. The perfect example is HashMap.