Indexes in SQL are used to speed up SQL queries. A database index works much like an index in a book. For example, if you have a database table with a list of people, a common query would be to lookup someone by name. Creating an index means the database will not have to scan the entire table looking for matches. Instead, it will restrict its search to a small portion of the rows. In this video we use a table with 100 million rows to illustrate how much an index can change the speed of a query.