Indexes help us retrieve data from tables quicker. Let's use an example to illustrate this point: Say we are interested in reading about how to grow peppers in a gardening book. Instead of reading the book from the beginning until we find a section on peppers, it is much quicker for us to go to the index section at the end of the book, locate which pages contain information on peppers, and then go to these pages directly. Going to the index first saves us time and is by far a more efficient method for locating the information we need. The same principle applies for retrieving data from a database table. Without an index, the database system reads through the entire table (this process is called a 'table scan') to locate the desired information. With the proper index in place, the database system can then first go through the index to find out where to retrieve the data, and then go to these locations directly to get the needed data. This is much faster. ...
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