title: Index vs Auto Increment ID set as PK
body: <p>In MySQL, what is the difference between Index and an <em>ID</em> set to <code>AUTO_INCREMENT</code> and as Primary Key?</p>
  
  <p>Will this also increase the speed to searching the database? Or is the <code>AUTO_INCREMENT</code> <em>ID</em> just for the purpose of the of the user and the computer doesn't consider it while searching the database? Reading about <code>INDEX</code> on w3schools.com I came across this line:</p>
  
  <blockquote>
    <p>Indexes are used to retrieve data from the database very fast. The
    users cannot see the indexes, they are just used to speed up
    searches/queries.</p>
  </blockquote>