title: Why use the INCLUDE clause when creating an index?
body: <p>While studying for the 70-433 exam I noticed you can create a covering index in one of the following two ways.</p>
  
  <pre><code>CREATE INDEX idx1 ON MyTable (Col1, Col2, Col3)
  </code></pre>
  
  <p>-- OR --</p>
  
  <pre><code>CREATE INDEX idx1 ON MyTable (Col1) INCLUDE (Col2, Col3)
  </code></pre>
  
  <p>The INCLUDE clause is new to me.  Why would you use it and what guidelines would you suggest in determining whether to create a covering index with or without the INCLUDE clause?</p>