title: Extract hours from SQL datetime format?
body: <p>I Have a dataset like this:</p>
  
  <pre><code>State  image_datetime
  WY      08/21/2017 
          18:02:20
  KY      08/21/2017
          17:36:23
  IL      08/21/2017
          18:23:04
  KY      08/21/2017 
          18:23:04.....
  </code></pre>
  
  <p>I want to extract only the hours part from the image_datetime column, so that the output looks like this:</p>
  
  <pre><code>State    image_datetime
  WY         18
  KY         17
  IL         18
  KY         18
  </code></pre>