title: MySql copy value from one row to another
body: <p>This should be pretty basic but i can't figure it out. Have a table 'values'</p>
  
  <pre><code>entity|attribute|value
  
  frank - shirt - red 
  frank - hat   - green
  sam   - shirt - blue
  sam   - hat   - orange
  </code></pre>
  
  <p>how do i set all hats color's to be the same as the shirt color, of the same person to give frank a red hat and sam a blue hat.</p>