title: How to update field to add value to existing value?
body: <p>How to update field to add value to existing value?<br>
  For example I have </p>
  
  <p>Table name: <code>table</code></p>
  
  <pre><code>id   credit
  1      4
  2      5
  3      3
  </code></pre>
  
  <p>Is there a way to simply add value to the credit?<br>
  like</p>
  
  <pre><code>UPDATE table SET credit = '+7' WHERE id='1' 
  </code></pre>
  
  <p>I want to add 7 to 4 so that the credit=11 where id='1'<br>
  How to do this?</p>