title: mysql on duplicate key update
body: <p>I am using mysql option to update result on duplicate. It works fine to update result. Now I was trying to concatenate existing row result with previous one and I used + and . concatenation operators but it is giving error. </p>
  
  <p>Here is the pseudo code</p>
  
  <pre><code>insert in table 1
  on duplicate key update prod_name = "abc" concatenate with existing result
  </code></pre>
  
  <p>so if there is record XYZ in the row then it should be XYZ, abc and on next 
  duplicate it should be XYZ, abc, dpg and so on</p>