title: Rails 4: How to replace primary key column using rails migration?
body: <p>I have an e-commerce application running in production, it was a Startup so when I created it I was a nobai, it has a big structural issue. My products table does not have an SKU column, Im working with default rails id's, I need to add a new column SKU and set it as primary key of <code>Product</code>, I found <a href="http://ruby-journal.com/how-to-override-default-primary-key-id-in-rails/" rel="nofollow">this</a> article that explains how to replace the default id with an SKU column, but it works when you are creating the table, but my app has thousands of products and thousands of users.</p>
  
  <p>So what is the best practice for a production app to replace the current primary key <code>id</code> of the products table with a string SKU column? How to fix this structural issue?</p>