title: Add UUID Primary Key in Rails and MySQL
body: <p>I have a table without ID. Now that I know it's a wrong design, I want to add a primary key ID to that table. Here's the script:</p>
  
  <pre><code>def up
    add_column :players, :id, :primary_key, first: true
  
    change_table :players do |t|
      t.change :id, :uuid
    end
  end
  
  def down
    remove_column :players, :id
  end
  </code></pre>
  
  <p>The thing is that script generate integer value for UUID column. How to properly add primary key UUID to the table?</p>
  
  <p>Edit:
  It's already in production. <strong>I can add ID column</strong>, but it will be filled with integer, not UUID as I expected.</p>