title: Differences between def up and def change in migration file
body: <p>What's the difference between <code>def up; end</code> and <code>def change; end</code> ?
  I've got code</p>
  
  <pre><code>class CreateTweets &lt; ActiveRecord::Migration
    def change
      create_table :tweets do |t|
        t.string :status
        t.integer :zombie_id
  
        t.timestamps
      end
    end
  end
  </code></pre>
  
  <p>what does it change if I define <code>def up</code> instead of <code>def change</code> ? </p>