title: Default size of integer in Rails tables (MySQL)
body: <p>When I run </p>
  
  <pre><code>rails g model StripeCustomer user_id:integer customer_id:integer
  annotate
  </code></pre>
  
  <p>I got </p>
  
  <pre><code># == Schema Information
  # Table name: stripe_customers
  #  id          :integer(4)      not null, primary key
  #  user_id     :integer(4)
  #  customer_id :integer(4)
  #  created_at  :datetime
  #  updated_at  :datetime
  </code></pre>
  
  <p>Does it mean I can only hold up to 9,999 records only? (I am quite surprise how small a default size for keys is).  How do I change default IDs to be 7 digits in existing tables?</p>
  
  <p>Thank you.</p>