title: add_column for references (Rails)
body: <p>I have the following Rails migration which works perfectly (irrelevant pieces removed):</p>
  
  <pre><code>create_table :comments do |t|
    t.text :body
    t.references :post
  end
  </code></pre>
  
  <p>Now I'd like to add an <code>author</code> column to my <code>comments</code> table (which is the userid of a user), but I have no idea how to do it (I'm tempted to just write the MySql-specific syntax using an <code>execute</code>). </p>
  
  <p>I've been looking at add_column <a href="http://api.rubyonrails.com/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#M001658" rel="noreferrer">here</a> which doesn't mention <code>references</code>. I've actually found <a href="http://api.rubyonrails.com/classes/ActiveRecord/ConnectionAdapters/TableDefinition.html#M001737" rel="noreferrer">TableDefinition#references</a> but I have no idea how to use it with an <code>add_column</code> statement.</p>
  
  <p>Is this possible? Also, is it true that, for MySql, the "references" functionality does not actually establish relationships between the tables?</p>