Create a under column to column

How to add an undercolumn to a column? Example:

class CreateMessages < ActiveRecord::Migration
  def change
    create_table :messages do |t|
        t.text :text
      t.timestamps
    end
  end
end

I want to add another column for every new text column. I think I have to use the text column's id, but i'm not sure. How should I do it?