title: ruby on rails add a column after a specific column name
body: <p>I tried to add a column to a table after a specific column in the table.
  Here is what I did:</p>
  
  <pre><code>rails generate migration add_reaction_id_to_patient_allergies reaction_id: integer :after =&gt; 'patient_id'
  </code></pre>
  
  <p>Here is what my migration file looks like:</p>
  
  <pre><code>class AddReactionIdToPatientAllergies &lt; ActiveRecord::Migration
    def change
      add_column :patient_allergies, :reaction_id, :string
      add_column :patient_allergies, :integer, :string
      add_column :patient_allergies, :, :after
      add_column :patient_allergies, :=, :string
    end
  end
  </code></pre>
  
  <p>I dont think the command went well. I see an '=' in the above file. I do not think it should be there. Can someone tell me if I missed anything?</p>
  
  <p>If so , how do I undo the above?</p>