title: Rails creating migration to add columns to table causes error when running rake db:migrate
body: <p>I have a model created called "users" and i created a new migration to add some columns to the  users table. Now when i run rake db:migrate, I get the error below b/c it's trying to create the users table again</p>
  
  <pre><code>$ rake db:migrate
  ==  DeviseCreateUsers: migrating ==============================================
  -- create_table(:users)
  rake aborted!
  An error has occurred, all later migrations canceled:
  
  Mysql::Error: Table 'users' already exists: CREATE TABLE `users`.....
  </code></pre>
  
  <p>Why is it trying to create the table again?</p>
  
  <p>Here's the command i used to create the new migration</p>
  
  <pre><code>$ rails generate migration AddDetailsToUsers home_phone:decimal cell_phone:decimal work_phone:decimal birthday:date home_address:text work_address:text position:string company:string
  </code></pre>
  
  <p>The new migration looks like this:</p>
  
  <pre><code>class AddDetailsToUsers &lt; ActiveRecord::Migration
    def change
      add_column :users, :home_phone, :decimal
      add_column :users, :cell_phone, :decimal
      add_column :users, :work_phone, :decimal
      add_column :users, :birthday, :date
      add_column :users, :home_address, :text
      add_column :users, :work_address, :text
      add_column :users, :position, :string
      add_column :users, :company, :string
    end
  end
  </code></pre>
  
  <p><strong>EDIT</strong></p>
  
  <p>20120511224920_devise_create_users</p>
  
  <pre><code>class DeviseCreateUsers &lt; ActiveRecord::Migration
    def change
      create_table(:users) do |t|
        ## Database authenticatable
        t.string :email,              :null =&gt; false, :default =&gt; ""
        t.string :username,           :null =&gt; false, :default =&gt; ""
        t.string :encrypted_password, :null =&gt; false, :default =&gt; ""
  
        ## Recoverable
        t.string   :reset_password_token
        t.datetime :reset_password_sent_at
  
        ## Rememberable
        t.datetime :remember_created_at
  
        ## Trackable
        t.integer  :sign_in_count, :default =&gt; 0
        t.datetime :current_sign_in_at
        t.datetime :last_sign_in_at
        t.string   :current_sign_in_ip
        t.string   :last_sign_in_ip
  
        ## Encryptable
        # t.string :password_salt
  
        ## Confirmable
        # t.string   :confirmation_token
        # t.datetime :confirmed_at
        # t.datetime :confirmation_sent_at
        # t.string   :unconfirmed_email # Only if using reconfirmable
  
        ## Lockable
        # t.integer  :failed_attempts, :default =&gt; 0 # Only if lock strategy is :failed_attempts
        # t.string   :unlock_token # Only if unlock strategy is :email or :both
        # t.datetime :locked_at
  
        ## Token authenticatable
        # t.string :authentication_token
  
  
        t.timestamps
      end
  
      add_index :users, :email,                :unique =&gt; true
      add_index :users, :reset_password_token, :unique =&gt; true
      # add_index :users, :confirmation_token,   :unique =&gt; true
      # add_index :users, :unlock_token,         :unique =&gt; true
      # add_index :users, :authentication_token, :unique =&gt; true
    end
  end
  </code></pre>
  
  <p>20120619023856_add_name_to_users</p>
  
  <pre><code>class AddNameToUsers &lt; ActiveRecord::Migration
    def change
      add_column :users, :first_name, :string
      add_column :users, :last_name, :string
    end
  end
  </code></pre>
  
  <p>20121031174720_add_details_to_users.rb</p>
  
  <pre><code>class AddDetailsToUsers &lt; ActiveRecord::Migration
    def change
      add_column :users, :home_phone, :decimal
      add_column :users, :cell_phone, :decimal
      add_column :users, :work_phone, :decimal
      add_column :users, :birthday, :date
      add_column :users, :home_address, :text
      add_column :users, :work_address, :text
      add_column :users, :position, :string
      add_column :users, :company, :string
    end
  end
  </code></pre>