Sometime you may need to modify multiple table columns in a migration. Here is my best practice when you need to update multiple table columns in a migration.

UpdateUsers1.rb

#The example below will easily get screwed up when your statements fails in the middle of migrations, i.e., fail after the line 9.
#It will require manual fix to recover your table to healthy state.   
#MySQL support does not support rollbacking DDL statements (Postgres does it though).

class UpdateUsers < ActiveRecord::Migration
  def change
    add_column(:users, :type, :string)
    remove_column(:users, :first_name)
    remove_column(:users, :last_name)
    rename_column(:users, :dob, :birth_date)
  end
end

UpdateUsers2.rb

#The better approach is using change_table command and turn :bulk option to true.
#With bulk option, change_table will generate a single ALTER TABLE statement, 
#which is much faster and this migration will fail UNLESS all modification are successful.
#More information, please check the api at http://apidock.com/rails/ActiveRecord/ConnectionAdapters/Table

class UpdateUsers < ActiveRecord::Migration
  def change
    change_table :users, :bulk => true do |t|
      t.column :type, :string
      t.remove :first_name
      t.remove :last_name
      t.rename :dob, :birth_date
    end
  end
end