Fast rename columns for MYSQL, very handy for huge tables

active_record_migration_ext.rb

class ActiveRecord::Migration

  def self.fast_add_columns(table_name, new_columns_count)
    tmp_table_name = "#{table_name}_tmp"
    execute "DROP TABLE IF EXISTS #{tmp_table_name}"
    execute "CREATE TABLE #{tmp_table_name} LIKE #{table_name}"

    yield tmp_table_name

    execute("INSERT INTO #{tmp_table_name} SELECT * #{', NULL' * new_columns_count} FROM #{table_name}")
    drop_table table_name
    rename_table tmp_table_name, table_name
  end

  def self.backup(table_name)
    backup_table_name = "#{table_name}_backup"
    execute "DROP TABLE IF EXISTS #{backup_table_name}"
    execute "CREATE TABLE #{backup_table_name} LIKE #{table_name}"
    execute("INSERT INTO #{backup_table_name} SELECT * FROM #{table_name}")
  end

  def self.restore(table_name)
    backup_table_name = "#{table_name}_backup"
    drop_table(table_name) if table_exists?(table_name)
    rename_table backup_table_name, table_name
    execute "DROP TABLE IF EXISTS #{backup_table_name}"
  end

  def self.table_exists?(name)
    ActiveRecord::Base.connection.tables.include?(name)
  end

end

Cool! Thanks!