    # File lib/active_record/vendor/mysql.rb, line 219
      def change_user(user="", passwd="", db="")
        if @pre_411
          data = user+"\0"+scramble(passwd, @scramble_buff, @protocol_version==9)+"\0"+db
        else
          data = user+"\0"+scramble41(passwd, @scramble_buff)+db
        end
        pkt = command COM_CHANGE_USER, data
        handle_auth_fallback(pkt, passwd)
        @user = user
        @passwd = passwd
        @db = db
      end