public function export(){
 // 從數據庫中獲取數據，為了節省內存，不要把數據一次性讀到內存，從句柄中一行一行讀即可
 // 輸出Excel文件頭，可把user.csv換成你要的文件名
 header('Content-Type: application/vnd.ms-excel');
 header('Content-Disposition: attachment;filename="order.csv"');
 header('Cache-Control: max-age=0');
 $where=array(
   "paid"=>1,
   "pay_type"=>array("NEQ","offline"),
   "status"=>array("lt",3),
 );
 $stmt = M("Group_order")->field("order_id,order_name,num,price,total_money,contact_name,phone,zipcode,adress,wx_cheap,balance_pay,payment_money,tuan_type,pay_time,pay_type,third_id,is_mobile_pay,paid,status")->where($where)->order("order_id DESC")->limit(1000)->select();
   // 打開PHP文件句柄，php://output 表示直接輸出到瀏覽器
 $fp = fopen('php://output', 'a');

 // 輸出Excel列名信息
 $head = array("訂單號","訂單名稱","購買數量","單價","總價","聯系人姓名","聯系人電話","郵編","詳細地址","微信優惠金額","余額支付金額","真實支付金額","特賣類型（2為實物）","支付時間","支付類型","第三方支付id","是否是手機支付","是否支付","訂單狀態");
 foreach ($head as $i => $v) {
 // CSV的Excel支持GBK編碼，一定要轉換，否則亂碼
   $head[$i] = iconv('utf-8', 'gbk', $v);
 }

 // 將數據通過fputcsv寫到文件句柄
 fputcsv($fp, $head);

 // 計數器
 $cnt = 0;
 // 每隔$limit行，刷新一下輸出buffer，不要太大，也不要太小
 $limit = 500;
 // 逐行取出數據，不浪費內存
 $count = count($stmt);
 for($t=0;$t<$count;$t++) {

 $cnt ++;
 if ($limit == $cnt) { //刷新一下輸出buffer，防止由于數據過多造成問題
   ob_flush();
   flush();
   $cnt = 0;
 }
 $row = $stmt[$t];
foreach ($row as $i => $v) {
  if($i=='pay_time'){
     $v=date("Y-m-d,H:i:s",$v);
  }
   $row[$i] = iconv('utf-8', 'gbk', $v);
 }
 fputcsv($fp, $row);
 }
   fclose($fp);
 }