Detailed explanation of the method of exporting from database to .csv file in PHP

public function export(){
 // 从数据库中获取数据，为了节省内存，不要把数据一次性读到内存，从句柄中一行一行读即可
 // 输出Excel文件头，可把user.csv换成你要的文件名
 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();
   // 打开PHP文件句柄，php://output 表示直接输出到浏览器
 $fp = fopen('php://output', 'a');

 // 输出Excel列名信息
 $head = array("订单号","订单名称","购买数量","单价","总价","联系人姓名","联系人电话","邮编","详细地址","微信优惠金额","余额支付金额","真实支付金额","特卖类型（2为实物）","支付时间","支付类型","第三方支付id","是否是手机支付","是否支付","订单状态");
 foreach ($head as $i => $v) {
 // CSV的Excel支持GBK编码，一定要转换，否则乱码
   $head[$i] = iconv('utf-8', 'gbk', $v);
 }

 // 将数据通过fputcsv写到文件句柄
 fputcsv($fp, $head);

 // 计数器
 $cnt = 0;
 // 每隔$limit行，刷新一下输出buffer，不要太大，也不要太小
 $limit = 500;
 // 逐行取出数据，不浪费内存
 $count = count($stmt);
 for($t=0;$t<$count;$t++) {

 $cnt ++;
 if ($limit == $cnt) { //刷新一下输出buffer，防止由于数据过多造成问题
   ob_flush();
   flush();
   $cnt = 0;
 }
 $row = $stmt[$t];
foreach ($row as $i => $v) {
  if($i==&#39;pay_time&#39;){
     $v=date("Y-m-d,H:i:s",$v);
  }
   $row[$i] = iconv(&#39;utf-8&#39;, &#39;gbk&#39;, $v);
 }
 fputcsv($fp, $row);
 }
   fclose($fp);
 }