生成 Excel 文件时出错

我这里有一个代码，如果单击提交按钮，可以生成一个 excel 文件。该文件填充了来自mysql的数据，当然是基于mysql查询的。在这里：

<?php
require("aacfs.php");
header("Content-type: application/ms-excel");
header("Content-Disposition: attachment; filename=Reservation Summary_sortbydate.xls");
header("Pragma: no-cache");
header("Expires: 0");
$head1="Ayala Aviation Corporation";
$head2="RESERVATION SUMMARY";
$head3="For the period ___________";

$heads="$head1'n$head2'n$head3'n";
$query = "select bdate as 'Date', cliename as 'Client', grpcode as 'Group Code', bperson as 'Contact', reservno as 'Reservation No.', acode as 'Aircraft', fdate as 'Flight Date', itinerary as 'Itinerary', etd as 'ETD', eta as 'ETA', pname as 'Passengers', status as 'Status', cutoff as 'Confirmation Cut-off', adminid as 'Reserved by' from reservation order by bdate";
$result = mysql_query($query);
if($result) {
    $count = mysql_num_rows($result);
   for($i=0; $i<$count; $i++) {
   for ($i = 0; $i < mysql_num_fields($result); $i++) 
    { 
    $schema_insert_rows.=mysql_field_name($result,$i) . "'t"; 
    } 
    $schema_insert_rows.="'n"; 
        while($row = mysql_fetch_row($result)) {
            $line = '';
            foreach($row as $value) {
                if((!isset($value)) OR ($value == "")) {
                    $value = "'t";
                } else {
                    $value = str_replace('"', '""', $value);
                    $value = '"'.$value.'"'."'t";
                }
                $line .= $value;
            }
            $data .= trim($line)."'n";
        }
        $data = str_replace("'r", "", $data);
        if($data == "") {
            $data = "'n(0) Records Found!'n";
        }
    }
    print mb_convert_encoding("$heads'n$schema_insert_rows'n$data", 'UTF-16LE', 'UTF-8');
} else die(mysql_error());
?>

执行需要很长时间，当它最终下载到我的计算机上时，该文件显示一条错误消息："超过最大执行时间 60 秒"。我尝试像这样设置时间限制： set_time_limit(0) 但是我仍然需要很长时间才能下载文件，当我打开下载的文件时，文件本身再次显示另一个错误："允许的内存大小为 134217728 字节已耗尽（尝试分配 133693422 字节）"

我有这个确切的代码，但在另一个 php 文件上运行不同的mysql_query，所以我真的很担心为什么这不起作用。前几天我的工作很顺利，但是当我今天再次检查它时，它显示了此错误。我做错了什么？任何帮助将不胜感激。提前谢谢你！上帝保佑！