php百万数据导出 存为excel表格

$DB_TBLName = $this->request->param('table');

// 设置php可使用内存
ini_set("memory_limit", "1024M");
//设置执行时间最大值
set_time_limit(0);

$savename = date("YmjHis");

//链接数据库 设置字符集
$Connect = mysqli_connect('localhost','root','root','dbname') or die("数据库连接失败");
mysqli_query($Connect,"set names utf8");

$file_type = "vnd.ms-excel";
$file_ending = ".xls";
header("content-type: application/$file_type;charset=big5");
header("content-disposition: attachment; filename=".$savename.$file_ending);
//header("Pragma: no-cache");

$now_date = date("Y-m-j H:i:s");
$title = "数据库名:excle,数据表:$DB_TBLName,备份日期:$now_date";

$sql = "Select * from $DB_TBLName";

$result = @mysqli_query($Connect,$sql) or die(mysqli_error($Connect));

echo iconv("UTF-8", "GB2312", ("$title\n"));
$sep = "\t";

$name = mysqli_fetch_fields($result);

for ($i=0;$i<mysqli_num_fields($result);$i++){
    echo $name[$i]->name."\t";
}

print("\n");
$i = 0;
while($row = mysqli_fetch_row($result)) {
    $schema_insert = "";
    for($j=0; $j<mysqli_num_fields($result);$j++) {
        if(!isset($row[$j]))
            $schema_insert .= "NULL".$sep;
        elseif ($row[$j] != "")
            $schema_insert .= "$row[$j]".$sep;
        else
            $schema_insert .= "".$sep;
    }

    $schema_insert = str_replace($sep."$", "", $schema_insert);

    $schema_insert .= "\t";
    print(iconv("UTF-8", "GB2312", trim($schema_insert)));
    print "\n";
    $i++;
}