PHP生成CSV文件只能第一次工作

我有以下脚本:

<?php
//Define basepath for codeigniter
define('BASEPATH', '/');
//Include constants.php config file from codeigniter
require_once "../../my_manager/system/application/config/constants.php";
//Check username and password from GET
if( $_GET['username'] != IMPORT_USERNAME || $_GET['password'] != IMPORT_PASSWORD )
{
    header('HTTP/1.0 401 Unauthorized');
    echo "Denied Access";
    return; 
}
//running scripts
include 'export_table1.php';
include 'export_table2.php';
include 'export_table3.php';
include 'export_table4.php';
?>

每个导出如下所示:

<?php
//$host="localhost";
$host="";
$user="";
$pass="";
$db_name="";
$table="table1";
$conn = mysqli_connect($host,$user,$pass,$db_name) or die("Connection Error");
$query = "SELECT * FROM $table ORDER BY ID";
$result = mysqli_query($conn,$query) or die("sql error");
if(mysqli_num_rows($result)>0)
{
$csv = "";
$row = mysqli_fetch_assoc($result);
$delim = "";
//retrieving first line fields
foreach($row as $k => $v)
{
$csv .= $delim . '"' . str_replace('"', '""', $k) . '"';
$delim= ";";
}
$csv .= "'n";
//retrieving value into fields
while($row = mysqli_fetch_assoc($result))
{
$delim = "";
foreach($row as $v)
{
$csv .= $delim . '"' . str_replace('"', '""', $v) . '"';
$delim = ";";
}
$csv .= "'n";
}
header("Content-type: text/csv");
header("Content-Disposition: attachment; filename=".$table.".csv");
echo $csv;
exit
}
else
{
echo "No records";
}
 exit
?>

问题是，只有第一个脚本被触发，所以我只能得到第一个表下载到csv文件。如果我首先启动表2导出，则只触发表2导出。我怎么能做到呢?提前感谢!