Kann in DB gespeicherte Daten nicht mehr auslesen

<?php
error_reporting( -1 );
ini_set('display_errors', TRUE);  

session_start (); 
#include ("checkuser.php");  
#echo $_GET ['id']; 
#echo $_SESSION["user_id"]; 
if(isset($_GET['id']) && isset ($_SESSION["user_id"]))    
{
  $connectionid = mysql_connect ("localhost", "user", "password");  
  #echo $_GET['todo']; 
  if($_GET['todo']==download)  
  {
      $id_files=$_GET['id'];  
      if (!mysql_select_db ("intranet", $connectionid)) die ("Keine Verbindung zur Datenbank");   
        $sql = "SELECT content, type, name, size FROM upload WHERE id=$id_files";  
        $result = mysql_query($sql, $connectionid);
      echo $sql;
      if ( !$result ) die('MySQL-Fehler:' . mysql_error());     
      $data = mysql_result($result, 0, "content");  
      $name = mysql_result($result, 0, "name");  
      $size = mysql_result($result, 0, "size");  
      $type = mysql_result($result, 0, "type");  
        
      #header("Content-type: $type"); 
      #header("Content-length: $size"); 
      #header("Content-Disposition: attachment; filename=$name"); 
      #header("Content-Description: PHP Generated Data"); 
      echo $data;
      
    }
    elseif ($_GET['todo']==delete)  
    {
        $id_files=$_GET['id'];  
        if (!mysql_select_db ("intranet", $connectionid)) die ("Keine Verbindung zur Datenbank");   
      $sql = "DELETE FROM upload WHERE id=$id_files";  
        $result = mysql_query($sql, $connectionid);
        if ( !$result ) die('MySQL-Fehler:' . mysql_error());     
     }
    mysql_close($connectionid);
    Header('Location: projekt_portal.php');  
  }
?>

<?php
#error_reporting( -1 );
error_reporting(E_ALL);
ini_set('display_errors', TRUE);  

session_start (); 
#include ("checkuser.php");  
#echo $_GET ['id']; 
#echo $_SESSION["user_id"]; 
if(isset($_GET['id']) && isset ($_SESSION["user_id"]))    
{
	$connectionid = mysqli_connect ("localhost", "intranet", "intranet");  
	#echo $_GET['todo']; 
	if($_GET['todo']=='download')  
	{
			$id_files=$_GET['id'];  
			if (mysqli_connect_errno($connectionid)) {
    			echo "Failed to connect to MySQL: " . mysqli_connect_error();  
				}
	  		$sql = "SELECT 'content', 'type', 'name', 'size' FROM upload WHERE 'id'=$id_files";  
	  		var_dump( $sql);
	  		if ($result = mysqli_query($connectionid, $sql)) {

		    /* fetch associative array */
    		while ($row = mysqli_fetch_assoc($result)) {
        			$name = $row["name"];  
        			$size =  $row["size"];  
        			$type =  $row["type"];  
        			$data=  $row["content"];  
        	}

    		/* free result set */
    		mysqli_free_result($result);
			}

			header("Content-type: $type");  
			header("Content-length: $size");  
			header("Content-Disposition: attachment; filename=$name");  
			header("Content-Description: PHP Generated Data");  
			echo $data;
	}
	  mysqli_close($connectionid);
	  Header('Location: projekt_portal.php');  
  }
?>

<?php 
session_start (); 
// DB
$link = mysqli_connect("localhost", "intranet", "intranet","intranet");   

if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());  
    exit();
}

if (isset($_GET['id']) &&  isset ($_SESSION["user_id"])) {   
	if($_GET['todo']=='download'){  
		// SQL String
		$sql = sprintf("SELECT * FROM upload WHERE id = '%s' LIMIT 1", mysqli_real_escape_string($link,$_GET['id']));  
		if ($result = mysqli_query($link, $sql)) {

				/* fetch associative array */
				while ($row = mysqli_fetch_assoc($result)) {
					printf ("%s (%s)\n", $row["Name"], $row["CountryCode"]);  
					// Den Browser zum Download zwingen 
					header("Content-type: " . $row["type"]);   
					header("Content-disposition: attachment; filename=".$row["name"].";");   
					header("Content-length: " . $row["size"]);   

					// Daten dekodieren und an den Browser senden 
					echo $row["content"];   

				}

				/* free result set */
				mysqli_free_result($result);
			}
		
		/* close connection */
		mysqli_close($link);
		exit; 
		}
	elseif ($_GET['todo']=='delete') {  
		$sql = sprintf("DELETE FROM upload WHERE id='%s'",mysqli_real_escape_string($link,$_GET['id']));  
	  	$result = mysqli_query($link,$sql);
	  	if ( !$result ) die('MySQL-Fehler:' . mysqli_error($link)); 	  
		}
		Header('Location: http://localhost/extranet/projekt_portal.php');  
} 
?>