Download dowcument from mysql database

I have uploaded a file into MySQL database while retrieving i am having some problem.

download.php

<?php

    $host="localhost";
                $username="root";
                $password="";
$db_name="application";

$con=mysqli_connect("$host", "$username", "$password","$db_name")or die("Your Connection is in error");

$a =$_GET['contactid'];

$query = "SELECT filename,filetype,filesize,filecontent FROM contact WHERE contactid = '$a' ";

$result = mysqli_query($con,$query) or die('Error, query failed');
list($filename, $filetype, $filesize, $filecontent) = mysqli_fetch_array($result);

header("Content-length: $filesize");
header("Content-type: $filetype");
header("Content-Disposition: attachment; filename=$filename");
echo $filecontent;
exit;
?>

$a which i get from previous screen is not working.Instead if i give contactid = 18.. file is getting downloaded.

previous screen.php

$GET =mysqli_fetch_array(mysqli_query($con,"SELECT contactid,groupname,firstname,lastname,mobile1,mobile2,email1,email2,city,country,designation,companyname,address1,address2,district,pincode,website,others,filename FROM contact WHERE contactid='$a'"));
$contactid   = $GET['contactid'];
$filename  = $GET['filename'];
<a href='download.php?contactid=".$contactid."'><?php echo $filename;?>    </a>