<?php
$servername = "rdbms.strato.de";
$username = "user";
$password = "pw";
$dbname = "name";
$key = $_GET['key'];
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
	die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT * FROM table WHERE urlkey='$key'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // output data of each row
	while($row = $result->fetch_assoc()) {
      header("Location:".$row['url']);
		  exit;
	}
} else {
	header("Location:/error");
	exit;
}
$conn->close();
?>