No database selected

<?php
$Serveur = 'xxxxxxx';
$Compte = 'xxxxxxx';
$Passwd = 'xxxxxx';
$Database = 'xxxxxxxx';
$db = mysql_connect($Serveur,$Compte,$Passwd);
mysql_select_db ($Database,$mysql_link);
?>

if(is_numeric($_GET['id']))
{
$id = $_GET['id'];

$db;
$sql = "SELECT * FROM Affichs WHERE id = '$id'";
$req = mysql_query($sql) or die (mysql_error());

$data = mysql_fetch_assoc($req);

$db = mysql_connect($Serveur, $Compte, $Passwd);
mysql_select_db ($Database, $db);

// ou
mysql_select_db ($Database);