[php]petite petite petite question

Bonjour,

voila mon petit code

<?php if(isset($_POST)) {

$id=mysql_connect("localhost","root","") or die("Echec de connexion au serveur de base de données." . mysql_error);
mysql_select_db("insert");
$v1 = $_POST['username'];
$v2 = $_POST['pwd'];
$sql = "SELECT * FROM users WHERE username ='$v1' and password ='$v2' " ;
$v3 = $data['username'];
$v4 = $data['passeword'];
$test = mysql_query($sql) or die('Erreur SQL !'.$sql.''.mysql_error());

if($data = mysql_fetch_array($test) )
{
if( $v3 = $v1 and $v4 = $v2){
header("location: index.php"); //c ici l'erreur je ve que index.php souvre automatiquemen si la condition est realise
} else if( $v1 = '' and $v2 = '') {
echo "l3azz";
}
} else echo "tla7";
mysql_close();

}
?>