perchè così non mi funziona?

<form name="prova" action="carica_database.php" method="GET"><td align=center align=center><input type=submit style='width:100%;' value='Carica database'> </td>
<td><input type="file" name="database" onchange="this.form.prova.value=this.value.substr( this.form.prova.value.lastIndexOf(/\/\\/)+1)"></td>
</form>