Codice PHP:
$sql3 = "SELECT *,$db_g_n_societa.id_societa as blabla FROM $db_g_n_societa LEFT JOIN $db_g_n_societa_serie ON $db_g_n_societa_serie.id_societa = $db_g_n_societa.id_societa WHERE $db_g_n_societa_serie.id_societa IS NULL";
$query3 = mysql_query($sql3);
while ($row3 = mysql_fetch_array($query3)) {
echo $row3['blabla'];
}