[PHP & MySQL] Problema con include

[Sbarboff2005]

Ciao a tutti,

non riesco a capire dove sta l'errore:

Notice: Undefined index: lg_expire in C:\Program Files\Xampp\htdocs\tsl-psy\inc\impostazioni.inc.php on line 8

if(isset($_GET['page']) && $_GET['page'] == "impostazioni") {
include"./config.inc.php";
mysql_select_db($database_name, $conn) or die (mysql_error());
$sql_imp = "SELECT * FROM tb_login WHERE lg_id = '".$_GET['usr']."'";
$query_imp = mysql_query($sql) or die (mysql_error());
$result_imp = mysql_fetch_assoc($query_imp);
 echo $result_imp['lg_expire'];
}