Problem to retreive data of a LONG column.

Hello everybody, I've the following function which execute all my queries I pass a parameter
Code :

function exec_query($query)
{
global $mdb2;

if(is_null($query))
{
die("Impossible d'exécuter une requête vide.");
return;
}

//$mdb2 = connect_DB();
$res=& $mdb2->query($query);
if (PEAR::isError($res))
{
echo $query;
die("Erreur lors de l'exécution de la requête : ". $res->getMessage()."-".$mdb2->getMessage());
}

$arr_res=$res->fetchAll(MDB2_FETCHMODE_ASSOC);
return $arr_res;
}

I'm connected to an Oracle database. When I call this function with a query which will return me a LONG coloum data, the array is returned empty.
I've done some verification and I've issued that the problem is that PEAR can't treat LONG columns.
Can anyone tell me how to do to resolve this problem.
Many thanks in advance.
Best regards.