database.php

...
$active_group = "default";
$active_record = TRUE;

$db['oracle']['hostname'] = '(DESCRIPTION =(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)
(HOST = 192.168.1.1)(PORT = 1521)))(CONNECT_DATA =(SERVICE_NAME = DATUBASIEN_IZENA)))';
$db['oracle']['username'] = "ERABILTZAILEA";
$db['oracle']['password'] = "PASAHITZA";
$db['oracle']['database'] = "";
$db['oracle']['dbdriver'] = "oci8";

$db['oracle']['dbprefix'] = "";
$db['oracle']['pconnect'] = TRUE;
$db['oracle']['db_debug'] = TRUE;
$db['oracle']['cache_on'] = FALSE;
$db['oracle']['cachedir'] = "";
//$db['oracle']['char_set'] = "utf8";
//$db['oracle']['dbcollat'] = "utf8_general_ci";

$db['mysql']['hostname'] = '192.168.1.2';
$db['mysql']['username'] = "ERABILTZAILEA";
$db['mysql']['password'] = "PASAHITZA";
$db['mysql']['database'] = "cmsforms";
$db['mysql']['dbdriver'] = "mysql";
$db['mysql']['dbprefix'] = "";
$db['mysql']['pconnect'] = TRUE;
$db['mysql']['db_debug'] = TRUE;
$db['mysql']['cache_on'] = FALSE;
$db['mysql']['cachedir'] = "";
$db['mysql']['char_set'] = "utf8";
$db['mysql']['dbcollat'] = "utf8_general_ci";
...

Oin geure programan:

$oracle = $this->load->database('oracle', true);
$mysql = $this->load->database('mysql', true);

$query = $mysql->query('select * from taula');
$result = $query->result();
echo 'mysql: ';
var_dump($result);

$query = $oracle->query('select * from taula');
$result = $query->result();
echo 'oracle: ';
var_dump($result);