MySql Connection Settings:


$active_group = 'default';
$active_record = TRUE;

$db['default']['hostname'] = 'localhost';  //your host
$db['default']['username'] = 'username'; //your database username
$db['default']['password'] = 'password'; //your database password
$db['default']['database'] = 'database_name'; //your database name
$db['default']['dbdriver'] = 'mysql';  //your database type


Oracle Connection Settings:


$active_group = 'default';
$active_record = TRUE;

$tnsname = '(DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
        (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = ORCL)))';

$db['default']['hostname'] = $tnsname ;  //your tns connection
$db['default']['username'] = 'username'; //your schema username
$db['default']['password'] = 'password'; //your schema password
$db['default']['database'] = ''; 
$db['default']['dbdriver'] = 'oci8';  //your database type


Enable extensions for oci8 (Oracle) in php.ini

Open php.ini file and remove ; before the line of extensions as bellows


before:
   ;extension=php_oci8.dll
   ;extension=php_oci8_11g.dll

after:
   extension=php_oci8.dll
   extension=php_oci8_11g.dll