Views and external DB Oracle my Drupal 6 installation is on a MySql server, while my own custom database is on Oracle.
I have made a custom module that can read and write data into my external database, but i would like to use Views module to handle the data to show. I know that I can programmatically build views, but i don't know if I can build one for Oracle DB while Drupal is on Mysql.
You can create a view to a non-drupal table/database but you need to create a connection to it first using either one of the two connector modules: the Data module or the Table Wizard module.

You can also set it up using the Views API with views_hook_data(). (See documentation on views/help/api-tables.html.)

You'll need to add your new database connection settings in your settings file.

// In settings.php for your site
// Your drupal (site) database needs to be called 'default'
$db_url['default'] = 'mysqli://user:pass@host/drupal_db';
$db_url['oracle_db'] = 'mysqli://user:pass@host/other_db';


Then, in your view hook, define the tables the view should have access to. 

$data[$table]['table']['base'] = array(
    'field' =&gt; 'Primary key',
    'title' =&gt; t('Field name'),
    'help' =&gt; t('Field description'),
    'database' =&gt; 'oracle_db',
    'weight' =&gt; -10,
);