Drupal 7: acceso a bases de datos externas

<?php
$databases = array();
$databases['default']['default'] = array(
  // Drupal's default credentials here.
  // This is where the Drupal core will store it's data.
);
$databases['my_other_db']['default'] = array(
  // Your secondary database's credentials here.
  // You will be able to explicitly connect to this database from your modules.
);
?>

<?php
// Use the database we set up earlier
db_set_active('my_other_db');
 
// Run some queries, process some data
// ...
 
// Go back to the default database,
// otherwise Drupal will not be able to access it's own data later on.
db_set_active();
?>

<?php
  $other_database = array(
      'database' => 'databasename',
      'username' => 'username', // assuming this is necessary
      'password' => 'password', // assuming this is necessary
      'host' => 'localhost', // assumes localhost
      'driver' => 'mysql', // replace with your database driver
  );
  // replace 'YourDatabaseKey' with something that's unique to your module
  Database::addConnectionInfo('YourDatabaseKey', 'default', $other_database);
  db_set_active('YourDatabaseKey');
 
  // execute queries here
 
  db_set_active(); // without the paramater means set back to the default for the site
  drupal_set_message(t('The queries have been made.'));
?>