Switch database based on parameter

You can configure multiple database groups in your /application/config/database.php (or /application/config/{ENVIRONMENT}/database.php) file: http://www.codeigniter.com/user_guide/da...ation.html

Then you can load a specific database group by manually connecting to the database and passing in the group name: http://www.codeigniter.com/user_guide/da...a-database

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide