In fact, this is not a difficult task. Because I just started CI, it still took a lot of trouble. Fortunately there is a manual.
Find the database configuration file and add the connection information of a new library. $config[XX].
In the controller,
a) $this->xx = $this->load->database('XX', TRUE) tip:XX represents the key name of the database information array you configured , it is recommended to set it to TRUE later, which means returning the connection ID and enabling the ActionRecord class
b) Then in the controller you can use $this->xx->query() to query your other library data. There is no need to create a model file for your other library