您刚刚回答了自己的问题 :)你可以这样做:

You've just answered your own question :) You can do something like this:

$query = $this->db->get();
$ret = $query->row();
return $ret->campaign_id;

您可以在此处阅读更多相关信息:http://www.codeigniter.com/user_guide/database/results.html

You can read more about it here: http://www.codeigniter.com/user_guide/database/results.html