如何在Codeigniter中加入三个表

I'm using codeigniter framework to develop one music cms. i have 3 tables in mysql database, Currently im working in "Album" Table and "Model, Controller". i want to SELECT "Album" Table 1 and JOIN "Album" -> "cat_id" with "Category" -> "cat_id", and fetch all categories records.I'm using codeigniter framework to develop one