How to use: INNER JOINS & IN



I am not clear about how to use INNER JOINS and IN(…) sub query in
rails. Is there a good tutorial which helps newbies step by step ?

I have a

model Library
model Authors
model Fictions

The relation maybe explained as:

Library has many fiction books
authors have many fictions

The authors table has information like full name, period of life,
country etc.

In that case, I want to select fictions from library, where the authors
are from countries US and FRANCE