Another little doubt:

I've already asked that in #postgresql at freenode, but I didn't
understand well.

I have two tables:

Books
- book_id
- name

Authors
- author_id
- name

One book can have many authors and one author can have many books. To
make that possible, I need a third table:

Intermediate
- book_id
- author_id

My question is about the indexes in Intermediate table. Is the
following index:

CREATE UNIQUE INDEX foo ON Intermediate(book_id, author_id);

enough for every query I want to perform? Or should I need

CREATE UNIQUE INDEX foo ON Intermediate(book_id, author_id);
CREATE UNIQUE INDEX bar ON Intermediate(book_id);
CREATE UNIQUE INDEX baz ON Intermediate(author_id);

too?

Thank you very much. Bye!