select "author".id, "author".name, count("author_book".book_id) as count_books
from "author"
left join "author_book" on "author_book".author_id="author".id
where (
        select count(books.author_id)
        from "author_book" as books
        inner join author_book as soauthor_book on soauthor_book.book_id=books.book_id and soauthor_book.author_id <> "author".id
        where books.author_id="author".id
    ) = 0
group by "author".id, "author".name
having count("author_book".book_id) > 2