Canonical paper on SQL query optimization. By Patricia Selinger. The dynamic programming algorithm for determining join order proposed in this paper still forms the basis for most of the query optimizers used in modern relational systems.
Thank you for posting this. I have the book Database System Concepts and I am yet to get to the point to relational algebra optimisation.
My SQL implementation I planned to do a hash join with the smaller table. It was very rudimentary. I don't have indexes though.