Bruce, It might help, maybe not, but Pragmatic Programmers has a book called SQL AntiPatterns with Chapter 3 dedicated to tree structures in databases
http://pragprog.com/book/bksqla/sql-antipatterns They show several alternatives to the usual starting point of adjacency lists to describe trees in databases. I don't understand your problem domain of MLM and I guess am not sure why there would be only left and right child nodes at a particular level, I would think a person could sponsor more than 2 people. The book discusses the SQL99 WITH keyword for recursive queries which PostgreSQL supports since 8.,4 as well as alternative ways to express a hierarchy in a table. Hope it is some use. Ron
