Short of a brute-force analysis of huge numbers of execution plans, perfect optimization of queries with many tables is beyond the state-of-the-art. Even with advances in the art, perfect optimization is likely to remain beyond the scope of manual tuning methods. If you make your living tuning SQL, this is actually good news: you are not about to be put out of business! The problem of SQL tuning is complex enough that this result is not surprising. What is surprising, perhaps, is that by focusing on robust execution plans and a few fairly simple rules, you can come close to perfect optimization for the overwhelming majority of queries. Local information about the nodes in a join diagramin particular, their filter ratiosturns out to be enough to choose an efficient, robust execution plan, without considering the problem in its full combinatorial complexity.