SQL Tuning [Electronic resources] نسخه متنی

8.4 Summary

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.