In the first three installments of this series I outlined the mechanisms used by Oracle to analyze a very simple query. Sticking with the informal approach, I’m going to look at the high-level strategy the optimizer takes when handling a more complex query. To do this I’ll be looking at query blocks, scratching the surface of query transformation, explaining why it’s a… Read more
When we examine an execution plan, we’re usually trying to work out the mechanical steps that Oracle took to produce a result set. When we do this, it’s important to remember that the text that Oracle optimized wasn’t necessarily the same as the statement we originally wrote. Oracle may have transformed our statement before passing it through the optimization engin… Read more
