Optimization
SQL statements are analyzed and optimized before the data is retrieved from the various tables. Optimization occurs during the parsing of the statement. It consists of determining the most efficient method of processing statements. Oracle evaluates the various methods and selects the best method. The best method is then included in the execution plan. Indexes, hints, and variations in the syntax of the statement affect the decisions that the optimizer makes. Thus there are a number of things that may be done to change the execution plan and, hopefully, the performance of the statement.
The Rule-Based Optimizer
Oracle has two optimizers, which are the tools that create and evaluate the various extract methods. The optimizer chooses ...
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