Explain rule-based optimizer and cost-based optimizer

Explain rule-based optimizer and cost-based optimizer.

Oracle decides how to retrieve the necessary data whenever a valid SQL statement is processed.

This decision can be made using one of two methods:

Rule Based Optimizer

If the server has no internal statistics relating to the objects referenced by the statement then the RBO method is used.
This method will be deprecated in the future releases of oracle.

Cost Based Optimizer

The CBO method is used if internal statistics are present.
The CBO checks several possible execution plans and selects the one with the lowest cost based on the system resources.
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