CHAPTER 2

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The Cost-Based Optimizer

Chapter 1 introduced the CBO. It is the job of the CBO to determine how to set about running your SQL statement. An approach to executing an SQL statement is known as an execution plan, and for very simple statements, there may only be one way to set about doing the task. Therefore, there will only be one possible execution plan. However, for the vast majority of SQL statements, there are different possible execution plans from which the CBO must choose. In English language, optimization means picking the best from a number of options, and in this case the CBO is trying to pick the optimal execution plan from ...

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