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Troubleshooting Oracle Performance by Christian Antognini

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CHAPTER 10Optimizing Joins

When a SQL statement references several tables, the query optimizer has to determine, in addition to the access path for each table, which order the tables are joined in and which join methods are used. The goal of the query optimizer is to minimize the amount of processing by filtering out unneeded data as soon as possible.

This chapter starts by defining key terms and explaining how the three basic join methods (nested loop join, merge join, and hash join) work. Some advice follows on how to choose the join methods. Finally, the chapter describes optimization techniques such as partition-wise joins and transformations.

Note In this chapter, several SQL statements contain hints. This is done not only to show you ...

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