CHAPTER 4System and Object Statistics

System and object statistics are essential because they describe both the system running the database engine and the data stored in the database. In fact, a query optimizer that is aware of only the SQL statement to be processed and the structure of the objects referenced by the SQL statement is not able to provide efficient execution plans. Simply put, it has to be able to quantify the amount of data to be processed.

The aim of this chapter is twofold. First, it describes available system and object statistics. What the query optimizer does with them will be described here for only a few cases. The purpose of most statistics will be explained in Chapter 5. This is because the query optimizer uses statistics ...

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