CHAPTER 6Execution Plans

An execution plan describes the operations carried out by the SQL engine to execute a SQL statement. Every time you have to analyze a performance problem related to a SQL statement, or simply question the decisions taken by the query optimizer, you must know the execution plan. Without it, you are like a blind man with his cane in the middle of the Sahara Desert, groping around trying to find his way. I can't stress enough that the first thing to do while analyzing or questioning the performance of a SQL statement is to get its execution plan.

Whenever you deal with an execution plan, you carry out three basic actions: you obtain it, you interpret it, and you judge its efficiency. The aim of this chapter is to describe ...

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