然而需要注意的是,先进的优化器在生成一个特定的访问计划时,必然有其原因,所以在应用指南之前,务必理解是什么原因导致查询的性能低下。
However, note that the state-of-the-art optimizer has a reason to generate a particular access plan, so it is important to ensure that we understand the inefficiency before we apply the guidelines.
优化器将选择该查询计划,因为其执行的估算成本是所有被估计划中最低的。
The optimizer chose this query plan because the estimated cost for its execution was the lowest among all the evaluated plans.
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