Sorting is required when no index satisfies the requested ordering of fetched rows, or the optimizer determines that a sort is less expensive than an index scan.

如果没有索引满足所取的行的要求顺序，或者优化器断定排序的代价低于索引扫描，那么就需要进行排序。

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Typically, a non-matching index scan is chosen by the optimizer when the underlying index provides benefits such as index-only access, avoids sort, or some similar benefit.

通常情况下，在基础索引提供好处(如唯一索引访问、避免排序或一些类似的好处)时，可通过优化器选择非匹配索引扫描。

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Therefore, when deciding which join method to choose, the optimizer balances the sort cost and the performance benefit for the inner table scan to drive the decision.

因此，在决定选择哪种联接方法时，优化器为内部表扫描平衡排序成本和性能优势以便促进决策。

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"In the old days, this was the sort of stuff the IRA would kill for, today an enemy could scan some photos and gain an insight into a base, " said Mr Black.

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Dr Hinterdorfer points out that, theoretically, any sort of molecule can be tethered to the end of the microscope's tip and used to scan for the presence of another molecule for which it has a particular affinity.

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