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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From the performance perspective, this is considered a very efficient join operation, because the cost for scanning the inner table is optimal via unique access through a unique index.

从性能的角度来看，这被认为是一个非常有效的联接操作，因为通过贯穿唯一索引的唯一访问扫描内部表的成本是最优的。

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If the inner table does not have an index, the database server will compare the cost of building an index on the table to the cost of a sequential scan, and will choose the one with the least cost.

如果内部表没有索引，那么数据库服务器就会将在表上构建索引的成本与连续扫描的成本进行比较，然后选择成本最低的那一种方法。

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The result is scattered, low-density development that keeps affordable housing out, increases the cost of infrastructure, separates inner-city residents from new jobs in the suburbs, and makes public transport less efficient.

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That is on the fringe of the area that attracts London cost-of-living allowances, so he will not benefit from the special deal for inner London.

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