But be careful with this tactic; you do not want to replicate a table in an index by including all of the table's columns in the index key.

但是要小心使用这一策略；您并不想以在索引键中包含数据表所有列的方式在索引中复制一个表。

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An index only scan is an index access that is not followed by a table access because the index itself contains all the requested data.

仅扫描索引是未包含表访问的索引访问，因为索引本身包含了所有被请求的数据。

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The optimizer ACTS based on statistical data about the number of rows in a table, the use of space by a table or index, and other information.

优化器的操作基于数据表中的行数、数据表或索引使用的空间以及其他信息的相关统计数据。

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The four iShares index funds (see table below), issued by the Global Investors unit of Barclays (nyse: BCS - news - people ), sport a rock-bottom expense ratio of 0.15 versus open-end bond fund averages of around 1.00 and the 0.20 charged by low-cost leader Vanguard.

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