静态文件、模板和代码都来自磁盘，组成数据库的数据表和索引也来自磁盘。

Static files, templates, and code are served from disk, as are the data tables and indexes that make up the database.

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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。

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.

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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。

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.

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