The SQL compiler USES query optimization to select the best performing access path for any given SQL statement (within a reasonable amount of time, of course).

SQL编译器使用查询优化来为任何给定的sql语句选择表现最好的访问路径(当然，这要在合理的时间内)。

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In this paper, first the query technology on database is analysed, then two optimization methods are offered: the disintegration query and the best access path selection.

本文对数据库的查询技术进行分析，给出两种优化方法：分解查询和选择最优存取路径。

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Path expression is one of the core components of most XML query languages. However, there are few researches on the issue of path expression optimization.

路径表达式是XML数据查询语言的核心部分，但是目前针对路径表达式本身进行优化的研究却相对较少。

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