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    • 14. 发明授权
    • Techniques of optimizing queries using NULL expression analysis
    • 使用NULL表达式分析优化查询的技术
    • US07739219B2
    • 2010-06-15
    • US11517969
    • 2006-09-08
    • Zhen Hua LiuMuralidhar KrishnaprasadHui Joe ChangAnand ManikuttyJames W. WarnerVikas AroraSusan Kotsovolos
    • Zhen Hua LiuMuralidhar KrishnaprasadHui Joe ChangAnand ManikuttyJames W. WarnerVikas AroraSusan Kotsovolos
    • G06F17/30
    • G06F17/30454
    • A method for optimizing queries is described. A query, which includes a first expression for determining whether each of a set of values evaluates to NULL or NOT NULL, is received. At compile-time, a first representation of the query is generated, where the first representation indicates that the query is to be performed based on the first expression. Based on the first expression, a second expression is determined. The second expression is such that the first expression would evaluate to any NOT NULL value if and only if the second expression would evaluate to any NOT NULL value. The second expression, when evaluated, is much more computationally efficient compared with the evaluation of the first expression. Based on the first representation, a second representation of the query is generated, where the second representation indicates that the query is to be performed based on the second expression. Thereafter, the query is executed based on the second representation.
    • 描述用于优化查询的方法。 一个查询,其中包含一个第一表达式,用于确定一组值中的每一个是否计算为NULL或NOT NULL。 在编译时,生成查询的第一个表示,其中第一个表示指示要根据第一个表达式执行查询。 基于第一个表达式,确定第二个表达式。 第二个表达式使得当且仅当第二个表达式计算为任何NOT NULL值时,第一个表达式将求值为任何NOT NULL值。 第二个表达式与评估第一个表达式相比,计算效率要高得多。 基于第一表示,生成查询的第二表示,其中第二表示指示将基于第二表达式执行查询。 此后,基于第二表示执行查询。
    • 17. 发明授权
    • Techniques of efficient XML query using combination of XML table index and path/value index
    • 使用XML表索引和路径/值索引的组合的高效XML查询技术
    • US09436779B2
    • 2016-09-06
    • US11601146
    • 2006-11-17
    • Zhen Hua LiuMuralidhar KrishnaprasadHui Joe ChangVikas Arora
    • Zhen Hua LiuMuralidhar KrishnaprasadHui Joe ChangVikas Arora
    • G06F17/30
    • G06F17/30917G06F17/30463G06F17/30911
    • A mechanism is provided for accessing XML data in a database system using a combination of a XML Table Index table and a XML Path Index table. By using a combination of a XML Table Index and a XML Path Index, both selection access and navigational access involved in a query can be optimized. For example, the XML Table Index gives the database system an ability to readily evaluate the predicate expression, thereby improving the selection access. Moreover, in some embodiments, the selection access can be further improved by using secondary indexes on columns contained in the XML Table Index table. In a complementary manner, the XML Path Index table gives the database system an ability to navigate to a specific location given a path expression, thereby improving the navigational access. Thus, by combining both tables, both selection and navigational accesses are improved.
    • 提供了一种机制,用于使用XML表索引表和XML路径索引表的组合来访问数据库系统中的XML数据。 通过使用XML表索引和XML路径索引的组合,可以优化查询中涉及的选择访问和导航访问。 例如,XML表索引使数据库系统能够容易地评估谓词表达式,从而改善选择访问。 此外,在一些实施例中,可以通过在XML表索引表中包含的列上使用辅助索引来进一步改进选择访问。 以互补的方式,XML路径索引表给数据库系统一个导航到指定路径表达式的特定位置的能力,从而改善导航访问。 因此,通过组合两个表,提高了选择和导航访问。