That means you can use them to index selected elements and attributes that are frequently used in predicates and joins.

这意味着可以使用它们来索引频繁在谓词和连接中使用的所选择的元素和属性。

youdao

The latter option with XMLCAST can be useful for joins on XML values which occur only once per document, because it allows the usage of a relational index on unit.manager.

查询 8 使用了 XMLCAST，对于各文档只需进行一次 XML 值连接非常有用，因为它允许在 unit.manager 上使用关系型索引。

youdao

For example, using the sample data in Figure 1, the following index idx1 would be useful for look-ups and joins based on author IDs across all documents in the XML column bookinfo of the table books.

例如，使用图1中的示例数据，可以根据author id使用下面的索引idx 1对表books的xml列bookinfo中的所有文档进行查找和连接。

youdao

The jump in the PCI index joins positive signals from other indexes including manufacturing, manufacturing shipments and retail sales, all of which have been rising steadily from mid-2009 lows.

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