动态索引域功能，可以随时增加新索引域。

Dynamic fields enables on-the-fly addition of new fields.

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树是空间搜索的动态索引树，它的结构是利用多个维中的区间来表示空间数据对象，它是矩形访问的一种有效方法。

R-tree is a dynamic index tree of space search. Its structure use multi-dimensional region to express spatial data object. R-tree is a valid way to visit rectangle.

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如果连接列上不存在索引，那么优化器将选择动态哈希连接。

The optimizer will choose dynamic hash join if none of the joined columns has index.

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