因为不能跨超类和子类的字段来建立复合索引，如果需要按这些列进行查询，性能会受影响。

Because you can't create a composite database index using columns across the super and a subclass, the performance will suffer if you need to query on such columns.

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后端搜索器和UI搜索器区别太大，因此我们不得不为它构造另一个复合索引，依次使用isold、participantCode和transactionType。

The backend search is too different from the UI searches, so we had to make another composite index for it using the order isoId, participantCode and transactionType.

youdao

提出了一种语义向量算法，构建了图像语义关键词网络，实现了图像底层视觉特征和语义的复合索引。

The thesis presents a semantic vector algorithm, builds up the network of image semantic keywords, and realizes the composite retrieval of the image low-level feature and semantics characteristics.

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