If you want the federated server to push down the evaluation of a function to a relational data source, you must use a function mapping for that data source.
如果您希望联邦服务器将函数的计算下推到一个关系数据源，那么必须使用那个数据源的一个函数映射。
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Infoq: You have a great criteria table for evaluating Open Source products, but it does not contain "Adherence to standards" as evaluation criteria.