> I don’t trust the typical Calcite user to be able to write a sub-class that >works correctly and efficiently.
People who sub-class RelMetadataQuery are almost those who has deep customization of the calcite-core, for example, the MaxCompute or the Apache Flink. We may assume that it is not that easy to implement a perfect extension of RelMetadataQuery, but let’s open this chance to them, give them the freedom to extension, we should have the confidence. Best, Danny Chan 在 2019年10月22日 +0800 AM9:58，dev@calcite.apache.org，写道： > > I don’t trust the typical Calcite user to be able to write a sub-class that > works correctly and efficiently.
