jinxing64 commented on issue #1469: [CALCITE-3367] Add AntiJoinRule to convert project-filter-join-aggreg… URL: https://github.com/apache/calcite/pull/1469#issuecomment-535064092 @julianhyde @hsyuan @danny0405 Thanks a lot for discussion, which helps a lot for my understanding. >A boolean context IN or existential subquery should be decorrelated directly into SEMI/ANTI SEMI join. I think this idea makes a lot of sense. It is more straightforward to transform IN/EXIST to SEMI/ANTI Join when decorrelation. But SemiJoinRule also provides a way to optimize `Join(Scan(emp), Aggregate(Scan(dept)))` to a simple semi-join, in which there's no operation of aggregation and only needs to output columns of the right hand side. Think about the scenario that `dept` is almost unique but not exactly unique. Removing the Aggregate will gain some benefit.
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