xiedeyantu commented on PR #4208:
URL: https://github.com/apache/calcite/pull/4208#issuecomment-2676498493

   > I saw the issue, and I agree that there is a bug, but the question I am 
asking is whether this is the bug or the bug is elsewhere. Perhaps someone who 
knows the intent of the digest can comment. I didn't try to investigate this 
myself by reading the code for digest in other classes.
   
   @mihaibudiu OK, I think this is indeed a summary calculation problem of the 
project. The corresponding relationship between the operator and Vertex will be 
recorded in mapDigestToVertex, which makes it easy to retrieve the 
corresponding operator in findBestExp. If the Project loses the field name 
information during calculation, it will be deduplicated by map and replaced by 
a project with the same field but only a different alias. This may depend on 
the order of the put operators. As for other operators, the only one I can 
think of is agg, because only operators with column clipping may be involved in 
this problem, but generally agg will have a project on it, so the overall plan 
may be fine.


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