[I] Add projection support to `SortMergeJoinExec` [datafusion]

["Dandandan (via GitHub)" <gi...@apache.org>]

Dandandan opened a new issue, #24518:
URL: https://github.com/apache/datafusion/issues/24518

   ### Is your feature request related to a problem or challenge?
   
   
   `SortMergeJoinExec` emits every column of both inputs.
   We can add projection support to only produce the output columns (saving some compute / copy).
   
   ```sql
   select * from t1 right join t2 on t1.c3 = t2.c3   -- c3 needs a cast
   ```
   
   ```text
   ProjectionExec: expr=[c1@0 as c1, ..., c4@8 as c4]
     SortMergeJoinExec: join_type=Right, on=[(CAST(t1.c3 AS Decimal128(10, 2))@4, c3@2)]
   ```
   
   The cast column is only there to be joined on, and every operator above the join
   carries it until the projection removes it.
   
   
   ### Describe the solution you'd like
   
   Add projection support to `SortMergeJoinExec`
   
   ### Describe alternatives you've considered
   
   _No response_
   
   ### Additional context
   
   _No response_


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Re: [I] Add projection support to `SortMergeJoinExec` [datafusion]

["Dandandan (via GitHub)" <gi...@apache.org>]

Dandandan closed issue #24518: Add projection support to `SortMergeJoinExec`
URL: https://github.com/apache/datafusion/issues/24518


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