[GitHub] [arrow-datafusion] alamb commented on pull request #2177: User Defined Table Function (udtf) support

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alamb commented on PR #2177:
URL: https://github.com/apache/arrow-datafusion/pull/2177#issuecomment-1135961673

   I think adding UDTFs (aka user defined table functions) that produce a 2 dimensional table output (aka `Vec<RecordBatch>` or a `SendableRecordBatchStream`) would be a valuable addition to DataFusion. 
   
   I think Spark calls these "table value functions":
   
   https://docs.databricks.com/spark/latest/spark-sql/language-manual/sql-ref-syntax-qry-select-tvf.html
   
   Postgres calls them table functions:
   
   https://www.postgresql.org/docs/7.3/xfunc-tablefunctions.html
   
   However, this PR does not implement table functions that I can see. I still don't fully understand the usecase for the code in this PR for a function that returns a single column of values and I don't know of any other system that implements such functions. Thus I feel that this PR adds a feature that is not widely usable to DataFusion users as a whole, and so I don't feel I can approve it.
   
   If others (users or maintainers) have a perspective on this issue, I would love to hear them too. If there is broader support for this feature, I won't oppose merging it. 
   


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