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  1. Spark
  2. SPARK-27589 Spark file source V2
  3. SPARK-27356

File source V2: return actual schema in method `FileScan.readSchema`

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    • Sub-task
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • 3.0.0
    • 3.0.0
    • SQL
    • None


      The method `Scan.readSchema` returns the actual schema of this data source scan.
      In the current file source V2 framework, the schema is not returned correctly. The result should be `readDataSchema + partitionSchema`, while the framework returns the schema which is pushed down in `SupportsPushDownRequiredColumns.requiredSchema`.
      This is normally OK. But if there are overlap columns between `dataSchema` and `partitionSchema`, the result of row-base scan will be wrong. The actual schema should be
      `dataSchema - overlapSchema + partitionSchema`, which is different from from the pushed down `requiredSchema`.

      This PR is to:
      1. Bug fix: fix the corner case that `dataSchema` overlaps with `partitionSchema`.
      2. Improvement: Prune partition column values if part of the partition columns are not required.
      3. Behavior change: To make it simple, the schema of `FileTable` is `dataSchema - overlapSchema + partitionSchema`, instead of mixing data schema and partitionSchema (see `PartitioningUtils.mergeDataAndPartitionSchema`)
      For example, the data schema is [a,b,c], the partition schema is [b,d],
      In V1, the schema of `HadoopFsRelation` is [a, b, c, d]
      in File source V2 , the schema of `FileTable` is [a, c, b, d]
      Putting all the partition columns to the end of table schema is more reasonable. Also, when there is `select *` operation and there is no schema pruning, the schema of `FileTable` and `FileScan` still matches.



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            Gengliang.Wang Gengliang Wang Assign to me
            Gengliang.Wang Gengliang Wang
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