Github user jinfengni commented on a diff in the pull request:
https://github.com/apache/drill/pull/379#discussion_r53361870
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/ParquetScanBatchCreator.java
---
@@ -87,9 +87,6 @@ public ScanBatch getBatch(FragmentContext context,
ParquetRowGroupScan rowGroupS
newColumns.add(column);
}
}
- if (newColumns.isEmpty()) {
--- End diff --
I went through all the ScanBatchCreator in Drill's code base. Seems
ParquetScanBatchCreator is the only one that is converting an empty column list
to ALL_COLUMNS. Looking at the history, seems DRILL-1845 added the code,
probably just to make it work in parquet for skipAll query.
With the patch of DRILL-4279, parquet record reader would be able to handle
empty column list.
Besides ParquetScanBatchCreator, this patch also modifies HBaseGroupScan,
EasyGroupScan where it originally interprets empty column lists into
ALL_COLUMNS.
I'll add some comment to the code to clarify the different meaning of NULL
and empty column list.
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