Github user hsuanyi commented on a diff in the pull request: https://github.com/apache/drill/pull/407#discussion_r55595195 --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/union/UnionAllRecordBatch.java --- @@ -162,6 +162,25 @@ private IterOutcome doWork() throws ClassTransformationException, IOException, S allocationVectors = Lists.newArrayList(); transfers.clear(); + // If both sides of Union-All are empty + if(unionAllInput.isBothSideEmpty()) { + for(int i = 0; i < outputFields.size(); ++i) { --- End diff -- For example, you could do: select a, b, c from empty union all select a, b, c from empty Then, the output should be (a, b, c) as column names.
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