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https://issues.apache.org/jira/browse/DRILL-4476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15188106#comment-15188106
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ASF GitHub Bot commented on DRILL-4476:
---------------------------------------
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.
> Enhance Union-All operator for dealing with empty left input or empty both
> inputs
> ---------------------------------------------------------------------------------
>
> Key: DRILL-4476
> URL: https://issues.apache.org/jira/browse/DRILL-4476
> Project: Apache Drill
> Issue Type: Bug
> Components: Execution - Relational Operators
> Reporter: Sean Hsuan-Yi Chu
> Assignee: Sean Hsuan-Yi Chu
>
> Union-All operator does not deal with the situation where left side comes
> from empty source.
> Due to DRILL-2288's enhancement for empty sources, Union-All operator now can
> be allowed to support this scenario.
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