Github user liufengdb commented on a diff in the pull request:
https://github.com/apache/spark/pull/20174#discussion_r160305419
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala
---
@@ -230,6 +236,7 @@ case class HashAggregateExec(
| private void $doAgg() throws java.io.IOException {
| // initialize aggregation buffer
| $initBufVar
+ | $hasInput = false;
--- End diff --
If the result expression is empty and `hasInput` is `false`, it should
return an empty iterator (this is exactly the corner case we want to fix). If
the result expression is empty but `hasInput` is `true`, it should append empty
rows.
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