Github user dilipbiswal commented on a diff in the pull request:
https://github.com/apache/spark/pull/22809#discussion_r228636110
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
---
@@ -282,6 +283,31 @@ trait RuntimeReplaceable extends UnaryExpression with
Unevaluable {
override lazy val canonicalized: Expression = child.canonicalized
}
+/**
+ * An aggregate expression that gets rewritten (currently by the
optimizer) into a
+ * different aggregate expression for evaluation. This is mainly used to
provide compatibility
+ * with other databases. For example, we use this to support every,
any/some aggregates by rewriting
+ * them with Min and Max respectively.
+ */
+trait UnevaluableAggregate extends DeclarativeAggregate {
+
+ override def nullable: Boolean = true
--- End diff --
@mgaido91 I think for aggregates, its different ? Please `Max`, `Min`, they
all define it to be nullable. I think they work on group of rows and can return
null on empty input.
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