Github user nongli commented on a diff in the pull request:
https://github.com/apache/spark/pull/9480#discussion_r44194583
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala
---
@@ -203,6 +203,10 @@ case class AttributeReference(
case _ => false
}
+ override def semanticHash(): Int = {
+ this.exprId.hashCode()
--- End diff --
It works fine currently because by the time this has run, the expression is
a bound attribute. We should consider running the logic of finding
subexpressions earlier, as chenghao suggests. I added a unit test that exposes
the problem of not defining this. As a general rule, I think any class that
defines semanticEquals should define semanticHash, even if it is the default
implementation.
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