Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/16581#discussion_r96121284
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/predicates.scala
---
@@ -86,6 +86,19 @@ trait PredicateHelper {
*/
protected def canEvaluate(expr: Expression, plan: LogicalPlan): Boolean =
expr.references.subsetOf(plan.outputSet)
+
+ /**
+ * Returns true iff `expr` could be evaluated as a condition within join.
+ */
+ protected def canEvaluateWithinJoin(expr: Expression): Boolean = {
+ expr.find {
+ case e: SubqueryExpression =>
+ // non-correlated subquery will be replaced as literal
+ e.children.nonEmpty
+ case e: Unevaluable => true
--- End diff --
`Unevaluable` is not evaluable. This block tries to find a case that is not
evaluable in a join, and then negates it by isEmpty. I have to admit that we
should document this.
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