Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/6570#discussion_r31492021
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala
---
@@ -37,6 +37,13 @@ abstract class Expression extends TreeNode[Expression] {
* - A [[Cast]] or [[UnaryMinus]] is foldable if its child is foldable
*/
def foldable: Boolean = false
+
+ /**
+ * Returns true when an expressions always return the same result for a
specific set of
+ * input values.
+ */
+ // TODO: Need to well define what are explicit input values and implicit
input values.
+ def deterministic: Boolean = true
--- End diff --
I think it depends on how you interpret this. The definition here is
whether this expression itself is deterministic or not (i.e. assuming fixed
input, is the output deterministic?)
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