Github user dbtsai commented on a diff in the pull request:
https://github.com/apache/spark/pull/21852#discussion_r205946975
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
---
@@ -416,6 +416,23 @@ object SimplifyConditionals extends Rule[LogicalPlan]
with PredicateHelper {
// these branches can be pruned away
val (h, t) = branches.span(_._1 != TrueLiteral)
CaseWhen( h :+ t.head, None)
+
+ case e @ CaseWhen(branches, Some(elseValue)) if {
--- End diff --
We can not. When no `elseValue`, all the conditions are required to
evaluated before hitting the default `elseValue` which is `null`.
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