Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/21852#discussion_r205309619
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
---
@@ -416,6 +416,21 @@ 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 {
+ val list = branches.map(_._2) :+ elseValue
+ list.tail.forall(list.head.semanticEquals)
+ } =>
+ // For non-deterministic conditions with side effect, we can not
remove it.
+ // Since the output of all the branches are semantic equivalence,
`elseValue`
+ // is picked for all the branches.
+ val newBranches =
branches.map(_._1).filter(!_.deterministic).map(cond => (cond, elseValue))
--- End diff --
All conds must be deterministic, otherwise a non deterministic one not run
before can be run after this rule.
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