[GitHub] [spark] viirya commented on a change in pull request #21850: [SPARK-24892] [SQL] Simplify `CaseWhen` to `If` when there is only one branch

[GitBox <gi...@apache.org>]

viirya commented on a change in pull request #21850:
URL: https://github.com/apache/spark/pull/21850#discussion_r480360191



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
##########
@@ -505,6 +505,9 @@ object SimplifyConditionals extends Rule[LogicalPlan] with PredicateHelper {
         } else {
           e.copy(branches = branches.take(i).map(branch => (branch._1, elseValue)))
         }
+
+      case CaseWhen(Seq((cond, trueValue)), elseValue) =>

Review comment:
       Is it better we limit to `BooleanType` case? I.e.,
   
   ```scala
   case cw @ CaseWhen(Seq((cond, trueValue)), elseValue) if cw.dataType == BooleanType =>
   ```
   
   The reason is because mostly the further optimization comes from #29567, and it is for boolean type case only.
   
   Or just rewrite it similarly like #29567?
   
   ```scala
   case CaseWhen(Seq((cond, l @ Literal(null, _))), FalseLiteral) if !cond.nullable => ...
   case CaseWhen(Seq((cond, l @ Literal(null, _))), TrueLiteral) if !cond.nullable => ...
   ```
   




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