[GitHub] [spark] cloud-fan commented on a change in pull request #33590: [SPARK-36359][SQL] Coalesce returns the first expression if it is non nullable

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

cloud-fan commented on a change in pull request #33590:
URL: https://github.com/apache/spark/pull/33590#discussion_r681071652



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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@@ -780,6 +780,8 @@ object NullPropagation extends Rule[LogicalPlan] {
           Literal.create(null, e.dataType)
         } else if (newChildren.length == 1) {
           newChildren.head
+        } else if (!newChildren.head.nullable) {

Review comment:
       can we generalize it? I think we should find the first non-nullable child, and drop all other children after it.
   ```
   else {
     Coalesce(newChildren.take(newChildren.indexWhere(_.nullable) + 1))
   }
   ```




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