[GitHub] [spark] Ngone51 commented on a change in pull request #28572: [SPARK-31750][SQL] Eliminate UpCast if child's dataType is DecimalType

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

Ngone51 commented on a change in pull request #28572:
URL: https://github.com/apache/spark/pull/28572#discussion_r427057191



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
##########
@@ -3071,15 +3071,31 @@ class Analyzer(
       case p => p transformExpressions {
         case u @ UpCast(child, _, _) if !child.resolved => u
 
-        case UpCast(child, dt: AtomicType, _)
+        case u @ UpCast(child, _, _)
             if SQLConf.get.getConf(SQLConf.LEGACY_LOOSE_UPCAST) &&
+              u.dataType.isInstanceOf[AtomicType] &&
               child.dataType == StringType =>
-          Cast(child, dt.asNullable)
-
-        case UpCast(child, dataType, walkedTypePath) if !Cast.canUpCast(child.dataType, dataType) =>
-          fail(child, dataType, walkedTypePath)
-
-        case UpCast(child, dataType, _) => Cast(child, dataType.asNullable)
+          Cast(child, u.dataType.asNullable)
+
+        case u @ UpCast(child, _, walkedTypePath)
+          if child.dataType.isInstanceOf[DecimalType]
+            && u.dataType.isInstanceOf[DecimalType]
+            && walkedTypePath.nonEmpty =>

Review comment:
       It's more like a sanity check to prevent the case of using `UpCast` outside of `ExpressionEncoder` in the future.




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