[GitHub] [spark] iRakson commented on a change in pull request #27580: [SPARK-27619][SQL]MapType should be prohibited in hash expressions

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iRakson commented on a change in pull request #27580: [SPARK-27619][SQL]MapType should be prohibited in hash expressions
URL: https://github.com/apache/spark/pull/27580#discussion_r379998771
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/hash.scala
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 @@ -249,10 +247,20 @@ abstract class HashExpression[E] extends Expression {
 
   override def nullable: Boolean = false
 
+  private def hasMapType(dt: DataType): Boolean = {
+    dt.existsRecursively(_.isInstanceOf[MapType])
+  }
+
   override def checkInputDataTypes(): TypeCheckResult = {
     if (children.length < 1) {
       TypeCheckResult.TypeCheckFailure(
         s"input to function $prettyName requires at least one argument")
+    } else if (children.forall(child => hasMapType(child.dataType)) &&
+      !SQLConf.get.getConf(SQLConf.LEGACY_USE_HASH_ON_MAPTYPE)) {
+      TypeCheckResult.TypeCheckFailure(
+        s"input to function $prettyName cannot contain elements of MapType. Logically same maps " +
+          "may have different hashcode, thus hash expressions are prohibited on MapType " +
+          "elements. To restore previous behavior set spark.sql.legacy.useHashOnMapType to true.")
 
 Review comment:
   I used `spark.sql.legacy.useHashOnMapType` to maintain consistency with what i updated in migration guide.

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