[GitHub] [spark] cloud-fan commented on a change in pull request #27478: [SPARK-25829][SQL] Add config `spark.sql.legacy.allowDuplicatedMapKeys` and change the default behavior

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cloud-fan commented on a change in pull request #27478: [SPARK-25829][SQL] Add config `spark.sql.legacy.allowDuplicatedMapKeys` and change the default behavior
URL: https://github.com/apache/spark/pull/27478#discussion_r379831096
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/ArrayBasedMapBuilder.scala
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 @@ -63,6 +68,11 @@ class ArrayBasedMapBuilder(keyType: DataType, valueType: DataType) extends Seria
       keys.append(key)
       values.append(value)
     } else {
+      if (!allowDuplicatedMapKey) {
+        throw new RuntimeException(s"Duplicate map key $key was founded, please set " +
 
 Review comment:
   We shouldn't recommend users to set legacy config to fix a problem. We should ask them to check the input data to see why there are duplicated keys. If they want to remove duplicated keys, tell them that they can set the legacy config which uses last wins policy.

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