[GitHub] [spark] gengliangwang commented on a change in pull request #25253: [SPARK-28470][SQL] Cast to decimal throws ArithemticException on overflow

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

gengliangwang commented on a change in pull request #25253: [SPARK-28470][SQL] Cast to decimal throws ArithemticException on overflow
URL: https://github.com/apache/spark/pull/25253#discussion_r307444819
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
 ##########
 @@ -498,22 +499,34 @@ case class Cast(child: Expression, dataType: DataType, timeZoneId: Option[String
       b => x.numeric.asInstanceOf[Numeric[Any]].toInt(b).toByte
   }
 
+  private val nullOnOverflow = SQLConf.get.decimalOperationsNullOnOverflow
+
   /**
    * Change the precision / scale in a given decimal to those set in `decimalType` (if any),
    * returning null if it overflows or modifying `value` in-place and returning it if successful.
    *
    * NOTE: this modifies `value` in-place, so don't call it on external data.
    */
   private[this] def changePrecision(value: Decimal, decimalType: DecimalType): Decimal = {
-    if (value.changePrecision(decimalType.precision, decimalType.scale)) value else null
+    if (value.changePrecision(decimalType.precision, decimalType.scale)) {
+      value
+    } else {
+      if (nullOnOverflow) {
+        null
+      } else {
+        throw new ArithmeticException(s"${value.toDebugString} cannot be represented as " +
+          s"Decimal(${decimalType.precision}, ${decimalType.scale}).")
 
 Review comment:
   Nit: should we just use ${decimalType.catalogString} here?

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