[SPARK-8285] [SQL] CombineSum should be calculated as unlimited decimal first

    case cs  CombineSum(expr) =>
        val calcType = expr.dataType
          expr.dataType match {
            case DecimalType.Fixed(_, _) =>
              DecimalType.Unlimited
            case _ =>
              expr.dataType
          }
calcType is always expr.dataType. credits are all belong to IntelliJ

Author: navis.ryu <navis@apache.org>

Closes #6736 from navis/SPARK-8285 and squashes the following commits:

20382c1 [navis.ryu] [SPARK-8285] [SQL] CombineSum should be calculated as unlimited decimal first

sql/core/src/main/scala/org/apache/spark/sql/execution/GeneratedAggregate.scala

@@ -118,7 +118,7 @@ case class GeneratedAggregate(
         AggregateEvaluation(currentSum :: Nil, initialValue :: Nil, updateFunction :: Nil, result)
 
       case cs @ CombineSum(expr) =>
-        val calcType = expr.dataType
+        val calcType =
           expr.dataType match {
             case DecimalType.Fixed(_, _) =>
               DecimalType.Unlimited
@@ -129,7 +129,7 @@ case class GeneratedAggregate(
         val currentSum = AttributeReference("currentSum", calcType, nullable = true)()
         val initialValue = Literal.create(null, calcType)
 
-        // Coalasce avoids double calculation...
+        // Coalesce avoids double calculation...
         // but really, common sub expression elimination would be better....
         val zero = Cast(Literal(0), calcType)
         // If we're evaluating UnscaledValue(x), we can do Count on x directly, since its