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[SPARK-24957][SQL][BACKPORT-2.2] Average with decimal followed by aggregation returns wrong result #21949

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[SPARK-24957][SQL][BACKPORT-2.2] Average with decimal followed by aggregation returns wrong result #21949

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2 changes: 1 addition & 1 deletion sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/DecimalPrecision.scala
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Expand Up @@ -85,7 +85,7 @@ object DecimalPrecision extends Rule[LogicalPlan] {
}

/** Decimal precision promotion for +, -, *, /, %, pmod, and binary comparison. */
private val decimalAndDecimal: PartialFunction[Expression, Expression] = {
private[catalyst] val decimalAndDecimal: PartialFunction[Expression, Expression] = {
// Skip nodes whose children have not been resolved yet
case e if !e.childrenResolved => e

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9 changes: 4 additions & 5 deletions ...catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/Average.scala
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Expand Up @@ -17,7 +17,7 @@

package org.apache.spark.sql.catalyst.expressions.aggregate

import org.apache.spark.sql.catalyst.analysis.TypeCheckResult
import org.apache.spark.sql.catalyst.analysis.{DecimalPrecision, TypeCheckResult}
import org.apache.spark.sql.catalyst.dsl.expressions._
import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.util.TypeUtils
Expand Down Expand Up @@ -77,10 +77,9 @@ case class Average(child: Expression) extends DeclarativeAggregate with Implicit

// If all input are nulls, count will be 0 and we will get null after the division.
override lazy val evaluateExpression = child.dataType match {
case DecimalType.Fixed(p, s) =>
// increase the precision and scale to prevent precision loss
val dt = DecimalType.bounded(p + 14, s + 4)
Cast(Cast(sum, dt) / Cast(count, DecimalType.bounded(DecimalType.MAX_PRECISION, 0)),
case _: DecimalType =>
Cast(
DecimalPrecision.decimalAndDecimal(sum / Cast(count, DecimalType.LongDecimal)),
resultType)
case _ =>
Cast(sum, resultType) / Cast(count, resultType)
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13 changes: 13 additions & 0 deletions sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/AggregationQuerySuite.scala
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Expand Up @@ -1002,6 +1002,19 @@ abstract class AggregationQuerySuite extends QueryTest with SQLTestUtils with Te
)
)
}

test("SPARK-24957: average with decimal followed by aggregation returning wrong result") {
val df = Seq(("a", BigDecimal("12.0")),
("a", BigDecimal("12.0")),
("a", BigDecimal("11.9999999988")),
("a", BigDecimal("12.0")),
("a", BigDecimal("12.0")),
("a", BigDecimal("11.9999999988")),
("a", BigDecimal("11.9999999988"))).toDF("text", "number")
val agg1 = df.groupBy($"text").agg(avg($"number").as("avg_res"))
val agg2 = agg1.groupBy($"text").agg(sum($"avg_res"))
checkAnswer(agg2, Row("a", BigDecimal("11.9999999994857142857143")))
}
}


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