[GitHub] [spark] srowen commented on a change in pull request #24286: [SPARK-27351][SQL] Wrong outputRows estimation after AggregateEstimation wit…

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srowen commented on a change in pull request #24286: [SPARK-27351][SQL] Wrong outputRows estimation after AggregateEstimation wit…
URL: https://github.com/apache/spark/pull/24286#discussion_r275136453
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/AggregateEstimation.scala
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 @@ -39,8 +39,16 @@ object AggregateEstimation {
       // Multiply distinct counts of group-by columns. This is an upper bound, which assumes
       // the data contains all combinations of distinct values of group-by columns.
       var outputRows: BigInt = agg.groupingExpressions.foldLeft(BigInt(1))(
-        (res, expr) => res *
-          childStats.attributeStats(expr.asInstanceOf[Attribute]).distinctCount.get)
+        (res, expr) => {
+          val columnStat = childStats.attributeStats(expr.asInstanceOf[Attribute])
+          val distinctValue: BigInt = if (columnStat.distinctCount.get == 0 &&
 
 Review comment:
   I'm slightly concerned about performance here. Can you save the value of distinctCount.get so it isn't accessed twice, or is it not actually recomputed twice as-is?

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