[GitHub] [spark] pengbo commented on a change in pull request #24286: [SPARK-27351][SQL] Wrong outputRows estimation after AggregateEstimation with only null value column

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

pengbo commented on a change in pull request #24286: [SPARK-27351][SQL] Wrong outputRows estimation after AggregateEstimation with only null value column
URL: https://github.com/apache/spark/pull/24286#discussion_r277229341
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/AggregateEstimation.scala
 ##########
 @@ -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 distinctCount = columnStat.distinctCount.get
+          val distinctValue: BigInt = if (distinctCount == 0 && columnStat.nullCount.get > 0) {
+            1
+          } else {
+            distinctCount
 
 Review comment:
   Good point.  
   I will try and test it out. Another PR will be submitted if the problem exists.
   

----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
 
For queries about this service, please contact Infrastructure at:
users@infra.apache.org


With regards,
Apache Git Services

---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscribe@spark.apache.org
For additional commands, e-mail: reviews-help@spark.apache.org