HyukjinKwon commented on a change in pull request #24436: [SPARK-27539][SQL]
Fix inaccurate aggregate outputRows estimation with column containing null
values
URL: https://github.com/apache/spark/pull/24436#discussion_r287070640
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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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@@ -42,8 +42,8 @@ object AggregateEstimation {
(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
+ val distinctValue: BigInt = if (columnStat.nullCount.get > 0) {
+ distinctCount + 1
Review comment:
Looking into the current impl, seems we ignore `null` as distinct values:
https://github.com/apache/spark/blob/239082d9667a4fa4198bd9524d63c739df147e0e/sql/core/src/main/scala/org/apache/spark/sql/execution/command/CommandUtils.scala#L270
https://github.com/apache/spark/blob/b1857a4d7dfe17663f8adccd7825d890ae70d2a1/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/EstimationUtils.scala#L50-L51
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