[GitHub] [spark] HyukjinKwon commented on a change in pull request #29983: [SPARK-13860][SQL] Change CentralMomentAgg to return null instead of Double.NaN when divideByZero

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HyukjinKwon commented on a change in pull request #29983:
URL: https://github.com/apache/spark/pull/29983#discussion_r503011445



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala
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@@ -2342,6 +2342,16 @@ object SQLConf {
       .booleanConf
       .createWithDefault(false)
 
+  val LEGACY_CENTRAL_MOMENT_AGG =
+    buildConf("spark.sql.legacy.centralMomentAgg")
+      .internal()
+      .doc("When set to true, central moment aggregation will return Double.NaN " +
+        "if divide by zero occurred during calculation. Otherwise, it will return null. " +
+        "Before version 3.1.0, it returns NaN in divideByZero case by default.")

Review comment:
       Shall we update migration guide (https://github.com/apache/spark/blob/master/docs/sql-migration-guide.md) too? Looks like it's more a behaviour change instead of a big fix.




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