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

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

cloud-fan commented on a change in pull request #29983:
URL: https://github.com/apache/spark/pull/29983#discussion_r503035473



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/CentralMomentAgg.scala
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@@ -174,7 +175,9 @@ case class StddevSamp(child: Expression) extends CentralMomentAgg(child) {
 
   override val evaluateExpression: Expression = {
     If(n === 0.0, Literal.create(null, DoubleType),
-      If(n === 1.0, Double.NaN, sqrt(m2 / (n - 1.0))))
+      If(n === 1.0,
+        if (SQLConf.get.legacyCentralMomentAgg) Double.NaN else Literal.create(null, DoubleType),

Review comment:
       can we put it as a method in the parent class `CentralMomentAgg`?




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