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

[GitBox]

cloud-fan commented on a change in pull request #29983:
URL: https://github.com/apache/spark/pull/29983#discussion_r503094201



##########
File path: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/CentralMomentAgg.scala
##########
@@ -62,6 +63,9 @@ abstract class CentralMomentAgg(child: Expression)
   protected val m3 = AttributeReference("m3", DoubleType, nullable = false)()
   protected val m4 = AttributeReference("m4", DoubleType, nullable = false)()
 
+  protected val divideByZeroEvalResult: Expression =
+    if (SQLConf.get.legacyStatisticalAggregate) Double.NaN else 
Literal.create(null, DoubleType)

Review comment:
       can we move the flag to constructor parameter? e.g.
   ```
   abstract class CentralMomentAgg(child: Expression, nullOnDivideByZero: 
Boolean) {
     ...
     protected def divideByZeroEvalResult: Expression = if (nullOnDivideByZero) 
...
   }
   ```




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