[GitHub] [spark] maropu commented on issue #27627: [WIP][SPARK-28067][SQL] Fix incorrect results for decimal aggregate sum by returning null on decimal overflow

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maropu commented on issue #27627: [WIP][SPARK-28067][SQL] Fix incorrect results for decimal aggregate sum by returning null on decimal overflow
URL: https://github.com/apache/spark/pull/27627#issuecomment-595108294
 
 
   For integral sum (e.g., int/long), overflow can happen in partial aggregate sides (via `Math.addExact`). We don't need to follow the behaviour in decimal sum, too, for consistency?
   ```
   scala> sql("SET spark.sql.ansi.enabled=true")
   res39: org.apache.spark.sql.DataFrame = [key: string, value: string]
   
   scala> spark.table("t").printSchema
   root
    |-- v: long (nullable = true)
   
   scala> sql("select * from t").show()
   +-------------------+
   |                  v|
   +-------------------+
   |9223372036854775807|
   |                  1|
   +-------------------+
   
   
   scala> sql("select sum(*) from t").show()
   // Throws an exception
   java.lang.ArithmeticException: long overflow
   	at java.lang.Math.addExact(Math.java:809)
   	at org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage2.agg_doConsume_0$(Unknown Source)
   	at org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage2.agg_doAggregateWithoutKey_0$(Unknown Source)
   	at org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage2.processNext(Unknown Source)
   	at org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43)
   	at org.apache.spark.sql.execution.WholeStageCodegenExec$$anon$1.hasNext(WholeStageCodegenExec.scala:729)
   	at ...
   
   scala> sql("SET spark.sql.ansi.enabled=false")
   scala> sql("select sum(*) from t").show()
   // Wrong result
   +--------------------+
   |              sum(v)|
   +--------------------+
   |-9223372036854775808|
   +--------------------+
   ```

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