Mithun Radhakrishnan created SPARK-32038:
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Summary: Regression in handling NaN values in COUNT(DISTINCT)
Key: SPARK-32038
URL: https://issues.apache.org/jira/browse/SPARK-32038
Project: Spark
Issue Type: Bug
Components: Optimizer, SQL
Affects Versions: 3.0.0
Reporter: Mithun Radhakrishnan
There seems to be a regression in Spark 3.0.0, with regard to how {{NaN}}
values are normalized/handled in {{COUNT(DISTINCT ...)}}. Here is an
illustration:
{code:scala}
case class Test( uid:String, score:Float)
val POS_NAN_1 = java.lang.Float.intBitsToFloat(0x7f800001)
val POS_NAN_2 = java.lang.Float.intBitsToFloat(0x7fffffff)
val rows = Seq(
Test("mithunr", Float.NaN),
Test("mithunr", POS_NAN_1),
Test("mithunr", POS_NAN_2),
Test("abellina", 1.0f),
Test("abellina", 2.0f)
).toDF.createOrReplaceTempView("mytable")
spark.sql(" select uid, count(distinct score) from mytable group by 1 order by
1 asc ").show
{code}
Here are the results under Spark 3.0.0:
{code:title=Spark 3.0.0 (single aggregation)}
+--------+---------------------+
| uid|count(DISTINCT score)|
+--------+---------------------+
|abellina| 2|
| mithunr| 3|
+--------+---------------------+
{code}
Note that the count against {{mithunr}} is {{3}}, accounting for each distinct
value for {{NaN}}.
The right results are returned when another aggregation is added to the GBY:
{code:scala|title=Spark 3.0.0 (multiple aggregations)}
scala> spark.sql(" select uid, count(distinct score), max(score) from mytable
group by 1 order by 1 asc ").show
+--------+---------------------+----------+
| uid|count(DISTINCT score)|max(score)|
+--------+---------------------+----------+
|abellina| 2| 2.0|
| mithunr| 1| NaN|
+--------+---------------------+----------+
{code}
Also, note that Spark 2.4.6 normalizes the `DISTINCT` expression correctly:
{code:scala|title=Spark 2.4.6}
scala> spark.sql(" select uid, count(distinct score) from mytable
group by 1 order by 1 asc ").show
+--------+---------------------+
| uid|count(DISTINCT score)|
+--------+---------------------+
|abellina| 2|
| mithunr| 1|
+--------+---------------------+
{code}
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