[jira] [Created] (SPARK-32110) -0.0 vs 0.0 is inconsistent

["Robert Joseph Evans (Jira)" <ji...@apache.org>]

Robert Joseph Evans created SPARK-32110:
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             Summary: -0.0 vs 0.0 is inconsistent
                 Key: SPARK-32110
                 URL: https://issues.apache.org/jira/browse/SPARK-32110
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 3.0.0
            Reporter: Robert Joseph Evans


This is related to SPARK-26021 where some things were fixed but there is still a lot that is not consistent.

When parsing SQL {{-0.0}} is turned into {{0.0}}. This can produce quick results that appear to be correct but are totally inconsistent for the same operators.
{code:java}
scala> import spark.implicits._
import spark.implicits._

scala> spark.sql("SELECT 0.0 = -0.0").collect
res0: Array[org.apache.spark.sql.Row] = Array([true])

scala> Seq((0.0, -0.0)).toDF("a", "b").selectExpr("a = b").collect
res1: Array[org.apache.spark.sql.Row] = Array([false])
{code}
This also shows up in sorts
{code:java}
scala> Seq((0.0, -100.0), (-0.0, 100.0), (0.0, 100.0), (-0.0, -100.0)).toDF("a", "b").orderBy("a", "b").collect
res2: Array[org.apache.spark.sql.Row] = Array([-0.0,-100.0], [-0.0,100.0], [0.0,-100.0], [0.0,100.0])
{code}
But not for a equi-join or for an aggregate
{code:java}
scala> Seq((0.0, -0.0)).toDF("a", "b").join(Seq((-0.0, 0.0)).toDF("r_a", "r_b"), $"a" === $"r_a").collect
res3: Array[org.apache.spark.sql.Row] = Array([0.0,-0.0,-0.0,0.0])

scala> Seq((0.0, 1.0), (-0.0, 1.0)).toDF("a", "b").groupBy("a").count.collect
res6: Array[org.apache.spark.sql.Row] = Array([0.0,2])
{code}
This can lead to some very odd results. Like an equi-join with a filter that logically should do nothing, but ends up filtering the result to nothing.
{code:java}
scala> Seq((0.0, -0.0)).toDF("a", "b").join(Seq((-0.0, 0.0)).toDF("r_a", "r_b"), $"a" === $"r_a" && $"a" <= $"r_a").collect
res8: Array[org.apache.spark.sql.Row] = Array()

scala> Seq((0.0, -0.0)).toDF("a", "b").join(Seq((-0.0, 0.0)).toDF("r_a", "r_b"), $"a" === $"r_a").collect
res9: Array[org.apache.spark.sql.Row] = Array([0.0,-0.0,-0.0,0.0])
{code}
Hive never normalizes -0.0 to 0.0 so this results in non-ieee complaint behavior everywhere, but at least it is consistently odd.

MySQL, Oracle, Postgres, and SQLite all appear to normalize the {{-0.0}} to {{0.0}}.

The root cause of this appears to be that the java implementation of {{Double.compare}} and {{Float.compare}} for open JDK places {{-0.0}} < {{0.0}}.

This is not documented in the java docs but it is clearly documented in the code, so it is not a "bug" that java is going to fix.

[https://github.com/openjdk/jdk/blob/a0a0539b0d3f9b6809c9759e697bfafd7b138ec1/src/java.base/share/classes/java/lang/Double.java#L1022-L1035]

It is also consistent with what is in the java docs for {{Double.equals}}
 [https://docs.oracle.com/javase/8/docs/api/java/lang/Double.html#equals-java.lang.Object-]

To be clear I am filing this mostly to document the current state rather than to think it needs to be fixed ASAP. It is a rare corner case, but ended up being really frustrating for me to debug what was happening.



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