Major Description
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.
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])
This also shows up in sorts
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])
But not for a equi-join or for an aggregate
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])
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.
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])
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.
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.
