[jira] [Created] (SPARK-19954) Joining to a unioned DataFrame does not produce expected result.

["Arun Allamsetty (JIRA)" <ji...@apache.org>]

Arun Allamsetty created SPARK-19954:
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             Summary: Joining to a unioned DataFrame does not produce expected result.
                 Key: SPARK-19954
                 URL: https://issues.apache.org/jira/browse/SPARK-19954
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 2.1.0
            Reporter: Arun Allamsetty
            Priority: Blocker


I found this bug while trying to update from Spark 1.6.1 to 2.1.0. The bug is that when we try to join two DataFrames, one of which is a result of a union operation, the result of the join results in data as if the table was joined only to the first table in the union. This issue is not present in Spark 2.0.0 or 2.0.1 or 2.0.2, only in 2.1.0. Here's how to reproduce it.

{{noformat}}
import spark.implicits._
import org.apache.spark.sql.functions.lit

case class A(id: Long, colA: Boolean)
case class B(id: Long, colB: Int)
case class C(id: Long, colC: Double)
case class X(id: Long, name: String)

val aData = A(1, true) :: Nil
val bData = B(2, 10) :: Nil
val cData = C(3, 9.73D) :: Nil
val xData = X(1, "a") :: X(2, "b") :: X(3, "c") :: Nil

val aDf = spark.createDataset(aData).toDF
val bDf = spark.createDataset(bData).toDF
val cDf = spark.createDataset(cData).toDF
val xDf = spark.createDataset(xData).toDF

val unionDf =
  aDf.select($"id", lit("a").as("name"), $"colA", lit(null).as("colB"), lit(null).as("colC")).union(
  bDf.select($"id", lit("b").as("name"), lit(null).as("colA"), $"colB", lit(null).as("colC"))).union(
  cDf.select($"id", lit("c").as("name"), lit(null).as("colA"), lit(null).as("colB"), $"colC"))
val result = xDf.join(unionDf, unionDf("name") === xDf("name") && unionDf("id") === xDf("id"))
result.show
{{noformat}}

The result being
{{noformat}}
+---+----+---+----+----+----+----+
| id|name| id|name|colA|colB|colC|
+---+----+---+----+----+----+----+
|  1|   a|  1|   a|true|null|null|
+---+----+---+----+----+----+----+
{{noformat}}

Force computing {{unionDf}} using {{count}} does not help change the result of the join. However, writing the data to disk and reading it back does give the correct result. But it is definitely not ideal. Interestingly caching the {{unionDf}} also gives the correct result.

{{noformat}}
+---+----+---+----+----+----+----+
| id|name| id|name|colA|colB|colC|
+---+----+---+----+----+----+----+
|  1|   a|  1|   a|true|null|null|
|  2|   b|  2|   b|null|  10|null|
|  3|   c|  3|   c|null|null|9.73|
+---+----+---+----+----+----+----+
{{noformat}}



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