Github user yhuai commented on a diff in the pull request: https://github.com/apache/spark/pull/13884#discussion_r68355194 --- Diff: sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala --- @@ -1541,4 +1541,13 @@ class DataFrameSuite extends QueryTest with SharedSQLContext { val df = Seq(1, 1, 2).toDF("column.with.dot") checkAnswer(df.distinct(), Row(1) :: Row(2) :: Nil) } + + test("SPARK-16181: outer join with isNull filter") { + val left = Seq("x").toDF("col") + val right = Seq("y").toDF("col").withColumn("new", lit(true)) + val joined = left.join(right, left("col") === right("col"), "left_outer") + + checkAnswer(joined, Row("x", null, null)) + checkAnswer(joined.filter($"new".isNull), Row("x", null, null)) --- End diff -- ah, this is subtle. `new` is replaced back to the original `col` from right, which is not nullable. Then, `isNull` just returns false.
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