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https://issues.apache.org/jira/browse/SPARK-13484?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15167292#comment-15167292
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Xiao Li commented on SPARK-13484:
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This is a bug. Let me show two queries.
{code}
val df2 = df.join(df1, $"a" === $"c", "outer").filter(isnull($"c"))
val df3 = df.join(df1, $"a" === $"c", "outer").filter(df1("c").isNull)
{code}
The first query can return a correct result, but the second will return an
empty result. Will try to do an investigation in this today. Thanks!
> Filter outer joined result using a non-nullable column from the right table
> ---------------------------------------------------------------------------
>
> Key: SPARK-13484
> URL: https://issues.apache.org/jira/browse/SPARK-13484
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.5.2, 1.6.0, 2.0.0
> Reporter: Xiangrui Meng
>
> Technically speaking, this is not a bug. But
> {code}
> val a = sqlContext.range(10).select(col("id"), lit(0).as("count"))
> val b = sqlContext.range(10).select((col("id") %
> 3).as("id")).groupBy("id").count()
> a.join(b, a("id") === b("id"), "left_outer").filter(b("count").isNull).show()
> {code}
> returns nothing. This is because `b("count")` is not nullable and the filter
> condition is always false by static analysis. However, it is common for users
> to use `a(...)` and `b(...)` to filter the joined result.
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