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https://issues.apache.org/jira/browse/SPARK-13496?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15171289#comment-15171289
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Xiao Li commented on SPARK-13496:
---------------------------------
If you use the latest Spark 2.0 upstream, you will not hit this problem.
{code}
Seq((1, "s")).toDF("a", "b").agg(countDistinct("a")).printSchema()
root
|-- count(DISTINCT a): long (nullable = false)
{code}
> Optimizing count distinct changes the resulting column name
> -----------------------------------------------------------
>
> Key: SPARK-13496
> URL: https://issues.apache.org/jira/browse/SPARK-13496
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.6.0
> Reporter: Ryan Blue
>
> SPARK-9241 updated the optimizer to rewrite count distinct. That change uses
> a count that is no longer distinct because duplicates are eliminated further
> down in the plan. This caused the name of the column to change:
> {code:title=Spark 1.5.2}
> scala> Seq((1, "s")).toDF("a", "b").agg(countDistinct("a"))
> res0: org.apache.spark.sql.DataFrame = [COUNT(DISTINCT a): bigint]
> == Physical Plan ==
> TungstenAggregate(key=[],
> functions=[(count(a#7),mode=Complete,isDistinct=true)],
> output=[COUNT(DISTINCT a)#9L])
> TungstenAggregate(key=[a#7], functions=[], output=[a#7])
> TungstenExchange SinglePartition
> TungstenAggregate(key=[a#7], functions=[], output=[a#7])
> LocalTableScan [a#7], [[1]]
> {code}
> {code:title=Spark 1.6.0}
> scala> Seq((1, "s")).toDF("a", "b").agg(countDistinct("a"))
> res0: org.apache.spark.sql.DataFrame = [count(a): bigint]
> == Physical Plan ==
> TungstenAggregate(key=[], functions=[(count(if ((gid#35 = 1)) a#36 else
> null),mode=Final,isDistinct=false)], output=[count(a)#31L])
> +- TungstenExchange SinglePartition, None
> +- TungstenAggregate(key=[], functions=[(count(if ((gid#35 = 1)) a#36 else
> null),mode=Partial,isDistinct=false)], output=[count#39L])
> +- TungstenAggregate(key=[a#36,gid#35], functions=[],
> output=[a#36,gid#35])
> +- TungstenExchange hashpartitioning(a#36,gid#35,500), None
> +- TungstenAggregate(key=[a#36,gid#35], functions=[],
> output=[a#36,gid#35])
> +- Expand [List(a#29, 1)], [a#36,gid#35]
> +- LocalTableScan [a#29], [[1]]
> {code}
> This has broken jobs that used the generated name. For example,
> {{withColumnRenamed("COUNT(DISTINCT a)", "c")}}.
> I think that the previous generated name is correct, even though the plan has
> changed.
> [~marmbrus], you may want to take a look. It looks like you reviewed
> SPARK-9241 and have some context here.
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