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https://issues.apache.org/jira/browse/SPARK-12725?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15125754#comment-15125754
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Xiao Li commented on SPARK-12725:
---------------------------------
You are right. : )
> SQL generation suffers from name conficts introduced by some analysis rules
> ---------------------------------------------------------------------------
>
> Key: SPARK-12725
> URL: https://issues.apache.org/jira/browse/SPARK-12725
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Reporter: Cheng Lian
>
> Some analysis rules generate auxiliary attribute references with the same
> name but different expression IDs. For example, {{ResolveAggregateFunctions}}
> introduces {{havingCondition}} and {{aggOrder}}, and
> {{DistinctAggregationRewriter}} introduces {{gid}}.
> This is OK for normal query execution since these attribute references get
> expression IDs. However, it's troublesome when converting resolved query
> plans back to SQL query strings since expression IDs are erased.
> Here's an example Spark 1.6.0 snippet for illustration:
> {code}
> sqlContext.range(10).select('id as 'a, 'id as 'b).registerTempTable("t")
> sqlContext.sql("SELECT SUM(a) FROM t GROUP BY a, b ORDER BY COUNT(a),
> COUNT(b)").explain(true)
> {code}
> The above code produces the following resolved plan:
> {noformat}
> == Analyzed Logical Plan ==
> _c0: bigint
> Project [_c0#101L]
> +- Sort [aggOrder#102L ASC,aggOrder#103L ASC], true
> +- Aggregate [a#47L,b#48L], [(sum(a#47L),mode=Complete,isDistinct=false)
> AS _c0#101L,(count(a#47L),mode=Complete,isDistinct=false) AS
> aggOrder#102L,(count(b#48L),mode=Complete,isDistinct=false) AS aggOrder#103L]
> +- Subquery t
> +- Project [id#46L AS a#47L,id#46L AS b#48L]
> +- LogicalRDD [id#46L], MapPartitionsRDD[44] at range at
> <console>:26
> {noformat}
> Here we can see that both aggregate expressions in {{ORDER BY}} are extracted
> into an {{Aggregate}} operator, and both of them are named {{aggOrder}} with
> different expression IDs.
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