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https://issues.apache.org/jira/browse/SPARK-20169?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15972300#comment-15972300
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Takeshi Yamamuro commented on SPARK-20169:
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oh, ... good work.
> Groupby Bug with Sparksql
> -------------------------
>
> Key: SPARK-20169
> URL: https://issues.apache.org/jira/browse/SPARK-20169
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.0.0, 2.1.0
> Reporter: Bin Wu
>
> We find a potential bug in Catalyst optimizer which cannot correctly
> process "groupby". You can reproduce it by following simple example:
> =========================
> from pyspark.sql.functions import *
> #e=sc.parallelize([(1,2),(1,3),(1,4),(2,1),(3,1),(4,1)]).toDF(["src","dst"])
> e = spark.read.csv("graph.csv", header=True)
> r = sc.parallelize([(1,),(2,),(3,),(4,)]).toDF(['src'])
> r1 = e.join(r, 'src').groupBy('dst').count().withColumnRenamed('dst','src')
> jr = e.join(r1, 'src')
> jr.show()
> r2 = jr.groupBy('dst').count()
> r2.show()
> =========================
> FYI, "graph.csv" contains exactly the same data as the commented line.
> You can find that jr is:
> |src|dst|count|
> | 3| 1| 1|
> | 1| 4| 3|
> | 1| 3| 3|
> | 1| 2| 3|
> | 4| 1| 1|
> | 2| 1| 1|
> But, after the last groupBy, the 3 rows with dst = 1 are not grouped together:
> |dst|count|
> | 1| 1|
> | 4| 1|
> | 3| 1|
> | 2| 1|
> | 1| 1|
> | 1| 1|
> If we build jr directly from raw data (commented line), this error will not
> show up. So
> we suspect that there is a bug in the Catalyst optimizer when multiple joins
> and groupBy's
> are being optimized.
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