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https://issues.apache.org/jira/browse/SPARK-17120?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15433780#comment-15433780
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Herman van Hovell commented on SPARK-17120:
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TL;DR the {{PushDownPredicate}} rule pushed the {{false}} join predicate down,
into the left hand side of the join (which should have been the right hand
side). This caused the {{EliminateOuterJoin}} rule to rewrite this into an
inner join.
The optimized plan before disabling the {{PushDownPredicate}} rule (I had to
disable the {{PruneFilters}} rule to prevent the plan from being erased):
{noformat}
Project [coalesce(int_col_1#12, int_col_6#4) AS int_col#16]
+- Join Inner
:- Project [value#2 AS int_col_6#4]
: +- Filter false
: +- SerializeFromObject [input[0, int, true] AS value#2]
: +- ExternalRDD [obj#1]
+- Project [value#10 AS int_col_1#12]
+- SerializeFromObject [input[0, int, true] AS value#10]
+- ExternalRDD [obj#9]
{noformat}
The optimized plan after disabling the {{PushDownPredicate}} rule:
{noformat}
== Optimized Logical Plan ==
Filter isnotnull(int_col#16)
+- Project [coalesce(int_col_1#12, int_col_6#4) AS int_col#16]
+- Join LeftOuter, false
:- Project [value#2 AS int_col_6#4]
: +- SerializeFromObject [input[0, int, true] AS value#2]
: +- ExternalRDD [obj#1]
+- Project [value#10 AS int_col_1#12]
+- SerializeFromObject [input[0, int, true] AS value#10]
+- ExternalRDD [obj#9]
{noformat}
Btw set {{spark.sql.crossJoin.enabled}} to {{true}} if you want to run this.
> Analyzer incorrectly optimizes plan to empty LocalRelation
> ----------------------------------------------------------
>
> Key: SPARK-17120
> URL: https://issues.apache.org/jira/browse/SPARK-17120
> Project: Spark
> Issue Type: Bug
> Affects Versions: 2.1.0
> Reporter: Josh Rosen
> Priority: Blocker
>
> Consider the following query:
> {code}
> sc.parallelize(Seq(97)).toDF("int_col_6").createOrReplaceTempView("table_3")
> sc.parallelize(Seq(0)).toDF("int_col_1").createOrReplaceTempView("table_4")
> println(sql("""
> SELECT
> *
> FROM (
> SELECT
> COALESCE(t2.int_col_1, t1.int_col_6) AS int_col
> FROM table_3 t1
> LEFT JOIN table_4 t2 ON false
> ) t where (t.int_col) is not null
> """).collect().toSeq)
> {code}
> In the innermost query, the LEFT JOIN's condition is {{false}} but
> nevertheless the number of rows produced should equal the number of rows in
> {{table_3}} (which is non-empty). Since no values are {{null}}, the outer
> {{where}} should retain all rows, so the overall result of this query should
> contain a single row with the value '97'.
> Instead, the current Spark master (as of
> 12a89e55cbd630fa2986da984e066cd07d3bf1f7 at least) returns no rows. Looking
> at {{explain}}, it appears that the logical plan is optimizing to
> {{LocalRelation <empty>}}, so Spark doesn't even run the query. My suspicion
> is that there's a bug in constraint propagation or filter pushdown.
> This issue doesn't seem to affect Spark 2.0, so I think it's a regression in
> master.
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