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https://issues.apache.org/jira/browse/SPARK-10707?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14977084#comment-14977084
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Apache Spark commented on SPARK-10707:
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User 'mbautin' has created a pull request for this issue:
https://github.com/apache/spark/pull/9308
> Set operation output columns may have incorrect nullability
> -----------------------------------------------------------
>
> Key: SPARK-10707
> URL: https://issues.apache.org/jira/browse/SPARK-10707
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Reporter: Mikhail Bautin
> Assignee: Mark Hamstra
>
> If "dual" is a one-row table, the query
> SELECT count(v) FROM (
> SELECT v FROM (
> SELECT NULL AS v FROM dual
> UNION ALL
> SELECT 'foo' AS v FROM dual
> ) my_union WHERE isnull(v)
> ) my_subview;
> returns 0 and the same query with union'ed sub-queries switched returns 1:
> SELECT count(v) FROM (
> SELECT v FROM (
> SELECT 'foo' AS v FROM dual
> UNION ALL
> SELECT NULL AS v FROM dual
> ) my_union WHERE isnull(v)
> ) my_subview;
> Example output (with Catalyst tracing turned on):
> https://gist.githubusercontent.com/mbautin/c916a2a7ce733d039137/raw
> This is caused by the behavior in set operation implementation where only the
> nullability of the first child is taken into account:
> SetOperation in org.apache.spark.sql.catalyst.plans.logical:
> https://github.com/apache/spark/blob/82268f07abfa658869df2354ae72f8d6ddd119e8/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicOperators.scala#L93
> Union in org.apache.spark.sql.execution:
> https://github.com/apache/spark/blob/e626ac5f5c27dcc74113070f2fec03682bcd12bd/sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala#L178
> Intersect in org.apache.spark.sql.execution:
> https://github.com/apache/spark/blob/e626ac5f5c27dcc74113070f2fec03682bcd12bd/sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala#L320
> Except in org.apache.spark.sql.execution:
> https://github.com/apache/spark/blob/e626ac5f5c27dcc74113070f2fec03682bcd12bd/sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala#L307
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