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https://issues.apache.org/jira/browse/SPARK-17298?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15446682#comment-15446682
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Srinath commented on SPARK-17298:
---------------------------------
You are correct that with this change, queries of the form
{noformat}
select * from A inner join B
{noformat}
will now throw an error where previously they would not.
The reason for this suggestion is that users may often forget to specify join
conditions altogether, leading to incorrect, long-running queries. Requiring
explicit cross joins helps clarify intent.
Turning on the spark.sql.crossJoin.enabled flag will revert to previous
behavior.
> Require explicit CROSS join for cartesian products
> --------------------------------------------------
>
> Key: SPARK-17298
> URL: https://issues.apache.org/jira/browse/SPARK-17298
> Project: Spark
> Issue Type: Story
> Components: SQL
> Reporter: Srinath
> Priority: Minor
>
> Require the use of CROSS join syntax in SQL (and a new crossJoin DataFrame
> API) to specify explicit cartesian products between relations.
> By cartesian product we mean a join between relations R and S where there is
> no join condition involving columns from both R and S.
> If a cartesian product is detected in the absence of an explicit CROSS join,
> an error must be thrown. Turning on the spark.sql.crossJoin.enabled
> configuration flag will disable this check and allow cartesian products
> without an explicit cross join.
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