[GitHub] spark pull request #14866: [SPARK-17298][SQL] Require explicit CROSS join fo...

[gatorsmile <gi...@git.apache.org>]

Github user gatorsmile commented on a diff in the pull request:

    https://github.com/apache/spark/pull/14866#discussion_r98750834
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala ---
    @@ -933,6 +936,47 @@ object CombineLimits extends Rule[LogicalPlan] {
     }
     
     /**
    + * Check if there any cartesian products between joins of any type in the optimized plan tree.
    + * Throw an error if a cartesian product is found without an explicit cross join specified.
    + * This rule is effectively disabled if the CROSS_JOINS_ENABLED flag is true.
    + *
    + * This rule must be run AFTER the ReorderJoin rule since the join conditions for each join must be
    + * collected before checking if it is a cartesian product. If you have
    + * SELECT * from R, S where R.r = S.s,
    + * the join between R and S is not a cartesian product and therefore should be allowed.
    + * The predicate R.r = S.s is not recognized as a join condition until the ReorderJoin rule.
    + */
    +case class CheckCartesianProducts(conf: CatalystConf)
    --- End diff --
    
    If we do it here, it does not cover all the cases, right? `Cartesian Product` might be chosen based on the statistics. 


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