Github user srinathshankar commented on a diff in the pull request:
https://github.com/apache/spark/pull/14866#discussion_r77219760
--- 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 --
As discussed, while it is probably best for this to be in analysis (does
throw an analysis exception after all), leaving it here until we want to
reorganize the analysis/optimizer rules.
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