Github user sameeragarwal commented on a diff in the pull request:
https://github.com/apache/spark/pull/14866#discussion_r76884744
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -933,6 +936,45 @@ 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)
+ extends Rule[LogicalPlan] with PredicateHelper {
+ /**
+ * Check if a join specified by left, right and condition is a cartesian
product. Returns true if
+ * there are no join conditions involving references from both left and
right.
+ */
+ def isCartesianProduct(left: LogicalPlan, right: LogicalPlan, condition:
Option[Expression])
+ : Boolean = {
+ val conditions =
condition.map(splitConjunctivePredicates).getOrElse(Nil)
+ !conditions.map(_.references).exists(refs =>
refs.exists(left.outputSet.contains)
+ && refs.exists(right.outputSet.contains))
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan =
+ if (conf.allowCartesianProduct) {
+ plan
+ } else plan transform {
+ case j @ Join(left, right, Inner(false) | LeftOuter | RightOuter |
FullOuter, condition)
+ if isCartesianProduct(left, right, condition) =>
+ throw new AnalysisException(
+ s"""Detected cartesian product for ${j.joinType.sql} join
between logical plans
+ |${left.treeString(false).trim}
+ |and
+ |${right.treeString(false).trim}
+ |Use a CROSS JOIN to allow cartesian products between these
relations""".stripMargin)
--- End diff --
Should we also talk about the conf flag here?
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