Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/18692#discussion_r152412423 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala --- @@ -152,3 +152,71 @@ object EliminateOuterJoin extends Rule[LogicalPlan] with PredicateHelper { if (j.joinType == newJoinType) f else Filter(condition, j.copy(joinType = newJoinType)) } } + +/** + * A rule that uses propagated constraints to infer join conditions. The optimization is applicable + * only to CROSS joins. + * + * For instance, if there is a CROSS join, where the left relation has 'a = 1' and the right + * relation has 'b = 1', then the rule infers 'a = b' as a join predicate. + */ +object InferJoinConditionsFromConstraints extends Rule[LogicalPlan] with PredicateHelper { --- End diff -- Yes. Since we decide to focus on cross join only, we should rename it to `EliminateCrossJoin `, like what you proposed.
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