Github user nongli commented on a diff in the pull request:
https://github.com/apache/spark/pull/10073#discussion_r46342571
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -712,6 +711,49 @@ object PushPredicateThroughAggregate extends
Rule[LogicalPlan] with PredicateHel
}
/**
+ * Reorder the joins so that the bottom ones have at least one condition.
+ */
+object ReorderJoin extends Rule[LogicalPlan] with PredicateHelper {
+
+ /**
+ * Reorder the joins so that the bottom ones have at least one
condition.
+ */
+ def reorder(
+ input: LogicalPlan,
+ joins: Seq[LogicalPlan],
+ conditions: Seq[Expression]): LogicalPlan = {
+ // filter out the conditions that could be pushed down to `joined`
+ val otherConditions = conditions.filterNot { cond =>
+ cond.references.subsetOf(input.outputSet)
+ }
+ if (joins.isEmpty) {
+ input
+ } else if (otherConditions.isEmpty) {
+ // no condition for these joins, so put them in original order
+ (Seq(input) ++ joins).reduceLeft(Join(_, _, Inner, None))
+ } else {
+ // find out the first join that have at least one condition
+ val conditionalJoin = joins.find { plan =>
+ val refs = input.outputSet ++ plan.outputSet
+ otherConditions.exists(cond => cond.references.subsetOf(refs))
+ }
+ assert(conditionalJoin.isDefined)
+ val picked = conditionalJoin.get
+ val joined = Join(input, picked, Inner, None)
+ reorder(joined, joins.filterNot(_ eq picked), otherConditions)
+ }
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ // TODO: support outer join
+ case FilterAndInnerJoins(input, joins, filterConditions) if joins.size
> 1 =>
--- End diff --
ExtractFiltersAndInnerJoins?
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