Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/12720#discussion_r61617468
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -866,71 +867,233 @@ class Analyzer(
* Note: CTEs are handled in CTESubstitution.
*/
object ResolveSubquery extends Rule[LogicalPlan] with PredicateHelper {
-
/**
- * Resolve the correlated predicates in the clauses (e.g. WHERE or
HAVING) of a
- * sub-query by using the plan the predicates should be correlated to.
+ * Resolve the correlated expressions in a subquery by using the an
outer plans' references. All
+ * resolved outer references are wrapped in an [[OuterReference]]
*/
- private def resolveCorrelatedSubquery(
- sub: LogicalPlan, outer: LogicalPlan,
- aliases: scala.collection.mutable.Map[Attribute, Alias]):
LogicalPlan = {
- // First resolve as much of the sub-query as possible
- val analyzed = execute(sub)
- if (analyzed.resolved) {
- analyzed
- } else {
- // Only resolve the lowest plan that is not resolved by outer
plan, otherwise it could be
- // resolved by itself
- val resolvedByOuter = analyzed transformDown {
- case q: LogicalPlan if q.childrenResolved && !q.resolved =>
- q transformExpressions {
- case u @ UnresolvedAttribute(nameParts) =>
- withPosition(u) {
- try {
- val outerAttrOpt = outer.resolve(nameParts, resolver)
- if (outerAttrOpt.isDefined) {
- val outerAttr = outerAttrOpt.get
- if (q.inputSet.contains(outerAttr)) {
- // Got a conflict, create an alias for the
attribute come from outer table
- val alias = Alias(outerAttr, outerAttr.toString)()
- val attr = alias.toAttribute
- aliases += attr -> alias
- attr
- } else {
- outerAttr
- }
- } else {
- u
- }
- } catch {
- case a: AnalysisException => u
+ private def resolveOuterReferences(plan: LogicalPlan, outer:
LogicalPlan): LogicalPlan = {
+ plan resolveOperators {
+ case q: LogicalPlan if q.childrenResolved && !q.resolved =>
+ q transformExpressions {
+ case u @ UnresolvedAttribute(nameParts) =>
+ withPosition(u) {
+ try {
+ outer.resolve(nameParts, resolver) match {
+ case Some(outerAttr) => OuterReference(outerAttr)
+ case None => u
}
+ } catch {
+ case _: AnalysisException => u
}
- }
- }
- if (resolvedByOuter fastEquals analyzed) {
- analyzed
- } else {
- resolveCorrelatedSubquery(resolvedByOuter, outer, aliases)
- }
+ }
+ }
}
}
+ /**
+ * Resolve the subqueries in a single LogicalPlan using the given
outer plans. This method
+ * alternates between applying the regular analyzer on the subquery
and applying the
+ * resolveOuterReferences rule.
+ */
+ private def resolveSubQueries(
+ plan: LogicalPlan,
+ outerPlans: Seq[LogicalPlan]): LogicalPlan = plan
transformExpressions {
+ case e: SubqueryExpression if !e.query.resolved =>
+ var previous: LogicalPlan = null
+ var current = e.query
+ do {
+ previous = current
+ // Try to resolve the subquery plan using the regular analyzer.
+ current = execute(current)
+
+ // Use the outer references to resolve the subquery plan if it
isn't resolved yet.
+ val i = outerPlans.iterator
+ while (!current.resolved && i.hasNext) {
+ current = resolveOuterReferences(current, i.next())
+ }
+ } while (!current.resolved && !current.fastEquals(previous))
+ e.withNewPlan(current)
+ }
+
+ /**
+ * Resolve a subquery using the outer plan. This rule creates a
dedicated analyzer which can
+ * also resolve outer plan references.
+ */
def apply(plan: LogicalPlan): LogicalPlan = plan resolveOperators {
- // Only a few unary node (Project/Filter/Aggregate/Having) could
have subquery
+ // In case of HAVING (a filter after an aggregate) we use both the
aggregate and its child for
+ // resolution.
+ case f @ Filter(_, a: Aggregate) if f.childrenResolved =>
+ resolveSubQueries(f, Seq(a, a.child))
+ // Only a few unary nodes (Project/Filter/Aggregate) can contain
subqueries.
case q: UnaryNode if q.childrenResolved =>
- val aliases = scala.collection.mutable.Map[Attribute, Alias]()
- val newPlan = q transformExpressions {
- case e: SubqueryExpression if !e.query.resolved =>
- e.withNewPlan(resolveCorrelatedSubquery(e.query, q.child,
aliases))
+ resolveSubQueries(q, Seq(q.child))
+ }
+ }
+
+ /**
+ * This rule pulls out correlated predicates out of a subquery and
finalize the resolution of
+ * subqueries. The rule transforms [[Exists]] and [[ListQuery]]
expressions into
+ * [[PredicateSubquery]] expressions.
+ */
+ object PullOutCorrelatedPredicates extends Rule[LogicalPlan] {
+ /**
+ * Pull out all (outer) correlated predicates from a given subquery.
This method removes the
+ * correlated predicates from subquery [[Filter]]s and adds the
references of these predicates
+ * to all intermediate [[Project]] and [[Aggregate]] clauses (if they
are missing) in order to
+ * be able to evaluate the predicates at the top level.
+ *
+ * This method returns the rewritten subquery and correlated
predicates.
+ */
+ private def pullOutCorrelatedPredicates(sub: LogicalPlan):
(LogicalPlan, Seq[Expression]) = {
+ val predicateMap = scala.collection.mutable.Map.empty[LogicalPlan,
Seq[Expression]]
+
+ /** Make sure a plans' subtree does not contain a tagged predicate.
*/
+ def failOnOuterReferenceInSubTree(p: LogicalPlan, msg: String): Unit
= {
+ if (p.collect(predicateMap).nonEmpty) {
+ failAnalysis(s"Accessing outer query column is not allowed in
$msg: $p")
}
- if (aliases.nonEmpty) {
- val projs = q.child.output ++ aliases.values
- Project(q.child.output,
- newPlan.withNewChildren(Seq(Project(projs, q.child))))
- } else {
- newPlan
+ }
+
+ /** Helper function for locating outer references. */
+ def containsOuter(e: Expression): Boolean = {
+ e.find(_.isInstanceOf[OuterReference]).isDefined
+ }
+
+ /** Make sure a plans' expressions do not contain a tagged
predicate. */
+ def failOnOuterReference(p: LogicalPlan): Unit = {
+ if (p.expressions.exists(containsOuter)) {
+ failAnalysis(
+ s"Correlated predicates are not supported outside of
WHERE/HAVING clauses: $p")
}
+ }
+
+ /** Determine which correlated predicate references are missing from
this plan. */
+ def missingReferences(p: LogicalPlan): AttributeSet = {
+ val localPredicateReferences = p.collect(predicateMap)
+ .flatten
+ .map(_.references)
+ .reduceOption(_ ++ _)
+ .getOrElse(AttributeSet.empty)
+ localPredicateReferences -- p.outputSet
+ }
+
+ val transformed = sub transformUp {
+ case f @ Filter(cond, child) =>
+ // Find all predicates with an outer reference.
+ val (correlated, local) =
splitConjunctivePredicates(cond).partition(containsOuter)
+
+ // Rewrite the filter without the correlated predicates if any.
+ correlated match {
+ case Nil => f
+ case xs if local.nonEmpty =>
+ val newFilter = Filter(local.reduce(And), child)
+ predicateMap += newFilter -> xs
+ newFilter
+ case xs =>
+ predicateMap += child -> xs
+ child
+ }
+ case p @ Project(expressions, child) =>
+ failOnOuterReference(p)
+ val referencesToAdd = missingReferences(p)
+ if (referencesToAdd.nonEmpty) {
+ Project(expressions ++ referencesToAdd, child)
+ } else {
+ p
+ }
+ case a @ Aggregate(grouping, expressions, child) =>
--- End diff --
`Window` is not a problem since it inherits its parents output.
We could support `Expand`, but what will the use case be? I am not sure if
grouping analytics should supported in subqueries. I am also thinking of
throwing an exception when I encounter an `Aggregate` with any grouping
expressions.
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