Github user chenghao-intel commented on a diff in the pull request:
https://github.com/apache/spark/pull/3249#discussion_r25551872
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -422,6 +424,108 @@ class Analyzer(catalog: Catalog,
Generate(g, join = false, outer = false, None, child)
}
}
+
+ /**
+ * Transforms the query which has subquery expressions in where clause
to left semi join.
+ * select T1.x from T1 where T1.x in (select T2.y from T2) transformed to
+ * select T1.x from T1 left semi join T2 on T1.x = T2.y.
+ */
+ object SubQueryExpressions extends Rule[LogicalPlan] {
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case p: LogicalPlan if !p.childrenResolved => p
+ case filter @ Filter(conditions, child) =>
+ val subqueryExprs = conditions.collect {
+ case In(exp, Seq(SubqueryExpression(subquery))) => (exp,
subquery)
+ }
+ // Replace subqueries with a dummy true literal since they are
evaluated separately now.
+ val transformedConds = conditions.transform {
+ case In(_, Seq(SubqueryExpression(_))) => Literal(true)
+ }
+ subqueryExprs match {
+ case Seq() => filter // No subqueries.
+ case Seq((exp, subquery)) =>
+ createLeftSemiJoin(
+ child,
+ exp,
+ subquery,
+ transformedConds)
+ case _ =>
+ throw new TreeNodeException(filter, "Only one SubQuery
expression is supported.")
+ }
+ }
+
+ /**
+ * Create LeftSemi join with parent query to the subquery which is
mentioned in 'IN' predicate
+ * And combine the subquery conditions and parent query conditions.
+ */
+ def createLeftSemiJoin(left: LogicalPlan,
+ value: Expression,
+ subquery: LogicalPlan,
+ parentConds: Expression) : LogicalPlan = {
+ val (transformedPlan, subqueryConds) =
transformAndGetConditions(value, subquery)
+ // Add both parent query conditions and subquery conditions as join
conditions
+ val allPredicates = And(parentConds, subqueryConds)
+ Join(left, transformedPlan, LeftSemi, Some(allPredicates))
+ }
+
+ /**
+ * Transform the subquery LogicalPlan and add the expressions which
are used as filters to the
+ * projection. And also return filter conditions used in subquery
+ */
+ def transformAndGetConditions(value: Expression,
+ subquery: LogicalPlan): (LogicalPlan, Expression) = {
+ val expr = new scala.collection.mutable.ArrayBuffer[Expression]()
+ // TODO : we only decorelate subqueries in very specific cases like
the cases mentioned above
+ // in documentation. The more complex queries like using of
subqueries inside subqueries can
+ // be supported in future.
+ val transformedPlan = subquery transform {
+ case project @ Project(projectList, f @ Filter(condition, child))
=>
+ // Don't support more than one item in select list of subquery
+ if(projectList.size > 1) {
+ throw new TreeNodeException(
+ project,
+ "SubQuery can contain only one item in Select List")
+ }
+ val resolvedChild = ResolveRelations(child)
--- End diff --
Why do you resolve the relation here? I believe the subquery should be
resolved already before entering the rule of `SubQueryExpressions`, is that the
limitation of using the `SubQueryExpression`, which can not check if children
logical plan if it's resolved?
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