Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/3249#discussion_r22363511
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -414,6 +418,123 @@ class Analyzer(catalog: Catalog,
Generate(g, join = false, outer = false, None, child)
}
}
+
+ /**
+ * Transforms the query which has subquery expressions in where clause
to join queries.
+ * Case 1 Uncorelated queries
+ * -- original query
+ * select C from R1 where R1.A in (Select B from R2)
+ * -- rewritten query
+ * Select C from R1 left semi join (select B as sqc0 from R2) subquery
on R1.A = subquery.sqc0
+ *
+ * Case 2 Corelated queries
+ * -- original query
+ * select C from R1 where R1.A in (Select B from R2 where R1.X = R2.Y)
+ * -- rewritten query
+ * select C from R1 left semi join (select B as sqc0, R2.Y as sqc1 from
R2) subquery
+ * on R1.X = subquery.sqc1 and R1.A = subquery.sqc0
+ *
+ * Refer:
https://issues.apache.org/jira/secure/attachment/12614003/SubQuerySpec.pdf
+ */
+ 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 = new scala.collection.mutable.ArrayBuffer[In]()
+ val nonSubQueryConds = new
scala.collection.mutable.ArrayBuffer[Expression]()
+ conditions.collect {
+ case s @ In(exp, Seq(SubqueryExpression(subquery))) =>
+ subqueryExprs += s
+ }
+ val transformedConds = conditions.transform {
+ // Replace with dummy
+ case s @ In(exp,Seq(SubqueryExpression(subquery))) =>
+ Literal(true)
+ }
+ if (subqueryExprs.size == 1) {
+ val subqueryExpr = subqueryExprs.remove(0)
+ createLeftSemiJoin(
+ child,
+ subqueryExpr.value,
+ subqueryExpr.list(0).asInstanceOf[SubqueryExpression].subquery,
+ transformedConds)
+ } else if (subqueryExprs.size > 1) {
+ // Only one subquery expression is supported.
+ throw new TreeNodeException(filter, "Only one SubQuery
expression is supported.")
+ } else {
+ filter
+ }
+ }
+
+ /**
+ * 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)
+ // Unify the parent query conditions and subquery conditions and add
these as join conditions
+ val unifyConds = And(parentConds, subqueryConds)
--- End diff --
This is a bit of a nit, but "unify" has [a pretty specific
meaning](http://en.wikipedia.org/wiki/Unification_%28computer_science%29) when
talking about predicates, and I don't think that is what is happening here.
Maybe `allPredicates` or something?
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