Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/3249#discussion_r22004962
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -314,6 +318,113 @@ class Analyzer(catalog: Catalog, registry:
FunctionRegistry, caseSensitive: Bool
protected def containsStar(exprs: Seq[Expression]): Boolean =
exprs.collect { case _: Star => true }.nonEmpty
}
+
+ /**
+ * 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 filter @ Filter(conditions, child) =>
+ val subqueryExprs = new
scala.collection.mutable.ArrayBuffer[SubqueryExpression]()
+ val nonSubQueryConds = new
scala.collection.mutable.ArrayBuffer[Expression]()
+ val transformedConds = conditions.transform{
+ // Replace with dummy
+ case s @ SubqueryExpression(exp,subquery) =>
+ subqueryExprs += s
+ Literal(true)
+ }
+ if (subqueryExprs.size == 1) {
+ val subqueryExpr = subqueryExprs.remove(0)
+ createLeftSemiJoin(
+ child, subqueryExpr.value,
+ subqueryExpr.subquery, transformedConds)
+ } else if (subqueryExprs.size > 1) {
+ // Only one subquery expression is supported.
+ throw new TreeNodeException(filter, "Only 1 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)
+ Join(left, transformedPlan, LeftSemi, Some(unifyConds))
+ }
+
+ /**
+ * 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]()
+ val transformedPlan = subquery transform {
+ case project @ Project(projectList, f @ Filter(condition, child))
=>
+ // Don't support more than 1 item in select list of subquery
+ if(projectList.size > 1) {
+ throw new TreeNodeException(project, "SubQuery can contain
only 1 item in Select List")
+ }
+ val resolvedChild = ResolveRelations(child)
+ // Add the expressions to the projections which are used as
filters in subquery
+ val toBeAddedExprs = f.references.filter(
+ a=>resolvedChild.resolve(a.name, resolver) != None &&
!projectList.contains(a))
--- End diff --
A few things here
- I'd add the guard above so we don't have to resolve here. Hand
resolution like you are doing here will work for simple cases but doesn't run
to fixed point.
- Never compare attributes by name, and don't inspect the project list to
see what the output will be. The reasons are as follows: names can be
ambiguous and the project list could have aliases and other things that confuse
the inspection. Instead use `outputSet` which returns an `AttributeSet` that
does comparisons correctly.
- if you need multi line lambas, prefer the following syntax:
```
list.filter { a =>
a....
}
```
All together I think you want something like:
```scala
f.references.filterNot(project.outputSet.contains)
```
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