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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