allisonwang-db commented on code in PR #42705:
URL: https://github.com/apache/spark/pull/42705#discussion_r1323305701
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala:
##########
@@ -1405,6 +1405,11 @@ trait CheckAnalysis extends PredicateHelper with
LookupCatalog with QueryErrorsB
failOnInvalidOuterReference(g)
checkPlan(g.child, aggregated, canContainOuter)
+ // Correlated subquery can have a LIMIT clause
+ case l@Limit(_, input) =>
Review Comment:
```suggestion
case l @ Limit(_, input) =>
```
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/DecorrelateInnerQuery.scala:
##########
@@ -655,6 +655,39 @@ object DecorrelateInnerQuery extends PredicateHelper {
val newProject = Project(newProjectList ++ referencesToAdd,
newChild)
(newProject, joinCond, outerReferenceMap)
+ case Limit(limit, input) =>
+ // LIMIT K (with potential ORDER BY) is decorrelated by computing
K rows per every
+ // domain value via a row_number() window function. For example,
for a subquery
+ // (SELECT T2.a FROM T2 WHERE T2.b = OuterReference(x) ORDER BY
T2.c LIMIT 3)
+ // -- we need to get top 3 values of T2.a (ordering by T2.c) for
every value of x.
+ // Following our general decorrelation procedure, 'x' is then
replaced by T2.b, so the
+ // subquery is decorrelated as:
+ // SELECT * FROM (
Review Comment:
Great explanation here!
##########
sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/DecorrelateInnerQuerySuite.scala:
##########
@@ -59,6 +59,25 @@ class DecorrelateInnerQuerySuite extends PlanTest {
joinCond.zip(conditions).foreach(e => compareExpressions(e._1, e._2))
}
+ private def check(
+ outputPlan: LogicalPlan,
+ joinCond: Seq[Expression],
+ correctAnswer: LogicalPlan,
+ conditions: Seq[Expression]): Unit = {
+ assert(!hasOuterReferences(outputPlan))
Review Comment:
nit: indent
```suggestion
private def check(
outputPlan: LogicalPlan,
joinCond: Seq[Expression],
correctAnswer: LogicalPlan,
conditions: Seq[Expression]): Unit = {
assert(!hasOuterReferences(outputPlan))
```
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