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new 898a0b46a0ab [SPARK-46640][FOLLOW-UP] Consider the whole expression
tree when excluding subquery references
898a0b46a0ab is described below
commit 898a0b46a0ab40bf201307a5d25f6028775740f2
Author: Nikhil Sheoran <[email protected]>
AuthorDate: Tue Apr 15 10:08:14 2025 +0800
[SPARK-46640][FOLLOW-UP] Consider the whole expression tree when excluding
subquery references
### What changes were proposed in this pull request?
- Context: In `RemoveRedundantAliases`, we exclude `outerAttrs` referenced
by subquery expressions when trying to identify aliases that can be removed.
Failure to do so could lead to scenarios where certain part of the plans (for
example: the join conditions in exists subquery) would end up with duplicated
expression ID(s). A fix for this was merged here in the PR here -
https://github.com/apache/spark/pull/44645.
- The fix there only accounted for the `plan.expressions` to be a
SubqueryExpression.
- We can have scenarios where the `SubqueryExpression` is wrapped in other
expressions -- for example, `Alias < CaseWhen < (SubqueryExpression)`.
- To correctly account for these, need to traverse the whole expression
tree and collect outer references from these.
- Consider plans of the form:
```
Project [CASE WHEN exists#2 [a#1 && (a#1 = a#0)] THEN 1 ELSE 2 END AS
result#3]
: +- LocalRelation <empty>, [a#0]
+- Project [a#0 AS a#1]
+- LocalRelation <empty>, [a#0]
```
- The current rule would have rewritten this as follows. Note the join
condition with conflicting expression ID(s) `a#0 = a#0`
```
Project [CASE WHEN exists#2 [a#0 && (a#0 = a#0)] THEN 1 ELSE 2 END AS
result#3]
: +- LocalRelation <empty>, [a#0]
+- LocalRelation <empty>, [a#0]
```
### Why are the changes needed?
- Queries that would have run successfully with this rule disabled would
fail.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
- Added unit tests
### Was this patch authored or co-authored using generative AI tooling?
No
Closes #50570 from nikhilsheoran-db/SPARK-46640-follow-up.
Lead-authored-by: Nikhil Sheoran
<[email protected]>
Co-authored-by: Nikhil Sheoran <[email protected]>
Signed-off-by: Wenchen Fan <[email protected]>
---
.../spark/sql/catalyst/optimizer/Optimizer.scala | 6 ++-
.../RemoveRedundantAliasAndProjectSuite.scala | 60 ++++++++++++++++++++++
2 files changed, 64 insertions(+), 2 deletions(-)
diff --git
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
index 3727b3ea19ed..7b437c302b14 100644
---
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
+++
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
@@ -671,8 +671,10 @@ object RemoveRedundantAliases extends Rule[LogicalPlan] {
val subQueryAttributes = if (conf.getConf(SQLConf
.EXCLUDE_SUBQUERY_EXP_REFS_FROM_REMOVE_REDUNDANT_ALIASES)) {
// Collect the references for all the subquery expressions in the
plan.
- AttributeSet.fromAttributeSets(plan.expressions.collect {
- case e: SubqueryExpression => e.references
+ AttributeSet.fromAttributeSets(plan.expressions.flatMap { e =>
+ e.collect {
+ case s: SubqueryExpression => s.references
+ }
})
} else {
AttributeSet.empty
diff --git
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAliasAndProjectSuite.scala
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAliasAndProjectSuite.scala
index 8a0a0466ca74..552a638f6e61 100644
---
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAliasAndProjectSuite.scala
+++
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAliasAndProjectSuite.scala
@@ -178,4 +178,64 @@ class RemoveRedundantAliasAndProjectSuite extends PlanTest
{
comparePlans(optimized, expectedWhenNotExcluded)
}
}
+
+ test("SPARK-46640: exclude outer references accounts for children of plan
expression") {
+ val a = $"a".int
+ val a_alias = Alias(a, "a")()
+ val a_alias_attr = a_alias.toAttribute
+
+ // The original input query
+ // Project [CASE WHEN exists#2 [a#1 && (a#1 = a#0)] THEN 1 ELSE 2 END AS
result#3]
+ // : +- LocalRelation <empty>, [a#0]
+ // +- Project [a#0 AS a#1]
+ // +- LocalRelation <empty>, [a#0]
+ // The subquery expression (`exists#2`) is wrapped in a CaseWhen and an
Alias.
+ // Without the fix on excluding outer references, the rewritten plan would
have been:
+ // Project [CASE WHEN exists#2 [a#0 && (a#0 = a#0)] THEN 1 ELSE 2 END AS
result#3]
+ // : +- LocalRelation <empty>, [a#0]
+ // +- LocalRelation <empty>, [a#0]
+ // This plan would then fail later with the error -- conflicting a#0 in
join condition.
+
+ val query = Project(Seq(
+ Alias(
+ CaseWhen(Seq((
+ Exists(
+ LocalRelation(a),
+ outerAttrs = Seq(a_alias_attr),
+ joinCond = Seq(EqualTo(a_alias_attr, a))
+ ), Literal(1))),
+ Some(Literal(2))),
+ "result"
+ )()),
+ Project(Seq(a_alias), LocalRelation(a))
+ )
+
+ // The alias would not be removed if excluding subquery references is
enabled.
+ val expectedWhenExcluded = query
+
+ // The alias would be removed and we would have conflicting expression
ID(s) in the join cond
+ val expectedWhenNotEnabled = Project(Seq(
+ Alias(
+ CaseWhen(Seq((
+ Exists(
+ LocalRelation(a),
+ outerAttrs = Seq(a),
+ joinCond = Seq(EqualTo(a, a))
+ ), Literal(1))),
+ Some(Literal(2))),
+ "result"
+ )()),
+ LocalRelation(a)
+ )
+
+
withSQLConf(SQLConf.EXCLUDE_SUBQUERY_EXP_REFS_FROM_REMOVE_REDUNDANT_ALIASES.key
-> "true") {
+ val optimized = Optimize.execute(query)
+ comparePlans(optimized, expectedWhenExcluded)
+ }
+
+
withSQLConf(SQLConf.EXCLUDE_SUBQUERY_EXP_REFS_FROM_REMOVE_REDUNDANT_ALIASES.key
-> "false") {
+ val optimized = Optimize.execute(query)
+ comparePlans(optimized, expectedWhenNotEnabled)
+ }
+ }
}
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