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Posted to reviews@spark.apache.org by "nikhilsheoran-db (via GitHub)" <gi...@apache.org> on 2024/01/09 23:07:52 UTC
[PR] [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes [spark]
nikhilsheoran-db opened a new pull request, #44645:
URL: https://github.com/apache/spark/pull/44645
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### What changes were proposed in this pull request?
- In `RemoveRedundantAliases`, we have an `excluded` AttributeSet argument denoting the references for which we should not remove aliases. For a query with subquery expressions, adding the attributes references by the subquery in the `excluded` set prevents rewrites that might remove presumedly redundant aliases. (Changes in RemoveRedundantAlias)
- Added a configuration flag to disable this fix, if not needed.
- Added a unit test with Filter exists subquery expression to show how the alias would have been removed.
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### Why are the changes needed?
- `RemoveRedundantAliases` does not take into account the outer attributes of a `SubqueryExpression` aliases, potentially removing them if it thinks they are redundant.
- This can cause scenarios where a subquery expression has conditions like `a#x = a#x` i.e. both the attribute names and the expression ID(s) are the same. This can then lead to conflicting expression ID(s) error.
- For example, in the query example below, the `RemoveRedundantAliases` would remove the alias `a#0 as a#1` and replace `a#1` with `a#0` in the Filter exists subquery expression which might create an issue if the subquery expression had an attribute with reference `a#0` (possible due to different scan relation instances possibly having the same attribute ID(s) (Ref: #40662)
```
Filter exists [a#1 && (a#1 = b#2)]
: +- LocalRelation <empty>, [b#2]
+- Project [a#0 AS a#1]
+- LocalRelation <empty>, [a#0]
```
becomes
```
Filter exists [a#0 && (a#0 = b#2)]
: +- LocalRelation <empty>, [b#2]
+- LocalRelation <empty>, [a#0]
```
- The changes are needed to fix this bug.
### Does this PR introduce _any_ user-facing change?
No
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### How was this patch tested?
- Added a unit test with Filter exists subquery expression to show how the alias would have been removed.
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### Was this patch authored or co-authored using generative AI tooling?
No
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Re: [PR] [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on PR #44645:
URL: https://github.com/apache/spark/pull/44645#issuecomment-1888316147
thanks, merging to master/3.5!
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Re: [PR] [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #44645:
URL: https://github.com/apache/spark/pull/44645#discussion_r1448871669
##########
sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAliasAndProjectSuite.scala:
##########
@@ -130,4 +131,63 @@ class RemoveRedundantAliasAndProjectSuite extends PlanTest {
correlated = false)
comparePlans(optimized, expected)
}
+
+ test("SPARK-46640: do not remove outer references from a subquery expression") {
+ val a = AttributeReference("a", IntegerType)() // a#0
+ // Keep the same name, otherwise the alias is not removed fearing schema change.
+ val a_alias = Alias(a, "a")() // a#0 as a#1
+ val a_alias_expression = AttributeReference("a", IntegerType)(exprId = a_alias.exprId) // a#1
+ val b = AttributeReference("b", IntegerType)()
+
+ // The original input query
+ // Filter exists [a#1 && (a#1 = b#2)]
+ // : +- LocalRelation <empty>, [b#2]
+ // +- Project [a#0 AS a#1]
+ // +- LocalRelation <empty>, [a#0]
+ val query = Filter(
+ Exists(
+ LocalRelation(b),
+ outerAttrs = Seq(a_alias_expression),
+ joinCond = Seq(EqualTo(a_alias_expression, b))
+ ),
+ Project(Seq(a_alias), LocalRelation(a))
+ )
+
+ // The alias would not be removed if excluding subquery references is enabled.
+ // Filter exists [a#1 && (a#1 = b#2)]
+ // : +- LocalRelation <empty>, [b#2]
+ // +- Project [a#0 AS a#1]
+ // +- LocalRelation <empty>, [a#0]
+ val expectedWhenExcluded = Filter(
Review Comment:
`val expectedWhenExcluded = query`?
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Re: [PR] [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #44645:
URL: https://github.com/apache/spark/pull/44645#discussion_r1448869794
##########
sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAliasAndProjectSuite.scala:
##########
@@ -130,4 +131,63 @@ class RemoveRedundantAliasAndProjectSuite extends PlanTest {
correlated = false)
comparePlans(optimized, expected)
}
+
+ test("SPARK-46640: do not remove outer references from a subquery expression") {
+ val a = AttributeReference("a", IntegerType)() // a#0
Review Comment:
let's follow the existing code style in this suite: `$"a".int`
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Re: [PR] [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes [spark]
Posted by "nikhilsheoran-db (via GitHub)" <gi...@apache.org>.
nikhilsheoran-db commented on PR #44645:
URL: https://github.com/apache/spark/pull/44645#issuecomment-1885740741
@jchen5 @agubichev Can you please take a look?
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Re: [PR] [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #44645:
URL: https://github.com/apache/spark/pull/44645#discussion_r1448870295
##########
sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAliasAndProjectSuite.scala:
##########
@@ -130,4 +131,63 @@ class RemoveRedundantAliasAndProjectSuite extends PlanTest {
correlated = false)
comparePlans(optimized, expected)
}
+
+ test("SPARK-46640: do not remove outer references from a subquery expression") {
+ val a = AttributeReference("a", IntegerType)() // a#0
+ // Keep the same name, otherwise the alias is not removed fearing schema change.
+ val a_alias = Alias(a, "a")() // a#0 as a#1
+ val a_alias_expression = AttributeReference("a", IntegerType)(exprId = a_alias.exprId) // a#1
Review Comment:
`a_alias.toAttribute`
##########
sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAliasAndProjectSuite.scala:
##########
@@ -130,4 +131,63 @@ class RemoveRedundantAliasAndProjectSuite extends PlanTest {
correlated = false)
comparePlans(optimized, expected)
}
+
+ test("SPARK-46640: do not remove outer references from a subquery expression") {
+ val a = AttributeReference("a", IntegerType)() // a#0
+ // Keep the same name, otherwise the alias is not removed fearing schema change.
+ val a_alias = Alias(a, "a")() // a#0 as a#1
+ val a_alias_expression = AttributeReference("a", IntegerType)(exprId = a_alias.exprId) // a#1
+ val b = AttributeReference("b", IntegerType)()
Review Comment:
ditto
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Re: [PR] [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes [spark]
Posted by "nikhilsheoran-db (via GitHub)" <gi...@apache.org>.
nikhilsheoran-db commented on PR #44645:
URL: https://github.com/apache/spark/pull/44645#issuecomment-1885801958
@cloud-fan Can you take a look at this?
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Re: [PR] [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan closed pull request #44645: [SPARK-46640][SQL] Fix RemoveRedundantAlias by excluding subquery attributes
URL: https://github.com/apache/spark/pull/44645
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