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Posted to reviews@spark.apache.org by "averyqi-db (via GitHub)" <gi...@apache.org> on 2024/08/26 19:50:50 UTC
[PR] [SPARK-49396][SQL] remain nullability while simplifyConditional [spark]
averyqi-db opened a new pull request, #47877:
URL: https://github.com/apache/spark/pull/47877
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### What changes were proposed in this pull request?
`SimplifyConditionals` has a simplification code where if any of the (not first) branches in `CaseWhen` is `TrueLiteral` we remove all the remaining branches including the elseValue.
```
case CaseWhen(branches, ) if branches.exists(._1 == TrueLiteral) => // a branch with a true condition eliminates all following branches,
// these branches can be pruned away
val (h, t) = branches.span(_._1 != TrueLiteral)
CaseWhen( h :+ t.head, None)
```
Now, the nullability check of CaseWhen checks that
(1) either of the branches including elseValue is nullable or
(2) elseValue is None.
The above simplification makes the elseValue as None. Combined with this nullability check makes the CaseWhen switch from non-nullable to nullable.
This ticket aims to fix this issue and remain the nullability of the expression by replacing the elsevalue to the value of the TrueLiteral expression.
### Why are the changes needed?
See the section above
### Does this PR introduce _any_ user-facing change?
<!--
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no
### How was this patch tested?
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unit tests
### Was this patch authored or co-authored using generative AI tooling?
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no
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Re: [PR] [SPARK-49396][SQL] remain nullability while simplifyConditional [spark]
Posted by "averyqi-db (via GitHub)" <gi...@apache.org>.
averyqi-db closed pull request #47877: [SPARK-49396][SQL] remain nullability while simplifyConditional
URL: https://github.com/apache/spark/pull/47877
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Re: [PR] [SPARK-49396][SQL] remain nullability while simplifyConditional [spark]
Posted by "averyqi-db (via GitHub)" <gi...@apache.org>.
averyqi-db commented on PR #47877:
URL: https://github.com/apache/spark/pull/47877#issuecomment-2333069404
Closed as alternative method https://github.com/apache/spark/pull/47981 is merged.
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Re: [PR] [SPARK-49396][SQL] remain nullability while simplifyConditional [spark]
Posted by "averyqi-db (via GitHub)" <gi...@apache.org>.
averyqi-db commented on PR #47877:
URL: https://github.com/apache/spark/pull/47877#issuecomment-2319152250
cc: @cloud-fan for review and merge
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Re: [PR] [SPARK-49396][SQL] remain nullability while simplifyConditional [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #47877:
URL: https://github.com/apache/spark/pull/47877#discussion_r1740486656
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala:
##########
@@ -598,7 +598,9 @@ object SimplifyConditionals extends Rule[LogicalPlan] {
// a branch with a true condition eliminates all following branches,
// these branches can be pruned away
val (h, t) = branches.span(_._1 != TrueLiteral)
- CaseWhen( h :+ t.head, None)
+ // Use the value of TrueLiteral expression as elseValue to maintain
+ // nullability of CaseWhen expressions
+ CaseWhen(h :+ t.head, t.head._2)
Review Comment:
shall we update `CaseWhen#nullable` to consider conditions that are true literal? My point is we should keep the expression tree small for the good of optimizer, and the else value will never be used here.
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Re: [PR] [SPARK-49396][SQL] remain nullability while simplifyConditional [spark]
Posted by "kelvinjian-db (via GitHub)" <gi...@apache.org>.
kelvinjian-db commented on code in PR #47877:
URL: https://github.com/apache/spark/pull/47877#discussion_r1731808873
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala:
##########
@@ -598,7 +598,7 @@ object SimplifyConditionals extends Rule[LogicalPlan] {
// a branch with a true condition eliminates all following branches,
// these branches can be pruned away
val (h, t) = branches.span(_._1 != TrueLiteral)
- CaseWhen( h :+ t.head, None)
Review Comment:
also, can we add a comment explaining why we need to populate the else value here?
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala:
##########
@@ -598,7 +598,7 @@ object SimplifyConditionals extends Rule[LogicalPlan] {
// a branch with a true condition eliminates all following branches,
// these branches can be pruned away
val (h, t) = branches.span(_._1 != TrueLiteral)
- CaseWhen( h :+ t.head, None)
Review Comment:
nit: fix extra space?
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Re: [PR] [SPARK-49396][SQL] remain nullability while simplifyConditional [spark]
Posted by "averyqi-db (via GitHub)" <gi...@apache.org>.
averyqi-db commented on PR #47877:
URL: https://github.com/apache/spark/pull/47877#issuecomment-2310962947
cc: @nikhilsheoran-db @kelvinjian-db for review
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Re: [PR] [SPARK-49396][SQL] remain nullability while simplifyConditional [spark]
Posted by "averyqi-db (via GitHub)" <gi...@apache.org>.
averyqi-db commented on code in PR #47877:
URL: https://github.com/apache/spark/pull/47877#discussion_r1742547158
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala:
##########
@@ -598,7 +598,9 @@ object SimplifyConditionals extends Rule[LogicalPlan] {
// a branch with a true condition eliminates all following branches,
// these branches can be pruned away
val (h, t) = branches.span(_._1 != TrueLiteral)
- CaseWhen( h :+ t.head, None)
+ // Use the value of TrueLiteral expression as elseValue to maintain
+ // nullability of CaseWhen expressions
+ CaseWhen(h :+ t.head, t.head._2)
Review Comment:
Got it. Yes, it is a good idea to change null check instead. I'll investigate this path.
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