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[SPARK-39963][SQL] Simplify SimplifyCasts.isWiderCast #37389

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[SPARK-39963][SQL] Simplify SimplifyCasts.isWiderCast #37389

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[SPARK-39963][SQL] Simplify the implementation of SimplifyCasts
beliefer Aug 3, 2022
99bf971
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beliefer Aug 4, 2022
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8 changes: 2 additions & 6 deletions sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1036,12 +1036,8 @@ object SimplifyCasts extends Rule[LogicalPlan] {

// Returns whether the from DataType can be safely casted to the to DataType without losing
// any precision or range.
private def isWiderCast(from: DataType, to: NumericType): Boolean = (from, to) match {
case (from: NumericType, to: DecimalType) if to.isWiderThan(from) => true
case (from: DecimalType, to: NumericType) if from.isTighterThan(to) => true
case (from: IntegralType, to: IntegralType) => Cast.canUpCast(from, to)
case _ => from == to

@xkrogen xkrogen Aug 3, 2022 •
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This refactor changes the behavior when from is non-numeric and from == to. Previously returns true, now false. Is this intentional?

To preserve behavior, and be more Scala-idiomatic by using pattern matching instead of isInstanceOf, I would suggest:

  private def isWiderCast(from: DataType, to: NumericType): Boolean = from match {
    case NumericType => Cast.canUpCast(from, to)
    case _ => from == to
  }

@beliefer beliefer Aug 4, 2022

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Previously, when from is non-numeric, from == to must be false.

@dongjoon-hyun dongjoon-hyun Aug 4, 2022

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Do we have an existing test coverage for the case discussed in this thread?

@beliefer beliefer Aug 4, 2022

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Previously, the existing test cases does't cover the case discussed above.
So, let's add one.

}
private def isWiderCast(from: DataType, to: NumericType): Boolean =
from.isInstanceOf[NumericType] && Cast.canUpCast(from, to)
}


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4 changes: 4 additions & 0 deletions sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/SimplifyCastsSuite.scala
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Expand Up @@ -95,6 +95,10 @@ class SimplifyCastsSuite extends PlanTest {
Optimize.execute(
input.select($"b".cast(DecimalType(10, 2)).cast(DecimalType(24, 2)).as("casted")).analyze),
input.select($"b".cast(DecimalType(10, 2)).cast(DecimalType(24, 2)).as("casted")).analyze)
comparePlans(
Optimize.execute(
input.select($"c".cast(DecimalType(10, 2)).cast(DecimalType(24, 2)).as("casted")).analyze),
input.select($"c".cast(DecimalType(10, 2)).cast(DecimalType(24, 2)).as("casted")).analyze)

comparePlans(
Optimize.execute(
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