Github user yucai commented on the pull request:
https://github.com/apache/spark/pull/11212#issuecomment-186077126
@rxin I tried your suggestion like creating PowDecimal for Decimal
specially like below:
```
case class PowDecimal(left: Expression, right: Expression)
extends BinaryMathExpression(math.pow, "POWER") {
override def inputTypes: Seq[AbstractDataType] = Seq(DecimalType,
IntegerType)
...
}
case class Pow(left: Expression, right: Expression)
extends BinaryMathExpression(math.pow, "POWER") {
...
}
```
But one concern is when "select pow(cast(2 as decimal(5,2)), 3)", how to
make the "PowDecimal" node created? The current path will create "Pow" node
anyway.
So we think of maybe we can still put Decimal processing in "Pow", but
byte/short/etc. to integer in type coercion, like below:
```
case class Pow(left: Expression, right: Expression)
extends BinaryMathExpression(math.pow, "POWER") {
override def inputTypes: Seq[AbstractDataType] = Seq(NumericType,
NumericType)
override def dataType: DataType = (left.dataType, right.dataType) match {
case (dt: DecimalType, ByteType | ShortType | IntegerType) => dt
case _ => DoubleType
}
protected override def nullSafeEval(input1: Any, input2: Any): Any =
(left.dataType, right.dataType) match {
case (dt: DecimalType, _) =>
input1.asInstanceOf[Decimal].pow(input2.asInstanceOf[Int])
case _ => math.pow(input1.asInstanceOf[Double],
input2.asInstanceOf[Double])
}
override def genCode(ctx: CodegenContext, ev: ExprCode): String = ...
}
In HiveTypeCoercion:
```
object PowCoercion extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan resolveExpressions {
case e if !e.childrenResolved => e
case e @ Pow(left, right) =>
(left.dataType, right.dataType) match {
case (dt: DecimalType, IntegerType) => e
case (DoubleType, DoubleType) => e
case (dt: DecimalType, ByteType | ShortType) =>
Pow(left, Cast(right, IntegerType))
case _ => Pow(Cast(left, DoubleType), Cast(right, DoubleType))
}
}
}
```
How do you think this way?
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