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[SPARK-33354][SQL] New explicit cast syntax rules in ANSI mode #30260

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[SPARK-33354][SQL] New explicit cast syntax rules in ANSI mode #30260

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18b49bf
ansi canCast
gengliangwang Nov 9, 2020
f74c488
add comment; rename requiredAnsiEnabledForOverflowTestCases
gengliangwang Nov 11, 2020
7bfb1a6
reorder
gengliangwang Nov 11, 2020
e6faf4b
upper case
gengliangwang Nov 11, 2020
33452cd
update doc
gengliangwang Nov 11, 2020
ce0e775
address comments
gengliangwang Nov 12, 2020
1d57a24
reorg tests
gengliangwang Nov 18, 2020
6003bef
address comments
gengliangwang Nov 18, 2020
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72 changes: 71 additions & 1 deletion sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@ import java.util.concurrent.TimeUnit._
import org.apache.spark.SparkException
import org.apache.spark.sql.catalyst.InternalRow
import org.apache.spark.sql.catalyst.analysis.{TypeCheckResult, TypeCoercion}
import org.apache.spark.sql.catalyst.expressions.Cast.{canCast, forceNullable, resolvableNullability}
import org.apache.spark.sql.catalyst.expressions.codegen._
import org.apache.spark.sql.catalyst.expressions.codegen.Block._
import org.apache.spark.sql.catalyst.util._
Expand Down Expand Up @@ -258,13 +259,18 @@ abstract class CastBase extends UnaryExpression with TimeZoneAwareExpression wit

def dataType: DataType

/**
* Returns true iff we can cast `from` type to `to` type.
*/
def canCast(from: DataType, to: DataType): Boolean

override def toString: String = {
val ansi = if (ansiEnabled) "ansi_" else ""
s"${ansi}cast($child as ${dataType.simpleString})"
}

override def checkInputDataTypes(): TypeCheckResult = {
if (Cast.canCast(child.dataType, dataType)) {
if (canCast(child.dataType, dataType)) {
TypeCheckResult.TypeCheckSuccess
} else {
TypeCheckResult.TypeCheckFailure(
Expand Down Expand Up @@ -1753,6 +1759,12 @@ case class Cast(child: Expression, dataType: DataType, timeZoneId: Option[String
copy(timeZoneId = Option(timeZoneId))

override protected val ansiEnabled: Boolean = SQLConf.get.ansiEnabled

override def canCast(from: DataType, to: DataType): Boolean = if (ansiEnabled) {
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@maropu maropu Nov 10, 2020

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How about describing this new behaviour in the usage above of ExpressionDescription?

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@gengliangwang gengliangwang Nov 11, 2020

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well, then we need to mention about the behavior of throwing overflow exceptions when ANSI flag enabled. I will add some content in the sql-ref-ansi-compliance.md

AnsiCast.canCast(from, to)
} else {
Cast.canCast(from, to)
}
}

/**
Expand All @@ -1770,6 +1782,64 @@ case class AnsiCast(child: Expression, dataType: DataType, timeZoneId: Option[St
copy(timeZoneId = Option(timeZoneId))

override protected val ansiEnabled: Boolean = true

override def canCast(from: DataType, to: DataType): Boolean = AnsiCast.canCast(from, to)
}

object AnsiCast {
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@maropu maropu Nov 10, 2020

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Could you leave some comments to summarize the current behaivour of the ANSI explicit cast as described in the PR description (references section 6.13 of the ANSI SQL standard and differences from the standard, e.g., Numeric <=> Boolean) ?

def canCast(from: DataType, to: DataType): Boolean = (from, to) match {
case (fromType, toType) if fromType == toType => true

case (NullType, _) => true

case (_: NumericType, _: NumericType) => true
case (StringType, _: NumericType) => true
case (BooleanType, _: NumericType) => true
Comment on lines +1854 to +1856
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@maropu maropu Nov 10, 2020

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(Just a suggestion) For readability, could you reorder these entries according to Cast.canCast where possible? For example, the numeric entries for Cast seems to be placed just before complex types:

spark/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala

Lines 70 to 74 in 35ac314

case (StringType, _: NumericType) => true
case (BooleanType, _: NumericType) => true
case (DateType, _: NumericType) => true
case (TimestampType, _: NumericType) => true
case (_: NumericType, _: NumericType) => true


case (_: NumericType, StringType) => true
case (_: DateType, StringType) => true
case (_: TimestampType, StringType) => true
case (_: CalendarIntervalType, StringType) => true
case (BooleanType, StringType) => true
case (BinaryType, StringType) => true

case (StringType, DateType) => true
case (TimestampType, DateType) => true

case (StringType, TimestampType) => true
case (DateType, TimestampType) => true

case (StringType, _: CalendarIntervalType) => true

case (StringType, BooleanType) => true
case (_: NumericType, BooleanType) => true

case (StringType, _: BinaryType) => true

case (ArrayType(fromType, fn), ArrayType(toType, tn)) =>
canCast(fromType, toType) &&
resolvableNullability(fn || forceNullable(fromType, toType), tn)

case (MapType(fromKey, fromValue, fn), MapType(toKey, toValue, tn)) =>
canCast(fromKey, toKey) &&
(!forceNullable(fromKey, toKey)) &&
canCast(fromValue, toValue) &&
resolvableNullability(fn || forceNullable(fromValue, toValue), tn)

case (StructType(fromFields), StructType(toFields)) =>
fromFields.length == toFields.length &&
fromFields.zip(toFields).forall {
case (fromField, toField) =>
canCast(fromField.dataType, toField.dataType) &&
resolvableNullability(
fromField.nullable || forceNullable(fromField.dataType, toField.dataType),
toField.nullable)
}

case (udt1: UserDefinedType[_], udt2: UserDefinedType[_]) if udt2.acceptsType(udt1) => true

case _ => false
}
}

/**
Expand Down
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