wangyum commented on a change in pull request #35220:
URL: https://github.com/apache/spark/pull/35220#discussion_r786765871
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
##########
@@ -1037,13 +1037,26 @@ object SimplifyCasts extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan =
plan.transformAllExpressionsWithPruning(
_.containsPattern(CAST), ruleId) {
case Cast(e, dataType, _, _) if e.dataType == dataType => e
+ case c @ Cast(Cast(e, dt1, _, _), dt2, _, _)
+ if isWiderCast(e.dataType, dt1) && isWiderCast(dt1, dt2) =>
+ c.copy(child = e)
case c @ Cast(e, dataType, _, _) => (e.dataType, dataType) match {
case (ArrayType(from, false), ArrayType(to, true)) if from == to => e
case (MapType(fromKey, fromValue, false), MapType(toKey, toValue, true))
if fromKey == toKey && fromValue == toValue => e
case _ => c
}
}
+
+ // 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: DataType): Boolean = (from, to)
match {
+ case _ if from == to => true
+ 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 _ => false
+ }
Review comment:
We only support `NumericType`. not all data types can combine. For
example:
```scala
sql("create table t1(id timestamp) using parquet")
sql("insert into t1 values(now())")
sql("select cast(cast(id as long) as string) from
t1").collect().foreach(println)
```
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