MaxGekk commented on code in PR #56810:
URL: https://github.com/apache/spark/pull/56810#discussion_r3481911342
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sql/api/src/main/scala/org/apache/spark/sql/types/UpCastRule.scala:
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@@ -36,10 +36,17 @@ private[sql] object UpCastRule {
case (from: NumericType, to: DecimalType) if to.isWiderThan(from) => true
case (from: DecimalType, to: NumericType) if from.isTighterThan(to) => true
case (f, t) if legalNumericPrecedence(f, t) => true
- case (DateType, TimestampType) => true
- case (DateType, TimestampNTZType) => true
- case (TimestampNTZType, TimestampType) => true
- case (TimestampType, TimestampNTZType) => true
+ // Widening DATE -> timestamp family (micro or nanos, LTZ or NTZ) is
lossless; the reverse
+ // (timestamp -> DATE) drops the time-of-day and is not matched here, so
it stays a non-up-cast.
+ case (DateType, t) if TimestampFamily.fractionalPrecision(t).isDefined =>
true
+ // Lossless widening within the timestamp family: target fractional-second
precision >= source.
+ // Covers micros <-> nanos and the cross-family LTZ <-> NTZ pairs
(mirroring how the micro
+ // TimestampType <-> TimestampNTZType pair is a mutual up-cast). Equal
precision is handled by
+ // the `from == to` short-circuit above; lossy narrowing falls through to
`case _ => false`.
+ case (f, t)
+ if TimestampFamily.fractionalPrecision(f).isDefined &&
+ TimestampFamily.fractionalPrecision(t).isDefined =>
+ TimestampFamily.fractionalPrecision(f).get <=
TimestampFamily.fractionalPrecision(t).get
Review Comment:
Thanks — adopted the `.exists` form in 2302117. I kept it as a guard with a
`=> true` body rather than a guardless `case (f, t) =>`, since a guardless
catch-all here would shadow the
`String`/`Null`/`Timestamp↔Long`/`Array`/`Map`/`Struct` cases just below and
return `false` for those non-timestamp pairs. Also tightened the adjacent
comment about equal-precision handling.
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