Toby1009 commented on code in PR #25526:
URL: https://github.com/apache/datafusion/pull/25526#discussion_r4056976150
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datafusion/physical-expr/src/expressions/cast.rs:
##########
@@ -283,26 +283,57 @@ impl CastExpr {
}
}
-pub(crate) fn is_order_preserving_cast_family(
- source_type: &DataType,
- target_type: &DataType,
-) -> bool {
- (source_type.is_numeric() || *source_type == Boolean) &&
target_type.is_numeric()
- || source_type.is_temporal() && target_type.is_temporal()
- || source_type.eq(target_type)
+/// Whether successful casts preserve order when conversion failures return
errors.
+/// Unlike `check_bigger_cast`, this allows precision loss and is not
sufficient
+/// for propagating distinct counts or the ordering of subsequent sort keys.
+fn is_order_preserving_cast(source_type: &DataType, target_type: &DataType) ->
bool {
+ use arrow::datatypes::TimeUnit::*;
+ if source_type == target_type
+ || (source_type.is_numeric() || *source_type == Boolean)
+ && target_type.is_numeric()
+ {
+ return true;
+ }
+ // Temporal casts are not generally monotonic: extracting time-of-day wraps
+ // at midnight, and timezone transitions can reverse the local date.
+ match (source_type, target_type) {
+ (Date32 | Date64, Date32 | Date64)
+ | (Date32 | Date64, Timestamp(_, None))
+ | (Timestamp(_, None), Date32) => true,
Review Comment:
Thanks, applied this suggestion. UTC and fixed-offset timezones now preserve
ordering for timestamp-to-Date32 and naive-to-fixed-offset timestamp casts. I
added the three requested unit cases and verified the EXPLAIN example no longer
contains the outer SortExec. The full required local test suite also passes.
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