adriangb commented on code in PR #25099:
URL: https://github.com/apache/datafusion/pull/25099#discussion_r3971249533
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datafusion/expr-common/src/casts.rs:
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@@ -120,10 +120,34 @@ fn is_lossy_temporal_cast(from_type: &DataType, to_type:
&DataType) -> bool {
if is_date_type(from_type) && is_date_type(to_type) {
return false;
}
+ if let (DataType::Timestamp(_, from_tz), DataType::Timestamp(_, to_tz)) =
+ (from_type, to_type)
+ && from_tz.is_some() != to_tz.is_some()
+ {
+ let tz = from_tz.as_ref().or(to_tz.as_ref()).unwrap().as_ref();
+ if !is_zero_offset_timezone(tz) {
+ return true;
+ }
+ }
(is_date_type(from_type) && to_type.is_temporal())
|| (is_date_type(to_type) && from_type.is_temporal())
}
+/// Returns true if the timezone is known to have a fixed zero offset from UTC.
+///
+/// This is used to determine if a cast between a timezone-aware and
timezone-naive
+/// timestamp is lossy. If the timezone is strictly UTC-equivalent, the cast is
+/// a lossless re-labeling of the integer value.
+fn is_zero_offset_timezone(tz: &str) -> bool {
+ match tz {
+ // Standard UTC identifiers
+ "UTC" | "Etc/UTC" | "GMT" | "Etc/GMT" | "Greenwich" | "Z" => true,
+ // Common fixed offset zero strings parsed by Arrow
+ "+00:00" | "-00:00" | "+0:00" | "-0:00" => true,
+ _ => false,
Review Comment:
Is there no function in arrow-rs or chrono we could use for this?
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