tustvold commented on code in PR #5603:
URL: https://github.com/apache/arrow-datafusion/pull/5603#discussion_r1137254192
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datafusion/common/src/scalar.rs:
##########
@@ -563,46 +843,154 @@ macro_rules! get_sign {
};
}
+#[derive(Clone, Copy)]
+enum IntervalMode {
+ Milli,
+ Nano,
+}
+
+/// This function computes subtracts `rhs_ts` from `lhs_ts`, taking timezones
+/// into account when given. Units of the resulting interval is specified by
+/// the argument `mode`.
+/// The default behavior of Datafusion is the following:
+/// - When subtracting timestamps at seconds/milliseconds precision, the output
+/// interval will have the type [`IntervalDayTimeType`].
+/// - When subtracting timestamps at microseconds/nanoseconds precision, the
+/// output interval will have the type [`IntervalMonthDayNanoType`].
+fn ts_sub_to_interval(
+ lhs_ts: i64,
+ rhs_ts: i64,
+ lhs_tz: &Option<String>,
+ rhs_tz: &Option<String>,
+ mode: IntervalMode,
+) -> Result<ScalarValue, DataFusionError> {
+ let lhs_dt = with_timezone_to_naive_datetime(lhs_ts, lhs_tz, mode)?;
+ let rhs_dt = with_timezone_to_naive_datetime(rhs_ts, rhs_tz, mode)?;
+ let delta_secs = lhs_dt.signed_duration_since(rhs_dt);
+
+ match mode {
+ IntervalMode::Milli => {
+ let as_millisecs = delta_secs.num_milliseconds();
+ Ok(ScalarValue::IntervalDayTime(Some(
+ IntervalDayTimeType::make_value(
+ (as_millisecs / MILLISECS_IN_ONE_DAY) as i32,
+ (as_millisecs % MILLISECS_IN_ONE_DAY) as i32,
+ ),
+ )))
+ }
+ IntervalMode::Nano => {
+ let as_nanosecs = delta_secs.num_nanoseconds().ok_or_else(|| {
+ DataFusionError::Execution(String::from(
+ "Can not compute timestamp differences with nanosecond
precision",
+ ))
+ })?;
+ Ok(ScalarValue::IntervalMonthDayNano(Some(
+ IntervalMonthDayNanoType::make_value(
+ 0,
+ (as_nanosecs / NANOSECS_IN_ONE_DAY) as i32,
+ as_nanosecs % NANOSECS_IN_ONE_DAY,
+ ),
+ )))
+ }
+ }
+}
+
+/// This function creates the [`NaiveDateTime`] object corresponding to the
+/// given timestamp using the units (tick size) implied by argument `mode`.
+#[inline]
+fn with_timezone_to_naive_datetime(
Review Comment:
> corresponding UTC offsets of these timestamps
The timezones may not be of the form `"+02:00"` they might also be
`"America/Los_Angeles"` in which case the offset to UTC depends on the date in
question. See
https://github.com/apache/arrow-rs/pull/3801/files#diff-5f92a7816bbae9b685c2f85ab84a268b85246bfaa14272c5afd339810ad471f3R22
My suggestion is to use the chrono `DateTime` abstraction to handle applying
the offset correctly, along with `Tz` to handle parsing the timezone string
correctly.
In particular
[as_datetime](https://docs.rs/arrow-array/latest/arrow_array/temporal_conversions/fn.as_datetime.html)
and
[as_datetime_with_timezone](https://docs.rs/arrow-array/latest/arrow_array/temporal_conversions/fn.as_datetime_with_timezone.html)
handle the cases of no timezone and a timezone respectively. You could perhaps
crib from them, or even use them directly
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