alamb commented on code in PR #18356:
URL: https://github.com/apache/datafusion/pull/18356#discussion_r2475359272
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datafusion/functions/src/datetime/date_trunc.rs:
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@@ -482,9 +482,20 @@ fn general_date_trunc_array_fine_granularity<T:
ArrowTimestampType>(
if let Some(unit) = unit {
let original_type = array.data_type();
- let array = arrow::compute::cast(array, &DataType::Int64)?;
- let array = arrow::compute::kernels::numeric::div(&array, &unit)?;
+ let input = arrow::compute::cast(array, &DataType::Int64)?;
+ let array = arrow::compute::kernels::numeric::div(&input, &unit)?;
let array = arrow::compute::kernels::numeric::mul(&array, &unit)?;
+ // For timestamps before 1970-01-01T00:00:00Z (negative values)
+ // it is possible that the truncated value is actually later
+ // than the original value. Correct any such cases by
+ // subtracting `unit`.
+ let too_late = arrow::compute::kernels::cmp::gt(&array, &input)?;
+ let array = if too_late.true_count() > 0 {
+ let earlier = arrow::compute::kernels::numeric::sub(&array,
&unit)?;
+ arrow::compute::kernels::zip::zip(&too_late, &earlier, &array)?
+ } else {
+ array
+ };
Review Comment:
> can we maybe express this logic directly
That is an excellent point -- I think we could use the code in
https://github.com/apache/datafusion/pull/18360 to do so directly
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