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fix: The inconsistency between scalar and array on the cast decimal to timestamp #16539

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Merged
findepi merged 6 commits into from
Jul 18, 2025
Merged

fix: The inconsistency between scalar and array on the cast decimal to timestamp #16539

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327530b
fix: The inconsistency between scalar and array on the cast of timestamp
chenkovsky Jun 24, 2025
1810f7d
fix for timeunit
chenkovsky Jun 25, 2025
92f26f1
fmt
chenkovsky Jun 25, 2025
d89f0f9
add slt
chenkovsky Jun 26, 2025
0b084f3
update based on findepi's suggestion
chenkovsky Jul 18, 2025
51ba6e2
Merge branch 'main' into fix/timestamp
chenkovsky Jul 18, 2025
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2 changes: 1 addition & 1 deletion datafusion/common/src/scalar/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3069,7 +3069,7 @@ impl ScalarValue {
ScalarValue::Decimal128(Some(decimal_value), _, scale),
DataType::Timestamp(time_unit, None),

@findepi findepi Jul 2, 2025

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In #16639 i tried to clear the path for more changes here.
If and once that one merged, we should be able to remove this whole code block.

@findepi findepi Jul 17, 2025

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#16639 is now merged.
please remove the whole let scalar_array = match (self, target_type) { ... } block, replacing it with just self.to_array()?.

) => {
let scale_factor = 10_i128.pow(*scale as u32);
let scale_factor = 10_i128.pow(*scale as u32 + 3);

@findepi findepi Jun 24, 2025

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Does this depend on the timestamp precision (time unit)? Can you please add tests for other units?

Do we need this special casing at all for casting decimal to timestamp?
or can we end up calling cast_with_options, just like we do for virtually all other type pairs?

@alamb alamb Jun 24, 2025

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I think the underlying arrow kernel may not support casting decimal --> timestamp (I bet this is something spark related) 🤔

@chenkovsky chenkovsky Jun 24, 2025

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I think the underlying arrow kernel may not support casting decimal --> timestamp (I bet this is something spark related) 🤔
@alamb here implements casting decimal --> timestamp
https://github.com/apache/arrow-rs/blob/b6240b32e235d4ca330372e3be31f784ba133252/arrow-cast/src/cast/mod.rs#L4032

@chenkovsky chenkovsky Jun 25, 2025

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Does this depend on the timestamp precision (time unit)? Can you please add tests for other units?

Do we need this special casing at all for casting decimal to timestamp? or can we end up calling cast_with_options, just like we do for virtually all other type pairs?

@findepi you are right, it's time unit related. I updated code.

@findepi findepi Jun 25, 2025

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I think the underlying arrow kernel may not support casting decimal --> timestamp

Can be!

So how does this work when the value is not constant-folded?
What code ends up executing in the 'normal query' case?

Can the same code be executed also in constant-folding case?

let seconds = decimal_value / scale_factor;
let fraction = decimal_value % scale_factor;

Expand Down
13 changes: 9 additions & 4 deletions datafusion/sqllogictest/test_files/timestamps.slt
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Expand Up @@ -421,12 +421,12 @@ SELECT to_timestamp(123456789.123456789) as c1, cast(123456789.123456789 as time
query PPP
SELECT to_timestamp(arrow_cast(1.1, 'Decimal128(2,1)')) as c1, cast(arrow_cast(1.1, 'Decimal128(2,1)') as timestamp) as c2, arrow_cast(1.1, 'Decimal128(2,1)')::timestamp as c3;
----
1970-01-01T00:00:01.100 1970-01-01T00:00:01.100 1970-01-01T00:00:01.100
1970-01-01T00:00:01.100 1970-01-01T00:00:00.001100 1970-01-01T00:00:00.001100

query PPP
SELECT to_timestamp(arrow_cast(-1.1, 'Decimal128(2,1)')) as c1, cast(arrow_cast(-1.1, 'Decimal128(2,1)') as timestamp) as c2, arrow_cast(-1.1, 'Decimal128(2,1)')::timestamp as c3;
----
1969-12-31T23:59:58.900 1969-12-31T23:59:58.900 1969-12-31T23:59:58.900
1969-12-31T23:59:58.900 1969-12-31T23:59:59.998900 1969-12-31T23:59:59.998900

query PPP
SELECT to_timestamp(arrow_cast(0.0, 'Decimal128(2,1)')) as c1, cast(arrow_cast(0.0, 'Decimal128(2,1)') as timestamp) as c2, arrow_cast(0.0, 'Decimal128(2,1)')::timestamp as c3;
Expand All @@ -436,12 +436,12 @@ SELECT to_timestamp(arrow_cast(0.0, 'Decimal128(2,1)')) as c1, cast(arrow_cast(0
query PPP
SELECT to_timestamp(arrow_cast(1.23456789, 'Decimal128(9,8)')) as c1, cast(arrow_cast(1.23456789, 'Decimal128(9,8)') as timestamp) as c2, arrow_cast(1.23456789, 'Decimal128(9,8)')::timestamp as c3;
----
1970-01-01T00:00:01.234567890 1970-01-01T00:00:01.234567890 1970-01-01T00:00:01.234567890
1970-01-01T00:00:01.234567890 1970-01-01T00:00:00.001234567 1970-01-01T00:00:00.001234567

query PPP
SELECT to_timestamp(arrow_cast(123456789.123456789, 'Decimal128(18,9)')) as c1, cast(arrow_cast(123456789.123456789, 'Decimal128(18,9)') as timestamp) as c2, arrow_cast(123456789.123456789, 'Decimal128(18,9)')::timestamp as c3;
----
1973-11-29T21:33:09.123456784 1973-11-29T21:33:09.123456784 1973-11-29T21:33:09.123456784
1973-11-29T21:33:09.123456784 1970-01-02T10:17:36.789123456 1970-01-02T10:17:36.789123456


# from_unixtime
Expand Down Expand Up @@ -3420,3 +3420,8 @@ select to_timestamp('-1');

query error DataFusion error: Arrow error: Parser error: Error parsing timestamp from '\-1': timestamp must contain at least 10 characters
select to_timestamp(arrow_cast('-1', 'Utf8'));

query B
SELECT CAST(CAST(x AS decimal(17,2)) AS timestamp(3)) = CAST(CAST(1 AS decimal(17,2)) AS timestamp(3)) from (values (1)) t(x);
----

@findepi findepi Jun 24, 2025

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Formatting like this will help see why these should be equal. Also it's enough to project the values. (They should be equal, but also they should be particular values).

SELECT CAST(CAST(1   AS decimal(17,2)) AS timestamp(3)) AS a UNION ALL
SELECT CAST(CAST(one AS decimal(17,2)) AS timestamp(3)) AS a FROM (VALUES (1)) t(one);

true