devanshu0987 commented on PR #20059:
URL: https://github.com/apache/datafusion/pull/20059#issuecomment-3821298661
Hi @comphead and @masonh22
- Preimage result is a `Interval::try_new(lower, upper)`
- Inside `Interval::try_new`, it does a data type assert
```
assert_eq_or_internal_err!(
lower.data_type(),
upper.data_type(),
"Endpoints of an Interval should have the same type"
);
```
- Data type asserts for Decimal types also include checking precision and
scale.
```
ScalarValue::Decimal32(_, precision, scale) => {
DataType::Decimal32(*precision, *scale)
}
```
- When we add 2 Decimals, the precision changes `result_precision = max(s1,
s2) + max(p1-s1, p2-s2) + 1`
- Which makes sense to handle the overflow case: 99 + 1 = 100
- Hence, when we add 1 to find the upper bound, the resulting data type is 1
more than the lower bound, and the Interval::try_new fails.
```
SELECT arrow_typeof(CAST(100.00 AS DECIMAL(5,2)) + CAST(1.00 AS
DECIMAL(5,2)));
+-----------------------------------------+
| arrow_typeof(Float64(100) + Float64(1)) |
+-----------------------------------------+
| Decimal128(6, 2) |
+-----------------------------------------+
```
- I am hesitant about the idea of writing my own manual calculation to keep
the precision the same post addition.
- Scale < 0, Scale > 0 etc.
- Can you advise on what I should do?
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