CuteChuanChuan opened a new pull request, #21988:
URL: https://github.com/apache/datafusion/pull/21988
## Which issue does this PR close?
- Closes #19536.
## Rationale for this change
`MEDIAN` over integer columns previously returned the input integer type,
which truncates the `.5` produced when averaging the two middle values of an
even-length input.
For example:
```sql
SELECT median(v) FROM (VALUES (arrow_cast(-128, 'Int8')),
(arrow_cast(127, 'Int8'))) AS t(v);
-- Old: 0 (truncated from -0.5)
-- New: -0.5
## What changes are included in this PR?
- Replace Median's Signature::numeric with Signature::one_of containing
three coercible arms:
- Decimal → preserved exactly
- Float → preserved exactly
- Integer → coerced implicitly to Float64
- Update SLT and insta snapshot expectations affected by the new return type
(column type indicators I → R, previously truncated values such as -17 → -17.5).
## Are these changes tested?
Yes. Includes:
- Existing SLT cases for median over Int8/16/32/64 and UInt8/16/32/64
- Boundary cases that previously truncated.
- insta snapshot tests.
## Are there any user-facing changes?
Yes — this is a breaking change for median(<integer_column>): Return type
changes from the input integer type to Float64.
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