Kevin-Li-2025 opened a new pull request, #23225:
URL: https://github.com/apache/datafusion/pull/23225
## What changed
Fixes #23045 by making `type_union_resolution` use the union-context
numeric/string coercion rule instead of the comparison-context rule.
This means union-resolution contexts such as `COALESCE` prefer a string type
when combining numeric and string inputs. That avoids inserting casts like
`CAST('' AS Int64)` for `coalesce(1, '')`, because arbitrary strings are not
guaranteed to parse as numbers.
## Why
`type_union_coercion` already documents and tests this distinction:
- comparison contexts prefer numeric semantics for numeric/string pairs
- union contexts prefer string semantics because every number can be
represented as text, but not every string can be represented as a number
`type_union_resolution` was still using `string_numeric_coercion`, which is
the comparison-style numeric preference. `COALESCE` calls
`try_type_union_resolution`, so `coalesce(1, '')` was typed as `Int64`.
## Testing
```text
cargo test -p datafusion-expr-common type_union
cargo test -p datafusion-expr-common string_numeric_coercion
cargo test -p datafusion-sqllogictest --test sqllogictests --
test_files/coalesce.slt
cargo fmt --all --check
git diff --check
```
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