adriangb opened a new pull request, #21389:
URL: https://github.com/apache/datafusion/pull/21389
## Which issue does this PR close?
- Related to #21387 and #19435
## Rationale for this change
DataFusion has individual introspection functions (`arrow_typeof`,
`arrow_metadata`, `is_nullable`) but no single function that returns the
complete Arrow `Field` representation. Having `arrow_field(expr)` that returns
a struct with all field info avoids multiple function calls when you need the
full picture, and provides a natural complement to the existing introspection
suite.
## What changes are included in this PR?
Adds `arrow_field(expr)` scalar UDF that returns a struct:
```sql
> SELECT arrow_field(x) FROM my_table;
{name: x, data_type: Int32, nullable: false, metadata: {}}
> SELECT arrow_field(x)['data_type'] FROM my_table;
Int32
```
The returned struct has four fields:
- `name` (Utf8) — the field name
- `data_type` (Utf8) — the Arrow data type as string
- `nullable` (Boolean) — whether the field is nullable
- `metadata` (Map<Utf8, Utf8>) — the field metadata
Individual fields are accessible via bracket syntax.
**Files:**
- `datafusion/functions/src/core/arrow_field.rs` — new UDF implementation
- `datafusion/functions/src/core/mod.rs` — registration
- `datafusion/sqllogictest/test_files/arrow_field.slt` — tests
## Are these changes tested?
Yes, sqllogictest covering literals (int, null, bool, string, float, list),
table columns, nullability, and struct field access.
## Are there any user-facing changes?
New SQL function `arrow_field(expr)` is available.
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