adriangb opened a new pull request, #19389:
URL: https://github.com/apache/datafusion/pull/19389
## Summary
This PR extends `get_field` to accept multiple field name arguments for
nested struct/map access, enabling `get_field(col, 'a', 'b', 'c')` as
equivalent to `col['a']['b']['c']`.
**The primary motivation is to make it easier for downstream optimizations
to match on and optimize struct/map field access patterns.** By representing
`col['a']['b']['c']` as a single `get_field(col, 'a', 'b', 'c')` call rather
than nested `get_field(get_field(get_field(col, 'a'), 'b'), 'c')` calls,
optimization rules can more easily identify and transform field access patterns.
## Changes
- **Variadic signature**: `get_field` now accepts 2+ arguments (base + one
or more field names)
- **Type validation at planning time**: Accessing a field on a
non-struct/map type (e.g., `get_field({a: 1}, 'a', 'b')`) fails during planning
with a clear error message indicating which argument position caused the failure
- **Bracket syntax optimization**: The `FieldAccessPlanner` now merges
consecutive bracket accesses into a single `get_field` call (e.g.,
`s['a']['b']` → `get_field(s, 'a', 'b')`)
- **Mixed access handling**: Array index access correctly breaks the
batching (e.g., `s['a'][0]['b']` → `get_field(array_element(get_field(s, 'a'),
0), 'b')`)
## Example
```sql
-- Direct function call with nested access
SELECT get_field(my_struct, 'outer', 'inner', 'value');
-- Equivalent bracket syntax (now optimized to single get_field)
SELECT my_struct['outer']['inner']['value'];
-- EXPLAIN shows single get_field call
EXPLAIN SELECT s['a']['b'] FROM t;
-- Projection: get_field(t.s, Utf8("a"), Utf8("b"))
```
## Backwards Compatibility
- The original 2-argument form `get_field(struct, 'field')` continues to
work unchanged
- Existing queries using bracket syntax will automatically benefit from the
optimization
## Test plan
- [x] Backwards compatibility test for 2-argument form
- [x] Multi-level get_field with 2, 3, and 5 levels of nesting
- [x] Type validation error tests at argument positions 2, 3, 4
- [x] Non-existent field error tests
- [x] Null handling (null at base, null in middle of chain)
- [x] Mixed array/struct access (verifies array index breaks batching)
- [x] Nullable parent propagation
- [x] EXPLAIN test verifying single get_field call for bracket syntax
- [x] Minimum argument validation (0 and 1 argument cases)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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