Zouxxyy opened a new pull request, #7976:
URL: https://github.com/apache/paimon/pull/7976
### Purpose
Route MERGE INTO assignment alignment through `PaimonOutputResolver`
so MERGE / UPDATE / INSERT share one name-based, depth-aware alignment
path with consistent merge-schema semantics.
Behavior is controlled by `spark.paimon.write.merge-schema`:
- Top-level alignment is by name. Unmentioned target columns are
NULL-filled under explicit clauses (matches Spark INSERT FILL).
- `INSERT *` / `UPDATE *` with a source column missing from the target
throws when `merge-schema=false`; when `true`, source-extras are kept
so `SchemaHelper` evolves the table at write time.
- Nested struct alignment follows `MissingFieldBehavior`:
- `FailMissing` (`merge-schema=false`): nested missing target /
source-extra throws.
- `NullForMissing` (`merge-schema=true`, INSERT and explicit UPDATE):
missing nested fields NULL-fill, source-extras kept at any depth.
- `PreserveTarget` (`merge-schema=true`, `UPDATE *` on a struct
target): missing source subfields are substituted with
`GetStructField(target, ordinal)` so unmentioned subfields keep
their current value instead of being nulled.
### Tests
New `MergeIntoAlignmentTest` (24 cases) covers basic `UPDATE *` /
`INSERT *`, source-extra drop under strict star, top-level and nested
merge-schema evolution, `PreserveTarget` semantics on nested struct
`UPDATE *`, explicit assignments to nested fields, and null-fill for
omitted columns.
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