[spark] Support merge schema in MERGE INTO#7789
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May 13, 2026
…7843) Follow-up of #7789. Extend `SchemaMergingUtils.diffSchemaChanges` to emit precise `AddColumn` for new struct fields nested inside `ARRAY` element / `MAP` value, instead of a coarse `UpdateColumnType` rewriting the whole nested type. Falls back to `UpdateColumnType` when a nested field is removed or a map key type changes.
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Purpose
Add schema evolution support for MERGE INTO and fix nested-field alignment.
spark.paimon.write.merge-schema=true,UPDATE */INSERT *evolves target schema with new source columns. Star clauses pull from source by name; explicit clauses fill NULL.FROM_STARTreeNodeTagpreserves the original star intent, so a fully-listed explicit clause is not mistaken for*.AssignmentAlignmentHelpernow reorders nested struct / array / map fields by name.Scope
UPDATE */INSERT *→ evolveTests
13 new cases in
MergeIntoTableTestBaseplusWHEN NOT MATCHED BY SOURCEcoverage inMergeIntoNotMatchedBySourceTest.