szehon-ho opened a new pull request, #56710: URL: https://github.com/apache/spark/pull/56710
### What changes were proposed in this pull request? This PR documents `MERGE WITH SCHEMA EVOLUTION` in the MERGE INTO SQL reference (`docs/sql-ref-syntax-dml-merge-into.md`), mirroring the existing INSERT INTO schema evolution documentation. Specifically it: - Adds `[ WITH SCHEMA EVOLUTION ]` to the **Syntax** and a `WITH SCHEMA EVOLUTION` entry to the **Parameters**. - Adds notes describing what triggers schema evolution: only columns referenced by a direct assignment are added/widened; `UPDATE SET *` / `INSERT *` count as direct assignments of every target column; and directly assigning a struct column counts as a direct assignment of every nested field. - Adds a `Schema Evolution` examples subsection (add a top-level column, add a nested struct field, widen a column's type). - Adds a `Schema Evolution Triggers` examples subsection (an extra column used only in an expression is not added; a wider value produced by an expression is not widened and overflows; directly assigning a struct adds its new nested fields). - Adds a `Schema Evolution When the Source Omits Columns` examples subsection. The examples and behavior were cross-checked against the `MergeIntoSchemaEvolution*` test suites under `sql/core`. ### Why are the changes needed? `MERGE WITH SCHEMA EVOLUTION` is supported but undocumented in the SQL reference, while the analogous `INSERT WITH SCHEMA EVOLUTION` is documented. This brings the MERGE INTO reference to parity. ### Does this PR introduce _any_ user-facing change? No (documentation-only change). ### How was this patch tested? Documentation-only change. The example behavior was verified against the existing `MergeIntoSchemaEvolution*` test suites. ### Was this patch authored or co-authored using generative AI tooling? Generated-by: Cursor (Claude Opus 4.8) -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
