szehon-ho opened a new pull request, #53326: URL: https://github.com/apache/spark/pull/53326
### What changes were proposed in this pull request? Keep existing behavior for MERGE INTO without SCHEMA EVOLUTION clause for UPDATE SET * and INSERT *, to throw exception if the source and target schemas are not exactly the same. ### Why are the changes needed? As @aokolnychyi tested this feature, he mentioned that as of Spark 4.1 the behavior is changed for MERGE INTO with UPDATE SET * and INSERT * , but without SCHEMA EVOLUTION clause. In particular: - Source has less columns/nested fields than target => we fill with NULL or DEFAULT for inserts, and existing value for Update. (though we disabled for nested structs by default in [[SPARK-54525](https://issues.apache.org/jira/browse/SPARK-54525))](https://github.com/apache/spark/pull/53229) - Source has more columns/fields than target => we drop the extra fields. Initially, I thought its a good improvement of MERGE INTO and is not related to SCHEMA EVOLUTION exactly because the schema is not altered. But Anton has a good point that it may be a surprise to some user. So it may be better for now to be more conservative and keep the exact same behavior for without SCHEMA EVOLUTION clause, and relax it later once there is more clarity. Instead, we can do this only if SCHEMA EVOLUTION is specified, as the user then is more explicit about the decision. ### Does this PR introduce _any_ user-facing change? No, this keeps behavior exactly the same as 4.0 without SCHEMA EVOLUTION clause. ### How was this patch tested? Added a test and changed existing test output to expect the exception if SCHEMA EVOLUTION is not specified. ### Was this patch authored or co-authored using generative AI tooling? No -- 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]
