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https://issues.apache.org/jira/browse/SPARK-54595?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dongjoon Hyun reassigned SPARK-54595:
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Assignee: Szehon Ho
> Keep existing behavior without SCHEMA EVOLUTION clause
> ------------------------------------------------------
>
> Key: SPARK-54595
> URL: https://issues.apache.org/jira/browse/SPARK-54595
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 4.1.0
> Reporter: Szehon Ho
> Assignee: Szehon Ho
> Priority: Major
> Labels: pull-request-available
>
> As [~aokolnychyi] tested this feature, he mentioned that as of Spark 4.1 the
> behavior is changed for MERGE INTO with UPDATE * , 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)
> * 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.
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