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https://issues.apache.org/jira/browse/FLINK-39700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18081721#comment-18081721
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david radley commented on FLINK-39700:
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[~arvid] Do we need to do anything special for nested columns?
> Fix name-based column matching in materialized table schema diff
> ----------------------------------------------------------------
>
> Key: FLINK-39700
> URL: https://issues.apache.org/jira/browse/FLINK-39700
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / Planner
> Affects Versions: 2.3.0
> Reporter: Arvid Heise
> Assignee: Arvid Heise
> Priority: Major
> Fix For: 2.4.0
>
>
> MaterializedTableUtils.validateAndExtractColumnChanges currently compares
> schemas positionally (by index). This makes it order-sensitive: if physical
> DDL columns appear in a different order between the old and new schema, the
> diff produces spurious ModifyPhysicalColumnType changes or incorrect
> validation errors. Since DDL column order is arbitrary, the comparison should
> be name-based.
> Additionally, when a physical column has a type change and a comment change
> at the same time, only ModifyPhysicalColumnType is emitted. The comment
> change is silently dropped because the early continue skips the
> comment-comparison block.
> Fix:
>
>
> 1. Build a Map<String, Column> from the old schema and match new columns by
> name, treating unmatched columns as additions or drops.
> 2. After emitting ModifyPhysicalColumnType, check whether the comment also
> changed before continuing.
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