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https://issues.apache.org/jira/browse/FLINK-14539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16960781#comment-16960781
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Kevin Zhang commented on FLINK-14539:
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I indend to implement this using a RexBiVisitor, because there are cases concat
and cast can each other inside, and it's more convenient to extend when we find
more cases that we can keep the unique key metadata. If it's ok and not breaks
some other issues, I'd like to open a pr for further review.
> Unique key metadata should be ketp when using concat or concat_ws in some
> cases
> -------------------------------------------------------------------------------
>
> Key: FLINK-14539
> URL: https://issues.apache.org/jira/browse/FLINK-14539
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / Planner
> Affects Versions: 1.9.0, 1.9.1
> Reporter: Kevin Zhang
> Priority: Major
>
> Currently unique key metadata of a project relnode are only kept in the
> following three situations:
> # project the child unique keys while not changing them
> # cast the child unique key when ignoring nulls and the original type of the
> field and cast type are the same
> # rename the child unique keys
> Besides these situations, concat and concat_ws should also keep the metadata
> if they won't break the uniqueness of the child unique keys, i.e. each
> operands is in one of the above situations, and the operands include all the
> child unique keys.
> Say the f0 and f1the child are the unique keys of the child node, the
> following sqls should keep the unique key metadata
> {code:sql}
> select concat(f0, f1)
> -- the type of f0 and f1 are both varchar originally and ignore nulls
> select concat(cast(f0 as varchar), f1)
> select cast(concat(f0, f1) as varchar)
> {code}
> while the following sqls should discard the unique key metadata
> {code:sql}
> -- the type of f0 and f1 are both varchar originally
> select concat(cast(f0 as bigint), f1)
> select cast(concat(f0, f1) as bigint)
> {code}
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