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https://issues.apache.org/jira/browse/FLINK-39125?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gustavo de Morais updated FLINK-39125:
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Summary: Support injective casts from BINARY/VARBINARY to CHAR/VARCHAR for
upsert key preservation (was: Support injective casts from CHAR/VARCHAR to
BINARY/VARBINARY for upsert key preservation)
> Support injective casts from BINARY/VARBINARY to CHAR/VARCHAR for upsert key
> preservation
> -----------------------------------------------------------------------------------------
>
> Key: FLINK-39125
> URL: https://issues.apache.org/jira/browse/FLINK-39125
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Planner
> Affects Versions: 2.2.0
> Reporter: Gustavo de Morais
> Assignee: Gustavo de Morais
> Priority: Major
> Fix For: 2.3.0
>
>
> When users cast a VARCHAR key column to VARBINARY, the upsert key uniqueness
> is lost because the cast is not recognized as injective.UTF-8 encoding is
> itself injective - distinct strings always produce distinct byte sequences -
> so we can safely mark these casts as injective when the binary target has
> sufficient capacity. The cast is injective under the following conditions:
> * VARCHAR(MAX) → VARBINARY(MAX): both sides are unbounded
> * VARCHAR → VARBINARY where y >= x * 4: target can hold the worst-case UTF-8
> encoding (4 bytes per character)
> * Bounded source to unbounded (MAX) target: always fits
> This applies to all four cross-family combinations: CHAR/VARCHAR to
> BINARY/VARBINARY.
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