Gustavo de Morais created FLINK-39125:
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Summary: Support injective casts from CHAR/VARCHAR to
BINARY/VARBINARY 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
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(x) → VARBINARY(y) 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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