Francesco Guardiani created CALCITE-5017:
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Summary: SqlTypeUtil#canCastFrom is hard to extend for downstream
projects
Key: CALCITE-5017
URL: https://issues.apache.org/jira/browse/CALCITE-5017
Project: Calcite
Issue Type: Wish
Reporter: Francesco Guardiani
Hi all,
In Flink SQL we're extending the matrix of supported casting pairs beyond what
Calcite provides and we hit a roadblock when dealing with
{{SqlTypeUtil#canCastFrom}}. Note that we also have a couple of types more than
what Calcite provides
The problem of this function is:
* It's hardcoded for structured types, so we can't essentially change anything
about those
* The {{SqlTypeMappingRule}} is not flexible enough, as it doesn't allow
matching types with parameters, but just type name pairs.
As a workaround, we're overriding `SqlCastFunction` in our classpath, invoking
our custom cast checking logic:
https://github.com/apache/flink/pull/18524/files#diff-8c1c5cdfd4ee1de9d54fd39db308ab1d7fa9fddb2db1e36cdd1c9b0b8fc90f4bR161
It would be nice if somehow this function can be extended with some custom
predicates.
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