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https://issues.apache.org/jira/browse/CALCITE-5557?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17696355#comment-17696355
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Julian Hyde commented on CALCITE-5557:
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In your examples please use Calcite types (BOOLEAN not BOOL) and single-quoted
character literals.
Type derivation is different from CAST. The result is nullable.
Simplification is tricky. You need to make sure that CAST simplifications are
not accidentally applied to SAFE_CAST, but you don't want to prevent them
altogether. How to prevent accidents? Consider making SAFE_CAST a different
operator from CAST, perhaps with the same SqlKind, perhaps with the same
operator class. I don't know.
You should read CALCITE-3215 and understand its idea of "safe" operators. And
also write some new simplification tests, to make sure everything works as
intended.
The implementor of CAST and SAFE_CAST can probably be shared.
Do the same process for SAFE_DIVIDE, even if you don't intend to implement it
now. The right design patterns are probably the ones that work for both
SAFE_CAST and SAFE_DIVIDE.
> Add SAFE_CAST (big BigQuery compatibility)
> ------------------------------------------
>
> Key: CALCITE-5557
> URL: https://issues.apache.org/jira/browse/CALCITE-5557
> Project: Calcite
> Issue Type: New Feature
> Reporter: Oliver Lee
> Assignee: Oliver Lee
> Priority: Minor
>
> Implement SAFE_CAST per BigQuery specifications
> [https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-and-operators#safe_casting]
> Equivalent to CAST(), except it will return {{null}} instead of throwing an
> exception if the casting fails.
> {quote}SAFE_CAST("1" as INT64) -> 1
> SAFE_CAST("a" as INT64) -> NULL
> SAFE_CAST("2022-12-12" as DATE) -> DATE('2022-12-12')
> SAFE_CAST(1 AS BOOL) -> true
> SAFE_CAST("A" AS BOOL) -> null
> {quote}
>
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