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https://issues.apache.org/jira/browse/CALCITE-5557?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17696343#comment-17696343
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Oliver Lee edited comment on CALCITE-5557 at 3/3/23 11:52 PM:
--------------------------------------------------------------
I'm currently investigating this task.
At a very high level, what I'm seeing for CAST("a" to INT64) is that it takes
the SqlFunction and does these series of steps:
* Parses {{CAST()}} in {{Parser.jj and makes call to SqlStdOperatorTable Cast
function.}}
* Some validation around number of operands but not the actual types, checks
on the nullability of the return (set to non-nullable for types like Integer),
* Converts to RexNodes, SqlToRelConverter.java , {{convertSelectImpl}}
* Attempts to simplify the expression in RexSimplify.java {{simplify()}} ->
{{{}simplifyCast{}}}()
* In the {{reduce}} steps it will try and execute the RexExecutable which is
where {{toInt(String s)}} is called and throws
Ideally we can reuse most of the code for CAST, and add in a flag that makes it
so it returns {{null}} if it throws, but since it is so nested I'm not sure
where that should go yet.
was (Author: JIRAUSER297744):
I'm currently investigating this task.
At a very high level, what I'm seeing for CAST("a" to INT64) is that it takes
the SqlFunction and does these series of steps:
* Parses {{CAST()}} in {{Parser.jj and makes call to SqlStdOperatorTable Cast
function.}}
* Some validation around number of operands but not the actual types, checks
on the nullability of the return (set to non-nullable for types like Integer),
* Converts to RexNodes, SqlToRelConverter.java \{{convertSelectImpl}}
* Attempts to simplify the expression in RexSimplify.java {{simplify()}} ->
{{{}simplifyCast{}}}()
* In the {{reduce}} steps it will try and execute the RexExecutable which is
where {{toInt(String s)}} is called and throws
Ideally we can reuse most of the code for CAST, and add in a flag that makes it
so it returns {{null}} if it throws, but since it is so nested I'm not sure
where that should go yet.
> 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 INT) -> 1
> SAFE_CAST('a' as INT) -> NULL
> SAFE_CAST("2022-12-12" as DATE) -> DATE('2022-12-12')
> SAFE_CAST(1 AS BOOLEAN) -> true
> SAFE_CAST('A' AS BOOLEAN) -> null
> {quote}
>
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