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https://issues.apache.org/jira/browse/CALCITE-4771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17713343#comment-17713343
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Dan Zou commented on CALCITE-4771:
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[~julianhyde], the reason I add `CastType` is to distinguish between `TRY_CAST`
and `SAFE_CAST`, e.g. [SqlOperatorFixture#getCastString
|https://github.com/apache/calcite/blob/1abb7ad737d691b0a1ef5e04c3deb7cb07ec44a8/testkit/src/main/java/org/apache/calcite/sql/test/SqlOperatorFixture.java#L623]
> Add TRY_CAST (MSSQL compatibility)
> ----------------------------------
>
> Key: CALCITE-4771
> URL: https://issues.apache.org/jira/browse/CALCITE-4771
> Project: Calcite
> Issue Type: Improvement
> Reporter: xuyang
> Assignee: Dan Zou
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.35.0
>
> Attachments: image-2021-09-16-11-43-55-743.png
>
> Time Spent: 2h 10m
> Remaining Estimate: 0h
>
> In the sql "SELECT CAST('haha' AS INT)",the value the function CAST returns
> will be parsed into NOT NULL, because when parsing, the type CAST returns is
> from the INT and the nullable attribute is from the 'haha', which doesn't
> consider the condition that parsing a string to an int could be invalid and
> return NULL values.
> I think there are two ways to improve this question:
> * One is to change the value of the CAST function to be nullable, which
> avoids the invalid parsing.
> * The other way is to introduce a function named TRY_CAST, which is used in
> SQL Server.If the parsing fails, TRY_CAST will return NULL instead of throws
> exception that a NOT NULL field will be set with our unexpected value NULL.
>
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