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https://issues.apache.org/jira/browse/CALCITE-4771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17415852#comment-17415852
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xzh_dz commented on CALCITE-4771:
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!image-2021-09-16-11-43-55-743.png|width=745,height=363!
When I test the MySQL database, I find that the converted values are different
for different data types.
mysql version : 8.0.26
+1 with [~julianhyde] , we should implement {{TRY_CAST function.}}
> change the value of the CAST function to be nullable
> -----------------------------------------------------
>
> Key: CALCITE-4771
> URL: https://issues.apache.org/jira/browse/CALCITE-4771
> Project: Calcite
> Issue Type: Improvement
> Reporter: xuyangzhong
> Priority: Major
> Attachments: image-2021-09-16-11-43-55-743.png
>
>
> 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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