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https://issues.apache.org/jira/browse/CALCITE-3005?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16847175#comment-16847175
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Julian Hyde commented on CALCITE-3005:
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This is not a surprise, because {{LEFT}} is a reserved keyword. You'll need to
modify the parser, probably {{BuiltinFunctionCall()}}, and look for the
{{<LEFT>}} tokens rather than an identifier. But once you've matched a function
call {{LEFT(<args>)}} you should convert {{LEFT}} to an identifier, and call
{{createCall}} as if {{NamedFunctionCall()}} had been matched. Then the
validator can figure out whether "LEFT" is a valid function name, and it has
the right number & type of arguments.
Similarly {{RIGHT}}.
> Implement string functions: LEFT, RIGHT
> ---------------------------------------
>
> Key: CALCITE-3005
> URL: https://issues.apache.org/jira/browse/CALCITE-3005
> Project: Calcite
> Issue Type: New Feature
> Reporter: Forward Xu
> Assignee: Forward Xu
> Priority: Major
> Labels: pull-request-available
> Time Spent: 6h 10m
> Remaining Estimate: 0h
>
> Some string functions including LEFT, RIGHT are not implemented now. It would
> be great if these functions can be implemented.
> [{{LEFT(_str_}},_{{len}}_)|https://dev.mysql.com/doc/refman/8.0/en/string-functions.html#function_left]
> Returns the leftmost _{{len}}_ characters from the string _{{str}}_, or
> {{NULL}} if any argument is {{NULL}}.
> [{{RIGHT(_str_}},_{{len}}_)|https://dev.mysql.com/doc/refman/8.0/en/string-functions.html#function_right]
> Returns the rightmost _{{len}}_ characters from the string _{{str}}_, or
> {{NULL}} if any argument is {{NULL}}.
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