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https://issues.apache.org/jira/browse/DRILL-7715?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Zhang Jingwang updated DRILL-7715:
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Priority: Minor (was: Major)
> SYSTEM ERROR: CompileException: Line 87, Column 32: Expression "right.end" is
> not an rvalue
> -------------------------------------------------------------------------------------------
>
> Key: DRILL-7715
> URL: https://issues.apache.org/jira/browse/DRILL-7715
> Project: Apache Drill
> Issue Type: Bug
> Components: Execution - Codegen, Functions - Drill
> Affects Versions: 1.17.0
> Reporter: Zhang Jingwang
> Priority: Minor
>
> Reproduce by:
> > select to_date('2019-01-12', `expr$0`) from (values ('yyyy-mm-dd'));
> Error: SYSTEM ERROR: CompileException: Line 87, Column 32: Expression
> "right.end" is not an rvalue
>
> I am deeply confused by the assumption of the UDF framework. Take simple
> functions for example, it has 'setup()' and 'eval()' methods. It seems that
> 'setup()' is meant to handle some immutable input and state across the entire
> table processing, and 'eval()' to handle state/output related to each row.
> However there are several problems:
> # The codegen would only generate argument reference for 'setup()' if the
> argument is a Constant (a runtime check). However if this is the case, then
> the check should not be a runtime check, it should be an annotation such as
> @Param(constant=true). Otherwise when users pass in a column reference
> instead of a constant, the above error occurs.
> # a NULL_IF_NULL simple functions could leave the null handling to the
> framework, so that it can focus on the situation where arguments are
> non-null. However the null handling code covers only 'eval()' function, it
> does not cover the 'setup()' function. Which might lead to problem when the
> argument is a constant OPTIONAL type (though it seems odd, it's possible when
> using a CASE WHEN expression)
> # UDF with Nullable parameters should be able to accept arguments of
> REQUIRED type. However current code of function resolving does not support
> such cases.
> Could someone please share more information about the UDF framework and the
> future development direction of it? Such as:
> # What's the purpose of the 'setup()' method, and should it refer to
> non-constant parameters?
> # Should a REQUIRED argument be accepted as a OPTIONAL parameter?
> Thank you very much.
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