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https://issues.apache.org/jira/browse/CALCITE-5526?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17776746#comment-17776746
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Julian Hyde commented on CALCITE-5526:
--------------------------------------

[~wnoble], I don't follow everything you're saying, but scenario 2 seems a 
better fit for Calcite. Calcite is a set of loosely-coupled components (parser, 
sql-to-rel, sql-to-dialect) and they work independently.

Whichever scenario you land on, it needs to be expressed in a simple test case. 
That is how we will all understand this issue when it has been fixed. So, write 
that test case now.

> Handle unparsing of literals based on type system
> -------------------------------------------------
>
>                 Key: CALCITE-5526
>                 URL: https://issues.apache.org/jira/browse/CALCITE-5526
>             Project: Calcite
>          Issue Type: Task
>            Reporter: Will Noble
>            Assignee: Will Noble
>            Priority: Minor
>
> CALCITE-5424 dealt with parsing date/time literals via a custom type system, 
> however there is still no way to unparse them via the same type system. This 
> is handled in 
> [SqlDialect.unparseDateTimeLiteral|https://github.com/apache/calcite/blob/a0e119ea42def418957f214f539469f1aba76c18/core/src/main/java/org/apache/calcite/sql/SqlDialect.java#L468]
>  which simply calls the literal object's {{toString()}} method.
> The literal object (a subclass of {{SqlAbstractDateTimeLiteral}}) should not 
> be able to determine it's own unparsed representation by itself since it 
> could be unparsed in any dialect. Since the current system for resolving 
> custom types relies on access to the catalog, it appears we'll need to 
> introduce to {{SqlDialect}} a dependency on {{CalciteCatalogReader}} so it 
> can use the same mappings for unparsing as it does for parsing.



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