[jira] [Assigned] (FLINK-8953) Resolve unresolved field references in FieldComputer expressions

["xueyu (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-8953?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

xueyu reassigned FLINK-8953:
----------------------------

    Assignee: xueyu

> Resolve unresolved field references in FieldComputer expressions
> ----------------------------------------------------------------
>
>                 Key: FLINK-8953
>                 URL: https://issues.apache.org/jira/browse/FLINK-8953
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API & SQL
>            Reporter: Timo Walther
>            Assignee: xueyu
>            Priority: Major
>
> When implementing the {{FieldComputer.getExpression}} method, it is not possible to use API classes but only internal expression case classes.
> It would be great to also define timestamp extractors like:
> {code}
>   def getExpression(fieldAccesses: Array[ResolvedFieldReference]): Expression = {
>     // 'x.cast(Types.LONG)
>     // ExpressionParser.parseExpression("x.cast(LONG)")
>   }
> {code}
> An even better solution would be to provide different `getExpression()` methods that an implementor can override. The general goal should be to define this as natural as possible. In the future we should also support SQL:
> {code}
>   def getJavaExpression(fieldAccesses: Array[ResolvedFieldReference]): String = {
>     "x.cast(LONG)"
>   }
>   def getSQLExpression(fieldAccesses: Array[ResolvedFieldReference]): String = {
>     "CAST(x AS LONG)"
>   }
> {code}
> The final design is still up for discussion. These are just ideas.



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