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https://issues.apache.org/jira/browse/FLINK-7271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17348947#comment-17348947
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Wenlong Lyu commented on FLINK-7271:
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hi, [~twalthr] [~xueyu] I investigate a bit on the case, the case still exists, 
found that it is because we have different presentation on some types like 
Date/Timestamp/Row etc, comparing with calcite, and the reduced value produced 
by ExpressionReducer was casted to string and so that we can make a rex node 
the same as the un-reduced value:

cast(String as Date) -- (ExpressionReducer) -->  Date (internal format Int) -- 
auto cast in RexBuilder#makeLiteral --> cast(String as Date)

> ExpressionReducer does not optimize string-to-time conversion
> -------------------------------------------------------------
>
>                 Key: FLINK-7271
>                 URL: https://issues.apache.org/jira/browse/FLINK-7271
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table SQL / Planner
>    Affects Versions: 1.3.1
>            Reporter: Timo Walther
>            Priority: Minor
>              Labels: auto-deprioritized-major
>
> Expressions like {{"1996-11-10".toDate}} or {{"1996-11-10 
> 12:12:12".toTimestamp}} are not recognized by the ExpressionReducer and are 
> evaluated during runtime instead of pre-flight phase. In order to optimize 
> the runtime we should allow constant expression reduction here.



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