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https://issues.apache.org/jira/browse/FLINK-25273?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Martijn Visser closed FLINK-25273.
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    Resolution: Not A Bug

Hi and thanks for opening this ticket. It's better to bring this up for 
discussion on the Dev mailing list. See https://flink.apache.org/community.html 
on how to do this. You could also comment on the Jira ticket you're referring 
to, but I think the Dev mailing list is better suited. 

> Some doubts about the FLINK-22848
> ---------------------------------
>
>                 Key: FLINK-25273
>                 URL: https://issues.apache.org/jira/browse/FLINK-25273
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table SQL / API
>            Reporter: Jianhui Dong
>            Priority: Major
>
> I have been in contact with Flink and Calcite for a while, and I have some 
> questions about this issue: https://issues.apache.org/jira/browse/FLINK-22848.
> First of all, the discussion about this issue mentioned that since calcite 
> did not support the syntax analysis of set a=b (without quotes), regular 
> expressions were used. However, I checked the commit history some days ago, 
> and I found that calcite should already support SET syntax parsing (see 
> SqlSetOption) in v1.14 or even earlier. but its problem is that it would 
> recognize the `true/false/unknown/null` tokens as keywords, causing the 
> parsing to be worse than expected, but this problem can be solved by 
> restricting the syntax, like use '' in the issue FLINK-22848.
> Then I investigated the earliest version of flink that introduced calcite, 
> flink should have introduced Calcite 1.16 in 1.5 at the earliest version. At 
> that time, calcite should already support the syntax of SET a=b (without 
> quotes), so I would like to find out What exactly does the "not supported" 
> mentioned in the issue FLINK-22848 means? Maybe you can give a more specific 
> case.
> In addition, I also have some doubts about the results of the discussion of 
> the issue. I think it is indeed a more elegant solution to use the SQL parser 
> to analyze it, but When calcite has built-in support for SET grammar, why do 
> we need to extend the SET grammar to re-support it? Even this change may 
> cause backward-incompatible.
> In my personal opinion of view, is that we can solve this problem by adding 
> special restrictions on the above tokens on the basis of native Calcite 
> analysis, such as in the user manual because values ​​such as `unknown` and 
> `null` are meaningless in the production environment. 



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