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https://issues.apache.org/jira/browse/FLINK-9559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16592536#comment-16592536
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ASF GitHub Bot commented on FLINK-9559:
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hequn8128 commented on issue #6519: [FLINK-9559] [table] The type of a union of
CHAR columns of different lengths should be VARCHAR
URL: https://github.com/apache/flink/pull/6519#issuecomment-415957994
@pnowojski Hi，I'm wrong at the root cause of the two examples I listed
above. Thanks for pointing it out and giving a detailed explanation. It should
be a comparison problem for CHAR/VARCHAR. We probably should implement support
for `CHAR` as you said, making trailing spaces insignificant in comparisons.
I think this pr tries to solve the output problem. Once we solve the
comparison problem, we still have to solve the output problem. Output `case
when` results to a nonbinary strings field in storages. Some storages treat
CHAR/VARCHAR with trailing spaces equally('a' equals to 'a '), like mysql, so
no problems here. Others don't, for example, kafka or elasticsearch. So, I
think we should not add trailing spaces in result of `case when`, just like
most DBMSs do.
What do you think?
Thanks again. Hequn
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> The type of a union of CHAR columns of different lengths should be VARCHAR
> --------------------------------------------------------------------------
>
> Key: FLINK-9559
> URL: https://issues.apache.org/jira/browse/FLINK-9559
> Project: Flink
> Issue Type: Bug
> Components: Table API & SQL
> Reporter: Hequn Cheng
> Assignee: Hequn Cheng
> Priority: Major
> Labels: pull-request-available
>
> Currently, If the case-when expression has two branches which return string
> literal, redundant white spaces will be appended to the short string literal.
> For example, for the sql: case 1 when 1 then 'a' when 2 then 'bcd' end, the
> return value will be 'a ' of CHAR(3) instead of 'a'.
> Although, this follows the behavior in strict SQL standard mode(SQL:2003). We
> should get the pragmatic return type in a real scenario without blank-padded.
> Happily, this problem has been fixed by
> [CALCITE-2321|https://issues.apache.org/jira/browse/CALCITE-2321], we can
> upgrade calcite to the next release(1.17.0) and override
> {{RelDataTypeSystem}} in flink to configure the return type, i.e., making
> {{shouldConvertRaggedUnionTypesToVarying()}} return true.
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