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https://issues.apache.org/jira/browse/FLINK-9559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16594884#comment-16594884
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ASF GitHub Bot commented on FLINK-9559:
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pnowojski edited a comment 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-416196736
@hequn8128, as I wrote before, we can not support hundreds of switches
modifying semantic of SQL, especially not in so minor ways. This PR also do not
fix your original issue - broken `CHAR(x)` support in Flink.
Output column type of `CHAR(x)` should be properly handled by each
connector. For example if Flink is processing some `CHAR(X)` column which is
then being written to some sink/connector, it's this Sink's responsibility to
correctly handle padding - whether that means trimming it or not depends on the
underlying column's type. Again, changing type of `case when` only partially
hides the problem.
> I think we should not add trailing spaces in result of case when, just
like most DBMSs do.
Below examples are incorrect. Please check my next message.
~Further more, please correct me if I'm wrong, but this sentence seems not
quite correct:~
~MySQL~ http://sqlfiddle.com/#!9/ce6d86/1
1. ~string literals seems to be of `VARCHAR(x)` type.~
2. ~`CONCAT` on `CHAR(x)` is broken~
3. ~indeed `case when` returns `VARCHAR(x)`~
~Oracle~ http://sqlfiddle.com/#!4/ce6d86/1
1. ~string literals seems to be `VARCHAR`~
2. ~type of `case when` calculated dynamically, depending which branch was
selected, but looks like `CHAR(x)`~
~PostgreSQL~
http://sqlfiddle.com/#!17/ce6d8/1
http://sqlfiddle.com/#!17/c6522/1/0
1. ~again, string literals are of `UNKNOWN` type~
2. ~`case when` return type is `CHARACTER`.~
~MSSQL~ http://sqlfiddle.com/#!18/ce6d8/2
1. ~again, string literals seems to be `VARCHAR`~
2. ~oO... I'm not even attempting to interpret those results... probably
`concat` on `VARCHAR` with trailing spaces is seriously broken~
Btw, if you look at those results, you should understand why I'm objecting
into providing a configuration switch (or more like a hundred of them) in order
to follow what "other DBMSs do". This is simply impossible...
Also as I wrote previously. The proper fix for the problem would be to
either fix `CHAR(x)` support or to change string literals' type to `VARCHAR(x)`.
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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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