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https://issues.apache.org/jira/browse/FLINK-9559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16591358#comment-16591358
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ASF GitHub Bot commented on FLINK-9559:
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pnowojski 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-415699060
@hequn8128 may I ask what is the use case that you are trying to solve? I'm
asking because I have mixed feelings with this:
1. as it is, it brakes standard, which is bad
2. adding configuration option `shouldConvertRaggedUnionTypesToVarying`,
which by default would be `true` is equally bad
3. making it by default `false` leaves us with an option that's very hard to
explain to the users what does it to. I would guess almost nobody would use it
4. having more configuration rises the complexity of the system - more
features that we need to maintain, support, refactor, test etc. This can
quickly become a nightmare.
5. it seems like very cosmetic change. In most cases it doesn't matter,
since either the result is being printed or being stored in an external system
that has it's own schema. As long as in this external system column is defined
as `VARCHAR(x)` this issue doesn't matter. Isn't the scope of this limited
purely to unit tests, where we need to compare to spaces?
6. if we agree to introduce this change, should we also agree when next time
someone reports that he/she would like to have things like:
- `123.456` literal being double or decimal?
- `'abc'` literal being `CHAR(3)` or `VARCHAR(3)`?
- `'A ' || 'B '` returning `'AB'` or `'A B '`
- 'NULL == 0` being true, false or null?
- `SUBSTRING('abc' FROM -2 FOR 4)` should yield 'a' or 'bc'?
and the list goes on and on. We definitely can not provide a switch for all
of such quirks. Having one switch like `mysql-compatibility-mode: true` would
have more sense, however it's impossible to implement/maintain for different
reasons.
That's why I don't like changing the default behaviour and I see more
problems then positives by introducing this as a configurable option.
However I see one issue here that would solve this problem. Since Flink does
not support `CHAR(x)` anywhere besides string literals, and our `CHAR(x)`
support seems to be broken (for example `'A ' || 'B '` should return `'A B
'`), maybe we should treat all string literals as varchars?
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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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