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https://issues.apache.org/jira/browse/FLINK-9559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16594750#comment-16594750
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ASF GitHub Bot commented on FLINK-9559:
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hequn8128 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-416501305
@pnowojski Thanks for looking into it.
I think there are bugs in all your 4 sqls, so we can't get the conclusions
from them.
- In mysql, trailing spaces are removed when CHAR values are retrieved from
a table.
- You use literal of length 3('aa ') to compare to CHAR(4) and VARCHAR(4).
- Except for mysql, other database will not remove trailing spaces so that
the result of `case when` contains blanks.
What result type of `case when`? Should we change case when result type to
varchar? I think we can get the answer form the following sqls.
1. Mysql
There are no doubt, since mysql Reference Manual says the return type is
VARCHAR.
2. Oracle
[http://sqlfiddle.com/#!4/cd577/2/0](http://sqlfiddle.com/#!4/cd577/2/0)
3. PostgreSql
[http://sqlfiddle.com/#!17/c20bd/3/0](http://sqlfiddle.com/#!17/c20bd/3/0)
4. SqlServer
[http://sqlfiddle.com/#!18/c20bd/10/0](http://sqlfiddle.com/#!18/c20bd/10/0)
From the results, we can see that
- There are no trailing spaces
- The result type length should not be 1, i.e., can not be char(1) or
varchar(1). It should be char(3) or varchar(3)
- Result of `concat(CAST('a' AS char(3)), '|')` contains blanks while
`concat(CAST('a' AS varchar(3)), '|')` not, so the result type of `case when`
should be varchar.
In Calcite, character constant, for example 'Hello, world!', '',
_N'Bonjour', _ISO-8859-1'It''s superman!' COLLATE SHIFT_JIS$ja_JP$2. These are
always CHAR, never VARCHAR. So it seems not possible or acceptable to change
all literals to VARCHAR in Calcite.
I think it is meaningful to turn the result type of `case when` to VARCHAR.
What do you think?
Thanks, 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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