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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-9559) The type of a union of CHAR columns of different lengths should be VARCHAR
Date Tue, 28 Aug 2018 12:05:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16594880#comment-16594880
] 

ASF GitHub Bot commented on FLINK-9559:
---------------------------------------

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-416559091
 
 
   Yes, sorry for my mistake there, I realised about it too late and was in the process of
fixing it, but it took me quite some time to find a way to determine the actual data type
returned from `case`. 
   
   In your examples, you are missing one important issue: what's the type of string literal.
Check out those examples:
   
   PostgreSQL
   http://sqlfiddle.com/#!17/c6522/1
   
   - string literals are of `UNKNOWN` type, that behaves like `VARCHAR`
   - `case when` on `CHAR` arguments returns `CHAR` type.
   
   MSSQL:
   http://sqlfiddle.com/#!18/50a92/1/0
   (click `browser` schema button)
   
   - string literals are `VARCHAR`
   - `case when` return type strictly follows the standard - `CHAR(8)`
   
   Oracle:
   http://sqlfiddle.com/#!4/50a92/1/0
   (click `browser` schema button)
   
   - string literals are `CHAR`
   - `case when` return type `VARCHAR`
   
   This is still hardly conclusive to motivate the change for me.
   
   I'm not sure why are you rejecting my proposal to change default string literal type to
`VARCHAR`. It would fix all of our `CHAR` problems (comparisons, connector support, functions
support, etc)  for now and `case when` would return `VARCHAR` automatically. Even if in the
future we would want to provide a configuration switch `string-literals-type: char/varchar`,
such configuration option would be cleaner and much easier to understand compared to `shouldConvertRaggedUnionTypesToVarying`.

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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 &amp; 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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