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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 08:44:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16594711#comment-16594711
] 

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

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-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.
   
   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 &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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