[GitHub] hequn8128 edited a comment on issue #6519: [FLINK-9559] [table] The type of a union of CHAR columns of different lengths should be VARCHAR

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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-415735866
 
 
   Hi @pnowojski , thanks for your reply. There are many cases need this 
feature. Not only `case when`, but also `nvl`, `greatest` and `least`.  Most 
users encounter the blank problem is `case when`. Examples have been added in 
the test cases. Below I will add some more examples:
   1. 
   ```
   SELECT country_name
   FROM (
        SELECT CASE id
                        WHEN 1 THEN 'GERMANY'
                        WHEN 2 THEN 'CANADA'
                        ELSE 'INVALID COUNTRY ID'
                END AS country_name
        FROM country_id
   )
   WHERE country_name = 'GERMANY'
   ```
   This sql will output nothing since the blank problem. It is very confused.
   
   2. 
   ```
   SELECT country_name, country_info 
   FROM (
        SELECT CASE id
                        WHEN 1 THEN 'GERMANY'
                        WHEN 2 THEN 'CANADA'
                        ELSE 'INVALID COUNTRY ID'
                END AS country_name
        FROM country_id
   ) nameTable join infoTable on nameTable.country_name = 
infoTable.country_name;
   ```
   This sql cannot join correctly since the blank problem. 'GERMANY' in 
nameTable becomes 'GERMANY-----------'.  BTW, '-' means the blank.
   
   It is true the sql standard returns CHAR type, but nearly all major DBMSs 
return VARCHAR without blank-padded. A tool for easy online testing: 
http://sqlfiddle.com/
   
   Thanks, Hequn
   

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