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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