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-415957994 @pnowojski Hi，I'm wrong at the root cause of the two examples I listed above. Thanks for pointing it out and giving a detailed explanation. It should be a comparison problem for CHAR/VARCHAR. We probably should implement support for `CHAR` as you said, making trailing spaces insignificant in comparisons. I think this pr tries to solve the output problem. Once we solve the comparison problem, we still have to solve the output problem. Output `case when` results to a nonbinary strings field in storages. Some storages treat CHAR/VARCHAR with trailing spaces equally('a' equals to 'a '), like mysql, so no problems here. Others don't, for example, kafka or elasticsearch. So, I think we should not add trailing spaces in result of `case when`, just like most DBMSs do. What do you think? Thanks again. Hequn
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