[GitHub] [spark] dongjoon-hyun commented on issue #25331: [SPARK-27768][SQL] Infinity, -Infinity, NaN should be recognized in a case insensitive manner.

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dongjoon-hyun commented on issue #25331: [SPARK-27768][SQL] Infinity, -Infinity, NaN should be recognized in a case insensitive manner.
URL: https://github.com/apache/spark/pull/25331#issuecomment-520314155
 
 
   Sorry for being late, guys.
   
   Hi, @srowen . I agree with you that `Any improvement or bug fix is a behavior change`. However, this PR causes a different SQL result which can be considered as a correctness issue to the existing Spark SQL apps. For example, we can imagine a SQL reporting app which processes two rows `nan` and `NaN`. Previously `nan` is considered as `NULL`, but now `nan` become a `NaN`. So, when you do `GROUP BY` on this values, Spark 3.0 will return one row while Spark 2.4 returns two rows. For the infinity values, the situation is the same.
   
   In this case, we had better have a SQL migration guide. Otherwise, during Spark migration acceptance tests, SQL result comparison will fail because this kind of corner cases are tested always.
   
   Also, cc @gatorsmile since he filed this issue.

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