Github user xuanyuanking commented on the issue: https://github.com/apache/spark/pull/19773 @maropu @dongjoon-hyun Great thanks for your guidance ! ``` Apache Spark already supports changing column types as a part of schema evolution. Especially, ORC vectorized reader support upcasting although it's not the same with canCast. For the detail support Spark coverage, see SPARK-23007. It covered all built-in data source at that time. ``` Great thanks, I'll study these background soon. ``` Please note that every data sources have different capability. So, this PR needs to prevent ALTER TABLE CHANGE COLUMN for those data sources case-by-case. And, we need corresponding test cases. ``` Got it, I'll keep following the cases in this PR, I roughly split these into 4 tasks and update the description of this PR firstly. I'll pay attention to the corresponding test cases in each task.
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