[GitHub] [spark] cloud-fan commented on issue #27444: [SPARK-30614][SQL] The native ALTER COLUMN syntax should change one property at a time

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cloud-fan commented on issue #27444: [SPARK-30614][SQL] The native ALTER COLUMN syntax should change one property at a time
URL: https://github.com/apache/spark/pull/27444#issuecomment-581724601
 
 
   BTW I'm not against having multiple column changes within one command, but we need more discussion to decide what syntax to use since it's non-standard.
   
   One candidate is the snowflake syntax
   ```
   ALTER TABLE <name> { ALTER | MODIFY } [ ( ]
                                                 [ COLUMN ] <col1_name> DROP DEFAULT
                                               , [ COLUMN ] <col1_name> SET DEFAULT <seq_name>.NEXTVAL
                                               , [ COLUMN ] <col1_name> { [ SET ] NOT NULL | DROP NOT NULL }
                                               , [ COLUMN ] <col1_name> [ [ SET DATA ] TYPE ] <type>
                                               , [ COLUMN ] <col1_name> COMMENT '<string>'
                                             [ , [ COLUMN ] <col2_name> ... ]
   ```
   
   We don't need to rush it for 3.0. We can be conservative in 3.0 to only support the SQL standard syntax, and think about how to extend it later.
   
   cc @viirya @maropu  @brkyvz @rdblue 

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