[jira] [Created] (SPARK-30614) The native ALTER COLUMN syntax should change one thing at a time

["Wenchen Fan (Jira)" <ji...@apache.org>]

Wenchen Fan created SPARK-30614:
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             Summary: The native ALTER COLUMN syntax should change one thing at a time
                 Key: SPARK-30614
                 URL: https://issues.apache.org/jira/browse/SPARK-30614
             Project: Spark
          Issue Type: New Feature
          Components: SQL
    Affects Versions: 3.0.0
            Reporter: Wenchen Fan


Our native ALTER COLUMN syntax is newly added in 3.0 and almost follows the SQL standard.

{{{
ALTER TABLE table=multipartIdentifier
  (ALTER | CHANGE) COLUMN? column=multipartIdentifier
  (TYPE dataType)?
  (COMMENT comment=STRING)?
  colPosition?   
}}}

The SQL standard (section 11.12) only allows changing one property at a time. This is also true on other recent SQL systems like snowflake(https://docs.snowflake.net/manuals/sql-reference/sql/alter-table-column.html) and redshift(https://docs.aws.amazon.com/redshift/latest/dg/r_ALTER_TABLE.html)

The snowflake has an extension that it allows changing multiple columns at a time, like ALTER COLUMN c1 TYPE int, c2 TYPE int. If we want to extend the SQL standard, I think this syntax is better. 

For now, let's be conservative and only allow changing one property at a time.



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