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https://issues.apache.org/jira/browse/SPARK-30614?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17027878#comment-17027878
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Terry Kim commented on SPARK-30614:
-----------------------------------
Currently, ALTER COLUMN requires TYPE property for v1 tables:
[https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveSessionCatalog.scala#L80]
For example, you have to run
{code:sql}
ALTER TABLE t ALTER COLUMN i TYPE bigint COMMENT 'new comment'
{code}
but not
{code:sql}
ALTER TABLE $tblName ALTER COLUMN i COMMENT 'new comment'
{code}
It's OK to break this behavior, right? (we can deduce the column type since the
table is already looked up.)
> 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
> Priority: Major
>
> Our native ALTER COLUMN syntax is newly added in 3.0 and almost follows the
> SQL standard.
> {code}
> ALTER TABLE table=multipartIdentifier
> (ALTER | CHANGE) COLUMN? column=multipartIdentifier
> (TYPE dataType)?
> (COMMENT comment=STRING)?
> colPosition?
> {code}
> 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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