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https://issues.apache.org/jira/browse/SPARK-23890?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Otto reopened SPARK-23890:
---------------------------------
This is fixed for DataSource v2 via {{{}alter table add column
nested.new_field0{}}}, but apparently there are few data sources that use the
DataSource v2 code path. Iceberg file works, but Hive, Parquet, ORC, JSON
still use the DataSource v1 code path to check if this is allowed.
Reopening and retitling more generically to allow nested column addition for
Parquet, etc.
> Hive ALTER TABLE CHANGE COLUMN for struct type no longer works
> --------------------------------------------------------------
>
> Key: SPARK-23890
> URL: https://issues.apache.org/jira/browse/SPARK-23890
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.0.0, 3.0.0
> Reporter: Andrew Otto
> Priority: Major
> Labels: bulk-closed, pull-request-available
> Fix For: 3.0.0
>
>
> As part of SPARK-14118, Spark SQL removed support for sending ALTER TABLE
> CHANGE COLUMN commands to Hive. This restriction was loosened in
> [https://github.com/apache/spark/pull/12714] to allow for those commands if
> they only change the column comment.
> Wikimedia has been evolving Parquet backed Hive tables with data originally
> from JSON events by adding newly found columns to the Hive table schema, via
> a Spark job we call 'Refine'. We do this by recursively merging an input
> DataFrame schema with a Hive table DataFrame schema, finding new fields, and
> then issuing an ALTER TABLE statement to add the columns. However, because
> we allow for nested data types in the incoming JSON data, we make extensive
> use of struct type fields. In order to add newly detected fields in a nested
> data type, we must alter the struct column and append the nested struct
> field. This requires CHANGE COLUMN that alters the column type. In reality,
> the 'type' of the column is not changing, it just just a new field being
> added to the struct, but to SQL, this looks like a type change.
> -We were about to upgrade to Spark 2 but this new restriction in SQL DDL that
> can be sent to Hive will block us. I believe this is fixable by adding an
> exception in
> [command/ddl.scala|https://github.com/apache/spark/blob/v2.3.0/sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala#L294-L325]
> to allow ALTER TABLE CHANGE COLUMN with a new type, if the original type and
> destination type are both struct types, and the destination type only adds
> new fields.-
>
> In this [PR|https://github.com/apache/spark/pull/21012], I was told that the
> Spark 3 datasource v2 would support this.
> However, it is clear that it does not. There is an [explicit
> check|https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/CheckAnalysis.scala#L1441]
> and
> [test|https://github.com/apache/spark/blob/e3f46ed57dc063566cdb9425b4d5e02c65332df1/sql/core/src/test/scala/org/apache/spark/sql/connector/AlterTableTests.scala#L583]
> that prevents this from happening.
>
>
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