ganeshashree opened a new pull request, #53593:
URL: https://github.com/apache/spark/pull/53593
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This PR adds support for the COMMENT ON COLUMN SQL syntax to set, update,
and remove comments on table columns.
The syntax follows the SQL standard:
`COMMENT ON COLUMN [catalog.][[database.]table.]column IS { 'comment_text' |
NULL }`
**Key features:**
Set/Update comment: `COMMENT ON COLUMN table.column IS 'text'` - Sets or
updates a column comment
Remove comment: `COMMENT ON COLUMN table.column IS NULL` - Removes the
comment
Flexible qualification: Supports table.column, database.table.column, and
catalog.database.table.column formats
Implementation highlights:
* Added CommentOnColumn logical plan node in v2AlterTableCommands.scala
* Parser support in SqlBaseParser.g4 and AstBuilder.scala
* Works with both V2 DataSource tables and V1/session catalog tables
### What changes were proposed in this pull request?
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### Why are the changes needed?
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Currently, Spark only supports setting column comments via:
1. CREATE TABLE with COMMENT clause
2. ALTER TABLE ... ALTER COLUMN ... COMMENT (doesn't support removal)
This PR provides a standard SQL syntax (COMMENT ON COLUMN) that:
* Follows SQL standard conventions (consistent with existing COMMENT ON
TABLE)
* Allows explicit removal of column comments via IS NULL
* Provides cleaner, more intuitive syntax for managing column-level
documentation
### Does this PR introduce _any_ user-facing change?
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Yes. New SQL syntax:
```
-- Set a column comment
COMMENT ON COLUMN my_table.my_column IS 'This is a column comment';
-- Update a column comment
COMMENT ON COLUMN my_table.my_column IS 'Updated comment';
-- Remove a column comment
COMMENT ON COLUMN my_table.my_column IS NULL;
-- Set empty string comment
COMMENT ON COLUMN my_table.my_column IS '';
-- Works with qualified names
COMMENT ON COLUMN my_catalog.my_db.my_table.my_column IS 'comment';
```
### How was this patch tested?
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Added comprehensive parser tests in DDLParserSuite.scala covering:
* Various qualification levels (table.column, database.table.column, etc.)
* NULL handling for comment removal
Added integration tests in DataSourceV2SQLSuite.scala covering:
* Setting, updating, and removing comments on V1 and V2 tables
* NULL vs. empty string behavior
* Different qualification formats
* Error cases (column not found)
### Was this patch authored or co-authored using generative AI tooling?
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No
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