ganeshashree opened a new pull request, #57311:
URL: https://github.com/apache/spark/pull/57311
Add SQL support for `COMMENT ON COLUMN`, in two forms:
- `COMMENT ON COLUMN table.column IS 'comment'` - the last identifier part
is the (top-level) column and the rest is the table path.
- `COMMENT ON TABLE table COLUMN (col1 IS 'c1', col2 IS 'c2', ...)` -
comment multiple columns in one command; supports nested fields (e.g.
`point.x`) at any depth.
Both forms parse into an `AlterColumns` plan over an `UnresolvedTable`, so a
view target is cleanly rejected with `EXPECT_TABLE_NOT_VIEW`, consistent with
`COMMENT ON TABLE` and `ALTER TABLE ... ALTER COLUMN`.
A new error condition
`INVALID_SQL_SYNTAX.COMMENT_ON_COLUMN_INCORRECT_IDENTIFIER` is raised when the
single-column form is given a bare column name.
A SQL reference doc page is added for the `COMMENT ON` statement.
`COMMENT ON COLUMN` is a common DDL command for documenting columns; it was
previously unsupported in Spark SQL.
Yes, it adds the `COMMENT ON COLUMN` SQL command.
New parser tests in `DDLParserSuite` and end-to-end tests in
`DataSourceV2SQLSuite` covering V1/V2 catalogs, multiple columns, nested
fields, `IS NULL`/empty comments, view rejection, and the nested-field boundary
of the single-column form.
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### What changes were proposed in this pull request?
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This PR adds SQL support for `COMMENT ON COLUMN` to set, update, and remove
comments on table columns, in two forms:
- Single column:
```sql
COMMENT ON COLUMN [catalog.][database.]table.column IS { 'comment' | NULL }
The last identifier part is the (top-level) column name; the preceding
parts
qualify the table.
- Multiple columns / nested fields, on one table:
COMMENT ON TABLE table COLUMN ( col1 IS 'c1', col2.field IS 'c2', ... )
- Each column may be a nested field path (e.g. point.x) at any depth.
IS NULL (or an empty string) clears the comment, consistent with
COMMENT ON TABLE.
Implementation notes:
- Grammar: two new #commentColumn alternatives in SqlBaseParser.g4, plus
columnCommentList / columnComment rules. No new lexer tokens are
introduced (COLUMN, COMMENT, TABLE, etc. already exist).
- AstBuilder.visitCommentColumn builds an AlterColumns plan over an
UnresolvedTable, reusing the existing ALTER TABLE ... ALTER COLUMN
resolution and execution path (ResolveFieldNameAndPosition, CheckAnalysis,
DataSourceV2Strategy). Because the target is an UnresolvedTable, a view is
rejected cleanly with EXPECT_TABLE_NOT_VIEW, matching
COMMENT ON TABLE and ALTER TABLE ... ALTER COLUMN.
- The single-column form requires at least two identifier parts; a bare
column
name raises the new error condition
INVALID_SQL_SYNTAX.COMMENT_ON_COLUMN_INCORRECT_IDENTIFIER.
- Adds a SQL reference doc page for the COMMENT ON statement.
This supersedes the earlier #53593 (closed); that version added a dedicated
CommentOnColumn plan node, whereas this reuses the existing AlterColumns
infrastructure and additionally supports the multi-column / nested-field
form.
### Why are the changes needed?
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Currently, Spark only supports setting column comments via:
1. CREATE TABLE with a COMMENT clause, or
2. ALTER TABLE ... ALTER COLUMN ... COMMENT (which cannot remove a comment).
COMMENT ON COLUMN provides standard SQL syntax that:
- follows SQL-standard conventions, consistent with the existing
COMMENT ON TABLE / COMMENT ON NAMESPACE commands,
- allows explicit removal of a column comment via IS NULL, and
- supports commenting multiple columns (and nested fields) in one statement.
### Does this PR introduce _any_ user-facing change?
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Yes. It adds the COMMENT ON COLUMN and COMMENT ON TABLE ... COLUMN (...) SQL
commands and a corresponding SQL reference documentation page. There is no
change
to existing behavior.
### How was this patch tested?
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New unit tests:
- DDLParserSuite: parsing of both syntax forms, identifier splitting,
IS NULL / empty / literal 'NULL' comments, nested-field paths, and the
INVALID_SQL_SYNTAX.COMMENT_ON_COLUMN_INCORRECT_IDENTIFIER error.
- DataSourceV2SQLSuite: end-to-end coverage over V1 (session) and V2
(non-session) catalogs — setting/updating/removing comments, multiple
columns,
deeply nested fields, view rejection (EXPECT_TABLE_NOT_VIEW), unknown column
(UNRESOLVED_COLUMN), the parent/child same-command restriction
(NOT_SUPPORTED_CHANGE_SAME_COLUMN), and the nested-field boundary of the
single-column form.
All added tests pass locally via
build/sbt "catalyst/testOnly *DDLParserSuite" and
build/sbt "sql/testOnly *DataSourceV2SQLSuiteV1Filter".
### Was this patch authored or co-authored using generative AI tooling?
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Generated-by: Claude Code (Claude Opus 4.8)
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