GitHub user jiangxb1987 opened a pull request:
https://github.com/apache/spark/pull/20696
[SPARK-23525] [SQL] Support ALTER TABLE CHANGE COLUMN COMMENT for external
hive table
## What changes were proposed in this pull request?
The following query doesn't work as expected:
```
CREATE EXTERNAL TABLE ext_table(a STRING, b INT, c STRING) PARTITIONED BY
(d STRING)
LOCATION 'sql/core/spark-warehouse/ext_table';
ALTER TABLE ext_table CHANGE a a STRING COMMENT "new comment";
DESC ext_table;
```
The comment of column `a` is not updated, that's because
`HiveExternalCatalog.doAlterTable` ignores table schema changes. To fix the
issue, we should call `doAlterTableDataSchema` instead of `doAlterTable`.
## How was this patch tested?
Updated `DDLSuite.testChangeColumn`.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/jiangxb1987/spark alterColumnComment
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/20696.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #20696
----
commit 92b2f317aca1c8fe96e4448c8d6dcedce02c9429
Author: Xingbo Jiang <xingbo.jiang@...>
Date: 2018-02-28T15:29:19Z
support change column comment for external hive table
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