GitHub user jiangxb1987 opened a pull request:
https://github.com/apache/spark/pull/15717
[SPARK-17910][SQL][WIP] Allow users to update the comment of a column
## What changes were proposed in this pull request?
Right now, once a user set the comment of a column with create table
command, he/she cannot update the comment. It will be useful to provide a
public interface (e.g. SQL) to do that.
This PR implements the following SQL statement:
```
ALTER TABLE table CHANGE COLUMN `col` `col` dataType "comment" (FIRST |
AFTER `otherCol`)
[, `col2` `col2` dataType "comment" (FIRST | AFTER `otherCol`), ...];
ALTER VIEW view CHANGE COLUMN `col` `col` dataType "comment" (FIRST | AFTER
`otherCol`)
[, `col2` `col2` dataType "comment" (FIRST | AFTER `otherCol`), ...];
```
For further expansion, we could support alter `name`/`dataType`/`index` of
a column too.
## How was this patch tested?
Add new test cases in `ExternalCatalogSuite` and `SessionCatalogSuite`.
(Plan to add sql file test for `ALTER TABLE CHANGE COLUMN` statement)
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/jiangxb1987/spark change-column
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15717.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 #15717
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