MySql对视图列的注释？

Question

Is it possible in MySql to store comments for the columns of a view?

I know how to add comments to normal tables and columns but I am not sure if it is possible to do so for views. All I know is that views (for some aspects) behave just like a table and for this reason it is possible to run a query as such:

SELECT 
  column_name, column_comment 
FROM 
  information_schema.columns 
WHERE 
  table_name='myview';

But I don't know how to add the comment in the first place and haven't found a solution yet!

The reason I am doing this is that I am storing metadata for my application in the comment field and I would like tables and views to be identical.

Answer 1

According to the create view syntax there is no way currently to add comments to the "columns" of a view even if the columns of a view are present in the information_schema.columns table:

http://dev.mysql.com/doc/refman/5.0/en/create-view.html

Answer 2

我不认为您可以向视图“列”添加注释，但您可以使用视图从基础表中检索注释，使用SHOW COLUMNS，就像查询表时一样。

Answer 3

Mysql has no metadata for view columns:

http://dev.mysql.com/doc/refman/5.0/en/views-table.html

So answer is NO.

Answer 4

We're up to version 5.7, and this feature still hasn't been implemented, even though it has been requested several times. There are four active tickets related to this functionality:

http://bugs.mysql.com/bug.php?id=5159
http://bugs.mysql.com/bug.php?id=64045
http://bugs.mysql.com/bug.php?id=52429
http://bugs.mysql.com/bug.php?id=15344

...and several marked as duplicates: http://bugs.mysql.com/bug.php?id=19602 , http://bugs.mysql.com/bug.php?id=19602 , http://bugs.mysql.com/bug.php?id=13109 , http://bugs.mysql.com/bug.php?id=14369 , http://bugs.mysql.com/bug.php?id=11082 , http://bugs.mysql.com/bug.php?id=42870 , http://bugs.mysql.com/bug.php?id=38137 , http://bugs.mysql.com/bug.php?id=38137 , http://bugs.mysql.com/bug.php?id=30729

If you are interested in this issue, go to the four active tickets, click the "affects me" button, and also add a comment, asking if anyone is working on this feature.

This will add visibility, and increase the likelyhood of it being implemented.

Answer 5

-- A view shows the column comments of the underlying table.

-- this does not show column comments
SHOW COLUMNS FROM zztable_vw;

-- this shows column comments from the underlying table
SHOW FULL COLUMNS FROM zztable_vw;

CREATE TABLE `zztable` (
-- A SQL statement comment. Not stored with the table. Just documents the create table code
  `zz_id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT 'unique primary key. auto increment',
  `zz_descr` varchar(255) NOT NULL COMMENT 'descriptive name. must be unique if not null',
  PRIMARY KEY (`zz_id`),
  UNIQUE KEY `zz_descr_UNIQUE` (`zz_descr`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='a table demonstrating table, column, and view comments. ';

-- select the table from information_schema
SELECT table_type, table_name, table_rows, table_comment
FROM information_schema.tables ta
WHERE ta.table_name LIKE 'zztable%'
ORDER BY ta.table_type, ta.table_name;

-- select the table_columns from information_schema
SELECT ta.table_type, co.table_name, co.column_name, co.column_comment
FROM information_schema.columns co
JOIN information_schema.tables ta
  ON co.table_name = ta.table_name
WHERE co.table_name LIKE 'zztable%'
ORDER BY ta.table_type, co.table_name, co.ordinal_position;

-- create a view over the commented table
CREATE OR REPLACE VIEW zztable_vw
AS
SELECT zz_id, zz_descr
FROM zztable;

-- now run the information_schema queries again to see the new view in the results

-- information_schema.tables query does not show table-level comments

 <table> <tr> <th>table_type</th> <th>table_name</th> <th>table_rows</th> <th>table_comment</th> </tr> <tr> <td>BASE TABLE</td> <td>zztable</td> <td>0</td> <td>a table demonstrating table, column, and view comments.</td> </tr> <tr> <td>VIEW</td> <td>zztable_vw</td> <td>NULL</td> <td>VIEW</td> </tr> </table> 

-- information_schema.columns query shows underlying table column comments

 <table> <tr> <th>table_type</th> <th>table_name</th> <th>column_name</th> <th>column_comment </tr> <tr> <td>BASE TABLE</td> <td>zztable</td> <td>zz_id</td> <td>unique primary key. auto increment</td> </tr> <tr> <td>BASE TABLE</td> <td>zztable</td> <td>zz_descr</td> <td>descriptive name. must be unique if not null</td> </tr> <tr> <td>VIEW</td> <td>zztable_vw</td> <td>zz_id</td> <td>unique primary key. auto increment</td> </tr> <tr> <td>VIEW</td> <td>zztable_vw</td> <td>zz_descr</td> <td>descriptive name. must be unique if not null</td> </tr> </table>