Create comments for views in mysql

Question

I see that the views have a comment field just like the regular tables, but is by default populated with the "VIEW" value.

[TABLE_CATALOG] => 
[TABLE_SCHEMA] => xxx
[TABLE_NAME] => view__xxxx
[TABLE_TYPE] => VIEW
[ENGINE] => 
[VERSION] => 
[ROW_FORMAT] => 
[TABLE_ROWS] => 
[AVG_ROW_LENGTH] => 
[DATA_LENGTH] => 
[MAX_DATA_LENGTH] => 
[INDEX_LENGTH] => 
[DATA_FREE] => 
[AUTO_INCREMENT] => 
[CREATE_TIME] => 
[UPDATE_TIME] => 
[CHECK_TIME] => 
[TABLE_COLLATION] => 
[CHECKSUM] => 
[CREATE_OPTIONS] => 
[TABLE_COMMENT] => VIEW

When I am trying to create a view with a comment I get an error.

CREATE OR REPLACE VIEW view__x AS
SELECT 
 * 
FROM `some_table`  
COMMENT = 'some comment'

Is there a way to modify the comment field or that field is used internally for something else and should stay like it is?

I've added a feature request to mysql.

Solution 1

According to the create view syntax there is no way currently to add comment a view:

• http://dev.mysql.com/doc/refman/5.7/en/create-view.html

This feature 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.

Solution 2

I had a similar need, and one way I hacked this in MySQL was to add a truthy predicate in the WHERE clause that served as documentation. I admit this is hacky, but wouldn't you agree any documentation is better than no documentation at all? Once nice side-effect of doing your commentary this way will survive a mysqldump. As far as I know, the optimizer will not be hindered by the extra truthy predicate.

Example view creation:

CREATE OR REPLACE VIEW high_value_employees AS
SELECT *
FROM `employees`
WHERE salary >= 200000
AND 'comment' != 'This view was made by Josh at the request of an important VP who wanted a concise list of who we might be overpaying. Last modified on 26 July 2019.';

And then viewing the documentation ...

> SHOW CREATE TABLE high_value_employees \G
*************************** 1. row ***************************
                View: high_value_employees
         Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`jhuber`@`%` SQL SECURITY 
DEFINER VIEW `high_value_employees` AS select `employees`.`salary` AS `salary` from
`employees` where ((`employees`.`salary` >= 200000) and ('comment' <> 'This view was
made by Josh at the request of an important VP who wanted a concise list of who we
might be overpaying. Last modified on 26 July 2019.'))
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
1 row in set (0.00 sec)