How Can I Add Comments in Mysql?

"A comment for a column can be specified with the COMMENT option. The comment is displayed by the SHOW CREATE TABLE and SHOW FULL COLUMNS statements. This option is operational as of MySQL 4.1. (It is allowed but ignored in earlier versions.)"

As an example

--
-- Table structure for table 'accesslog'
--

CREATE TABLE accesslog (
aid int(10) NOT NULL auto_increment COMMENT 'unique ID for each access entry', 
title varchar(255) default NULL COMMENT 'the title of the page being accessed',
path varchar(255) default NULL COMMENT 'the local path of teh page being accessed',
....
) TYPE=MyISAM;

You can use single-line comments:

-- this is a comment
# this is also a comment

Or a multiline comment:

/*
   multiline
   comment
*/

From here you can use:

#  For single line comments
-- Also for single line, must be followed by space/control character
/*
    C-style multiline comment
*/

/* comment here */

Here is an example:

SELECT 1 /* this is an in-line comment */ + 1;

Reference: 9.7 Comments

Three types of commenting are supported:

1. Hash base single line commenting using #

   Select * from users ; # this will list users
   

2. Double Dash commenting using --

   Select * from users ; -- this will list users
   

   Note: It's important to have single white space just after --

3. Multi line commenting using /* */

   Select * from users ; /* this will list users */