Cannot add a column to an InnoDB table in Mariadb
What I did

MariaDB [test]&gt; select version();
+---------------------+
| version()           |
+---------------------+
| 10.0.15-MariaDB-log |
+---------------------+
1 row in set (0.00 sec)


Are you using 5.5?

CREATE TABLE terms_of_use
( 

  id int(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
  current_version  varchar(20),  
  last_updated     timestamp,    
  keyx              varchar(256),  &lt;== note keyx - fails if I use 'key'
  language         varchar(20),
  text 
);


It appears that the problem is partly to do with the use of 'key' as 
a field name.

INSERT INTO terms_of_use (current_version, last_updated, keyx, language, text) VALUES( 'afsdf', NOW(), 'asdfadsf', 'adfs', 'terewe');
INSERT INTO terms_of_use (current_version, last_updated, keyx, language, text) VALUES( 'afsdf', NOW(), 'asdfadsf', 'adfs', 'terewe');
INSERT INTO terms_of_use (current_version, last_updated, keyx, language, text) VALUES( 'afsdf', NOW(), 'asdfadsf', 'adfs', 'terewe');
INSERT INTO terms_of_use (current_version, last_updated, keyx, language, text) VALUES( 'afsdf', NOW(), 'asdfadsf', 'adfs', 'terewe');
INSERT INTO terms_of_use (current_version, last_updated, keyx, language, text) VALUES( 'afsdf', NOW(), 'asdfadsf', 'adfs', 'terewe');
INSERT INTO terms_of_use (current_version, last_updated, keyx, language, text) VALUES( 'afsdf', NOW(), 'asdfadsf', 'adfs', 'terewe');


MariaDB [test]&gt; select * from terms_of_use;
+----+-----------------+---------------------+----------+----------+--------+
| id | current_version | last_updated        | keyx     | language | text   |
+----+-----------------+---------------------+----------+----------+--------+
|  1 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |
|  2 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |
|  3 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |
|  4 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |
|  5 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |
|  6 | afsdf           | 2015-01-28 20:45:06 | asdfadsf | adfs     | terewe |
+----+-----------------+---------------------+----------+----------+--------+
6 rows in set (0.00 sec)


Then I added the column

alter table terms_of_use add column `weight` int(11) not null default 0;


Then SELECT again

MariaDB [test]&gt; select * from terms_of_use;
+----+-----------------+---------------------+----------+----------+--------+--------+
| id | current_version | last_updated        | keyx     | language | text   | weight |
+----+-----------------+---------------------+----------+----------+--------+--------+
|  1 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |      0 |
|  2 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |      0 |
|  3 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |      0 |
|  4 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |      0 |
|  5 | afsdf           | 2015-01-28 20:45:05 | asdfadsf | adfs     | terewe |      0 |
|  6 | afsdf           | 2015-01-28 20:45:06 | asdfadsf | adfs     | terewe |      0 |
+----+-----------------+---------------------+----------+----------+--------+--------+
6 rows in set (0.00 sec)

MariaDB [test]&gt;