MySql one time event never runs? Please have a look at below events 

1) create EVENT Test1 ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 20 second ON COMPLETION PRESERVE ENABLE DO ... 

2) create EVENT Test2 ON SCHEDULE EVERY 20 SECOND STARTS CURRENT_TIMESTAMP ON COMPLETION PRESERVE ENABLE DO ... 


I expect event Test1 to run one time after 20 seconds but it never runs. 
Event Test2 is working fine. 

Any idea? Thanks.

Ok sorry it is the alter that is not working

At first I did

CREATE EVENT Test1 ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 20 second ON COMPLETION PRESERVE ENABLE DO


Then shortly after I did

ALTER EVENT Test1 ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 20 second ON COMPLETION PRESERVE ENABLE DO


I expected event Test1 to run again in another 20 secs but it didn't.
It appears to work for me

mysql&gt; SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `data` varchar(255) NOT NULL DEFAULT '',
  `subdata` varchar(255) NOT NULL DEFAULT '',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql&gt; CREATE EVENT Test1 ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 20 second ON COMPLETION PRESERVE ENABLE DO ALTER TABLE t1 DROP `subdata`;
Query OK, 0 rows affected (0.00 sec)

mysql&gt; SELECT SLEEP(20);
+-----------+
| SLEEP(20) |
+-----------+
|         0 |
+-----------+
1 row in set (20.01 sec)

mysql&gt; SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `data` varchar(255) NOT NULL DEFAULT '',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql&gt; SHOW EVENTS;
+------+-------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+
| Db   | Name  | Definer        | Time zone | Type     | Execute at          | Interval value | Interval field | Starts | Ends | Status   | Originator | character_set_client | collation_connection | Database Collation |
+------+-------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+
| test | Test1 | root@localhost | SYSTEM    | ONE TIME | 2013-06-04 11:46:49 | NULL           | NULL           | NULL   | NULL | DISABLED |          0 | latin1               | latin1_swedish_ci    | utf8_general_ci    |
+------+-------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)

mysql&gt; 


So my question is what does SHOW EVENTS display before and after the set runtime of the event?