mysql> show create event online_event;
+--------------+-----------------------------------------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| Event        | sql_mode                                | time_zone | Create Event                                                                                                                                                                                        | character_set_client | collation_connection | Database Collation |
+--------------+-----------------------------------------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| online_event | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER | SYSTEM    | CREATE EVENT `online_event` ON SCHEDULE EVERY 1 SECOND STARTS '2009-06-03 06:54:16' ON COMPLETION NOT PRESERVE ENABLE DO DELETE FROM online where webserver_id is null and jabber_server_id is null | utf8                 | utf8_general_ci      | utf8_general_ci    |
+--------------+-----------------------------------------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)

mysql>

它是通过以下方式创建的：

CREATE EVENT online_event
    ON SCHEDULE EVERY 1 SECOND
    DO 
      DELETE FROM online where webserver_id is null and jabber_server_id is null;

一段时间后，我发现：

mysql> select *from online;
+----+------------+---------------------+--------------+------------------+
| id | account_id | since               | webserver_id | jabber_server_id |
+----+------------+---------------------+--------------+------------------+
|  1 |         30 | 2009-06-03 06:24:38 |         NULL |             NULL |
+----+------------+---------------------+--------------+------------------+
1 row in set (0.00 sec)

因此，我发现该事件根本没有运行。