using Workbench to add "Extra".. (no replies)

Hi there:

+-----------------+-------------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+-------------------+------+-----+-------------------+-----------------------------+

| record_datetime | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |


How can I add this "Extra" column in Workbench as I work on the EER diagram tab?

Thanks
(Workbench 5.2.41 on Mac OSX Lion)