Add a field to Module Database

1. Site administration -> Development -> XMLDB editor
2. Find your module and click [Load]
3. Click [Edit]
4. At the Tables section, click the table you want to add field
5. Click [New field] and fill in the detail
6. [View PHP code]
7. Select action: add field
8. Select field/key/index: your_new_field_name
9. Click "View"
10. Copy the code to mod/your_mod/db/upgrade.php
11. Change XXXXXXXXXX to new version number (e.g. 2011022301)
12. Open mod/your_mod/version.php, change $module->version to the new version number
13. Notification 
14. Done