If you have the Resolve User Hostnames app installed, you can get hostname information for messages. This gives you insight into how users are connecting to the helpdesk, since the hostname often indicates the user's ISP, university, section of your network etc.
To retrieve a message hostname, use tickets_messages.hostname. Note that this is a field of the tickets_messages table, so you must select FROM tickets_messages, but you can use cross-referencing to include fields from other tables.
Here's a simple example query to display hostnames for all user messages, split up by ticket:
SELECT tickets_messages.ticket.person, tickets_messages.hostname
WHERE tickets_messages.hostname <> '' AND tickets_messages.person.is_user = 1
SPLIT BY tickets_messages.ticket.id
The hostname field will be empty for messages created before you installed the app. Specifying
WHERE tickets_messages.hostname <> ''
means that messages where the hostname is empty are not listed.
tickets_messages.person.is_user = 1
in the WHERE clause filters out agent messages.