Thank you, Simon and team
I have data explorer enabled and have created the query:
`–[params]
– int :topic_id
SELECT acting_user_id FROM user_actions WHERE action_type = 15 AND target_topic_id = :topic_id`
Presume I need to be pointing to topic, but how then do I run the query?
Ah it seems I need to copy the topic_id into the prompted window. 
Cheers
Ian