Event ID and Service ID
select t1.event_id, t1.service_id from events as t1 join participants_in_events as t2 on t1.event_id = t2.event_id group by t1.event_id having count ( * ) > 1
I mean the details of the events that have more than one participant.
select t1.event_details from events as t1 join participants_in_events as t2 on t1.event_id = t2.event_id group by t1.event_id having count ( * ) > 1