How many events are there?
select count ( distinct event_id ) from participants_in_events
How many of them had participants whose details had substring "Dr"?
select count ( * ) from participants as t1 join participants_in_events as t2 on t1.participant_id = t2.participant_id where t1.participant_details like '%dr.%'
What is his name?
select participant_details from participants as t1 join participants_in_events as t2 on t1.participant_id = t2.participant_id where t1.participant_details like '%dr.%'