CREATE TABLE participants (participant_id NUMBER, participant_type_code CLOB, participant_details CLOB)
CREATE TABLE participants_in_events (event_id NUMBER, participant_id NUMBER)
CREATE TABLE events (event_id NUMBER, service_id NUMBER, event_details CLOB)
CREATE TABLE services (service_id NUMBER, service_type_code CLOB)

What is the most common participant type?
SELECT participant_type_code FROM participants GROUP BY participant_type_code ORDER BY COUNT(*) DESC LIMIT 1
SELECT "participant_type_code" FROM "participants" GROUP BY "participant_type_code" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY