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

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 NULLS LAST LIMIT 1