CREATE TABLE country (country_id DECIMAL, name TEXT, population DECIMAL, area DECIMAL, languages TEXT)
CREATE TABLE roller_coaster (roller_coaster_id DECIMAL, name TEXT, park TEXT, country_id DECIMAL, length DECIMAL, height DECIMAL, speed TEXT, opened TEXT, status TEXT)

What are the speeds of the longest roller coaster?
SELECT speed FROM roller_coaster ORDER BY length DESC LIMIT 1
SELECT "speed" FROM "roller_coaster" ORDER BY "length" DESC NULLS LAST LIMIT 1