CREATE TABLE ship (ship_id DECIMAL, name TEXT, type TEXT, nationality TEXT, tonnage DECIMAL)
CREATE TABLE mission (mission_id DECIMAL, ship_id DECIMAL, code TEXT, launched_year DECIMAL, location TEXT, speed_knots DECIMAL, fate TEXT)

Show different types of ships and the average tonnage of ships of each type.
SELECT type, AVG(tonnage) FROM ship GROUP BY type
SELECT "type", AVG("tonnage") FROM "ship" GROUP BY "type"