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)

For each type, what is the average tonnage?
SELECT type, AVG(tonnage) FROM ship GROUP BY type
SELECT "type", AVG("tonnage") FROM "ship" GROUP BY "type"