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

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"