CREATE TABLE mission (Mission_ID INT, Ship_ID INT, Code TEXT, Launched_Year INT, Location TEXT, Speed_knots INT, Fate TEXT)
CREATE TABLE ship (Ship_ID INT, Name TEXT, Type TEXT, Nationality TEXT, Tonnage INT)

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"