CREATE TABLE "mission" (
"Mission_ID" int,
"Ship_ID" int,
"Code" text,
"Launched_Year" int,
"Location" text,
"Speed_knots" int,
"Fate" text,
PRIMARY KEY ("Mission_ID"),
FOREIGN KEY ("Ship_ID") REFERENCES `ship`("Ship_ID")
)

CREATE TABLE "ship" (
"Ship_ID" int,
"Name" text,
"Type" text,
"Nationality" text,
"Tonnage" int,
PRIMARY KEY ("Ship_ID")
)
SELECT TYPE ,  avg(Tonnage) FROM ship GROUP BY TYPE
Show different types of ships and the average tonnage of ships of each type.