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)

Show the types of ships that have both ships with tonnage larger than 6000 and ships with tonnage smaller than 4000.
SELECT type FROM ship WHERE tonnage > 6000 INTERSECT SELECT type FROM ship WHERE tonnage < 4000
SELECT "type" FROM "ship" WHERE "tonnage" > 6000 INTERSECT SELECT "type" FROM "ship" WHERE "tonnage" < 4000