CREATE TABLE stock (shop_id NUMBER, device_id NUMBER, quantity NUMBER)
CREATE TABLE device (device_id NUMBER, device CLOB, carrier CLOB, package_version CLOB, applications CLOB, software_platform CLOB)
CREATE TABLE shop (shop_id NUMBER, shop_name CLOB, location CLOB, open_date CLOB, open_year NUMBER)

Show the carriers of devices in stock at more than one shop.
SELECT T2.carrier FROM stock AS T1 JOIN device AS T2 ON T1.device_id = T2.device_id GROUP BY T1.device_id HAVING COUNT(*) > 1
SELECT "T2"."carrier" FROM "stock" "T1" JOIN "device" "T2" ON "T1"."device_id" = "T2"."device_id" GROUP BY "T1"."device_id" HAVING COUNT(*) > 1