CREATE TABLE affected_region (region_name VARCHAR2, region_id VARCHAR2)
CREATE TABLE region (region_name VARCHAR2, region_id VARCHAR2)

Show the name for regions not affected.
SELECT region_name FROM region WHERE NOT region_id IN (SELECT region_id FROM affected_region)
SELECT "region_name" FROM "region" WHERE NOT "region_id" IN (SELECT "region_id" FROM "affected_region")