CREATE TABLE student (stuid NUMBER, lname CLOB, fname CLOB, age NUMBER, sex CLOB, major NUMBER, advisor NUMBER, city_code CLOB)
CREATE TABLE has_allergy (stuid NUMBER, allergy CLOB)
CREATE TABLE allergy_type (allergy CLOB, allergytype CLOB)

Which students are unaffected by allergies?
SELECT stuid FROM student EXCEPT SELECT stuid FROM has_allergy
SELECT "stuid" FROM "student" EXCEPT SELECT "stuid" FROM "has_allergy"