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

What are the student ids of students who don't have any allergies?
SELECT stuid FROM student EXCEPT SELECT stuid FROM has_allergy
SELECT "stuid" FROM "student" EXCEPT SELECT "stuid" FROM "has_allergy"