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)
CREATE TABLE has_allergy (stuid DECIMAL, allergy TEXT)

Which allergy type is the least common?
SELECT allergytype FROM allergy_type GROUP BY allergytype ORDER BY COUNT(*) LIMIT 1
SELECT "allergytype" FROM "allergy_type" GROUP BY "allergytype" ORDER BY COUNT(*) NULLS FIRST LIMIT 1