CREATE TABLE Has_allergy (fname VARCHAR, sex VARCHAR, StuID VARCHAR, Allergy VARCHAR)
CREATE TABLE Student (fname VARCHAR, sex VARCHAR, StuID VARCHAR, Allergy VARCHAR)

Find the first name and gender of the student who has allergy to milk but not cat.
SELECT fname, sex FROM Student WHERE StuID IN (SELECT StuID FROM Has_allergy WHERE Allergy = "Milk" EXCEPT SELECT StuID FROM Has_allergy WHERE Allergy = "Cat")
SELECT "fname", "sex" FROM "Student" WHERE "StuID" IN (SELECT "StuID" FROM "Has_allergy" WHERE "Allergy" = "Milk" EXCEPT SELECT "StuID" FROM "Has_allergy" WHERE "Allergy" = "Cat")