CREATE TABLE Has_allergy (fname VARCHAR2, sex VARCHAR2, StuID VARCHAR2, Allergy VARCHAR2)
CREATE TABLE Student (fname VARCHAR2, sex VARCHAR2, StuID VARCHAR2, Allergy VARCHAR2)

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")