CREATE TABLE Student (StuID VARCHAR, sex VARCHAR, sportname VARCHAR)
CREATE TABLE Sportsinfo (StuID VARCHAR, sex VARCHAR, sportname VARCHAR)

Show all male student ids who don't play football.
SELECT StuID FROM Student WHERE sex = 'M' EXCEPT SELECT StuID FROM Sportsinfo WHERE sportname = "Football"
SELECT "StuID" FROM "Student" WHERE "sex" = 'M' EXCEPT SELECT "StuID" FROM "Sportsinfo" WHERE "Football" = "sportname"