CREATE TABLE Sportsinfo (StuID VARCHAR2, sex VARCHAR2, sportname VARCHAR2)
CREATE TABLE Student (StuID VARCHAR2, sex VARCHAR2, sportname VARCHAR2)

Show student ids who are female and play football.
SELECT StuID FROM Student WHERE sex = 'F' INTERSECT SELECT StuID FROM Sportsinfo WHERE sportname = "Football"
SELECT "StuID" FROM "Student" WHERE "sex" = 'F' INTERSECT SELECT "StuID" FROM "Sportsinfo" WHERE "Football" = "sportname"