填空题 设有关系S(S#,SNAME,AGE,SEX)、C(C#,CNAME,TEACHER)和SC(S#,C#,GRADE),请将实现以下功能的SQL语句填写完整: (4)检索全部学生都选修的课程的课程号(C#)和课程名(CNAME). 方法1: SELECT C#,CNAME FROM C WHERE (SELECT * FROM S WHERE (SELECT * FROM SC WHERE C.C#=SC.C# AND S.S#=SC.S#)) 方法2: select c#,cname from c where c# in( select c# from sc group by having count(distinct s#)=(select count(*) from ))