【单选题】有如下的SQL语句: Ⅰ.SELECT sname FROMs,sc WHERE grade<60 Ⅱ.SELECT sname FROMs WHERE sno IN(SELECT sno FROM sc WHERE grade<60 Ⅲ.SELECT sname FROMs,sc WHERE s.sno=Sc.sno AND grade<60 若要查找分数(grade)不及格的学生姓名(snam...
【单选题】设有关系模式SC(Sno,Sname,Sex,Birthdar,Cno,Cname,Grade,Tno,Tname)满足函数依赖集:{Sno→Sname,Sno→Sex,Sno→Birthday,Cno→Cname,(Sno,Cno)→Grade,Tno→Tname}。SC的主码和属性集(Sno,Tno)的闭包分别是______。 A) (Sno,Tno)和{Cno,Cname,Grade,Tno...