针对S_T数据库，查询既选修了1号课程又选修3号课程的学生学号，以下不正确的SQL命令是（ ）。 A: select snofrom scwhere cno='1' and cno='3' B: select snofrom scwhere cno='1'intersectselect snofrom scwhere cno='3' C: select snofrom scwhere cno='1' and sno in(select snofrom scwhere cno='3') D: select a.snofrom sc a,sc bwhere a.sno=b.sno and a.cno='1' and b.cno='3'

针对学生选课表sc（sno, cno, grade），其中sno为学号，cno为课程号，grade为成绩。以下（）语句可查询选修了两门以上成绩在90分以上课程的学生学号。 A: select snofrom scwhere grade>;90group by snohaving count(cno)>;2 B: select snofrom scwhere grade>;90group by snohaving count(*)>;2 C: select snofrom scwhere grade>;90 and count(*)>;2group by sno D: select snofrom scwhere grade>;90group by snohaving count(distinct sno)>;2

查询计算机系任意学生选修过的课程号，不正确的查询语句是： A: SELECT DISTINCT CnoFROM SCWHERE NOT EXISTS (SELECT SnoFROM StudentWHERE Sdept = 'CS'AND SSno = Student.Sno); B: SELECT DISTINCT CnoFROM SCWHERE EXISTS (SELECT SnoFROM StudentWHERE Sdept = 'CS'AND SSno = Student.Sno); C: SELECT DISTINCT CnoFROM SCWHERE Sno IN (SELECT SnoFROM StudentWHERE Sdept = 'CS'); D: SELECT DISTINCT CnoFROM SCLEFT JOIN StudentON SSno = Student.SnoWHERE Sdept = 'CS';

查询计算机系任意学生选修过的课程号，不正确的查询语句是： A: SELECT DISTINCT CnoFROM SCWHERE NOT EXISTS (SELECT SnoFROM StudentWHERE Sdept = 'CS'AND SC.Sno = Student.Sno); B: SELECT DISTINCT CnoFROM SCWHERE EXISTS (SELECT SnoFROM StudentWHERE Sdept = 'CS'AND SC.Sno = Student.Sno); C: SELECT DISTINCT CnoFROM SCWHERE Sno IN (SELECT SnoFROM StudentWHERE Sdept = 'CS'); D: SELECT DISTINCT CnoFROM SCLEFT JOIN StudentON SC.Sno = Student.SnoWHERE Sdept = 'CS';

查询没有选修1号课程的学生姓名（）。 A: select snamefrom student,scwhere student.sno=sc.sno and cno!='1' B: select snamefrom sno not in(select snofrom scwhere cno='1' ) C: select snamefrom sno in(select snofrom scwhere cno!='1' ) D: select snamefrom sno not exists(select*from scwhere student.sno and sc.sno and cno='1' )

查询计算机系任意学生选修过的课程号，可以使用如下语句：SELECT DISTINCT CnoFROM SCWHERE Sno IN (SELECT SnoFROM StudentWHERE Sdept = 'CS');