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');

‏下列SQL语句中，_____________可以在“学生-课程”数据库正确实现“计算1号课程的学生平均成绩”。‍ A: SELECT AVG(Grade)FROM SCWHERE Cno= ' 1 ' B: SELECT MAX(Grade)FROM SCWHERE Cno= 1 C: SELECT MIN(Grade)FROM SCWHERE Cno= 1 D: SELECT AVG(Grade)FROM SCWHERE Cno= 1

已知学生选课信息表：sc（sno，cno，grade）。查询“至少选修了一门课程，但没有学习成绩的学生学号和课程号”的SQL语句是（ ）。 A: SELECT sno,cno FROM sc WHERE grade=NULL B: SELECT sno,cno FROM sc WHERE grade IS C: SELECT sno,cno FROM sc WHERE grade IS NULL D: SELECT sno,cno FROM sc WHERE grade=