针对学生选课数据库S_T，可以利用以下视图插入数据。 create view view1 as select cno,avg（grade) from sc group by cno

A、create view view4 as select student.sno,sname,sc.sno,cno,grade from sc,student where sc.sno=student.sno and cno='1' 1

B、create view view2 as select sno,sname,sdept from student where sdept='CS' 2

C、create view view3 as select sno,sage+20 from student where ssex='女' 3

D、create view view1 as select sno,avg(grade) from sc group by sno 4

A、create view view1 as select sno,avg(grade) from sc group by sno

B、create view view2 as select sno,sname,sdept from student where sdept='CS'

C、create view view3 as select sno,sage+20 from student where ssex='女'

D、create view view4 as select student.sno,sname,sc.sno,cno,grade from sc,student where sc.sno=student.sno and cno='1'

A、select count(cno) from sc

B、select count(sno) from sc

C、select count(*) from sc

D、select count(distinct sno) from sc

A、select student.* , cno, grade from student join sc on student.sno=sc.sno

B、select student.* , sc.* from student , sc where student.sno=sc.sno

C、select student.sno, sname, ssex, sage, sdept , cno, grade from student , sc where student.sno=sc.sno

D、select student.* , cno, grade from student , sc where student.sno=sc.sno

S ( SNO , SNAME , SEX , AGE ) , SC ( SNO , CNO , GRADE )

则与 SQL 命令 SELECT sname FROM s WHERE sno IN （ SELECT sno FROM sc WHERE grade<60 ）

等价的关系代数表达式是 __________ 。

S （ sno,shame,sex,age,dept ）， C （ cno,cname,teacher ）， SC （ sno,cno,grade ）

查找选修 “ 数据库技术 ” 课程的学生的姓名和成绩，用关系代数表达式可表示为

S(S#，SNAME，SEX，AGE，DEPARTMENT)，主码是S#

C(C#，CNAME，TEACHER)，主码是C#

SC(S#，C#，GRADE)，主码是(S#，C#)

下面的SQL语句定义了一个反映学生出生年份的视图：

CREATE VIEW S BDAY(S#，SNAME，BIRTH)AS

SELECT S#，SNAME，2010-AGE FROM S

这是一个( )。

A．行列子集视图

B．带表达式视图

C．分组视图

D．连接视图

S(SNO，SNAME，SEX，AGE)，

SC(SNO，CNO，GRADE)，

C(CNO，CNAME，TEACHER)。

查找选修“数据库技术”这门课的学生的学生姓名和成绩，若使用连接查询的SQL语句是：SELECTSNAME，GRADEFROMS，SC，C WHERE子句。其中的WHERE子句应该是

A．CNAME＝"数据库技术"ANDS.SNO＝SC.SNO ANDSC.CNO＝C.CNO

B．CNAME＝"数据库技术" ANDS.SNO＝SC.SNO ANDSC.CNO＝CNO

C．CNAME＝"数据库技术" ANDS.SNO＝SC.SNO ANDSC.CNO＝C.CNO

D．CNAME="数据库技术" ANDS.SNO＝SC.SNO

A.ПCNAME, GRADE (σCNAME=’数据库技术’(C) ∞ПSNO, CNO, GRADE (SC) ∞ПSNO, SNAME (S) )

B.ПCNAME, GRADE (σCNAME=’数据库技术’(C) ∞ SC ∞ S)

C.ПCNAME, GRADE (C ∞ SC ∞ SC)

D.ПCNAME, GRADE (σCNAME=’数据库技术’ (ПCNAME (C)) ∞ПSNO, CNO, GRADE (SC) ∞ПSNO, SNAME (S) )