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在关系SC(student_id, student_name, course_id, grade)中，有 student_id, course_id →grade student_id →student_name 关系SC最高达到

A．不满足

B．1NF

C．2NF

D．3NF

在关系SC(student_id,student_name,course_id,grade)中，有 student_id,course_id→grade student_id→student_name 关系SC最高达到______范式。

A．不满足

B．1NF

C．2NF

D．3NF

_NAME VARCHAR2(30)COURSE_ID VARCHAR2(10) NOT NULLMARKS NUMBERSTART_DATE DATEFINISH_DATE DATEYou need to create a report of the 10 students who achieved the highest ranking in the course INT SQL and who completed the course in the year 1999.Which SQL statement accomplishes this task？ （）

A. SELECT student_ id, marks, ROWNUM "Rank" FROM students WHERE ROWNUM <= 10 AND finish_date BETWEEN ‘01-JAN-99‘ AND ‘31-DEC-99 AND course_id = ‘INT_SQL‘ ORDER BY mark DESC;

B. SELECT student_id, marks, ROWID "Rank" FROM students WHERE ROWID <= 10 AND finish_date BETWEEN ‘01-JAN-99‘ AND ‘31-DEC-99‘ AND course_id = ‘INT_SQL‘ ORDER BY mark;

C. SELECT student_id, marks, ROWNUM "Rank" FROM (SELECT student_id, marks FROM students WHERE ROWNUM <= 10 AND finish_date BETWEEN ‘01-JAN-99‘ AND ‘31-DEC- 99‘ AND course_id = ‘INT_SQL‘ ORDER BY mark DESC;

D. SELECT student_id, marks, ROWNUM "Rank" FROM (SELECT student_id, marks FROM students WHERE (finish_date BETWEEN ‘01-JAN-99 AND ‘31-DEC-99‘ AND course_id = ‘INT_SQL‘ ORDER BY marks DESC) WHERE ROWNUM <= 10;

E. SELECT student id, marks, ROWNUM "Rank" FROM (SELECT student_id, marks FROM students ORDER BY marks) WHERE ROWNUM <= 10 AND finish date BETWEEN ‘01-JAN-99‘ AND ‘31-DEC-99‘ AND course _ id ‘INT_SQL‘;

A、DELETE FROM SC WHERE GRADE IS NULL；

B、DELETE FROM SC；

C、DELETE FROM SC WHERE GRADE = NULL；

D、DELETE FROM SC WHERE GRADE IS NOT NULL；

在关系SC中，查询学习课程号为′DB′，且成绩在60至90之间的学生学号的正确的 SQL命令是

A．SELECT SNO FROM SC WHERE CNO=′DB′AND GRADE DETWEEN 60 AND 90

B．SELECT SNO FROM SC WHERE CNO=′DB′OR GRADE BETWEEN 60 AND 90

C．SELECT SNO FROM SC WHERE CNO=′DB′AND GRADE＞=60 AND 90

D．SELECT SNO FROM SC WHERE CNO=′DB′AND GRADE＜=60 AND GRADE＞=90

对于数据库设计来说( )是进行详细的数据收集和数据分析所获得的主要成果。

A．数据流图

B．数据字典

C．ER图

D．关系模式

数据库的逻辑结构设计任务就是把( )转换为与所选用的DBMS支持的数据模型扣符合的过程。

A．逻辑结构

B．物理结构

C．概念结构

D．层次结构

在数据库逻辑设计中，当将E-R图转换为关系模式时，下面的做法哪一个是不正确 的? ( )。

A．一个实体类型可以转换为一个关系模式

B．一个联系类型可以转换为一个关系模式

C．由实体类型转换成的关系模式的主键是该实体类型的主键

D．由联系类型转换成的关系模式的属性是与该联系类型相关的诸实体类型属性的全体