吉大20春学期《数据库应用技术》在线作业一-0003参考答案

吉大20春学期《数据库应用技术》在线作业一-0003

试卷总分:100

一、单选题(共25 道试题,共100 分)

1.如果选用循环日志方式，辅助日志文件何时分配？

A.数据库建立的时候

B.数据库服务器启动的时候

C.需要的时候

D.以上都不对

正确答案:C

2.Given the following table: CREATE TABLE employee (name CHAR(10), salary DEC NOT NULL WITH DEFAULT) INSERT INTO employee (name, salary) V ALUES ('SMITH', 30000) INSERT INTO employee (name) V ALUES ('JONES') INSERT INTO employee (name, salary) V ALUES ('ALI', 35000) Which of the following statements will retrieve more than one row?

A.SELECT salary FROM employee WHERE salary IN (SELECT (salary/(SELECT SUM(salary) FROM employee)) FROM employee)

B.SELECT COALESCE(A VG(salary)) FROM employee

C.SELECT SUM(salary)/COUNT(*) FROM employee

D.SELECT salary/(SELECT SUM(salary) FROM employee) FROM employee

正确答案:D

3.据库系统和文件系统的主要区别是：