1)Which statement shows the maximum salary paid in each job category of each department?_______
A. select dept_id, job_cat,max(salary) from employees where salary > max(salary);
B. select dept_id, job_cat,max(salary) from employees group by dept_id,job_cat;
C. select dept_id, job_cat,max(salary) from employees;
D. select dept_id, job_cat,max(salary) from employees group by dept_id;
E. select dept_id, job_cat,max(salary) from employees group by dept_id,job_cat,salary;

2)description of the students table:
  sid_id                       number
  start_date                   date
  end_date                     date
which two function are valid on the start_date column?_________。
A. sum(start_date)
B. avg(start_date)
C. count(start_date)
D. avg(start_date,end_date)
E. min(start_date)
F. maximum(start_date)

3)for which two constraints does the oracle server implicitly create a unique index?______。
A. not null
B. primary
C. foreign key
D. check
E. unique

4)in a select statement that includes a where clause,where is the group by clause placed in the select statement?______。
A. immediately after the select clause
B. before the where clause
C. before the from clause
D. after the order by clause
E. after the where clause

5)in a select statement that includes a where clause,where is the order by clause placed in the select statement?______.
A.immediately after the select clause
B.before the where clause
C.after all clause
D.after the where clause
E.before the from clause

6)evaluate there two sql statements______.
Select last_name,salary from employees order by salary;
Select last_name,salary from employees order by 2 asc;
A.the same result  B.different result C.the second statement returns a syntax error

7) you would like to display the system date in the format“20051110 14：44：17”。Which select statement should you use?______。
A. select to_date(sydate,’yearmmdd hh:mm:ss’)from dual;
B. select to_char(sydate,’yearmonthday hh:mi:ss’)from dual;
C. select to_date(sydate,’yyyymmdd hh24:mi:ss’)from dual;
D. select to_char(sydate,’yyyymmdd hh24:mi:ss’)from dual;
E. select to_char(sydate,’yy-mm-dd hh24:mi:ss’)from dual;

8)which select statement will the result ‘ello world’from the string‘Hello world’?______.
A. select substr(‘Hello World’,1)from dual;
B. select substr(trim(‘Hello World’,1,1))from dual;
C. select lower(substr(‘Hello World’,1))from dual;
D. select lower(trim(‘H’from‘Hello World’))from dual;

9)which are DML statements(choose all that apply)______.
A.commit  B.merge   C.update  D.delete E.creat  F.drop

10)Select 语句中用来连接字符串的符号是______.
A. “+”   B. “&” C.“||” D.“|”

问答题： 什么是聚集索引，什么是非聚集索引，什么又是主键？